Cyclin D1 Regulation of Nuclear Receptor Function

描述（由申请人提供）：ErbB 2跨膜受体在约30%的人类肿瘤中过表达。乳腺靶向ErbB 2过表达足以在体内发生乳腺肿瘤。细胞周期蛋白D1基因产物在30-50%的人乳腺癌中过表达。细胞周期蛋白D1反义阻断ErbB 2诱导的乳腺肿瘤生长，细胞周期蛋白D1 -/-小鼠对ErbB 2诱导的肿瘤生长具有抗性。PPARgamma核激素受体抑制细胞增殖并促进分化。已经在几种癌症中鉴定了PPARgamma的突变、重排和改变的表达，这表明PPARgamma可以起到肿瘤抑制剂的作用。我们已经证明细胞周期蛋白D1抑制培养细胞中的PPARgamma分化功能、反式激活和表达。我们已经表明，CD 1-/-小鼠具有反映增加的PPARgamma表达和活性的遗传和表型变化，这暗示了在肿瘤抗性表型中增加的PPARgamma。目前的研究将确定细胞周期蛋白D1在体内抑制PPARgamma信号的分子机制。我们将使用乳腺靶向诱导型转基因来确定细胞周期蛋白D1调节PPARgamma功能的分子机制，并确定PPARgamma在ErbB 2背景下作为乳腺肿瘤抑制因子的作用。这些研究将： 1.确定细胞周期蛋白D1抑制PPARgamma反式激活的机制。将测定细胞周期蛋白D1抑制PPARgamma共激活因子亚组的能力。由于PPARgamma是乙酰化的，并且细胞周期蛋白D1 HDAC募集结构域控制PPARgamma抑制，因此将确定PPARgamma乙酰化在细胞周期蛋白D1抑制中的作用。 2.确定细胞周期蛋白D1抑制PPAR γ功能和表达的机制。细胞周期蛋白D1阻断PPAR γ诱导的成纤维细胞向脂肪细胞的分化。我们将确定调控PPARgamma分化的细胞周期蛋白D1的结构域。将在CD-/-小鼠、细胞周期蛋白E敲除CD-/-小鼠和ponasterone诱导的细胞周期蛋白D1反义小鼠中评估细胞周期蛋白D1对PPAR γ的调节。PPARgamma和细胞周期蛋白D1的相关表达研究将在“良性”乳腺疾病和乳腺癌中进行。 3.确定PPARgamma作为ErbB 2诱导的乳腺肿瘤发生的肿瘤抑制因子的作用。我们将确定ErbB 2和PPARgamma在培养细胞和ponasterone诱导的乳腺靶向PPARgamma转基因小鼠中的功能相互作用。使用可诱导的转基因将允许在乳腺肿瘤发病和进展期间测定PPARgamma功能。如果PPARgamma是ErbB 2诱导的肿瘤发生的抑制剂，并且PPARgamma肿瘤抑制功能涉及细胞周期蛋白D1抑制，则这些研究为识别这种相互作用的激动剂以用于潜在的治疗应用提供了合理的基础。此外，如果在乳腺癌的前驱病变中PPARgamma水平降低，则在良性乳腺疾病中的PPARgamma研究可提供乳腺癌进展的预测因子。因此，拟议的研究可能具有重要的翻译意义。

DESCRIPTION (provided by applicant): The ErbB2 transmembrane receptor is overexpressed in approximately 30% of human tumors. Mammary gland targeted ErbB2 overexpression is sufficient for mammary tumorigenesis in vivo. The cyclin D1 gene product is overexpressed in 30-50% of human breast cancers. Cyclin D1 anti-sense blocks ErbB2-induced mammary tumor growth and cyclin D1 -/- mice are resistant to ErbB2-induced tumor growth. The PPARgamma nuclear hormone receptor inhibits cellular proliferation and promotes differentiation. Mutations, rearrangements and altered expression of PPARgamma have been identified in several cancers suggesting PPARgamma may function as a tumor suppressor. We have shown cyclin D1 inhibits PPARgamma differentiation function, transactivation and expression in cultured ceils. We have shown CD1 -/- mice have genetic and phenotypic changes reflecting increased PPARgamma expression and activity, implicating increased PPARgamma in the tumor-resistant phenotype. The current studies will determine the molecular mechanisms by which cyclin D1 inhibits PPARgamma signaling in vivo. We will use mammary gland-targeted inducible transgenics to identify the molecular mechanisms by which cyclin D1 regulates PPARgamma function and determine the role of PPARgamma as a mammary gland tumor suppressor in the context of ErbB2. These studies will: 1. Determine the mechanism by which cyclin D1 inhibits PPARgamma transactivation. The ability of cyclin D1 to inhibit a subset of PPARgamma coactivators will be determined. As PPARgamma is acetylated and the cyclin D1 HDAC recruitment domain governs PPARgamma repression, the role of PPARgamma acetylation in repression by cyclin D1 will be determined. 2. Determine the mechanisms by which cyclin D1 inhibits PPARgamma function and expression. Cyclin D1 blocks PPARgamma induced differentiation of fibroblasts to adipocytes. We will identify the domain of cyclin D1 regulating PPARgamma differentiation. Cyclin D1 regulation of PPARgamma will be assessed in CD-/- mice, cyclin E knockin-CD-/- mice and in ponasterone-inducible cyclin D1 anti-sense mice. Correlative expression studies of PPARgamma and cyclin D1 will be conducted in 'benign' breast disease and breast cancers. 3. Determine the role of PPARgamma as a tumor suppressor of ErbB2-induced mammary tumorigenesis. We will determine the functional interactions between ErbB2 and PPARgamma in cultured cells and in ponasterone-inducible mammary gland-targeted PPARgamma transgenic mice. The use of inducible transgenics will allow the determination of PPARgamma function during mammary tumor onset and progression. If PPARgamma is an inhibitor of ErbB2-induced tumorigenesis and PPARgamma tumor suppressor function involves cyclin D1 repression, these studies provide a rational basis for identifying agonists of this interaction for potential therapeutic applications. Moreover, if PPARgamma levels are decreased in precursor lesions of breast cancer, the studies of PPARgamma in benign breast disease may provide a predictor of breast cancer progression. The proposed studies therefore may have important translational implications.