Aberrant Function of the Ras-Related Protein TC21/R-Ras2 Triggers Malignant Transformation

Abstract

Although the human Ras proteins are members of a large superfamily of Ras-related proteins, to date, only the proteins encoded by the three mammalian ras genes have been found to possess oncogenic potential. Among the known Ras-related proteins, TC21/R-Ras2 exhibits the most significant amino acid identity (55%) to Ras proteins. We have generated mutant forms of TC21 that possess amino acid substitutions analogous to those that activate Ras oncogenic potential [designated TC21(22V) and TC21(71L)] and compared the biological properties of TC21 with those of Ras proteins in NIH 3T3 and Rat-1 transformation assays. Whereas wild-type TC21 did not show any transforming potential in vitro, both TC21(22V) and TC21(71L) displayed surprisingly potent transforming activities that were comparable to the strong transforming activity of oncogenic Ras proteins. Like Ras-transformed cells, NIH 3T3 cells expressing mutant TC21 proteins formed foci of morphologically transformed cells in monolayer cultures, proliferated in low serum, formed colonies in soft agar, and developed progressive tumors in nude mice. Thus, TC21 is the first Ras-related protein to exhibit potent transforming activity equivalent to that of Ras. Furthermore, mutant TC21 proteins also stimulated constitutive activation of mitogen-activated protein kinases as well as transcriptional activation from Ras-responsive promoter elements (Ets/AP-1 and NF-kappa B). We conclude that aberrant TC21 function may trigger cellular transformation via a signal transduction pathway similar to that of oncogenic Ras and suggest that deregulated TC21 activity may contribute significantly to human oncogenesis.

Characterization of mutant versions of the R-RAS2/TC21 GTPase found in tumors

“…The Q72L, G23V and Dup24-26 RRAS2 mutations, analogous to the Q61L, G12V and Dup13-15 mutations in RAS proteins [ 22 ], can activate the transforming function of R-RAS2 in cell culture [ 2 , 11 , 32 , 33 ]. We have also recently shown that the Rras2 Q72L mutation acts as a potent oncogenic driver when somatically expressed in mice [ 18 ].…”

“…R-RAS2 (originally known as teratocarcinoma clone 21 or TC21) received significant attention upon its discovery in 1990 [ 1 , 2 ] since it was considered a potential surrogate oncogenic pathway for cancer cells lacking gain-of-function mutations in the classical RAS GTPases (H-RAS, K-RAS, N-RAS; referred to hereafter as RAS proteins). This idea was based on several features of R-RAS2 that were unique among the rest of RAS superfamily members: (i) 100% homology at the protein level of the two effector regions (switch I and switch II) with those present in RAS proteins [ 1 ]; (ii) binding to a similar spectrum of RAS regulators and proximal effectors such as PI3K, the RAL GDP dissociation stimulator (RAL GDS), and RAF family members [ 3 – 10 ]; (iii) similar subcellular localization as RAS proteins [ 3 – 5 ]; and (iv) transforming activity of some of gain-of-function R-RAS2 mutant versions similar to (or even higher than) RAS oncoproteins [ 2 , 11 ]. Despite these data, the interest in this GTPase faded away subsequently due to the inability to find gain-of-function RRAS2 mutations in human tumors with the techniques available before the emergence of next-generation sequencing.…”

NGS and Mutational Profile Analysis of Non-Small-Cell Lung Carcinoma (NSCLC)

“…Resistance to cisplatin, carboplatin, and EGFR-TKIs is inevitable in treating NSCLCs [7]. In lung cancer deregulation of TC21 can trigger cellular transformation and contribute to human oncogenesis because similar signal transduction pathway is used by oncogenic Ras [8]. Recent studies show that Rabl3 is a novel oncogene which regulates the oncological behaviour of human cancer cells.…”

Mice Overexpressing Wild Type RRAS2: A Novel Preclinical Model for Testing Anti-Chronic Lymphocytic Leukemia Therapies

“…RAS-related proteins (R-RAS) share several domains and regulatory factors with classical RAS proteins, mediating their activation and inactivation cycles, including guanine exchange factors (GEF) and GTPase activating proteins (GAP) [26]. Mutation of R-RAS2 in analogous residues to G12V and Q61L in classical RAS proteins has induced comparable cell transformation in culture and tumor growth in mice [27,28]. A key distinction is the high intrinsic nucleotide exchange activity of R-RAS2, allowing it to exchange GDP for GTP independently of specific GEF proteins at rates similar to those observed with H-RAS after GEF addition [29].…”