Regulation of Ras activity by the p38 pathway

描述（由申请人提供）：已知MAPK（促分裂原活化蛋白激酶），包括ERK（细胞外信号调节激酶）、JNK（c-Jun NH 2-末端激酶）和p38，通过磷酸化依赖性机制在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，p38通路反过来通过负反馈抑制Ras增殖活性。在这里，我们提出，Ras激活p38 γ MARK通过增加其表达，而不刺激其磷酸化，并诱导p38 γ是Ras转化所需的通过与ERK蛋白的物理相互作用独立的磷酸化。p38 γ的这种活性与其家族成员p38 α的活性相反，p38 α通过磷酸化被Ras激活，导致Ras转化的抑制。这一假设是基于我们的初步研究表明，K-Ras诱导p38 γ蛋白的表达，但抑制其磷酸化，诱导的p38 γ的耗竭抑制K-Ras转化大鼠肠上皮IEC-6细胞。此外，基因阵列显示p38 γ转录物在一组原发性人类结肠癌中比在匹配的正常组织中增加。以下具体目标将检验这一假设：I）证明p38 γ在MEK/ERK通路下游起作用以促进Ras转化而不依赖于磷酸化; II）确定p38 γ是否通过与ERK蛋白形成复合物而为Ras转化所需; III）研究p38 γ在K-Ras突变的人结肠癌中是否上调，并且是否是体外和小鼠中K-Ras依赖性恶性生长所需的。本研究将证明应激p38 γ MARK作为Ras效应子通过诱导表达而不依赖于磷酸化的新功能，从而揭示Ras癌基因活性由抑癌p38 α和促癌p38 γ之间的信号整合决定的机制。所获得的信息将通过证明p38 γ表达增加的诊断价值和p38 γ缺失的治疗意义，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.