Tumor suppressor protein p53-mediated repression of human mitotic centromere-associated kinesin gene expression is exerted via down-regulation of Sp1 level.

The repressive role of p53 on the human mitotic centromere-associated kinesin (MCAK) core promoter from ‒266 to +54, relative to the transcription start site, has been determined. The MCAK mRNA and protein levels were 2.1- and 3.0-fold higher, respectively, in HCT116 (p53‒/‒) than in HCT116 (p53+/+) cells. Enforced down-regulation of p53 levels either in HCT116 (p53+/+) cells by p53 RNAi treatment or in MCF-7 cells using shRNA for p53 (shp53) resulted in a remarkable increase in the MCAK protein level. Site-directed mutagenesis and ChIP analyses showed that p53-mediated repression of the MCAK core promoter activity was not directly exerted by p53-binding to putative p53-response elements (p53-RE1 at -173/-166 and p53-RE2 at -245/-238), but indirectly by attenuating Sp1 binding to GC-motifs (GC1 at -93/-84 and GC2 at -119/-110). Treatment of HEK-293 cells bearing the MCAK core promoter-reporter (pGL2-320-Luc) with mithramycin A, which down-regulates Sp1 gene expression, reduced the promoter activity as well as endogenous MCAK levels. Exposure of HCT116 (p53+/+) cells to nutlin-3a, a validated activator of p53, caused a simultaneous reduction in Sp1 and MCAK protein levels, but not in HCT116 (p53-/-) cells. In contrast to wild-type (wt)-p53, tumor-derived p53 mutants (p53V143A, p53R248W, and p53R273H) failed to repress the Sp1-dependent activation of the MCAK promoter and to down-regulate endogenous levels of Sp1 and MCAK proteins. Collectively, these findings demonstrate that p53 can repress MCAK promoter activity indirectly via down-regulation of Sp1 expression level, and suggest that MCAK elevation in human tumor cells might be due to p53 mutation.

Anti-inflammatory action of 2-carbomethoxy-2,3-epoxy-3-prenyl-1,4-naphthoquinone (CMEP-NQ) suppresses both the MyD88-dependent and TRIF-dependent pathways of TLR4 signaling in LPS-stimulated RAW264.7 cells.

ETHNOPHARMACOLOGICAL RELEVANCE: The roots of Rubia cordifolia L. have been widely used as a traditional herbal medicine in Northeast Asia for treating inflammatory diseases. AIM OF THE STUDY: To elucidate the anti-inflammatory mechanism of 2-carbomethoxy-2,3-epoxy-3- prenyl-1,4-naphthoquinone (CMEP-NQ), purified from the roots of R. cordifolia L. as the major anti-inflammatory component, in LPS-treated RAW264.7 murine macrophage cells. MATERIALS AND METHODS: Anti-inflammatory activity of CMEP-NQ was investigated in LPS-treated RAW264.7 cells by measuring the levels of NO, PGE2, and cytokines (IL1ß, IL-6, TNF-α) in the culture supernatants and the TLR4-mediated intracellular events including association of MyD88 with IRAK1, activation of IRAK1, TAK1, MAPKs, NF-κB/AP-1, and IRF3, and generation of ROS. RESULTS: Pretreatment of RAW264.7 cells with CMEP-NQ reduced LPS-induced production of NO and PGE2 by suppressing iNOS and COX-2 gene expression. CMEP-NQ also reduced the secretion of IL-1ß, IL-6, and TNF-α by down-regulating mRNA levels. Under these conditions, TLR4-mediated MyD88-dependent events were inhibited by CMEP-NQ, including the association of MyD88 with IRAK1, phosphorylation of IRAK1, TAK1, and MAPKs (ERK, JNK and p38 MAPK), and activation of NF-κB and AP-1. As TRIF-dependent events of TLR4 signaling, phosphorylation of IRF3 and induction of iNOS protein expression were also inhibited by CMEP-NQ. However, the binding of FITC-conjugated LPS to cell surface TLR4 was not affected by CMEP-NQ. Following LPS stimulation, intracellular ROS production was first detected by DCFH-DA staining at 1h; then it continuously increased until 16h. Although CMEP-NQ failed to exhibit DPPH radical- or ABTS radical-scavenging activity in vitro, LPS-induced ROS production in RAW264.7 cells was more efficiently blocked by CMEP-NQ than by NAC. CONCLUSIONS: These results demonstrate that the suppressive effect of CMEP-NQ on LPS-induced inflammatory responses in RAW264.7 cells was mainly exerted via its inhibition of TLR4-mediated proximal events, such as MyD88-dependent NF-κB/AP-1 activation and ROS production, and TRIF-dependent IRF3 activation.

Discovery and synthesis of novel allylthioaralkylthiopyridazines: their antiproliferative activity against MCF-7 and Hep3B cells.

A new series of 6-allylthio-3-aralkylthio-4,5-dimethylpyridazines 5a-5k and 1-allylthio-4-alkylthio-5,6,7,8-tetrahydrophthalazine 6a-6j was synthesized from maleic anhydride derivatives for development of new anticancer agents. The process involves the formation of pyridazine and phthalazine rings, dichlorination, allylthiolation, and aralkylthiolation. These new compounds showed antiproliferative activities against breast cancer (MCF-7) and hepatocarcinoma (Hep3B) cells in CCK-8 assays, and could be promising candidates for chemotherapy of carcinomas. Among 21 synthesized compounds, five compounds (5a, 5b, 6b, 6d, and 6f) showed higher potency than 5-FU for inhibiting the growth of cell line. The results indicated that compound 6f had the highest activity towards MCF-7 and Hep3B cells. These results suggest the potential anticancer activity of compounds 5a, 5b, 6b, 6d, and 6f.

Proteasome inhibitor MG132-induced apoptosis via ER stress-mediated apoptotic pathway and its potentiation by protein tyrosine kinase p56lck in human Jurkat T cells.

Exposure of human Jurkat T cells to MG132 caused apoptosis along with upregulation of Grp78/BiP and CHOP/GADD153, activation of JNK and p38MAPK, activation of Bak, mitochondrial membrane potential (Δψm) loss, cytochrome c release, activation of caspase-12, -9, -3, -7, and -8, cleavage of Bid and PARP, and DNA fragmentation. However, these MG132-induced apoptotic events, with the exceptions of upregulation of Grp78/BiP and CHOP/GADD153 and activation of JNK and p38MAPK, were abrogated by overexpression of Bcl-xL. Pretreatment with the pan-caspase inhibitor z-VAD-fmk prevented MG132-induced apoptotic caspase cascade, but allowed upregulation of Grp78/BiP and CHOP/GADD153 levels, activation of JNK and p38MAPK, Δψm loss, and cleavage of procaspase-9 (47kDa) to active form (35kDa). Further analysis using selective caspase inhibitors revealed that caspase-12 activation was required for activation of caspase-9 and -3 to the sufficient level for subsequent activation of caspase-7 and -8. MG132-induced cytotoxicity, apoptotic sub-G(1) peak, Bak activation, and Δψm loss were markedly reduced by p38MAPK inhibitor, but not by JNK inhibitor. MG132-induced apoptotic changes, including upregulation of Grp78/BiP and CHOP/GADD153 levels, activation of caspase-12, p38MAPK and Bak, and mitochondria-dependent activation of caspase cascade were more significant in p56(lck)-stable transfectant JCaM1.6/lck than in p56(lck)-deficient JCaM1.6/vector. The cytotoxicity of MG132 toward p56(lck)-positive Jurkat T cell clone was not affected by the Src-like kinase inhibitor PP2. These results demonstrated that MG132-induced apoptosis was caused by ER stress and subsequent activation of mitochondria-dependent caspase cascade, and that the presence of p56(lck) enhances MG132-induced apoptosis by augmenting ER stress-mediated apoptotic events in Jurkat T cells.

Mollugin induces apoptosis in human Jurkat T cells through endoplasmic reticulum stress-mediated activation of JNK and caspase-12 and subsequent activation of mitochondria-dependent caspase cascade regulated by Bcl-xL.

Exposure of Jurkat T cells to mollugin (15-30 microM), purified from the roots of Rubia cordifolia L., caused cytotoxicity and apoptotic DNA fragmentation along with mitochondrial membrane potential disruption, mitochondrial cytochrome c release, phosphorylation of c-Jun N-terminal kinase (JNK), activation of caspase-12, -9, -7, -3, and -8, cleavage of FLIP and Bid, and PARP degradation, without accompanying necrosis. While these mollugin-induced cytotoxicity and apoptotic events including activation of caspase-8 and mitochondria-dependent activation of caspase cascade were completely prevented by overexpression of Bcl-xL, the activation of JNK and caspase-12 was prevented to much lesser extent. Pretreatment of the cells with the pan-caspase inhibitor (z-VAD-fmk), the caspase-9 inhibitor (z-LEHD-fmk), the caspase-3 inhibitor (z-DEVD-fmk) or the caspase-12 inhibitor (z-ATAD-fmk) at the minimal concentration to prevent mollugin-induced apoptosis appeared to completely block the activation of caspase-7 and -8, and PARP degradation, but failed to block the activation of caspase-9 and -3 with allowing a slight enhancement in the level of JNK phosphorylation. Both FADD-positive wild-type Jurkat clone A3 and FADD-deficient Jurkat clone I2.1 exhibited a similar susceptibility to the cytotoxicity of mollugin, excluding involvement of Fas/FasL system in triggering mollugin-induced apoptosis. Normal peripheral T cells were more refractory to the cytotoxicity of mollugin than were Jurkat T cells. These results demonstrated that mollugin-induced cytotoxicity in Jurkat T cells was mainly attributable to apoptosis provoked via endoplasmic reticulum (ER) stress-mediated activation of JNK and caspase-12, and subsequent mitochondria-dependent activation of caspase-9 and -3, leading to activation of caspase-7 and -8, which could be regulated by Bcl-xL.

Protein tyrosine kinase p56lck-deficiency confers hypersusceptibility to rho-fluorophenylalanine (pFPhe)-induced apoptosis by augmenting mitochondrial apoptotic pathway in human Jurkat T cells.

Phenylalanine analog, rho-fluorophenylalanine (pFPhe)-mediated cytotoxicity and several apoptotic events including mitochondrial cytochrome c release, activation of caspase-9, -3, and -8, Bid cleavage, degradation of PARP and PLCgamma-1, and DNA fragmentation were more significant in p56(lck)-deficient Jurkat T cells (JCaM1.6) than in wild-type Jurkat T cells (E6.1). The susceptibility of JCaM1.6 toward apoptogenic activity of pFPhe decreased after acquisition of p56(lck) by transfection. The p56(lck) kinase activity increased 1.6-fold at 15-30 min after pFPhe treatment. The pan-caspase inhibitor (z-VAD-fmk) completely blocked the pFPhe-mediated apoptotic changes except caspase-9 activation. The caspase-8 inhibitor (z-IETD-fmk), which failed to influence pFPhe-induced caspase-9 activation, completely blocked caspase-8 activation and PLCgamma-1 degradation with a marked reduction in caspase-3 activation and PARP degradation, indicating pFPhe-induced caspase-8 activation as a downstream event of mitochondria-dependent activation of caspase-9. These results indicate that the deficiency of p56(lck) augments pFPhe-induced mitochondrial cytochrome c release and resultant apoptotic cell death in Jurkat T cells.

17Alpha-estradiol arrests cell cycle progression at G2/M and induces apoptotic cell death in human acute leukemia Jurkat T cells.

A pharmacological dose (2.5-10 microM) of 17alpha-estradiol (17alpha-E(2)) exerted a cytotoxic effect on human leukemias Jurkat T and U937 cells, which was not suppressed by the estrogen receptor (ER) antagonist ICI 182,780. Along with cytotoxicity in Jurkat T cells, several apoptotic events including mitochondrial cytochrome c release, activation of caspase-9, -3, and -8, PARP degradation, and DNA fragmentation were induced. The cytotoxicity of 17alpha-E(2) was not blocked by the anti-Fas neutralizing antibody ZB-4. While undergoing apoptosis, there was a remarkable accumulation of G(2)/M cells with the upregulatoin of cdc2 kinase activity, which was reflected in the Thr56 phosphorylation of Bcl-2. Dephosphorylation at Tyr15 and phosphorylation at Thr161 of cdc2, and significant increase in the cyclin B1 level were underlying factors for the cdc2 kinase activation. Whereas the 17alpha-E(2)-induced apoptosis was completely abrogated by overexpression of Bcl-2 or by pretreatment with the pan-caspase inhibitor z-VAD-fmk, the accumulation of G(2)/M cells significantly increased. The caspase-8 inhibitor z-IETD-fmk failed to influence 17alpha-E(2)-mediated caspase-9 activation, but it markedly reduced caspase-3 activation and PARP degradation with the suppression of apoptosis, indicating the contribution of caspase-8; not as an upstream event of the mitochondrial cytochrome c release, but to caspase-3 activation. In the presence of hydroxyurea, which blocked the cell cycle progression at the G(1)/S boundary, 17alpha-E(2) failed to induce the G(2)/M arrest as well as apoptosis. These results demonstrate that the cytotoxicity of 17alpha-E(2) toward Jurkat T cells is attributable to apoptosis mainly induced in G(2)/M-arrested cells, in an ER-independent manner, via a mitochondria-dependent caspase pathway regulated by Bcl-2.

Positive regulation of promoter activity of human 3-phosphoglycerate dehydrogenase (PHGDH) gene is mediated by transcription factors Sp1 and NF-Y.

The PHGDH gene encodes the 3-phosphoglycerate dehydrogenase that catalyzes the transition of 3-phosphoglycerate into 3-phosphohydroxy pyruvate for the phosphorylated pathway of serine biosynthesis. To understand transcriptional regulation of the human PHGDH promoter, a genomic clone containing the 5'-flanking region of the PHGDH gene was isolated from a human genomic library. The 1192-bp PHGDH promoter region was cloned by PCR using the genomic DNA isolated from the PHGDH genomic clone. Sequence analysis of the promoter region exhibited several putative transcription factor binding sites for NF-Y, Sp1, GATA-1, p53, AP2, and AP1, with no TATA-box motif at an appropriate position. Transfection of a series of deletion constructs of the promoter region into HeLa cells revealed that the core positive promoter activity resided in the -276 to +1, which contains two GC-motifs for binding Sp1 and one CCAAT-motif for NF-Y. Mutational analysis and electrophoretic mobility shift assay indicated that both the proximal GC-motif and CCAAT-motif were crucial for full induction of the promoter activity. Chromatin immunoprecipitation analysis confirmed the recruitment of Sp1 and NF-Y to the promoter region in vivo. These results demonstrated that the promoter activity of the human PHGDH gene was positively regulated by the action of transcription factors Sp1 and NF-Y.

Regulation of the human mitotic centromere-associated kinesin (MCAK) promoter by the transcription factors Sp1 and E2F1.

To understand transcriptional regulation of the human mitotic centromere-associated kinesin (MCAK) promoter, the 1,151-bp promoter region of the human MCAK gene in Jurkat T cells was cloned by polymerase chain reaction (PCR). Although a bioinformatic analysis of the promoter sequence predicted several putative transcription factor binding sites for E2F, Sp1, c-Myb, p53, p300, NF-1, AML-1a, Ap-1, E-box factor, and C/EBPalpha/beta with no consensus TATA-box motif, deletion constructs of the promoter region revealed that the core positive promoter activity resided at -266/-66, containing three GC-motifs for binding Sp1. Site-directed disruption and chromatin immunoprecipitation analysis indicated that Sp1-binding to the GC-motifs was crucial for promoter activation, but the E2F1-binding to the E2F-motif (-57/-50) was crucial for promoter repression. Cotransfection of the luciferase reporter with either Sp1- or E2F1-expression plasmid further verified the role of Sp1 as a transcriptional activator and E2F1 as a transcriptional repressor in the human MCAK promoter.

Cytotoxicity of diacetoxyscirpenol is associated with apoptosis by activation of caspase-8 and interruption of cell cycle progression by down-regulation of cdk4 and cyclin B1 in human Jurkat T cells.

To understand the mechanism underlying T-cell toxicity of diacetoxyscirpenol (DAS) from Fusarium sambucinum, its apoptogenic as well as growth retardation activity was investigated in human Jurkat T cells. Exposure to DAS (0.01-0.15 microM) caused apoptotic DNA fragmentation along with caspase-8 activation, Bid cleavage, mitochondrial cytochrome c release, activation of caspase-9 and caspase-3, and PARP degradation, without any alteration in the levels of Fas or FasL. Under these conditions, necrosis was not accompanied. The cytotoxicity of DAS was not blocked by the anti-Fas neutralizing antibody ZB-4. Although the DAS-induced apoptotic events were completely prevented by overexpression of Bcl-xL, the cells overexpressing Bcl-xL were unable to divide in the presence of DAS, resulting from the failure of cell cycle progression possibly due to down-regulation in the protein levels of cdk4 and cyclin B1. The DAS-mediated apoptosis and activation of caspase-8, -9, and -3 were abrogated by either pan-caspase inhibitor (z-VAD-fmk) or caspase-8 inhibitor (z-IETD-fmk). While the DAS-mediated apoptosis and activation of caspase-9 and caspase-3 were slightly suppressed by the mitochondrial permeability transition pore inhibitor (CsA), both caspase-8 activation and Bid cleavage were not affected by CsA. The activated normal peripheral T cells possessed a similar susceptibility to the cytotoxicity of DAS. These results demonstrate that the T-cell toxicity of DAS is attributable to not only apoptosis initiated by caspase-8 activation and subsequent mitochondrion-dependent or -independent activation of caspase cascades, which can be regulated by Bcl-xL, but also interruption of cell cycle progression caused by down-regulation of cdk4 and cyclin B1 proteins.

Active and passive intranasal immunizations with streptococcal surface protein C5a peptidase prevent infection of murine nasal mucosa-associated lymphoid tissue, a functional homologue of human tonsils.

C5a peptidase, also called SCPA (surface-bound C5a peptidase), is a surface-bound protein on group A streptococci (GAS), etiologic agents for a variety of human diseases including pharyngitis, impetigo, toxic shock, and necrotizing fasciitis, as well as the postinfection sequelae rheumatic fever and rheumatic heart disease. This protein is highly conserved among different serotypes and is also expressed in human isolates of group B, C, and G streptococci. Human tonsils are the primary reservoirs for GAS, maintaining endemic disease across the globe. We recently reported that GAS preferentially target nasal mucosa-associated lymphoid tissue (NALT) in mice, a tissue functionally analogous to human tonsils. Experiments using a C5a peptidase loss-of-function mutant and an intranasal infection model showed that this protease is required for efficient colonization of NALT. An effective vaccine should prevent infection of this secondary lymphoid tissue; therefore, the potential of anti-SCPA antibodies to protect against streptococcal infection of NALT was investigated. Experiments showed that GAS colonization of NALT was significantly reduced following intranasal immunization of mice with recombinant SCPA protein administered alone or with cholera toxin, whereas a high degree of GAS colonization of NALT was observed in control mice immunized with phosphate-buffered saline only. Moreover, administration of anti-SCPA serum by the intranasal route protected mice against streptococcal infection. These results suggest that intranasal immunization with SCPA would prevent colonization and infection of human tonsils, thereby eliminating potential reservoirs that maintain endemic disease.

The M protein is dispensable for maturation of streptococcal cysteine protease SpeB.

The streptococcal pyrogenic exotoxin B (SpeB) is an important virulence factor of group A streptococci (GAS) with cysteine protease activity. Maturation of SpeB to a proteolytically active form was suggested to be dependent on cell-wall-anchored M1 protein, the major surface protein of GAS (M. Collin and A. Olsen, Mol. Microbiol. 36:1306-1318, 2000). Collin and Olsen showed that mutant GAS strains expressing truncated M protein secrete a conformationally different form of unprocessed SpeB with no proteolytic activity. Alternatively, we hypothesized that a truncated M protein may interfere with processing of this secreted protease, and therefore we tested cysteine protease activity in genetically defined mutant strains that express either no M protein or membrane-anchored M protein with an in-frame deletion of the AB repeat region. Measurements of SpeB activity by cleavage of a substrate n-benzoyl-Pro-Phe-Arg-p-nitroanilide hydrochloride showed that the proteolytic activities in culture supernatants of both mutants were similar to those from the wild-type strain. In addition, Western blot analysis of culture supernatants showed that SpeB expression and processing to a mature form was unaffected by either deletion mutation. Therefore, we conclude that M protein is not required for maturation of the streptococcal cysteine protease SpeB.

Primary induction of CD4 T cell responses in nasal associated lymphoid tissue during group A streptococcal infection.

CD4 T cells are important for development of long-term immunity to bacterial infections. Here we describe construction of a group A streptococcus (GAS) strain that expresses the model ovalbumin epitope (OVA) on its surface, and the use of this strain in adoptive transfer experiments to study CD4 T cell response to bacterial infection in nasal-associated lymphoid tissue (NALT), which was previously shown to be a specific target for GAS colonization. The OVA(+) GAS, but not the wild-type strain was shown to activate CD4 T cells in an antigen-specific manner both in vitro and in vivo. After intranasal infection of mice with this strain, OVA-specific CD4 T cells were first activated in NALT, which is functionally equivalent to human tonsils, rather than in the cervical lymph nodes. During localized infection, OVA(+) GAS induced rapid and prolonged activation of CD4 T cells at higher magnitudes in the NALT than in draining lymph nodes and spleen, where CD4 T cells underwent little or no activation. In contrast, systemic infection induced significantly higher activation of CD4 T cells in both lymph nodes and spleens, compared to when the infection was localized in NALT. Further investigation of cellular immune responses in NALT during GAS infection using adoptive T cell transfer, combined with the model antigen on the pathogen may ultimately shed light on mechanisms for failure of children to develop protective immune responses following streptococcal tonsillitis.

Promotion of fibronectin independent invasion by C5a peptidase into epithelial cells in group A Streptococcus.

BACKGROUND & OBJECTIVES: Group A Streptococcus, causative agent of several clinical manifestations codes for multiple protein invasins which help the bacterium to enter non-phagocytic cells. C5a peptidase (SCPA) is a surface protein conserved among different serotypes of M1 strain. The present study was taken up to study SCPA promoted fibronectin independent entry of GAS into epithelial cells. METHODS: An isogenic 90226 emm1deltaAB (M1(-)) mutant was constructed with thermosensitive pGhost vector. This isogenic M1(-) mutant expressed SCPA on the surface as determined by Western blotting and immunofluorescence. RESULTS: On preincubation with anti-SCPA serum, the isogenic M1(-) strain exhibited 54 per cent decreased invasion as compared to the bacteria incubated with control serum. Also, purified recombinant SCPA proteins blocked internalization of M1(-) streptococci into HEp-2 cells. The M1(-) strain invaded at the same efficiency in the presence or absence of fibronectin. INTERPRETATION & CONCLUSION: These results suggested that SCPA acted as a potential invasin of group A streptococcus and promoted invasion independent of fibronectin.

Nasal associated lymphoid tissue & M cells, a window to persistent streptococcal infections.

BACKGROUND & OBJECTIVES: Intranasal infection of mice has been used as a model of streptococcal pharyngitis, as nasal associated lymphoid tissue (NALT) in this animal is structurally and functionally analogous to human tonsils. The present study was carried out to determine whether group A streptococci preferentially colonized or invaded NALT. METHODS: Lux(+) strain Sp3 was created and exponential phase bacteria were introduced intranasally into BALB/C female mice, total photon emission from selected areas was quantified, sections of NALT tissues were used for immunofluorescent staining and M cell staining. RESULTS: Intranasal infection of mice with bioluminescent group A streptococci or unlabeled streptococci demonstrated that NALT was a primary target of this pathogen. Streptococci readily gained access to the blood stream from this site of infection. Immunofluorescence microscopy studies showed that M cells, dispersed along the mucosal epithelium adjacent to NALT, were preferentially infected and likely to provide the window through which streptococci reached the underlying tissue. INTERPRETATION & CONCLUSION: The present study suggests that this upper respiratory Gram positive pathogen uses a mechanism similar to that of enteric pathogens in the intestine to gain access to underlying tissue, lymphatics and blood.

Membranous cells in nasal-associated lymphoid tissue: a portal of entry for the respiratory mucosal pathogen group A streptococcus.

Human tonsils are suspected to be an antibiotic-impervious human reservoir for group A streptococcus. An intranasal infection model in mice and a bioluminescent-tagged strain were used to investigate this possibility. Viable streptococci were predominantly found both intra- and extracellularly in nasal-associated lymphoid tissue (NALT), a human tonsil homologue. Ulex europaeus-1, a membranous (M) cell-specific lectin, identified cells harboring streptococci at the epithelial surface of NALT and blocked bacterial colonization of this tissue. These results suggest that M cells in NALT transport this Gram-positive pathogen across the epithelial layers in a manner similar to those in Peyer's patches, which permit enteric pathogens to invade deeper tissues from the gastrointestinal tract.

Modification of type IV pilus-associated epithelial cell adherence and multicellular behavior by the PilU protein of Neisseria gonorrhoeae.

Expression of type IV pili (Tfp) correlates with the ability of Neisseria gonorrhoeae to colonize the human host, as well as with adherence to human epithelial tissue, twitching motility, competence for natural transformation, and autoagglutination. N. gonorrhoeae PilF (required for Tfp biogenesis) and PilT (required for twitching motility and transformation) share significant identities with members of a family of putative ATPases involved in membrane trafficking of macromolecules. An open reading frame downstream of the pilT locus encoding a 408-amino-acid protein with 33% identity with the gonococcal PilT protein and 45% identity with the PilU protein in Pseudomonas aeruginosa was characterized, and the corresponding gene was designated pilU. Unlike N. gonorrhoeae pilT mutants, pilU mutants express twitching motility and are competent for DNA transformation. However, loss-of-function mutations in pilU increased bacterial adherence to ME-180 human epithelial cells eightfold and disrupted in vitro Tfp-associated autoagglutination. Comparative alignment of N. gonorrhoeae PilU with other members of the TrbB-like family of traffic ATPases revealed a conserved carboxy-terminal domain unique to family members which are not essential for Tfp biogenesis but which specifically modify Tfp-associated phenotypes. Studies of the pilT-pilU locus by using Northern blotting, transcriptional fusions, and reverse transcription-PCR showed that the two genes encoding closely related proteins with dissimilar effects on Tfp phenotypes are transcribed from a single promoter.