Cox A D, Brtva T R, Lowe D G, Der C J
Department of Pharmacology, School of Medicine, University of North Carolina at Chapel Hill 27599-7365.
Oncogene. 1994 Nov;9(11):3281-8.
Although previous studies have not identified transforming properties of the Ras-related protein R-Ras, two recent observations have prompted our further evaluation of R-Ras function. First, we observed that mutant forms of the closely related R-Ras2/TC21 protein (approximately 70% identity) exhibited the same potent transforming activity as oncogenic Ras proteins. Second, R-Ras association with Bcl-2 suggested a possible role for R-Ras in apoptotic growth control. Therefore, we have performed a detailed analysis of R-Ras transforming potential in NIH3T3 cells. Whereas expression of a mutant R-Ras protein (38V; analogous to the 12V activating Ras mutation) did not induce morphologic transformation of NIH3T3 cells, R-Ras(38V)-expressing cells proliferated in low serum, formed colonies in soft agar, and formed progressive tumors in nude mice. Like Ras-transformed cells, R-Ras(38V)-transformed cells exhibited constitutively activated mitogen activated protein kinases. Furthermore, R-Ras(38V) stimulated transcriptional activation of Ras-responsive promoter elements, and this activity (and transformation) was blocked by Raf dominant negative proteins. Finally, whereas co-expression of Bcl-2 did not cause significant alteration in wild type or mutant R-Ras transforming activity, coexpression of v-Myc and R-Ras(38V) induced a striking morphologic transformation of NIH3T3 cells. Taken together, these observations suggest that aberrant R-Ras function may stimulate malignant transformation, in the absence of morphologic transformation, via up-regulation of part of the Ras signal transduction pathway.
尽管先前的研究尚未确定Ras相关蛋白R-Ras的转化特性，但最近的两项观察结果促使我们进一步评估R-Ras的功能。首先，我们观察到密切相关的R-Ras2/TC21蛋白（约70%的同源性）的突变形式表现出与致癌性Ras蛋白相同的强大转化活性。其次，R-Ras与Bcl-2的结合表明R-Ras在凋亡生长控制中可能发挥作用。因此，我们对NIH3T3细胞中R-Ras的转化潜力进行了详细分析。虽然突变型R-Ras蛋白（38V；类似于激活Ras的12V突变）的表达并未诱导NIH3T3细胞发生形态转化，但表达R-Ras(38V)的细胞在低血清中增殖，在软琼脂中形成集落，并在裸鼠中形成进行性肿瘤。与Ras转化的细胞一样，R-Ras(38V)转化的细胞表现出持续激活的丝裂原活化蛋白激酶。此外，R-Ras(38V)刺激了Ras反应性启动子元件的转录激活，并且这种活性（以及转化）被Raf显性负性蛋白所阻断。最后，虽然Bcl-2的共表达并未导致野生型或突变型R-Ras转化活性的显著改变，但v-Myc和R-Ras(38V)的共表达诱导了NIH3T3细胞显著的形态转化。综上所述，这些观察结果表明，异常的R-Ras功能可能通过上调Ras信号转导途径的一部分，在无形态转化的情况下刺激恶性转化。
