Comparison of OG1RF and an isogenic fsrB deletion mutant by transcriptional analysis: the Fsr system of Enterococcus faecalis is more than the activator of gelatinase and serine protease.

The FsrABC system of Enterococcus faecalis controls the expression of gelatinase and a serine protease via a quorum-sensing mechanism, and recent studies suggest that the Fsr system may also regulate other genes important for virulence. To investigate the possibility that Fsr influences the expression of additional genes, we used transcriptional profiling, with microarrays based on the E. faecalis strain V583 sequence, to compare the E. faecalis strain OG1RF with its isogenic mutant, TX5266, an fsrB deletion mutant. We found that the presence of an intact fsrB influences expression of numerous genes throughout the growth phases tested, namely, late log to early stationary phase. In addition, the Fsr regulon is independent of the activity of the proteases, GelE and SprE, whose expression was confirmed to be activated at all three time points tested. While expression of some genes (i.e., ef1097 and ef0750 to -757, encoding hypothetical proteins) was activated in late log phase in OG1RF versus the fsrB deletion mutant, expression of ef1617 to -1634 (eut-pdu orthologues) was highly repressed by the presence of an intact Fsr at entry into stationary phase. This is the first time that Fsr has been characterized as a negative regulator. The newly recognized Fsr-regulated targets include other factors, besides gelatinase, described as important for biofilms (BopD), and genes predicted to encode the surface proteins EF0750 to -0757 and EF1097, along with proteins implicated in several metabolic pathways, indicating that the FsrABC system may be an important regulator in strain OG1RF, with both positive and negative effects.

Protease-activated receptor-1 signaling plays a major role in melanoma growth and metastasis

Overexpression of the thrombin receptor (Protease-Activated-Receptor-1), PAR-1, in cell lines and tissue specimens correlates with the metastatic potential of human melanoma. Utilizing lentiviral shRNA to stably silence PAR-1 in metastatic melanoma cell lines results in decreased tumor growth and lung metastasis in vivo. Since the use of viral technology is not ideal for clinical therapies, neutral liposomes (DOPC) were utilized as a delivery vehicle for PAR-1 siRNA. Our data suggest that PAR-1 siRNA-DOPC treatment by systemic delivery significantly decreases tumor growth and lung metastasis in nude mice. Concomitant decreases in angiogenic and invasive factors (IL-8, VEGF, MMP-2) were observed in PAR-1 siRNA-DOPC-treated mice. Utilizing a cDNA microarray platform, several novel PAR-1 downstream target genes were identified, including Connexin 43 (Cx-43) and Maspin. Cx-43, known to be involved in tumor cell diapedesis and attachment to endothelial cells, is decreased after PAR-1 silencing. Furthermore, the Cx-43 promoter activity was significantly inhibited in PAR-1-silenced cells suggesting transcriptional regulation of Cx-43 by PAR-1. ChIP analysis revealed a reduction in SP-1 and AP-1 binding to the Cx-43 promoter. Moreover, melanoma cell attachment to HUVEC was significantly decreased in PAR-1-silenced cells as well as in Cx-43 shRNA transduced cells. As both SP-1 and AP-1 transcription factors act as positive regulators of Cx-43, our data provide a novel mechanism for the regulation of Cx-43 expression by PAR-1. Maspin, a serine protease inhibitor with tumor-suppressor function, was found to be upregulated after PAR-1 silencing. Our results indicate that PAR-1 transcriptionally regulates Maspin, as the promoter activity was significantly increased after PAR-1 silencing. ChIP analysis revealed that silencing PAR-1 increased binding of Ets and c-Jun to the Maspin promoter. As Maspin was recently found to be a tumor-suppressor in melanoma by reducing the invasive capacity of melanoma cells, invasion assays revealed a decrease in invasion after PAR-1 silencing and in cells transduced with a Maspin expression vector. We propose that PAR-1 is key to the progression and metastasis of melanoma in part by regulating the expression of Cx-43 and Maspin. Taken together, we propose that PAR-1 is an attractive target for the treatment of melanoma.^

Identification and characterization of virulence factors in Enterococcus faecalis

Enterococci are one of the leading causes of nosocomial infections, and Enterococcus faecalis causes the majority of enterococcal infections. However, the mechanisms of enterococcal pathogenesis are still not yet understood. In our initial screening of E. faecalis strain OG1RF genomic libraries, autolysin and a homolog of a protein of Enterococcus faecium previously designated P54 were found to be two major antigens that reacted with human patient sera, and an antigen designated MH-1 antigen that reacted with serum from a endocarditis patient was also identified. To explore a possible role for these antigens in enterococcal infections, the genes encoding these three antigens were disrupted in Enterococcus faecalis OG1RF. ^ To explore a possible role of an E. faecalis gelatinase (encoded by gelE), which belongs to a family of Zn-metalloproteases that have been shown to be virulence factors in other organisms, in enterococcal infections, an insertion mutant was constructed in OG1RF and tested in the mouse peritonitis model. The mice infected with the gelE mutant showed a significantly prolonged survival compared to the wild type strain. To study the expression of gelE, the regions flanking gelE were sequenced. Sequence analysis of the gelE flanking regions revealed three genes (fsrA, fsrB and fsrC) upstream of gelE that show homology to the genes in a locus (agr) that globally regulates the expression of virulence factors in Staphylococcus aureus and one open reading frame (sprE) with homology to bacterial serine protease downstream of gelE. ^ In conclusion, in this study of identification of possible virulence factors in E. faecalis surface and secreted proteins, of three genes encoding antigens detected by human patient sera, none could be shown to effect virulence in the mouse peritonitis model. Inactivation of one of these antigens (autolysin) was shown to slightly increase the tolerance of E. faecalis to penicillin. A serine protease and a locus (fsr) that regulates the expression of gelE and sprE were shown to be important for enterococcal infection in the mouse peritonitis model. (Abstract shortened by UMI.)^

Catalytic antibody response to the Staphylococcus aureus virulence factor Efb

Staphylococcus aureus is a globally prevalent pathogen that can cause a wide variety of acute and chronic diseases in both adults and children, in both immune susceptible populations and healthy individuals. Its ability to cause persistent infections has been linked to multiple immune evasion strategies, including Efb-mediated complement inhibition. As new multi-drug-resistant strains emerge, therapeutic alternatives to traditional antibiotics must be developed. These experiments assessed the ability of healthy patient immunoglobulin to cleave Efb and disable the complement-inhibitory properties of Efb in vitro. Levels of immunoglobulin-mediated Efb catalysis varied both between immunoglobulin isoform/isotype and between individuals. Serum IgG showed the strongest catalytic activity of the immunoglobulin isotypes tested. Additionally, IgG hydrolyzed the virulence factor in a way that enabled only minimal binding to the complement component C3b, effectively blocking Efb-mediated inhibition of complement lysis. Salivary IgA and serum IgM did not block Efb-mediated inhibition of complement. Catalytic IgG selectively cleaved Efb and showed no cleavage of a variety of other proteins tested. Catalytic activity of IgG was inhibited by serine protease inhibitors, but not by other protease inhibitors, suggesting a serine-protease mechanism of catalysis. It is proposed that varying concentrations and activity levels of catalytic IgG between healthy individuals and those with current or recurrent S. aureus infections in both adult and pediatric populations be studied in order to assess the potential effectiveness of passive immunization therapy with catalytic monoclonal IgG. ^

Antigen-specific proteolytic antibodies

The antigen recognition site of antibodies is composed of residues contributed by the variable domains of the heavy and light chain subunits (VL and VH domains). VL domains can catalyze peptide bond hydrolysis independent of VH domains (Mei S et al. J Biol Chem. 1991 Aug 25;266(24):15571-4). VH domains can bind antigens noncovalently independent of V L domains (Ward et al. Nature. 1989 Oct 12;341(6242):544-6). This dissertation describe the specific hydrolysis of fusion proteins containing the hepatitis C virus coat protein E2 by recombinant hybrid Abs composed of the heavy chain of a high affinity anti-E2 IgG1 paired with light chains expressing promiscuous catalytic activity. The proteolytic activity was evident from electrophoresis assays using recombinant E2 substrates containing glutathione S-transferase (E2-GST) or FLAG peptide (E2-FLAG) tags. The proteolytic reaction proceeded more rapidly in the presence of the hybrid IgG1 compared to the unpaired light chain, consistent with accelerated peptide bond hydrolysis due to noncovalent VH domain-E2 recognition. An active site-directed inhibitor of serine proteases inhibited the proteolytic activity of the hybrid IgG, indicating a serine protease mechanism. Binding studies confirmed that the hybrid IgG retained detectable noncovalent E2 recognition capability, although at a level smaller than the wildtype anti-E2 IgG. Immunoblotting of E2-FLAG treated with the hybrid IgG suggested a scissile bond within E2 located ∼11 kD from the N terminus of the protein. E2-GST was hydrolyzed by the hybrid IgG at peptide bonds located in the GST tag. The differing cleavage pattern of E2-FLAG and E2-GST can be explained by the split-site model of catalysis, in which conformational differences in the E2 fusion protein substrates position alternate peptide bonds in register with the antibody catalytic subsite despite a common noncovalent binding mechanism. This is the first proof-of principle that the catalytic activity of a light chain can be rendered antigen-specific by pairing with a noncovalently binding heavy chain subunit. ^

Caspase 8: Mediating the effects of a novel proteasome inhibitor, NPI-0052

Targeting the proteasome with the sole FDA approved proteasome inhibitor (PI), bortezomib, has been fruitful in specific cancers. Its success has generated an interest in next-generation PIs that might have a therapeutic advantage in cancers, such as leukemia, where bortezomib monotherapy was less effective. This study focuses on a novel, clinically relevant PI, NPI-0052. Experiments show that NPI-0052 targets chymotrypsin- and caspase-like activities more potently than the trypsin-like activity in leukemia cells. NPI-0052 induced apoptosis, as determined by caspase-3 activation and DNA fragmentation. Using caspase inhibitors and caspase-8 (I9.2) or FADD (I2.1) deficient cells revealed that caspase-8 was essential for NPI-0052-induced apoptosis. NPI-0052 killed cells via a caspase-8-tBid-mitochondrial pathway, relying on caspase-8, whereas bortezomib relies on several caspases. NPI-0052 increased reactive oxygen species (ROS) levels, which contributed towards cytotoxicity since an antioxidant conferred protection. To improve the clinical efficacy of PIs, NPI-0052 was combined with epigenetic anti-cancer agents, histone deacetylase inhibitors (HDACi). NPI-0052 with MS-275 or vorinostat (FDA approved HDACi), synergistically induced apoptosis more effectively than an HDACi/bortezomib regimen in Jurkat cells. Caspase-8 and ROS contributed towards NPI-0052/HDACi cytotoxicity and caspase-8 mediated superoxide production by NPI-0052 or NPI-0052/HDACi. The proximal targets of these agents: proteasome activity and histone acetylation were examined to determine if they contributed towards synergistic effects. HDACi targeted proteasomal β subunits and corresponding catalytic activities responsible for degrading proteins. Immunoblotting showed increases in histone-H3 expression and its acetylation with NPI-0052 or NPI-0052/HDACi in Jurkat and primary cells. Importantly, the hyper-acetylation by NPI-0052 was not detected with bortezomib, suggesting that this effect may be unique to NPI-0052. An antioxidant attenuated histone-H3 expression and acetylation induced by NPI-0052 alone or with HDACi. Furthermore, the hyper-acetylation by NPI-0052 relied on caspase-8. These novel results show that a PI is eliciting classical epigenetic alterations, demonstrated by hyper-acetylation of histone-H3. This alteration was oxidant and caspase-8 dependent. Overall, results reveal that caspase-8 mediates many effects induced by NPI-0052. Data show overlapping activities by NPI-0052 and HDACi which are contributing, along with caspase-8 activation and oxidative stress, to cytotoxic interactions in leukemia cells, reinforcing the potential clinical utility of combining these two compounds. ^

Cellular Uptake of Neutrohpil Elastase Links Inflammation to Adaptive Immunity

Many tumors arise from sites of inflammation providing evidence that innate immunity is a critical component in the development and progression of cancer. Neutrophils are primary mediators of the innate immune response. Upon activation, an important function of neutrophils is release of an assortment of proteins from their granules including the serine protease neutrophil elastase (NE). The effect of NE on cancer has been attributed primarily to its ability to degrade the extracellular matrix thereby promoting invasion and metastasis. Recently, it was shown that NE could be taken up by lung cancer cells leading to degradation of insulin receptor substrate-1 thereby promoting hyperactivity of the phosphatidylinositol-3 kinase (PI3K) pathway and tumor cell proliferation. To our knowledge, nobody has investigated uptake of NE by other tumor types. In addition, NE has broad substrate specificity suggesting that uptake of NE by tumor cells could impact processes regulating tumorigenensis other than activation of the PI3K pathway. Neutrophil elastase has been identified in breast cancer specimens where high levels of NE have prognostic significance. These studies have assessed NE levels in whole tumor lysates. Because the major source of NE is from activated neutrophils, we hypothesized that breast cancer cells do not have endogenous NE but may take up NE released by tumor associated neutrophils in the tumor microenvironment and that this could provide a link between the innate immune response to tumors and specific adaptive immune responses. In this thesis, we show that breast cancer cells lack endogenous NE expression and that they are able to take up NE resulting in increased generation of low molecular weight cyclin E (CCNE) and enhanced susceptibility to lysis by CCNE-specific cytotoxic T lymphocytes. We also show that after taking up NE and proteinase 3 (PR3), a second primary granule protease with significant homology to NE, breast cancer cells cross-present the NE- and PR3-derived peptide PR1 rendering them susceptible to PR1-targeted therapies. Taken together, our data support a role for NE uptake in modulating adaptive immune responses against breast cancer.

Activation of DegP chaperone-protease via formation of large cage-like oligomers upon binding to substrate proteins.

Cells use molecular chaperones and proteases to implement the essential quality control mechanism of proteins. The DegP (HtrA) protein, essential for the survival of Escherichia coli cells at elevated temperatures with homologues found in almost all organisms uniquely has both functions. Here we report a mechanism for DegP to activate both functions via formation of large cage-like 12- and 24-mers after binding to substrate proteins. Cryo-electron microscopic and biochemical studies revealed that both oligomers are consistently assembled by blocks of DegP trimers, via pairwise PDZ1-PDZ2 interactions between neighboring trimers. Such interactions simultaneously eliminate the inhibitory effects of the PDZ2 domain. Additionally, both DegP oligomers were also observed in extracts of E. coli cells, strongly implicating their physiological importance.

Analyses of pp60$\sp{{\rm c}-src}$ and epidermal growth factor receptor protein tyrosine kinases in a human colon adenocarcinoma cell line following induction of goblet cell-like characteristics by tumor necrosis factor-alpha

Regulation of colonic epithelial cell proliferation and differentiation remains poorly understood due to the inability to design a model system which recapitulates these processes. Currently, properties of "differentiation" are studied in colon adenocarcinoma cell lines which can be induced to express some, but not all of the phenotypes of normal cells. In this thesis, the DiFi human colon adenocarcinoma cell line is utilized as an in vitro model system in which to study mucin production. In response to treatment with tumor necrosis factor-alpha, DiFi cells acquire some properties of mucin-producing goblet cells including altered morphology, increased reactivity to wheat germ agglutinin, and increased mucin production as determined by RNA expression as well as reactivity with the MUC-1 antibodies, HMFG-1 and SM-3. Thus, TNF-treated DiFi cells represent one of the few in vitro systems in which mucin expression can be induced.^ DiFi cells express an activated pp60$\sp{{\rm c}-src},$ as do most colon adenocarcinomas and derived cell lines, as well as an amplified epidermal growth factor (EGF) receptor. To assess potential changes in these enzymes during induction of differentiation characteristics, potential changes in the levels and activities of these enzymes were examined. For pp60$\sp{{\rm c}-src},$ no changes were observed in protein levels, specific activity of the kinase, cellular localization, or phosphorylation pattern as determined by Staphylococcus aureus V8 protease partial proteolytic mapping after induction of goblet cell-like phenotypic changes. These results suggest that pp60$\sp{{\rm c}-src}$ is regulated differentially in goblet cells than in absorptive cells, as down-modulation of pp60$\sp{{\rm c}-src}$ kinase occurs in the latter. Therefore, effects on pp60$\sp{{\rm c}-src}$ may be critical in colon regulation, and may be important in generating the various colonic epithelial cell types.^ In contrast to pp60$\sp{{\rm c}-src},$ EGF receptor tyrosine kinase activity decreased ($<$5-fold) after TNF treatment and at the time in which morphologic changes were observed. Similar decreases in tyrosine phosphorylation of EGF receptor were observed as assessed by immunoblotting with an anti-phosphotyrosine antibody. In addition, ($\sp{125}$I) -EGF cell surface binding was reduced approximately 3-fold following TNF treatment with a concomitant reduction in receptor affinity ($<$2-fold). These results suggest that modulation of EGF receptor may be important in goblet cell differentiation. In contrast, other published studies have demonstrated that increases in EGF receptor mRNA and in ($\sp{125}$I) -EGF binding accompany differentiation toward the absorptive cell phenotype. Therefore, differential regulation of both EGF receptor and pp60$\sp{{\rm c}-src}$ occur along the goblet cell and absorptive cell differentiation pathways. Thus, my results suggest that TNF-treated DiFi cells represent a unique system in which to study distinct patterns of regulation of pp60$\sp{{\rm c}-src}$ and EGF receptor in colonic cells, and to determine if increased MUC-1 expression is an early event in goblet cell differentiation. ^

Involvement of heparin-like glycosaminoglycans and expression of a novel heparan sulfate binding protein (p24) during human placentation and in a model for human implantation

Previous studies in our laboratory have indicated that heparan sulfate proteoglycans (HSPGs) play an important role in murine embryo implantation. To investigate the potential function of HSPGs in human implantation, two human cell lines (RL95 and JAR) were selected to model uterine epithelium and embryonal trophectoderm, respectively. A heterologous cell-cell adhesion assay showed that initial binding between JAR and RL95 cells is mediated by cell surface glycosaminoglycans (GAG) with heparin-like properties, i.e., heparan sulfate and dermatan sulfate. Furthermore, a single class of highly specific, protease-sensitive heparin/heparan sulfate binding sites exist on the surface of RL95 cells. Three heparin binding, tryptic peptide fragments were isolated from RL95 cell surfaces and their amino termini partially sequenced. Reverse transcription-polymerase chain reaction (RT-PCR) generated 1 to 4 PCR products per tryptic peptide. Northern blot analysis of RNA from RL95 cells using one of these RT-PCR products identified a 1.2 Kb mRNA species (p24). The amino acid sequence predicted from the cDNA sequence contains a putative heparin-binding domain. A synthetic peptide representing this putative heparin binding domain was used to generate a rabbit polyclonal antibody (anti-p24). Indirect immunofluorescence studies on RL95 and JAR cells as well as binding studies of anti-p24 to intact RL95 cells demonstrate that p24 is distributed on the cell surface. Western blots of RL95 membrane preparations identify a 24 kDa protein (p24) highly enriched in the 100,000 g pellet plasma membrane-enriched fraction. p24 eluted from membranes with 0.8 M NaCl, but not 0.6 M NaCl, suggesting that it is a peripheral membrane component. Solubilized p24 binds heparin by heparin affinity chromatography and $\sp{125}$I-heparin binding assays. Furthermore, indirect immunofluorescence studies indicate that cytotrophoblast of floating and attached villi of the human fetal-maternal interface are recognized by anti-p24. The study also indicates that the HSPG, perlecan, accumulates where chorionic villi are attached to uterine stroma and where p24-expressing cytotrophoblast penetrate the stroma. Collectively, these data indicate that p24 is a cell surface membrane-associated heparin/heparan sulfate binding protein found in cytotrophoblast, but not many other cell types of the fetal-maternal interface. Furthermore, p24 colocalizes with HSPGs in regions of cytotrophoblast invasion. These observations are consistent with a role for HSPGs and HSPG binding proteins in human trophoblast-uterine cell interactions. ^

Characterization of a Novel Role for the Tousled- like Kinase in Kinetochore Assembly and Function in Caenorhabditis elegans

Chromosome segregation is a critical step during cell division to avoid aneuploidy and promote proper organismal development. Correct sister chromatid positioning and separation during mitosis helps to achieve faithful transmission of genetic material to daughter cells. This prevents improper chromosome partitioning that can potentially result in extrachromosomal fragments, increasing the tumorigenic potential of the cells. The kinetochore is a protenaicious structure responsible for the initiation and orchestration of chromosome movement during mitosis. This highly conserved structure among eukaryotes is required for chromosome attachment to the mitotic spindle and failure to assemble the kinetochore results in aberrant chromosome segregation. Thus elucidating the mechanism of kinetochore assembly is important to have a better understanding of the regulation that controls chromosome segregation. Our previous work identified the C. elegans Tousled-like kinase (TLK-1) as a mitotic kinase and depletion of TLK-1 results in embryonic lethality, characterized by nuclei displaying poor mitotic chromosome alignment, lagging chromosome, and chromosome bridges during anaphase. Additionally, previous studies from our group revealed that TLK-1 is phosphorylated independently by Aurora B at serine 634, and by CHK-1 at threonine T610. The research presented herein reveals that both phosphorylated forms of TLK-1 associate with the kinetochore during mitosis. Moreover, by systematic depletion of kinetochore proteins, I uncovered that pTLK-1 is bona fide kinetochore component that is located at the outer kinetochore layer, influencing the microtubule-binding interface. I also demonstrated that TLK-1 is necessary for the kinetochore localization of the microtubule interacting proteins CLS-2 and LIS-1 and I show that embryos depleted of TLK-1 presented an aberrant twisted kinetochore pattern. Furthermore, I established that the inner kinetochore protein KNL-2 is an in vitro substrate of TLK-1 indicating a possible role of TLK-1 in regulating centromeric assembly. Collectively, these results suggest a novel role for the Tousled-like kinase in regulation of kinetochore assembly and microtubule dynamics and demonstrate the necessity of TLK-1 for proper chromosome segregation in C. elegans.