PPAR-gamma regulation of micro RNA metabolism in colon cancer

描述(由申请人提供)： 过氧化物酶体增殖物激活受体-γ(PPAR？)是一种有效的抑制早期结肠癌发生的药物，因此是结肠癌化学预防的一个特别有吸引力的靶点。多项研究表明，PPAR？在结肠癌细胞中抑制增殖和诱导分化，提示PPAR？是由于有能力逆转早期结肠癌细胞的转化。然而，解释这一过程的机制尚不清楚。我们最近完成了一组PPAR？敏感和耐药的人结肠癌细胞系。我们的数据表明，转化表型的逆转与microRNA(MiR)代谢的抑制有关。具体来说，PPAR？抑制Dicer1的表达，Dicer1催化将失活的75nt前miRs转化为活性的21-23nt miRs的限速步骤。PPAR下调Dicer1？与抑制已知的致癌微小RNA mir21的成熟有关。最近的数据表明，转化表型的维持可能依赖于结肠癌特异性miRs(所谓的oncomir)的表达。我们观察到PPAR？抑制Dicer1的表达提示PPAR？可能是由于抑制了维持转化表型所需的oncomiR依赖过程。为了验证这一假设，我们将确定Dicer1基因敲除是否抑制早期结肠癌细胞的转化。我们确定Dicer1的过表达是否阻断了PPAR？的肿瘤抑制作用，并检验了PPAR？的某些亚集的假设。靶基因在抑制Dicer1和抑制miR代谢之后受到次级调节。对这一新机制的阐明将为我们理解PPAR是如何实现的提供了新的视角。抑制肿瘤的形成，miR代谢在结肠中是如何调节的，以及特定的oncomir如何促进结肠上皮细胞的转化。此外，我们将确定一组PPAR？/Dicer1靶标mRNAs和miRs，它们可能是维持转化状态所必需的，因此可能是结肠癌化学预防的潜在新靶点。

DESCRIPTION (provided by applicant): Peroxisome proliferator-activated receptor-gamma (PPAR?) is a potent suppressor of early stage colon carcinogenesis, and therefore a particularly attractive target for colon cancer chemoprevention. A number of studies have shown that activation of PPAR? in colon cancer cells inhibits proliferation and induces differentiation, suggesting that the tumor-suppressive effects of PPAR? are due to the ability to revert the transformation of early stage colon cancer cells. However, the mechanism that accounts for this process is unknown. We have recently completed a genomic profile of a battery of PPAR? sensitive and resistant human colon cancer cell lines. Our data reveal that reversion of the transformed phenotype is associated with inhibition of micro RNA (miR) metabolism. Specifically, PPAR? inhibits expression of Dicer1, which catalyzes the rate limiting step in conversion of inactive 75nt pre-miRs to active 21-23nt miRs. Downregulation of Dicer1 by PPAR? is associated with inhibition of maturation of a known oncogenic micro RNA, mir21. Recent data indicate that maintenance of the transformed phenotype may depend upon expression of colon cancer specific miRs (so-called oncomirs). Our observation that PPAR? inhibits Dicer1 expression suggests that the tumor suppressive effects of PPAR? may result from inhibition of oncomir-dependent processes that are required for maintenance of the transformed phenotype. To test this hypothesis, we will determine if knockdown of Dicer1 inhibits transformation in early stage colon cancer cells. We determine if overexpression of Dicer1 blocks the tumor suppressive effects of PPAR?, and we will test the hypothesis that some subset of PPAR? target genes are regulated secondary to repression of Dicer1 and inhibition of miR metabolism. Elucidation of this novel mechanism will provide fundamental new insight into our understanding of how PPAR? suppresses tumor formation, how miR metabolism is regulated in the colon, and how specific oncomirs contribute to transformation of colonic epithelial cells. Furthermore, we will identify a cohort of PPAR?/Dicer1 target mRNAs and miRs that may be essential for maintenance of the transformed state and therefore potential new targets for colon cancer chemoprevention.