Transforming growth factor beta signaling pathways

描述（由申请人提供）：我们的长期目标是了解调节disabled-2 （Dab2）蛋白表达水平的分子机制。Dab2是一种细胞质接头分子，与网格蛋白介导的内吞作用有关。它最初被确定为卵巢癌中下调的一种蛋白，并已确定其表达水平对细胞增殖、分化和癌症发展有重要影响。由于其在卵巢癌、乳腺癌、前列腺癌和胰腺癌细胞中的表达水平降低，它已被指定为推定的肿瘤抑制因子。我们已经获得的初步数据表明，除了转录调控外，细胞Dab2的表达水平还通过转录后机制维持，包括转录特异性翻译控制和泛素介导的蛋白酶体降解。在两种细胞分化系统中，tgfβ介导的小鼠乳腺上皮（NMuMG）细胞上皮向间充质转分化模型和维甲酸（RA）诱导的F9畸胎癌细胞内脏内胚层分化模型，我们提供的数据表明，转录诱导的Dab2 mRNA不能单独解释诱导的Dab2蛋白表达水平。我们在基底下证明。条件下，Dab2的表达水平通过Dab2 3'-非翻译区（3'-UTR）中包含的序列元件驱动的机制被翻译沉默。tgfβ处理的NMuMG或ra处理的F9细胞的细胞质提取物可以克服这种3'- utr介导的沉默，导致Dab2蛋白表达增加。我们进一步表明，一旦合成，Dab2水平通过gsk -3beta依赖的磷酸化和泛素介导的降解途径进行调节。这些结果表明Dab2的表达受到高度调控，并支持其表达水平决定其增殖和分化功能的假设。在这项提议中，我们希望进一步探索Dab2表达水平调控的分子机制，并确定这些机制的失调是否可能是其在癌症中的异常表达的基础。

DESCRIPTION (provided by applicant): Our long-term goal is to understand the molecular mechanisms regulating disabled-2 (Dab2) protein expression levels. Dab2 is a cytoplasmic adaptor molecule that is associated with clathrin mediated endocytosis. It was originally identified as a protein down-regulated in ovarian carcinoma and it has since been established that its expression levels have significant impact on cellular proliferation, differentiation, and cancer development. It has been designated as a putative tumor suppressor due to its decreased expression levels in ovarian, breast, prostate and pancreatic carcinoma cells. We have obtained preliminary data suggesting that, in addition to transcriptional regulation, cellular Dab2 expression levels are also maintained through post-transcriptional mechanisms involving transcript-specific translational control and ubiquitin-mediated proteasomal degradation. In two cellular differentiation systems, a TGFbeta-mediated epithelial to mesenchymal transdifferentiation model in mouse mammary epithelial (NMuMG) cells and a retinoic acid (RA)-induced visceral endoderm differentiation model in F9 teratocarcinoma cells, we present data suggesting that transcriptional induction of Dab2 mRNA alone can not account for induced Dab2 protein expression levels. We demonstrate that under basal .conditions, Dab2 expression levels are translationally silenced through a mechanism driven by sequence elements contained in the Dab2 3'-untranslated region (3'-UTR). Cytosolic extracts from TGFbeta-treated NMuMG or RA-treated F9 cells can overcome this 3'- UTR-mediated silencing, resulting in increased Dab2 protein expression. We further show that once synthesized, Dab2 levels are regulated through a GSK-3beta-dependent phosphorylation and ubiquitin-mediated degradation pathway. These results demonstrate that Dab2 expression is highly regulated and support the hypothesis that its expression levels underlie its proliferate and differentiative functions. In this proposal, we wish to further explore the molecular mechanisms through which Dab2 expression levels are regulated and determine whether dysregulation of these mechanisms might underlie its aberrant expression in cancer.