An activated mutant of R-Ras inhibits cell death caused by cytokine deprivation in BaF3 cells in the presence of IGF-I

Abstract

R-Ras belongs to a family of low molecular weight GTPbinding proteins and exhibits 55% amino acid identity to H-Ras. It has been demonstrated that H-Ras inhibits cell death caused by interleukin-3 (IL-3) withdrawal in BaF3 cells (Kinoshita et al. (1995b);Terada et al. (1995)). In the present study, we examined whether R-Ras also rescues BaF3 cells from the factor-deprived cell death. To do this, several BaF3 transfectants were established, in which expression of wild-type as well as mutant R-Ras was regulated by an inducible promoter. Using these transfectants, we found that expression of an activated R-Ras mutant, R-Ras (Q87L), suppressed the death of IL-3-deprived BaF3 cells. On the other hand, expression of the wild-type and the dominant-negative mutant of RRas showed no inhibitory eect on cell death, indicating that R-Ras⋅GTP abrogated cell death caused by deprivation of IL-3. Furthermore, it was found that IGF-I in serum was required for the anti-apoptotic activity of R-Ras. Suppression of cell death by RRas(Q87L) was inhibited by wortmannin, LY294002 (phosphatidylinositol 3-kinase (PI3K) inhibitors), or PD98059 (inhibitor for MEK, a speci®c activator of mitogen-activated protein kinase (MAPK)). In addition, we have shown that, in HEK293 cells, R-Ras and IGF-I could activate MAPK synergistically. Also, PI3K activity was co-immunoprecipitated with an activated mutant of R-Ras. These results suggest that R-Ras in collaboration with IGF-I suppressed apoptotic cell death of BaF3 caused by IL-3 deprivation, presumably by modulating the activitites of MAPK and PI3K.

R‐Ras promotes tumor growth of cervical epithelial cells

“…Several groups have indicated that R-Ras functions through PI 3-K. 25,26,35,39,40 We were unable to detect PI 3-K activity in R-Ras immunoprecipitates, and we did not detect R-Ras in PI 3-K immunoprecipitates (data not shown). Despite these findings, R-Ras87L clearly caused a strong constitutive activation of PI 3-K in C33A cells (Fig.…”

Regulation of Proliferation, Differentiation and Survival by the IL-3/IL-5/GM-CSF Receptor Family

“…An activated form of the R-Ras protein, Q87L, was shown to suppress cell the ␤c chain down to amino acid 544 completely inhibited cellular survival by GM-CSF in BaF3 cells. This deletion death in IL-3-starved BaF3 cells in a manner dependent on the presence of serum IGF-I [143]. Interestingly, this effect includes the region of the ␤c chain involved in activation of the Ras-ERK pathway.…”

Anti-apoptotic function of Rac in hematopoietic cells

“…Also, the factor in FBS responsible for this action remains to be identi®ed. IGF1 is a feasible candidate because it behaves as a co-stimulator of survival and elicits Akt activation in various types of cells including BaF3 (Suzuki et al, 1997).…”

“…For this function, PI3-K and ERK were identi®ed as important players downstream of Ras . R-Ras, a close relative of Ha-, Ki-and N-Ras, was also able to prevent apoptosis of the BaF3 cell line in concert with insulin-like growth factor 1 (IGF1), when expressed in its active form (Suzuki et al, 1997). As the case for Ras, PI3-K and ERK seemed to be involved in R-Ras and IGF1-dependent cell survival (Suzuki et al, 1997).…”