Regulation of Stat3 by p53 in cancer Cells

在这项拟议的研究中，我们将研究P53对STAT3(信号转导和转录激活因子3)的调节作用，在表达STAT3活性的乳腺和卵巢癌细胞中。STAT3可能在正常细胞向恶性细胞的致癌转化过程中起重要作用，并可能抑制细胞凋亡。最近的研究表明，STAT3信号通过刺激细胞增殖、促进肿瘤血管生成和防止细胞凋亡而参与肿瘤的发生。STAT3的结构性激活经常在多种癌症样本和癌细胞系中被检测到。这些研究表明，结构性激活的STAT3在人类癌症的发生中发挥了作用。P53抑癌基因突变是人类癌症中最常见的基因改变之一。我们的初步研究表明，野生型(Wt)P53的表达而不是突变型P53的表达显著减少了乳腺癌、卵巢癌和前列腺癌中表达活性STAT3的磷酸化或活性形式的STAT3。WT-P53也能诱导这些癌细胞发生显著的凋亡。我们推测wtp53的抗增殖活性与STAT3在癌细胞中的结构性激活不相容。上游激活剂(S)对STAT3的结构性激活可能激活P53活性，从而诱导细胞生长停滞/凋亡。激活的P53可能诱导P53下游靶点，以负反馈的方式抑制STAT3。然后，p53可能会起到一种保护作用，防止STAT3的致癌基因去调控。只有进一步突变P53或使P53途径失活的癌细胞才能逃脱P53依赖的凋亡/生长停滞，并能够继续肿瘤进展。因此，STAT3的结构性激活可能选择性地存在于含有P53基因失活突变或缺失的癌细胞中。这是一个可验证的假说，这一假说部分得到了我们对一组人类癌细胞中STAT3和P53状态的调查的支持。我们发现，所有表达成分活性STAT3的乳腺、卵巢和前列腺癌细胞株只表达突变的或空的P53。在这个提案中，我们试图研究两个在乳腺癌和卵巢癌中经常改变的潜在重要基因的功能调节，它们是STAT3和P53。为解决这些问题，将研究以下具体目标： 1.研究P53抑制STAT3表达的癌细胞中STAT3的分子机制。 2.检测P53的转录活性是否是抑制STAT3所必需的。 3.评估固有活性STAT3的下调是否与P53诱导的细胞凋亡有关。 4.检测STAT3是否选择性地发生在乳腺癌和卵巢癌细胞系以及含有P53突变或缺失的癌症标本中。

In the proposed studies, we will examine the regulation of Stat3 (Signal transducer and activator of transcription 3) by p53 in breast and ovarian cancer cells expressing constitutively active Stat3. Constitutively active Stat3 may play a important role of oncogenic transformation of normal cells to malignant cells and may inhibit apoptosis. Recent studies suggest that constitutively Stat3 signaling contribute to oncogenesis by stimulating cell proliferation, promoting tumor angiogenesis, and preventing apoptosis. Constitutive activation of Stat3 has been frequently detected in a variety of cancer samples and cancer cell lines. These studies suggest that constitutively activated Stat3 plays a role on the human cancer carcinogenesis. Mutation of the p53 tumor suppressor is one of the most commonly detected genetic alterations in human cancer. Our preliminary studies demonstrated that expression of wild-type (wt) p53 but not mutant p53 significantly reduced phosphorylated or active form of Stat3 in breast, ovarian and prostate cancer cells that express constitutively active Stat3. Wt p53 also induced dramatic apoptosis in these cancer cell lines. We hypothesize that the anti-proliferative activities of wt p53 are not compatible with the constitutive activation of Stat3 in cancer cells. Constitutive activation of Stat3 by upstream activator(s) may activate p53 activities to induce growth arrest/apoptosis of cells. Activated p53 may induce a p53 downstream target that inhibits Stat3 in a negative feed back manner. p53 may then serve a safeguard against oncogenic deregulation of Stat3. Only cancer cells that further mutate p53 or inactivate p53 pathway may be able to escape p53-dependent apoptosis/growth arrest and be able to continue tumor progression. Therefore, constitutive activation of Stat3 may be selectively present in cancer cells that have harbored inactivating mutation or deletion of the p53 gene. This is a testable hypothesis and this hypothesis is partially supported by our survey from the published reports of the status of Stat3 and p53 in a panel of human cancer cell lines. We found that all breast, ovarian and prostate cancer cell lines that express constitutively active Stat3 only express mutant or null p53. In this proposal, we seek to examine the functional regulation of two potentially important genes that frequently altered in breast and ovarian cancers, Stat3 and p53. The following specific aims will be studied to address these questions: 1. Examine the molecular mechanism by which p53 inhibits Stat3 in cancer cells expressing constitutively active Stat3. 2. Examine whether the transcription activity of p53 is necessary to inhibit Stat3. 3. Evaluate whether down regulation of constitutively active Stat3 is associated with apoptosis induced by p53. 4. Examine whether constitutive activation of Stat3 selectively occurs in breast and ovarian cancer cell lines and cancer specimens containing p53 mutations or deletions.