Regulation of Ras activity by the p38 pathway

描述(由申请人提供)：MAPK(丝裂原激活蛋白激酶)，包括ERK(细胞外信号调节激酶)、JNK(c-jun氨基末端激酶)和p38，已知通过磷酸化依赖的机制在RAS癌基因活性的转导和调节中发挥关键作用。我们以前的工作表明，RAS激活p38通路，而p38通路通过负反馈抑制RAS的增殖活性。在这里，我们认为RAS通过增加其表达而不刺激其磷酸化来激活P38Gamma Mark，而诱导P38Gamma是RAS转化所必需的，通过与ERK蛋白的物理相互作用而不依赖于磷酸化。P38Gamma的这种活性与其家族成员p38α的活性相反，后者被RAS通过磷酸化激活，导致抑制RAS的转化。这一假说是基于我们的初步研究表明，K-RAS诱导大鼠肠上皮细胞IEC-6细胞中P38Gamma蛋白的表达但抑制其磷酸化，而诱导的P38Gamma蛋白的缺失抑制了K-Ras的转化。此外，基因阵列显示，在一组原发人类结肠癌中，p38伽马转录本比匹配的正常组织中增加。以下特定目的将检验这一假说：i)证明p38Gamma在MEK/ERK通路下游促进RAS转化而不依赖于磷酸化；ii)确定p38Gamma是否通过与ERK蛋白形成的复合体促进RAS转化；iii)研究p38Gamma在K-RAS突变的人结肠癌中是否上调表达，并在体外和小鼠中是否需要K-RAS依赖的恶性肿瘤生长。本研究将通过不依赖于磷酸化的诱导表达来证明应激p38Gamma Mark作为RAS效应分子的新功能，从而揭示Ras癌基因活性是由抑癌基因p38α和促癌基因p38Gamma之间的信号整合决定的机制。所获得的信息将直接有助于人类结肠癌的预防和治疗，因为它证明了P38伽马表达增加的诊断价值和P38伽马缺失的治疗意义。

DESCRIPTION (provided by applicant): MAPKs (mitogen-activated protein kinases), including ERK (extracellular signal-regulated kinase), JNK (c- Jun NH2-terminal kinase), and p38, are known to play a critical role in transduction and regulation of Ras oncogene activity by phosphorylation-dependent mechanisms. Our previous work demonstrated that Ras activates the p38 pathway, which in turn inhibits Ras proliferative activity by negative feedback. Here we propose that Ras activates p38gamma MARK by increasing its expression without stimulating its phosphorylation, and induced p38gamma is required for Ras transformation through a physical interaction with ERK proteins independent of phosphorylation. This activity of p38gamma contrasts with that of its family member p38alpha, which is activated by Ras through phosphorylation, leading to an inhibition of Ras transformation. This hypothesis is based on our preliminary studies showing that K-Ras induces p38gamma protein expression but inhibits its phosphorylation, and that depletion of induced p38gamma suppresses K-Ras transformation in rat intestinal epithelial IEC-6 cells. Furthermore, gene arrays showed that p38gamma transcripts are increased in a set of primary human colon cancers than in matched normal tissues. The following specific aims will test this hypothesis: I) To demonstrate that p38gamma acts downstream of the MEK/ERK pathway to promote Ras transformation independent of phosphorylation; II) To determine whether p38gamma is required for Ras transformation through a complex formation with ERK proteins; III) To investigate if p38gamma is up-regulated in K-Ras mutated human colon cancer and required for K-Ras-dependent malignant growth in vitro and in mice. This study will demonstrate a novel function of stress p38gamma MARK as a Ras effector through induced expression independent of phosphorylation and thereby reveal a mechanism by which Ras oncogene activity is determined by a signaling integration between anti-oncogenic p38alpha and pro-oncogenic p38gamma. Information obtained will directly contribute to human colon cancer prevention and treatment by demonstrating the diagnostic value of increased p38gamma expression and the therapeutic significance of p38gamma depletion.