Oncogenic Ras blocks anoikis by activation of a novel effector pathway independent of phosphatidylinositol 3-kinase
Oncogenic Ras blocks anoikis by activation of a novel effector pathway independent of phosphatidylinositol 3-kinase
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DOI：
10.1128/mcb.21.16.5488-5499.2001
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发表时间：
2001-08-01
影响因子：
5.3
通讯作者：
Der, CJ
中科院分区：
文献类型：
--
作者：
McFall, A;Ülkü, A;Der, CJ
激活的Ras，而不是大鼠，导致RIE-1大鼠肠上皮细胞的转化，证明了Raf-independent效应信号在介导Ras转化中的重要性。为了进一步评估Raf-dependent和Raf-independent功能在致癌Ras转化中的作用，我们评估了单基因Ras阻断悬浮诱导的RIE-1细胞凋亡或失巢凋亡的机制。我们确定，致癌版本的H-，K-和N-Ras，以及Ras相关蛋白TC 21和R-Ras，保护RIE-1细胞的失巢凋亡。令人惊讶的是，我们对Ras效应子结构域突变体或组成性激活效应子的分析表明，单独激活Raf-1、磷脂酰肌醇3-激酶（PI 3 K）或RalGDS不足以促进Ras抑制失巢凋亡。用U 0126 MEK抑制剂处理Ras转化细胞导致部分逆转为失巢凋亡敏感状态，表明细胞外信号调节激酶激活有助于抑制失巢凋亡。出乎意料的是，致癌Ras未能激活Akt，并且用LY 294002 PI 3 K抑制剂处理Ras转化的RIE-1细胞不影响失巢凋亡抗性或在软琼脂中的生长。因此，虽然Ras转化成纤维细胞是重要的。PI 3 K可能不参与RIE-I细胞的Ras转化。最后，表皮生长因子受体激酶活性的抑制没有克服Ras对失巢凋亡的抑制，表明这种对转化至关重要的自分泌回路不参与失巢凋亡保护。我们得出结论，PI 3 K和RalGEF独立的Ras效应子可能与Raf合作，赋予RIE-1细胞抗失巢凋亡，从而强调Ras转化细胞的复杂性质。
Activated Ras, but not Rat, causes transformation of RIE-1 rat intestinal epithelial cells, demonstrating the importance of Raf-independent effector signaling in mediating Ras transformation. To further assess the contribution of Raf-dependent and Raf-independent function in oncogenic Ras transformation, we evaluated the mechanism by which oneogenic Ras blocks suspension-induced apoptosis, or anoikis, of RIE-1 cells. We determined that oncogenic versions of H-, K-, and N-Ras, as well as the Ras-related proteins TC21 and R-Ras, protected RIE-1 cells from anoikis. Surprisingly, our analyses of Ras effector domain mutants or constitutively activated effectors indicated that activation of Raf-1, phosphatidylinositol 3-kinase (PI3K), or RalGDS alone is not sufficient to promote Ras inhibition of anoikis. Treatment of Ras-transformed cells with the U0126 MEK inhibitor caused partial reversion to an anoikis-sensitive state, indicating that extracellular signal-regulated kinase activation contributes to inhibition of anoikis. Unexpectedly, oncogenic Ras failed to activate Akt, and treatment of Ras-transformed RIE-1 cells with the LY294002 PI3K inhibitor did not affect anoikis resistance or growth in soft agar. Thus, while important for Ras transformation of fibroblasts. PI3K may not be involved in Ras transformation of RIE-I cells. Finally, inhibition of epidermal growth factor receptor kinase activity did not overcome Ras inhibition of anoikis, indicating that this autocrine loop essential for transformation is not involved in anoikis protection. We conclude that a PI3K- and RalGEF-independent Ras effector(s) likely cooperates with Raf to confer anoikis resistance upon RIE-1 cells, thus underscoring the complex nature by which Ras transforms cells.