Regulation of Ras activity by the p38 pathway

描述（由申请人提供）：MAPKs（丝裂原活化蛋白激酶），包括ERK（细胞外信号调节激酶），JNK （c- Jun nh2末端激酶）和p38，已知通过磷酸化依赖机制在Ras癌基因活性的转导和调节中发挥关键作用。我们之前的工作表明Ras激活p38通路，p38通路反过来通过负反馈抑制Ras的增殖活性。在这里，我们提出Ras通过增加其表达而不刺激其磷酸化来激活p38gamma MARK，并且通过与ERK蛋白独立于磷酸化的物理相互作用诱导p38gamma是Ras转化所必需的。p38 γ的这种活性与其家族成员p38 α形成对比，p38 α通过磷酸化被Ras激活，从而抑制Ras转化。这一假设基于我们的初步研究，该研究表明K-Ras诱导p38gamma蛋白表达但抑制其磷酸化，并且诱导的p38gamma的耗尽抑制了大鼠肠上皮IEC-6细胞中K-Ras的转化。此外，基因阵列显示p38 γ转录本在一组原发性人类结肠癌中比在匹配的正常组织中增加。以下具体目的将检验这一假设：I)证明p38gamma在MEK/ERK通路下游作用，促进Ras转化独立于磷酸化；II)通过与ERK蛋白形成复合物，确定Ras转化是否需要p38 γ；III)在体外和小鼠实验中，研究p38 γ在K-Ras突变的人类结肠癌中是否上调，是否需要K-Ras依赖性恶性生长。本研究将证明应激p38gamma MARK作为Ras效应物的新功能，通过诱导独立于磷酸化的表达，从而揭示Ras癌基因活性由抗癌基因p38alpha和促癌基因p38gamma之间的信号整合决定的机制。通过证明p38gamma表达升高的诊断价值和p38gamma缺失的治疗意义，所获得的信息将直接有助于人类结肠癌的预防和治疗。

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.