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CD46 in Neisseria pathogenesis Darcy B. Gill and John P. Atkinson Washington University School of Medicine, Department of Medicine, Rheumatology Division, Campus Box 8045, 660 S. Euclid, St Louis, MO 63110, USA

CD46 is a complement regulator that serves as a cellular pilus receptor for the human pathogens Neisseria gonorrhoeae and Neisseria meningitidis. The role of CD46 in N. gonorrhoeae infection has been further characterized through the identification of domains that are required for bacterial adhesion, as well as the delineation of CD46-dependent signaling responses that promote this adhesion. In addition, the adherence of N. gonorrhoeae to human epithelial cell lines results in cell-surface downregulation followed by the liberation of CD46 into the surrounding milieu. Recently, transgenic mice expressing human CD46 were used in a mouse model of meningitis, in which CD46 enhanced meningococcal traversal of the blood–brain barrier. Although the role of CD46 in infection by the pathogenic Neisseria remains incompletely defined, these advances indicate a dynamic and important contribution of CD46 to Neisseria pathogenesis. The human complement regulator CD46 is a cellular receptor for multiple human pathogens, including Neisseria gonorrhoeae (gonococcus) and Neisseria meningitidis (meningococcus) [1]. The Type IV pilus of Neisseria mediates the initial bacterial attachment to the human epithelium, initiating a multistep cascade that results in tight bacterial adhesion [2]. Under some experimental conditions, CD46 has a role in this interaction between the host and the pathogen by serving as a receptor for the Type IV pilus and the subsequent signaling events. The pathogenic Neisseriae N. gonorrhoeae and N. meningitidis are the causative agents of gonorrhea and meningitis, respectively. These infections are responsible for substantial morbidity and mortality worldwide. Individuals infected with N. gonorrhoeae typically present with inflammation of the urethra or cervix. The clinical manifestations vary, ranging from asymptomatic carriage to pelvic inflammatory disease and sepsis. N. meningitidis is a part of the normal nasopharyngeal flora of 3–30% of the human population. Under circumstances that are poorly understood, this organism traverses the mucosal epithelium, resulting in bacteraemia and, occasionally, sepsis. Once in the bloodstream, meningococci can then cross the blood– brain barrier to cause a fulminant meningitis. The colonization of and persistence in the human mucosal epithelium of the nasopharynx (N. meningitidis) Corresponding author: John P. Atkinson ( [email protected]). Available online 11 August 2004

and the genitourinary tract (N. gonorrhoeae) are essential for the survival of these pathogens. Recent studies of colonization by the pathogenic Neisseriae have revealed a multistep process of adhesion involving interactions between multiple bacterial proteins and host-cell receptors (reviewed in [2–7]). The Type IV pilus is an important colonization factor for both N. gonorrhoeae and N. meningitidis that facilitates the initial attachment of the bacteria to host cells (Figure 1). This organelle has been most intensely studied in gonococci, in which it has been characterized as a multifunctional filamentous appendage that mediates bacterial autoagglutination, competency for DNA transformation, a mode of surface translocation known as twitching motility and adhesion to host cells (reviewed in [2]). Here, we review recent studies investigating the role of the human cell-surface glycoprotein CD46 in pilusmediated adhesion of Neisseria and the subsequent host-cell response.

CD46 function, structure and microbial interactions CD46, or membrane cofactor protein (MCP), is a type I transmembrane glycoprotein (Figures 2 and 3). It is a member of the regulators of complement activation (RCA) protein family, a group of structurally, functionally and genetically related proteins that protect host cells against complement attack and serve as receptors for complement-coated antigens. Following the deposition of C3b and C4b on host cells, CD46 prevents further complement activation by serving as a cofactor in the limited proteolysis of C3b and C4b by the plasma serine protease factor I (Figure 2) (reviewed in [8]). CD46 is expressed by nearly every human cell type with the exception of erythrocytes [8]. Four major isoforms (BC1, BC2, C1 and C2) are expressed through the alternative splicing of a 46 kb gene. Isoforms vary in their quantity of O-glycosylation, as a result of the presence or absence of the B module, and in the expression of one of two possible cytoplasmic tails (Cyt-1 or Cyt-2) (Figure 3). All four isoforms are expressed in most cells, with the exceptions being the kidney, which expresses mainly the BC2 isoform, and the brain and spermatozoa, which predominantly express the C2 isoform [9]. Apart from these exceptions, tissues within a given individual express the same ratio of BC to C isoforms. This is an inherited trait, with 66% of individuals expressing predominantly the BC isoforms, 29% expressing equal quantities of the B and C isoforms and 6% expressing predominantly the C isoform [10,11].

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Figure 1. The type IV pilus of Neisseria mediates interactions with host cells. (a) Electron micrograph of a diplococcus showing pili (filamentous appendages radiating outward from the bacterial surface). Magnification ! 39 000. Electron micrograph reproduced with permission from [54]. (b) Confocal image showing microcolonies of piliated gonococci (yellow arrows) adhering to an ME-180 human cervical epithelial cell after a 4 h incubation. Following formaldehyde fixation, adherent bacteria were stained with propidium iodide. (c) Diagram depicting gonococcal pilus components. The pilus fiber itself is composed of the subunit PilE (blue). Pilin subunits originate on the inner membrane (IM) and, upon assembly, extrude through the outer membrane (OM) via the PilQ secretin (grey). PilC (green), a pilus-associated protein and putative adhesin, has been described to localize to the tip of the fibrillum and to the outer membrane of the bacterium [55,56]. PilV (yellow), a minor pilus-associated protein, has yet to be conclusively localized to the pilus, but has been suggested to function in the proper presentation of PilC [57]. PilT (red), an ATPase, is necessary for pilus retraction and has been demonstrated on the inner membrane of the bacterium [58]. Other pilus components are not shown. Although several pilus components of Neisseria exhibit significant variation in sequence and/or glycosylation among strains and species, the overall architecture and general function of the pilus is believed to be similar in Neisseria gonorrhoeae and Neisseria meningitidis.

The crucial role of this protein for preventing excessive complement activation was recently highlighted by the description of CD46 mutations in patients with hemolytic uremic syndrome (HUS) [12–14]. In addition, CD46 has been identified as a key component in fertilization (reviewed in [15]), T regulatory cell differentiation [16] and host-cell interactions with a growing list of human pathogens, including the measles virus [17,18], Streptococcus pyogenes [19], the pathogenic Neisseriae [1], human herpesvirus 6 [20] and group B and D adenoviruses [21–23].

CD46 as a cellular pilus receptor for pathogenic Neisseria Based on three lines of experimentation in a report by Kallstrom et al. [1], CD46 was identified as a cellular receptor for the Neisseria pilus (Figure 4A). First, in an

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Figure 2. Cofactor activity of CD46. CD46 binds efficiently to C3b or C4b that are deposited on the surface of the cell on which it is expressed. Upon the binding of a plasma serine protease (factor I) to this complex, the cleavage of C3b (a) to C3bi and C3f and the cleavage of C4b (b) to C4c and C4d occurs. The cleavage products C3f and C4c are released into the surrounding milieu and the resulting target-bound cleavage products (C3bi and C4d) are inactive relative to further complement activation. Once cleavage occurs, CD46 and factor I dissociate from the complex and are available to continue the process on additional C3b and C4b molecules. All four commonly expressed isoforms of CD46 exhibit cofactor activity. www.sciencedirect.com

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Figure 3. Diagram of CD46 structure. CD46 is a type I transmembrane glycoprotein that is expressed on most tissues as four major isoforms (BC1, BC2, C1 and C2) that arise from alternative splicing of a single gene. All four isoforms have identical N-terminal regions consisting of four complement control protein repeats (CCPs 1–4, ovals). CCPs 1, 2 and 4 have N-linked sugar moieties (forks). The serine– threonine–proline rich (STP) region (triangles) is the site of alternative splicing. All four major isoforms use the C region, whereas the B exon is alternatively spliced, resulting in the BC or C STP regions. Following the STP domain is a 12 amino acid region of unknown function, a hydrophobic transmembrane domain, a charged cytoplasmic anchor and a C-terminal cytoplasmic tail. The C-terminus is also alternatively spliced, giving rise to expression of either Cyt-1 (of isoforms BC1 and C1) or Cyt-2 (of isoforms BC2 and C2). Cyt-1 is a 16 amino acid peptide and has phosphorylation sites for casein kinase II and protein kinase C. Cyt-2 is a 23 amino acid peptide and also has a casein kinase II site as well as a src kinase site. Regions of CD46 that have been identified as important for attachment of Neisseria are indicated in green in the BC1 isoform. These regions were identified by deletion mutagenesis of the BC1 isoform.

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Figure 4. CD46-dependent host cell responses to Neisseria gonorrhoeae adherence. (a) Neisseria (black) adheres to the host cell through an interaction between pilusassociated adhesins and CD46 [1]. Other surface molecules might be involved in this process. (b) Purified pili of Neisseria induce an adhesion-promoting transient release of calcium from intracellular stores [45]. (c) Neisseria attachment leads to tyrosine phosphorylation of CD46 and clustering of the src kinase c-yes at the site of microcolony attachment [46]. Both (b) and (c) promote bacterial adhesion and probably facilitate downstream signaling responses in the host. (d) CD46 clusters at the site of microcolony adhesion in a manner similar to other components of the cortical actin plaque described by Merz et al. [48,49,†]. (e) Following incubation with Neisseria, CD46 is lost from the cell surface and accumulates in the supernatant [37,†]. The mechanism by which CD46 is released is unknown.

overlay assay, labeled outer membrane preparations of piliated N. gonorrhoeae bound to a protein from ME-180 human cervical epithelial-cell lysates with an electrophoretic mobility that was consistent with CD46. Second, the preincubation of cultured epithelial cells with monoclonal antibodies (mAbs) against CD46 or with the purified recombinant CD46 ectodomain inhibited gonococcal adherence. Third, piliated N. gonorrhoeae and N. meningitidis adhered to Chinese hamster ovary (CHO) cells that were transfected with human CD46, but not to untransfected cells. These adherence studies also demonstrated that the expression of the BC1 and BC2 isoforms of CD46 in CHO cells conferred higher adherence than did the C1 or C2 isoforms [1]. In a subsequent study, COS-7 cells that expressed deletion constructs of the BC1 isoform of CD46 were used to assess which domains fo CD46 are required for gonococcal adhesion (Figure 3) [24]. Reduced gonococcal adhesion was observed in cells expressing constructs lacking complement control protein repeat (CCP)-3, the serine– threonine–proline rich (STP) region and the cytoplasmic tail. A puzzling observation was that, although the deletion of CCP-4 had no effect, gonococcal adhesion was almost eliminated by loss of the N-glycosylation site in this domain. CD46 interacts with the Neisseria pilus components PilE (the major pilus subunit) and PilC (a pilus-associated protein that influences pilus fiber assembly) (Figure 1). Both of these proteins have been identified as pilusassociated adhesins (reviewed in [2]). A truncated, secreted form of PilE known as soluble pilin (S-pilin) of N. gonorrhoeae adheres to a protein with an SDS–PAGE electrophoretic pattern similar to that of CD46 in an overlay assay and can inhibit the adhesion of gonococci to ME-180 cells [25]. A direct interaction has also been reported between CD46 and purified PilC from N. meningitidis (unpublished data*). Supporting the evidence for a CD46–PilC interaction, outer membrane preparations from meningococci with mutations in the * Albiger, B and Jonsson, A-B. (2000) 12th International Pathogenic Neisseria Conference, Galveston, TX, USA (Abstract 156) www.sciencedirect.com

PilC1 gene (which results in piliated meningococci that do not adhere to host cells) fail to adhere to CD46 in the overlay assay that was used for the initial identification of the CD46–pilus interaction [1]. CD46 is an attractive candidate as a pilus receptor because its expression has been demonstrated in tissues that are relevant to Neisseria infection, including female genital tissues [36], as well as neurons and blood vessel endothelial cells of the brain [9,27]. Additionally, an increased expression of CD46 has been described in oviductal tissue explants of one group of women with increased susceptibility to N. gonorrhoeae due to use of the subdermal contraceptive device Norplant [28]. Although CD46 expression is thought to be predominantly basolateral in epithelial cells [29,30], immunostaining data presented in several reports indicate that CD46 expression is not limited to the basolateral surface [26,28,31], suggesting that CD46 might be present on the apical surface of tissues that are targeted by the pathogenic Neisseria. Controversies surrounding CD46–Neisseria interactions However, the identity of CD46 as a cellular pilus receptor is associated with some controversy. Two independent groups assessed gonococcal adhesion relative to CD46 expression in several human cell lines [24,32]. Both studies demonstrated that the highest levels of bacterial adherence did not correspond to highest levels of CD46 expression, as might be expected if CD46 were acting solely as a ‘classical’ pilus receptor. Variations in the isoform distribution pattern among these cell lines did not account for these results. In considering these studies, the limitations of cancer cell models must be considered. It is known that cancer cells and cultured cancer cell lines exhibit altered protein expression, including increased amounts of CD46 compared with the non-malignant tissues of the same origin [33–35]. It is, therefore, of concern that in a primary human cervical cell model [36], as well as a model using human epithelial cell lines [37], mAbs against CD46 failed to inhibit the adherence of N. gonorrhoeae.

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An additional observation that complicates the interpretation of CD46 as a cellular pilus receptor involves the agglutination of human erythrocytes (which lack CD46 expression [38]) by piliated gonococci [39]. However, this might be explained by the studies of Rudel et al. [40] and Scheuerpflug et al. [41], which indicate that pilusmediated adhesion of N. gonorrhoeae and N. meningitidis to epithelial cells is mediated by different adhesins to those that are involved in hemagglutination. These studies argue that CD46-dependent adhesion to epithelial cells is facilitated by an interaction with PilC, whereas agglutination of the CD46-negative red blood cells occurs through interactions that are facilitated by PilE. Interestingly, controversy also exists regarding the use of CD46 as a receptor for the measles virus (MV) hemagglutinin. Many reports have established that vaccine strains of MV bind to CD46 with high affinity whereas wild-type strains preferentially use an alternative receptor known as SLAM (CDw150) [42]. Studies of the MV–CD46 interaction have defined a site on CD46 that is capable of low affinity and constitutive interaction with both vaccine and wild-type strains of MV. This is distinct from the high-affinity site that is used almost exclusively by vaccine strains [43]. CD46 usage by Neisseria might involve a similar scenario, in which CD46 contributes to adhesion through low-affinity interactions that require the coordinate engagement of a second (unidentified) receptor. CD46 transgenic mouse model of Neisseria infection Recent publications indicate a greater involvement of CD46 in the Neisseria–host encounter than a static interaction between CD46 and the pilus. Using transgenic mice that expressed human CD46, a recent study highlighted the importance of CD46 in N. meningitidis infection. These mice, which exhibit a human-like tissue distribution of CD46 [44], display enhanced susceptibility to meningococcal disease following experimental inoculation via either the intraperitoneal or intranasal route [30]. Following intraperitoneal infection, there was an increase in bacteraemia and mortality of the mice expressing CD46. Furthermore, bacteria were present in the cerebrospinal fluid, meninges and choriod plexus, suggesting that CD46 facilitated the passage of the meningococci across the blood–brain barrier. The role of the pilus was evaluated by infecting the transgenic mice with isogenic strains of N. meningitidis, one expressing pili and one lacking pili. Following intraperitoneal inoculation, nonpiliated bacteria were more virulent than the piliated strain, as evidenced by an increased mortality rate: a surprise given the purported role of CD46 as a pilus receptor. Intranasal inoculation, which more closely mimics the natural route of infection, resulted in no mortality among non-transgenic animals and only 15% lethality among CD46-transgenic mice that were infected with the piliated strain. Furthermore, in contrast to the increased virulence that was observed following intraperitoneal inoculation, non-piliated meningococci were avirulent following an intranasal challenge of the transgenic animals. Notably, the pilus-dependent lethality in the CD46-transgenic mice following intranasal inoculation www.sciencedirect.com

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was only observed if the mice were pretreated with antibiotics to reduce the natural flora. The low mortality rate that was observed via the natural (intranasal) inoculation route and the unexpected virulence exhibited by non-piliated meningococci following intraperitoneal inoculation emphasize the complexity of the role of CD46 in Neisseria disease progression. Nevertheless, these results illustrate an important role for CD46 in the development of lethal meningococcal disease, particularly in traversing the blood–brain barrier. Future experiments using this model to assess the role of pilus components of N. meningitidis, such as PilC and PilT, should further define the contribution of these proteins to meningococcal disease progression. CD46 as a mediator of Neisseria-induced cell signaling The signaling capability of CD46 in microbial pathogenesis has been characterized for MV infection, in which CD46-dependent responses contribute both to infectivity and to the host response. CD46 might be similarly exploited by Neisseria, especially in processes that are related to adherence. One study demonstrated a CD46-dependent calcium flux that promoted adherence of gonococci to human cells (Figure 4b) [45]. This rapid transient release of calcium from intracellular stores was observed after a w10 min incubation of ME-180 cells with outer membrane preparations of piliated N. gonorrhoeae or N. meningitidis. Additionally, the pre-incubation of cells with an adhesionblocking mAb directed against CD46 [1] inhibited the N. gonorrhoeae-induced calcium flux [45]. The pharmacological depletion of intracellular calcium stores before the addition of bacteria resulted in decreased gonococcal adhesion. Accordingly, a direct correlation was observed between the free cytosolic Ca2C concentration and gonococcal adhesion. Interestingly, the selective inhibition of casein kinase II (CKII, for which there is a site on both cytoplasmic tails of CD46) decreased gonococcal adhesion but did not inhibit the calcium flux, suggesting that CKII activation contributes to N. gonorrhoeae adhesion but is downstream of the pilus-induced calcium flux [45]. In further support for a role of the cytoplasmic domains of CD46 in bacterial attachment, COS-7 cells that were transfected with CD46 deletion mutants lacking portions of the cytoplasmic tail had decreased bacterial adhesion [24]. A later study by Lee et al. [46] indicated that the tyrosine phosphorylation of the cytoplasmic tail of CD46 by the src kinase c-yes promotes bacterial adhesion (Figure 4c). Tyrosine 354 on Cyt-2 was phosphorylated within five minutes following infection with gonococci. Treatment with an inhibitor of src family kinases reduced both tyrosine phosphorylation and gonococcal adhesion. In addition, c-yes was observed to aggregate at the site of gonococcal microcolony attachment, co-immunoprecipitate with CD46, and, following purification, phosphorylate CD46 in vitro [46]. In addition to inducing CD46-dependent signaling pathways, the adherence of N. gonorrhoeae to human epithelial cells alters the expression and cell-surface distribution of CD46 (Figure 4d). The adherence of N. gonorrhoeae to ME-180 cervical epithelial cells causes up to an 80% loss of CD46 from the cell; this is

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accompanied by the accumulation of apparently intact CD46 in the cell culture media [37]. N. gonorrhoeae mutants exhibiting reduced attachment because of the deletion of the adhesion-promoting pilus constituents PilE, PilV and PilC were unable to induce CD46 downregulation, suggesting that bacterial attachment is a requisite for this response. Interestingly, in this study, the preincubation of host cells with mAbs against CD46 (including some that have been shown to inhibit gonococcal adhesion [1]) inhibited neither CD46 downregulation nor the adhesion of gonococci [37]. However, N. gonorrhoeae mutants lacking the expression of the pilus retraction protein PilT are hyperadherent, yet incapable of inducing CD46 downregulation [37]. The induction of PilT expression in this mutant restored CD46 downregulation, confirming that the downregulation of CD46 requires PilT. CD46 downregulation is also influenced by alterations in pilE expression that arise from the passage of N. gonorrhoeae through the human host. Following experimental intraurethral inoculation of human male volunteers with N. gonorrhoeae, gonococci were re-isolated from the urine and pilE (pilin) sequences characterized. Five variants were chosen that displayed pilin sequences representative of those that arise with high frequency in vivo and become predominant [47]. The inoculating variant did not exhibit CD46 downregulation, yet three of the five variants re-isolated from the volunteers did induce this response. Additionally, of the two non-downregulating variants, one was isolated from the urine early in infection (days 1 and 2) but not later (days 3 and 4), suggesting a reduced level of in vivo fitness. The other exhibited low levels of adherence to the ME-180 cells used in the study, which would account for the lack of CD46 downregulation. These results point to selective in vivo pressures favoring N. gonorrhoeae that are capable of inducing CD46 downregulation. In addition to its downregulation, the cell-surface distribution of CD46 changes following the attachment of N. gonorrhoeae to host cells. The aggregation of CD46 at the site of N. gonorrhoeae microcolony adhesion following a 4–6 h incubation with gonococci has been observed in polarized ectocervical and endocervical cell monolayers [48] and in cultured cervical epithelial cells (unpublished data†). This observation might be related to the enrichment of cytoskeleton and integral membrane proteins in the form of a cortical actin plaque that occurs at the site of gonococcal attachment [49]. Interestingly, CD46 downregulation, cortical actin plaque formation and aggregation at the site of gonococcal adherence are all dependent upon the expression of PilT. These processes might, therefore, be interrelated and dependent upon the expression of retractile pili. It has been suggested that tensile forces exerted on the cell surface by the retraction of the pili of adherent gonococci activate mechanosensory pathways in the host cell [2]. † Gill, D.B. et al. (2004) Piliated Neisseria gonorrhoeae induce shedding and surface redistribution of CD46. Molecular Immunology 41, 236 www.sciencedirect.com

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CD46 as protection against complement The complement system is crucial to the control of Neisseria infections, as evidenced by the increased susceptibility to Neisserial infections of individuals with complement deficiencies [50]. Neisseria is also known to usurp the protective functions of other human complement regulators, such as factor H and C4 binding protein [51]. It is therefore tempting to speculate that Neisseria benefit from the complement regulatory activity of CD46. However, complement deposition on bacterial surfaces probably occurs in the extracellular milieu, before interaction with the host cell. The cofactor activity of CD46 is intrinsic: it is primarily active on C3b and C4b that are deposited to the same surface on which CD46 is expressed. Therefore, opsonins (C3b and C4b) on the bacterial surface might be inaccessible to CD46. In addition, the N. gonorrhoeae-induced loss of CD46 from the host cell probably renders the infected cell more susceptible to complement attack, as is observed following CD46 downregulation in MV-infected cells [52,53]. Alternatively, the N. gonorrhoeae-induced aggregation of CD46 at the site of adhesion and release of CD46 might be a protective scheme orchestrated by the pathogen to concentrate CD46 in close proximity to adherent N. gonorrhoeae and thereby inhibit complement activation at the site.

Concluding remarks The importance of CD46 in Neisseria infection has been demonstrated in vivo through the analysis of CD46 transgenic mice and in vitro by experimentation with primary explants and cultured human cell lines. However, the role of CD46 in gonococcal and meningococcal pathogenesis remains incompletely defined. A direct interaction has been described between CD46 and the Neisseria pilus but there are also studies indicating that this is not a classical receptor–ligand interaction. Therefore, it is likely that other receptors are also involved. CD46 has been related to several N. gonorrhoeae-induced cellular responses, such as alterations in the cell-surface distribution and cellular levels of CD46, a calcium flux and CD46 tyrosine phosphorylation. These CD46-dependent signaling responses result in changes in the microenvironment of the host– pathogen interface that promote strong adhesion and possibly protect the bacteria from complement activation. The encounter between Neisseria and human cells represents a fascinating and complex interplay between bacterial and host factors. A more precise understanding of these events will provide valuable insights into the pathogenesis of N. gonorrhoeae and N. meningitidis and the biology of CD46. Such understanding might reveal novel treatment and prevention strategies that interfere either with the CD46–pilus interaction or with CD46dependent host cell responses to bacterial adhesion that promote infectivity. Because of the involvement of CD46 in the pathogenesis of an ever-growing and diverse list of human pathogens, the insight gained through further study of the role of CD46 in Neisseria infection will increase our understanding of the pathogenesis of multiple infectious diseases.

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References 1 Kallstrom, H. et al. (1997) Membrane cofactor protein (MCP or CD46) is a cellular pilus receptor for pathogenic Neisseria. Mol. Microbiol. 25, 639–647 2 Merz, A.J. and So, M. (2000) Interactions of pathogenic Neisseriae with epithelial cell membranes. Annu. Rev. Cell Dev. Biol. 16, 423–457 3 Plant, L. and Jonsson, A-B. (2003) Contacting the host: insights and implications of pathogenic Neisseria cell interactions. Scand. J. Infect. Dis. 35, 608–613 4 Naumann, M. et al. (1999) Host cell interactions and signalling with Neisseria gonorrhoeae. Curr. Opin. Microbiol. 2, 62–70 5 Gray-Owen, S.D. (2003) Neisserial Opa proteins: impact on colonization, dissemination and immunity. Scand. J. Infect. Dis. 35, 614–618 6 Hauck, C.R. and Meyer, T.F. (2003) ‘Small’ talk: Opa proteins as mediators of Neisseria–host-cell communication. Curr. Opin. Microbiol. 6, 43–49 7 Massari, P. et al. (2003) The role of porins in neisserial pathogenesis and immunity. Trends Microbiol. 11, 87–93 8 Hourcade, D. et al. (2000) Functional domains, structural variations and pathogen interactions of MCP, DAF and CR1. Immunopharmacology 49, 103–116 9 Johnstone, R.W. et al. (1993) Identification and quantification of complement regulator CD46 on normal human tissues. Immunology 79, 341–347 10 Ballard, L. et al. (1987) A polymorphism of the complement regulatory protein MCP (membrane cofactor protein or gp 45–70). J. Immunol. 138, 3850–3855 11 Bora, N.S. et al. (1991) Membrane cofactor protein of the complement system: A Hind III restriction fragment length polymorphism that correlates with the expression polymorphism. J. Immunol. 146, 2821–2825 12 Richards, A. et al. (2003) Mutations in human complement regulator, membrane cofactor protein (CD46), predispose to development of familial hemolytic uremic syndrome. Proc. Natl. Acad. Sci. U. S. A. 100, 12966–12971 13 Noris, M. et al. (2003) Familial haemolytic uraemic syndrome and an MCP mutation. Lancet 362, 1542–1547 14 Goodship, T.H.J. et al. (2004) Mutations in CD46, a complement regulatory protein, predispose to atypical HUS. Trends Mol. Med. 10, 226–231 15 Riley, R.C. et al. (2002) Characterization of human membrane cofactor protein (MCP; CD46) on spermatozoa. Mol. Reprod. Dev. 62, 534–546 16 Kemper, C. et al. (2003) Activation of human CD4C cells with CD3 and CD46 induces a T-regulatory cell 1 phenotype. Nature 421, 388–392 17 Naniche, D. et al. (1993) Measles virus haemagglutinin induces downregulation of gp57/67, a molecule involved in virus binding. J. Gen. Virol. 74, 1073–1079 18 Dorig, R.E. et al. (1993) The human CD46 molecule is a receptor for measles virus (Edmonston strain). Cell 75, 295–305 19 Okada, N. et al. (1995) Membrane cofactor protein (CD46) is a keratinocyte receptor for the M protein of the group A streptococcus. Proc. Natl. Acad. Sci. U. S. A. 92, 2489–2493 20 Santoro, F. et al. (1999) CD46 is a cellular receptor for human herpesvirus 6. Cell 99, 817–827 21 Gaggar, A. et al. (2003) CD46 is a cellular receptor for group B adenoviruses. Nat. Med. 9, 1408–1412 22 Segerman, A. et al. (2003) Adenovirus type 11 uses CD46 as a cellular receptor. J. Virol. 77, 9183–9191 23 Wu, E. et al. (2004) Membrane cofactor protein is a receptor for adenoviruses associated with epidemic keratoconjunctivitis. J. Virol. 78, 3897–3905 24 Kallstrom, H. et al. (2001) Attachment of Neisseria gonorrhoeae to the cellular pilus receptor CD46: identification of domains important for bacterial adherence. Cell. Microbiol. 3, 133–143 25 Rytkonen, A. et al. (2001) Soluble pilin of Neisseria gonorrhoeae interacts with human target cells and tissue. Infect. Immun. 69, 6419–6426 26 Johnstone, R.W. et al. (1993) Polymorphic expression of CD46 protein isoforms due to tissue-specific RNA splicing. Mol. Immunol. 30, 1231–1241 27 Fernandez, R. et al. (2001) Increased adhesiveness and internalization www.sciencedirect.com

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of Neisseria gonorrhoeae and changes in the expression of epithelial gonococcal receptors in the Fallopian tube of copper T and Norplant users. Hum. Reprod. 16, 463–468 Maisner, A. et al. (1996) Two different cytoplasmic tails direct isoforms of the membrane cofactor protein (MCP; CD46) to the basolateral surface of Madin–Darby canine kidney (MDCK) cells. J. Biol. Chem. 271, 18853–18858 Teuchert, M. et al. (1999) Importance of the carboxyl-terminal FTSL motif of membrane cofactor protein for basolateral sorting and endocytosis. Positive and negative modulation by signals inside and outside the cytoplasmic tail. J. Biol. Chem. 274, 19979–19984 Johansson, L. et al. (2003) CD46 in meningococcal disease. Science 301, 373–375 Oglesby, T.J. et al. (1996) Human complement regulator expression by the normal female reproductive tract. Anat. Rec. 246, 78–86 Tobiason, D.M. and Seifert, H.S. (2001) Inverse relationship between pilus-mediated gonococcal adherence and surface expression of the pilus receptor, CD46. Microbiology 147, 2333–2340 Murray, K.P. et al. (2000) Expression of complement regulatory proteins – CD 35, CD 46, CD 55, and CD 59 – in benign and malignant endometrial tissue. Gynecol. Oncol. 76, 176–182 Seya, T. et al. (1990) Quantitative analysis of membrane cofactor protein (MCP) of complement. J. Immunol. 145, 238–245 Hara, T. et al. (1995) High expression of membrane cofactor protein of complement (CD46) in human leukaemia cell lines: implication of an alternatively spliced form containing the STA domain in CD46 up-regulation. Scand. J. Immunol. 42, 581–590 Edwards, J.L. et al. (2002) A co-operative interaction between Neisseria gonorrhoeae and complement receptor 3 mediates infection of primary cervical epithelial cells. Cell. Microbiol. 4, 571–584 Gill, D.B. et al. (2003) Down-regulation of CD46 by piliated Neisseria gonorrhoeae. J. Exp. Med. 198, 1313–1322 McNearney, T.M. et al. (1989) Membrane cofactor protein of complement is present on human fibroblast, epithelial and endothelial cells. J. Clin. Invest. 84, 538–545 Koransky, J. (1975) Bacterial hemagglutination by Neisseria gonorrhoeae. Infect. Immun. 12, 495–498 Rudel, T. et al. (1992) Interaction of two variable proteins (PilE and PilC) required for pilus-mediated adherence of Neisseria gonorrhoeae to human epithelial cells. Mol. Microbiol. 6, 3439–3450 Scheuerpflug, I. et al. (1999) Roles of PilC and PilE proteins in pilus-mediated adherence of Neisseria gonorrhoeae and Neisseria meningitidis to human erythrocytes and endothelial and epithelial cells. Infect. Immun. 67, 834–843 Schneider-Schaulies, J. et al. (2003) Measles infection of the central nervous system. J. Neurovirol. 9, 247–252 Masse, N. et al. (2002) Identification of a second major site for CD46 binding in the hemagglutinin protein from a laboratory strain of measles virus (MV): potential consequences for wild-type MV infection. J. Virol. 76, 13034–13038 Kemper, C. et al. (2001) Membrane cofactor protein (MCP; CD46) expression in transgenic mice. Clin. Exp. Immunol. 124, 180–189 Kallstrom, H. et al. (1998) Cell signaling by the type IV pili of pathogenic Neisseria. J. Biol. Chem. 273, 21777–21782 Lee, S.W. et al. (2002) CD46 is phosphorylated at tyrosine 354 upon infection of epithelial cells by Neisseria gonorrhoeae. J. Cell Biol. 156, 951–957 Hamrick, T.S. et al. (2001) Antigenic variation of gonococcal pilin expression in vivo: analysis of the strain FA1090 pilin repertoire and identification of the pilS gene copies recombining with pilE during experimental human infection. Microbiology 147, 839–849 Edwards, J.L. et al. (2000) Neisseria gonorrhoeae elicits membrane ruffling and cytoskeletal rearrangements upon infection of primary human endocervical and ectocervical cells. Infect. Immun. 68, 5354–5363 Merz, A.J. et al. (1999) Type IV pili of pathogenic Neisseriae elicit cortical plaque formation in epithelial cells. Mol. Microbiol. 32, 1316–1332 Vogel, U. and Frosch, M. (1999) Mechanisms of neisserial serum resistance. Mol. Microbiol. 32, 1133–1139 Ram, S. et al. (1999) The contrasting mechanisms of serum resistance of Neisseria gonorrhoeae and group B Neisseria meningitidis. Mol. Immunol. 36, 915–928

Review

TRENDS in Molecular Medicine

52 Schnorr, J.J. et al. (1995) Measles virus-induced down-regulation of CD46 is associated with enhanced sensitivity to complementmediated lysis of infected cells. Eur. J. Immunol. 25, 976–984 53 Tishon, A. et al. (1996) A model of measles virus-induced immunosuppression: enhanced susceptibility of neonatal human PBLs. Nat. Med. 2, 1250–1254 54 Park, H.S. et al. (2002) Modification of type IV pilus-associated epithelial cell adherence and multicellular behavior by the PilU protein of Neisseria gonorrhoeae. Infect. Immun. 70, 3891–3903

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55 Rudel, T. et al. (1995) Neisseria PilC protein identified as type-4 pilus tip-located adhesin. Nature 373, 357–359 56 Rahman, M. et al. (1997) PilC of pathogenic Neisseria is associated with the bacterial cell surface. Mol. Microbiol. 25, 11–25 57 Winther-Larsen, H.C. et al. (2001) Neisseria gonorrhoeae PilV, a type IV pilus-associated protein essential to human epithelial cell adherence. Proc. Natl. Acad. Sci. U. S. A. 98, 15276–15281 58 Brossay, L. et al. (1994) Identification, localization, and distribution of the PilT protein in Neisseria gonorrhoeae. Infect. Immun. 62, 2302–2308

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