STRAP and Smad 7 Signaling in Colorectal Carcinomas

描述（由申请人提供）：结直肠癌的发生涉及遗传和表观遗传变化的积累，这些变化导致正常结直肠上皮、原位癌和最终的侵袭性和转移性癌症的改变。TGF-¿-诱导的肿瘤抑制功能的丧失在这一转变中起着关键作用。结直肠癌对TGF-¿的抗性可以通过多种机制发生。然而，TGF- II型受体和选定的TGF-¿信号转导器（Smad2/4）的失活突变和受体表达的减少不足以（约55%）解释肿瘤中TGF-¿不敏感的高频率。目前尚不清楚在其他（约45%）病例中结肠癌是如何对TGF-¿的抗增殖反应产生耐药性的。我们发现了一种新的含有wd结构域的蛋白STRAP（丝氨酸苏氨酸激酶受体相关蛋白），它与TGF-¿受体复合物和Smad7结合，并抑制TGF-¿信号传导。我们已经报道了STRAP和Smad7在结直肠癌中上调，刺激细胞生长，诱导非锚定生长并增强致瘤性。我们的初步数据表明，STRAP通过独立于TGF-¿调节e -钙粘蛋白来诱导上皮到间质转化（EMT）。STRAP还增加了可能促进细胞增殖的claudin1和CyclinD1的表达。我们有证据表明，STRAP上调活性MMP9和纤维连接蛋白，诱导细胞迁移和侵袭。此外，我们已经证明Smad7在结肠癌细胞中的稳定表达可诱导转移。基于背景资料，我们提出了以下假设：STRAP消除了TGF-¿诱导的生长抑制作用，并且STRAP诱导TGF-¿不依赖于TGF-¿的细胞增殖、EMT、迁移和侵袭是结直肠癌恶性表型获得的关键。我们进一步假设，STRAP和Smad7在阻断TGF-¿抑瘤功能方面的功能合作参与了结肠肿瘤的进展和转移。这些假设将通过以下具体目标进行验证：1)确定STRAP促进上皮细胞向间质细胞转化（EMT）的机制。2)确定TGF-依赖型和非依赖型的TGF-调控癌细胞增殖、迁移和侵袭的机制。3)确定STRAP与Smad7在结肠肿瘤转移中的功能协同作用，以及STRAP在人类结直肠癌中的上调机制。本研究的长期目标是在分子水平上了解结直肠肿瘤对TGF-¿抑瘤作用产生耐药性的机制。更好地了解EMT、迁移、侵袭和转移的调控因子将有助于改善结直肠癌的药物开发和治疗。公共卫生相关性：肿瘤中转化生长因子-¿（TGF-¿）诱导的肿瘤抑制功能的丧失在正常结直肠癌上皮向原位癌转变，最终侵袭性和转移性结直肠癌的进展和转移中起着关键作用。更好地了解这些机制将有助于改进这种致命疾病的药物开发和治疗。

DESCRIPTION (provided by applicant): Colorectal carcinogenesis involves an accumulation of genetic and epigenetic changes that lead to alterations in normal colorectal epithelium, in situ carcinoma, and finally invasive and metastatic cancers. The loss of TGF-¿-induced tumor suppressor function plays a pivotal role in this transition. Resistance to TGF-¿ in colorectal cancers can occur through a variety of mechanisms. However, inactivating mutations in the TGF-¿ type II receptor and selected TGF-¿ signal transducers (Smad2/4), and reduced expression of receptors are not enough (around 55%) to account for the high frequency of TGF-¿ insensitivity among carcinomas. It is still unknown how colon cancers become resistant to the antiproliferative responses to TGF-¿ in the other (approximately 45%) cases. We identified a novel WD-domain containing protein STRAP (Serine Threonine Kinase Receptor Associated Protein) that binds with both TGF-¿ receptor complex and Smad7, and that inhibits TGF-¿ signaling. We have reported that STRAP and Smad7 are upregulated in colorectal cancers, stimulate cell growth, induce anchorage-independent growth and enhance tumorigenicity. Our preliminary data suggest that STRAP induces epithelial-to-mesenchymal transition (EMT) by deregulating E-cadherin independently of TGF-¿. STRAP also increases the expression of claudin1 and CyclinD1 that may contribute to cell proliferation. We have evidence that STRAP upregulates active MMP9 and fibronectin, and induces cell migration and invasion. In addition, we have demonstrated that stable expression of Smad7 in colon cancer cells induces metastasis. Based on the background information, we have developed the following hypotheses: Abrogation of TGF-¿-induced growth inhibition by STRAP, and TGF-¿-independent effects of STRAP including induction in cell proliferation, EMT, migration and invasion are critical for the acquisition of malignant phenotype in colorectal cancer. We further hypothesize that functional cooperation between STRAP and Smad7 in blocking TGF-¿ tumor suppressor function is involved in colon tumor progression and metastasis. These hypotheses will be tested by following specific aims: 1) Determine the mechanism by which STRAP promotes epithelial-to-mesenchymal transition (EMT). 2) Determine the TGF-¿-dependent and -independent mechanism of STRAP-regulation of cancer cell proliferation, migration and invasion. 3) Determine how functional cooperation between STRAP and Smad7 contributes to colon tumor metastasis and the mechanism of upregulation of STRAP in human colorectal cancer. The long-term objective of this study is to understand, at the molecular level, the mechanism by which colorectal tumors become resistant to TGF-¿ tumor suppressor effects. A better understanding of the regulators of EMT, migration, invasion and metastasis will help to improve drug development and treatment of colorectal cancer. PUBLIC HEALTH RELEVANCE: The loss of transforming growth factor-¿ (TGF-¿)-induced tumor suppressor function in tumors plays a pivotal role in the transition from normal colorectal epithelium, to in situ carcinoma, and finally invasive and metastatic colorectal cancer progression and metastasis. A better understanding of these mechanisms will help to improve drug development and treatment of this lethal disease.