Multiple ras functions can contribute to mammalian cell transformation

Abstract

We have developed a generalized approach, using two hybrid interactions, to isolate Ha-Ras effector loop mutations that separate the ability of Ha-Ras to interact with different downstream effectors. These mutations attenuate or eliminate Ha-ras(G12V) transformation of mammalian cells, but retain complementary activity, as demonstrated by synergistic induction of foci of growth-transformed cells, and by the ability to activate different downstream components. The transformation defect of Ha-ras(G12V, E37G) is rescued by a mutant, raf1, that restores interaction. These results indicate that multiple cellular components, including Raf1, are activated by Ha-Ras and contribute to Ha-Ras-induced mammalian cell transformation.

Ras signaling through PI3K confers hormone-independent proliferation that is compatible with differentiation

“…Ras activates multiple downstream pathways (White et al, 1995) including Raf-1 and the MAPK cascade (Marias and Marshall, 1996), RalGDS and Ral proteins (Feig et al, 1996), and PI3K (Downward, 1997) and Rac1 (Qiu et al, 1995;Khosravi-Far et al, 1995). Alterations in the balance of the activity of these pathways may contribute to the di erential cellular responses elicited by Ras.…”

Ras, but not Src, transformation of RIE-1 epithelial cells is dependent on activation of the mitogen-activated protein kinase cascade

“…First, the recent identi®cation of mutant Ras proteins which failed to bind Raf-1 [designated Ras(12V/37G) and Ras(12V/40C)], yet retained signaling activities that cause tumorigenic transformation of NIH3T3 cells, suggests that Raf-1-independent pathways are also important for promoting full Ras transformation (White et al, 1995;Khosravi-Far et al, 1996). Second, there is evidence that Ras transformation requires the function of speci®c Rho family proteins (RhoA, RhoB, Rac1 and CDC42) for full Ras transforming activity (Qiu et al, 1995a(Qiu et al, ,b, 1997Prendergast et al, 1995;Khosravi-Far et al, 1995).…”

Changes in p53 expression can modify cell shape of ras-transformed fibroblasts and epitheliocytes

“…Several signalling pathways contribute to ras-induced cell transformation (White et al, 1995;Qiu et al, 1995). Along with possible but poorly characterised intercytoplasmic ras-rho/rac-cytoskeleton signalling (for review see Machesky and Hall, 1996;Zigmond, 1996) at least three other pathways transduce signals to the nucleus: ras-raf-MAPK-AP1 (White et al, 1995), ras-rac SAPK-AP1 (Coso et al, 1995;Minden et al, 1995), and ras-rho/rac-SRF (Hill et al, 1995).…”

“…Several signalling pathways contribute to ras-induced cell transformation (White et al, 1995;Qiu et al, 1995). Along with possible but poorly characterised intercytoplasmic ras-rho/rac-cytoskeleton signalling (for review see Machesky and Hall, 1996;Zigmond, 1996) at least three other pathways transduce signals to the nucleus: ras-raf-MAPK-AP1 (White et al, 1995), ras-rac SAPK-AP1 (Coso et al, 1995;Minden et al, 1995), and ras-rho/rac-SRF (Hill et al, 1995). Since (i) mos activates MAPK (Posada et al, 1993;Mansour et al, 1994;Fukasawa et al, 1995), (ii) dominant-negative Mek1 (MAPKK) mutant abrogates v-mos-induced transformation (Okazaki and Sagata, 1995), and (iii) v-mos-transformed cells show no morphological reversion after introduction of p53-His273 (Table 1) it seems reasonable to propose that p53 may interfere with the changes caused by ras-rho/ rac rather than by ras-raf-MAPK signalling.…”