Rifaximin-mediated changes to the epithelial cell proteome: 2-D gel analysis

Diarrhea remains a significant cause of worldwide morbidity and mortality. Over 4 million children die of diarrhea annually. Although antibiotics can be used as prophylaxis or for treatment of diarrhea, concern remains over antibiotic resistance. Rifaximin is a semi-synthetic rifamycin derivative that can be used to treat symptoms of infectious diarrhea, inflammatory bowel syndrome, bacterial overgrowth of the small bowel, pouchitis, and fulminant ulcerative colitis. Rifaximin is of particular interest because it is poorly adsorbed in the intestines, shows no indication of inducing bacterial resistance, and has minimal effect on intestinal flora. In order to better understand how rifaximin functions, we sought to compare the protein expression profile of cells pretreated with rifaximin, as compared to cells treated with acetone, rifamycin (control antibiotic), or media (untreated). 2-D gel electrophoresis identified 38 protein spots that were up- or down-regulated by over 2-fold in rifaximin treated cells compared to controls. 16 of these spots were down-regulated, including keratin, annexin A5, intestinal-type alkaline phosphatase, histone h4, and histone-binding protein RbbP4. 22 spots were up-regulated, including heat shock protein HSP 90 alpha, alkaline phosphatase, and fascin. Many of the identified proteins are associated with cell structure and cytoskeleton, transcription and translation, and cellular metabolism. A better understanding of the functionality of rifaximin will identify additional potential uses for rifaximin and determine for whom the drug is best suited. ^

The Role Of IL-8-Mediated Src Family Kinase Activation In Tumor-Tumor And Tumor-Stromal Interactions In Metastasis Of Prostate Cancer

Men with localized prostate cancer (PCa) have a 100% five-year survival rate, but this rate drops to 33% for men with metastatic disease. A better understanding of the metastatic process is needed to develop better therapies for PCa. Aberrant activation of protein tyrosine kinases, including Src Family Kinases (SFKs) contribute to metastasis through numerous functions, one of which leads to increased expression of cytokines, such as IL-8. However, the relationship between Src activity and IL-8 regulation is not completely understood. In cell line models, I determined that IL-8 activates Src and in turn Src activates IL-8 demonstrating a feed forward loop contributing to the migration and invasion of PCa cells. However, IL-8 is also produced by tumor-associated stromal cells. In bone marrow derived stromal cells (HS5), I demonstrated a feed forward loop occurs as was observed in tumor cells. HS5 conditioned media increased Src activity in PCa cells. By silencing IL-8 in HS5 cells, Src activity was decreased to control levels in PCa cells as was migration and invasion. Thus, stromal cells producing IL-8 contribute to metastatic properties of PCa by a paracrine mechanism. To examine the effect of stromal cells on tumor growth and metastatic potential of PCa in vivo, I mixed HS5 and PCa cells and co-injected them intraprostatically. I determined that tumor growth and metastases were increased. By silencing IL-8 in HS5 cells and co-injecting them with PCa cells intraprostatically, tumor growth and metastases were still increased relative to injection of PCa cells alone, but decreased relative to co-injections with PCa cells and HS5 cells. These studies demonstrated: (1) a feed forward loop in both tumor and stromal cells, whereby IL-8 activates Src, derepressing IL-8 expression in PCa cells in vitro; (2) stromal produced IL-8 activates Src and contributes to the migration and invasion of PCa cells in vitro; and (3) stromal produced IL-8 is responsible, in part, for increases in PCa tumor growth and metastatic potential. Together, these studies demonstrated that IL-8-mediated Src activity increases the metastatic potential of PCa and therapeutic agents interfering with the IL-8/SFK signaling axis may be useful for prevention and treatment of metastases.

The Influence of Immunization Route on the Adjuvant Effect of alpha-Galactosylceramide

Potent vaccine formulations ideally include adjuvants to activate innate immune responses and enhance antigen-specific adaptive immunity. The synthetic glycolipid alpha-Galactosylceramide (α-GalCer) effectively activates the innate immune mediating NKT cells to produce cytokines and activate downstream immune cells, resulting in development of humoral and cell mediated immune responses to co-administered antigens. While a single intravenous immunization of α-GalCer strongly activates NKT cells, multiple doses by this route are well documented to induce anergy in NKT cells. Anergy is defined as the deficiency in NKT proliferation and cytokine production, including IL-4 and IFNγ. However, our studies have shown that two doses of α-GalCer administered intranasally by the intranasal route leads to reactivation of NKT cells and improved adaptive immune responses after each subsequent dose. I therefore investigated the role of multiple routes of immunization in activation of NKT cells, i.e. anergy versus repeated activation. Specifically, I hypothesized that the differential capacity of NKT cells to produce IFNγ, as a result of route of immunization with α-GalCer, influences the induction of adaptive immune responses to co-administered antigen. Our experimental design utilizes the observation that intranasal immunization primarily induces immune responses in the lungs while intravenous immunization induces responses in the liver. Using intracellular cytokine staining for IFNγ production and Elispot analyses for determining NKT and T cell activation, respectively, it was determined that administering two consecutive intravenous doses resulted in anergy to NKT cells (no IFNγ production) in the liver and lack of adaptive immunity while second immunization by the intranasal route overcame anergy in the lung. The outcome in the other tissues analyzed was mixed and could be the result of tissue microenvironment among others possible reasons. When intranasal dosing preceded systemic, NKT cells were reactivated to produce IFNγ and induced positive adaptive immune responses in the responding lung tissue. These results indicate that the mechanism by which mucosal and systemic immunization routes activate NKT cells may differ in that there is a differential tissue-specific effect induced by each route. Future studies are necessary to determine the reason for these tissue-specific effects and how they relate to NKT cell activation.

Mechanism of mRNA stability control mediated by AU -rich element: Characterization of cis-elements and trans-factors

Regulation of cytoplasmic deadenylation, the first step in mRNA turnover, has direct impact on the fate of gene expression. AU-rich elements (AREs) found in the 3′ untranslated regions of many labile mRNAs are the most common RNA-destabilizing elements known in mammalian cells. Based on their sequence features and functional properties, AREs can be divided into three classes. Class I or class III ARE directs synchronous deadenylation, whereas class II ARE directs asynchronous deadenylation with the formation of poly(A)-intermediates. Through systematic mutagenesis study, we found that a cluster of five or six copies of AUUUA motifs forming various degrees of reiteration is the key feature dictating the choice between asynchronous versus synchronous deadenylation. A 20–30 nt AU-rich sequence immediately 5 ′ to this cluster of AUUUA motifs can greatly enhance its destabilizing ability and is an integral part of the AREs. These two features are the defining characteristics of class II AREs. ^ To better understand the decay mechanism of AREs, current methods have several limitations. Taking the advantage of tetracycline-regulated promoter, we developed a new transcriptional pulse strategy, Tet-system. By controlling the time and the amount of Tet addition, a pulse of RNA could be generated. Using this new system, we showed that AREs function in both growth- and density-arrested cells. The new strategy offers for the first time an opportunity to investigate control of mRNA deadenylation and decay kinetics in mammalian cells that exhibit physiologically relevant conditions. ^ As a member of heterogeneous nuclear RNA-binding protein, hnRNP D 0/AUF1 displays specific affinities for ARE sequences in vitro . But its in vivo function in ARE-mediated mRNA decay is unclear. AUF1/hnRNP D0 is composed of at least four isoforms derived by alternative RNA splicing. Each isoform exhibits different affinity for ARE sequence in vitro. Here, we examined in vivo effect of AUF1s/hnRNP D0s on degradation of ARE-containing mRNA. Our results showed that all four isoforms exhibit various RNA stabilizing effects in NIH3T3 cells, which are positively correlated with their binding affinities for ARE sequences. Further experiments indicated that AUF1/hnRNP D0 has a general role in modulating the stability of cytoplasmic mRNAs in mammalian cells. ^

Axl -Gas6 signaling counteracts adenovirus type 5 E1A-mediated cell growth suppression and proapoptotic activity

The adenovirus type 5 E1A (abbreviated E1A) has previously been known as an immortalization oncogene because E1A is required for transforming oncogenes, such as ras and E1B, to transform cells in primary cultures. However, E1A has also been shown to downregulate the overexpression of the Her-2/neu oncogene, resulting in suppression of transformation and tumorigenesis induced by that oncogene. In addition, E1A is able to promote apoptosis induced by anticancer drugs, irradiation, and serum deprivation. Many tyrosine kinases, such as the EGF receptor, Her-2/Neu, Src, and Axl are known to play a role in oncogenic signals in transformed cells. To study the mechanism underlying the E1A-mediated tumor-suppressing function, we exploited a modified tyrosine kinase profile assay (Proc. Natl. Acad. Sci, 93, 5958–5962, 1996) to identify potential tyrosine kinases regulated by E1A. RT-PCR products were synthesized with two degenerate primers derived from the conserved motifs of various tyrosine kinases. A tyrosine kinase downregulated by E1A was identified as Axl by analyzing the Alu I-digested RT-PCR products. We isolated the DNA fragment of interest, and found that E1A negatively regulated the expression of the transforming receptor tyrosine kinase Axl at the transcriptional level. To study whether downregulation of the Axl receptor is involved in E1A-mediated growth suppression, we transfected axl cDNA into E1A-expressing cells (ip1-E1A) to establish cells that overexpressed Axl (ip1-E1A-Axl). The Axl ligand Gas6 triggered a greater mitogenic effect in these ip1-E1A-Axl cells than in the control cells ip1-E1A and protected the Axl-expressing cells from serum deprivation-induced apoptosis. Further study showed that Akt is required for Axl-Gas6 signaling to prevent ip1-E1A-Axl cells from serum deprivation-induced apoptosis. These results indicate that downregulation of the Axl receptor by E1A is involved in E1A-mediated growth suppression and E1A-induced apoptosis, and thereby contributes to E1A's anti-tumor activities. ^

The antiapoptotic effect of overexpression c -erBb2 in breast cancer

Overexpression of the receptor tyrosine kinase p185ErbB2 confers taxol resistance in breast cancers and activation of p34Cdc2 is required for taxol-induced apoptosis and cytotoxicity. Here, we investigated the underlying mechanisms and found that overexpression of p185 ErbB2 inhibits taxol-induced apoptosis through two branches to inhibit activation of p34Cdc2. ^ Overexpression of p185ErbB2 in MDA-MB-435 cells by transfection transcriptionally upregulated p21Cip1, which associates with p34Cdc2, inhibits taxol-mediated p34Cdc2 activation, delays cell entrance to G2/M phase, and thereby inhibits taxol-induced apoptosis. In p21Cip1 antisense-transfected MDA-MB-435 cells or in p21−/− MEF cells, p185ErbB2 was unable to inhibit taxol-induced apoptosis. Therefore, p21Cip1 participates in the regulation of a G2/M checkpoint that contributes to resistance to taxol-induced apoptosis in p185ErbB2-overexpressing breast cancer cells. ^ Direct phosphorylation on Tyrosine-15 of p34Cdc2 by p185 ErbB2 receptor tyrosine kinase inhibits p34Cdc2 activation. The wild-type p185ErbB2 but not the kinase-defective mutant, when overexpressed in breast cancer cells, can phosphorylate p34Cdc2 on tyrosine (Tyr)15, an inhibitory phosphorylation site of p34 Cdc2. The kinase domain of the ErbB2 receptor was sufficient for binding to p34Cdc2 and directly phosphorylating the recombinant Cdc2. Phosphospecific Cdc2-Tyr15 immunoblot analyses, immunocomplex kinase assays, and phospho-amino acid analyses revealed that p185ErbB2 specifically phosphorylates Cdc2 on Tyr15. Phosphorylation of Cdc2-Tyr15 by ErbB2 is modulated during cell cycle and corresponded with delayed cell entry into G2/M phase. The kinase-defective p185ErbB2, which incapable of phosphorylating Cdc2-Tyr15, failed to inhibit taxol-induced activation and apoptosis, whereas the wild-type and the constitutive-active p185ErbB2 did. Increased Cdc2-Tyr15 phosphorylation was found in Erb132-overexpressing tumors from breast cancer patients. Thus, direct phosphorylation of Cdc2-Tyr15 by p185 ErbB2 RTK in breast cancer cells inhibits taxol-induced p34 Cdc2 activation and apoptosis, thereby conferring taxol resistance. ^

Upregulation of VEGF through p70S6K in ErbB2 -mediated angiogenesis and inhibition by combined herceptin plus taxol therapy

ErbB2 overexpression in breast tumors increases metastasis, angiogenesis, and reduces survival. To study ErbB2 signaling mechanisms in metastasis and angiogenesis, a spontaneous metastasis assay was performed using human breast cancer cells transfected with constitutively active ErbB2 kinase (V659E), an ErbB2 kinase-dead mutant (K753M), or vector control. Mice injected with V659E had increased metastasis and tumor microvessel density; and the increased angiogenesis in vivo from the V659E transfectants paralleled increased angiogenic potential in vitro, which resulted from increased VEGF by increased protein synthesis. This appeared to be mediated through a PI3K, Akt, mTOR, p70S6K-signaling pathway. Furthermore, V659E xenografts had significantly increased phosphorylated Akt, phosphorylated p70S6K, and VEGF compared with control. To validate the clinical relevance of these findings, human breast tumor samples were examined. Tumors overexpressing ErbB2 correlated with p70S6K phosphorylation and VEGF expression, which significantly correlated with higher levels of Akt and mTOR phosphorylation. Additionally, patients with tumors having increased p70S6K phosphorylation showed a trend for worse disease-free survival and increased metastasis. Together, ErbB2 increases VEGF expression by activating the p70S6K signaling pathway, which may serve as targets for antiangiogenic and antimetastatic therapies. ^ Herceptin is an anti-ErbB2 antibody that demonstrated anti-tumor function, especially in combination with other chemotherapies such as Taxol, in patients with ErbB2-overexpressing tumors. Since the repeated administration of low-dose chemotherapy endorsed an antiangiogenic effect in vitro, and Herceptin was shown to inhibit angiogenesis in tumor xenografts, I investigated whether combined Taxol plus Herceptin treatment inhibits ErbB2-mediated angiogenic responses more effectively. Mice with ErbB2-overexpressing xenografts were treated with control, Herceptin, Taxol, or combination Herceptin plus Taxol. Mice treated with the combination exhibited reduced tumor volumes, tumor microvessel densities, and lung metastasis; and ErbB2-overexpressing cells treated with the combination secreted less VEGF, and stimulated less endothelial cell migration. Furthermore, Akt phosphorylation contributed to VEGF upregulation and was most effectively reduced by combination treatment. ^ In summary, ErbB2 activates signaling to Akt and p70S6K leading to increased VEGF and angiogenesis. Combination Herceptin plus Taxol treatment most effectively inhibited ErbB2-mediated angiogenesis, resulting in pronounced tumoricidal effects, and may be mediated through reduction of phosphorylated Akt, a positive regulator in the p70S6K pathway. ^