It has been demonstrated that overexpression of Pin1, a novel cell cycle regulator, in human breast cancer and might play an important role in tumorigenesis. However, the role of Pin1 and whether Pin1 is overexpressed in esophageal squamous cell carcinoma (ESCC) remained unclear. There are two specific aims in this study. The first specific aim is to study the correlation between Pin1 and human ESCC cancer. The second specific aim is to discover drugs that can intervent the Pin1 mediated signaling and provide a novel chemotherapy for human ESCC. In this dissertation, we have demonstrated that Pin1 was overexpressed in more than 65% of clinical esophageal cancer tissues and its level correlated with £]-catenin and Cyclin D1 expression by western blotting and immunohistochemistry analyses. The RT-PCR results suggested that Pin1 overexpression maybe due to the up-regulation of Pin1 transcription. By statistic analysis, we have demonstrated that ESCC patients with Pin1 overexpression had significantly poorer survival rate than those non-Pin1 overexpression patients (p< 0.001). Pin1 therefore can be used as a prognosis marker for ESCC. In addition, we have demonstrated that Pin1 suppression by shRNA could downregulate £]-catenin and Cyclin D1 expression and inhibit ESCC cell proliferation efficiently. Taken together, these results suggest that Pin1-£]-catenin and Cyclin D1 could be used as a potential chemotherapy target for ESCC. In order to discover novel drugs in the chemoprevention or therapy of human ESCC, we screened a chemical library using cell proliferation assay. Among them, compound VGHKS-040 not only effectively inhibited the cell proliferation rate in ESCC cell lines with IC50 value of 4.8¡Ó0.6£gM but also abated protein levels of Pin1, £]-catenin, and cyclin D1. By colony forming assay as well as the Xenograft SCID and nude mice model, we have demonstrated that VGHKS-040 can inhibit the tumor growth in vitro and in vivo. These results suggested that VGHKS-040 provide a new avenue for chemotherapy of esophageal squamous cell carcinoma.

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<p>An important step in tumorgenesis is the acquisition of cellular immortality. Tumor cells accomplish this by activating the enzyme telomerase, and thereby avoiding replicative senescence. The aim of this thesis was to study the activity and regulation of telomerase in a panel of malignant cell types.</p><p>We found that TGF-β1 (transforming growth factor-β1) mediated differential effects on telomerase activity in five ATC (anaplastic thyroid carcinoma) cell lines. Cells that harbored a <i>p53</i> mutation responded by up-regulation of telomerase activity after TGF-β1 treatment, whereas cell lines displaying wt <i>p53 </i>responded by down-regulation of telomerase activity. Thus, these results indicate a possible connection between <i>p53</i> genotype and telomerase response to TGF-β1 treatment. Furthermore, the decreased telomerase activity appeared to be due to transcriptional repression of the <i>hTERT</i> promoter and the increased activity possibly involved hTERT activation via phosphorylation. </p><p>We have previously shown that IFNs (interferons) sensitize MM (multiple myeloma) cells to Fas-mediated apoptosis. In the present investigation both IFN-α and IFN-γ down regulated telomerase activity in the MM cell line U-266-1970. The mechanism underlying the reduction of telomerase activity by IFN was shown to be transcriptional repression of the <i>hTERT </i>gene. We suggest that one potential mechanism whereby IFN sensitize MM cells to Fas-mediated apoptosis is by repressing <i>hTERT</i> activity at the transcriptional level. </p><p>In the next study we demonstrated that basal telomerase activity is not a key determinant of sensitivity to cytotoxic drugs in ESCC (esophageal squamous cell carcinoma) cell lines. Furthermore, we observed no correlation between <i>c-Myc</i> amplification, <i>p53</i> mutations and high telomerase activity levels in these cell lines. </p><p>Finally, neuroblastoma cell lines were shown to up-regulate telomerase activity in response to hypoxic exposure and the main regulatory mechanism was not mediated by increased hTERT mRNA expression. This finding might constitute an adaptive stress response of tumor cells exposed to hypoxia. </p>

An important step in tumorgenesis is the acquisition of cellular immortality. Tumor cells accomplish this by activating the enzyme telomerase, and thereby avoiding replicative senescence. The aim of this thesis was to study the activity and regulation of telomerase in a panel of malignant cell types. We found that TGF-β1 (transforming growth factor-β1) mediated differential effects on telomerase activity in five ATC (anaplastic thyroid carcinoma) cell lines. Cells that harbored a p53 mutation responded by up-regulation of telomerase activity after TGF-β1 treatment, whereas cell lines displaying wt p53 responded by down-regulation of telomerase activity. Thus, these results indicate a possible connection between p53 genotype and telomerase response to TGF-β1 treatment. Furthermore, the decreased telomerase activity appeared to be due to transcriptional repression of the hTERT promoter and the increased activity possibly involved hTERT activation via phosphorylation. We have previously shown that IFNs (interferons) sensitize MM (multiple myeloma) cells to Fas-mediated apoptosis. In the present investigation both IFN-α and IFN-γ down regulated telomerase activity in the MM cell line U-266-1970. The mechanism underlying the reduction of telomerase activity by IFN was shown to be transcriptional repression of the hTERT gene. We suggest that one potential mechanism whereby IFN sensitize MM cells to Fas-mediated apoptosis is by repressing hTERT activity at the transcriptional level. In the next study we demonstrated that basal telomerase activity is not a key determinant of sensitivity to cytotoxic drugs in ESCC (esophageal squamous cell carcinoma) cell lines. Furthermore, we observed no correlation between c-Myc amplification, p53 mutations and high telomerase activity levels in these cell lines. Finally, neuroblastoma cell lines were shown to up-regulate telomerase activity in response to hypoxic exposure and the main regulatory mechanism was not mediated by increased hTERT mRNA expression. This finding might constitute an adaptive stress response of tumor cells exposed to hypoxia.