Activated H-ras Rescues E1A-Induced Apoptosis and Cooperates with E1A To Overcome p53-Dependent Growth Arrest

Abstract

The adenovirus E1A oncogene products stimulate DNA synthesis and cell proliferation but fail to transform primary baby rat kidney (BRK) cells because of the induction of p53-mediated programmed cell death (apoptosis). Overexpression of dominant mutant p53 (to abrogate wild-type p53 function) or introduction of apoptosis inhibitors, such as adenovirus E1B 19K or Bcl-2 oncoproteins, prevents E1A-induced apoptosis and permits transformation of BRK cells. The ability of activated Harvey-ras (H-ras) to cooperate with E1A to transform BRK cells suggests that H-ras is capable of overcoming the E1A-induced, p53-dependent apoptosis. We demonstrate here that activated H-ras was capable of suppressing apoptosis induced by E1A and wild-type p53. However, unlike Bcl-2 and the E1B 19K proteins, which completely block apoptosis but not p53-dependent growth arrest, H-ras expression permitted DNA synthesis and cell proliferation in the presence of high levels of wild-type p53. The mechanism by which H-ras regulates apoptosis and cell cycle progression is thereby strikingly different from that of the E1B 19K and Bcl-2 proteins. BRK cells transformed with H-ras and the temperature sensitive murine mutant p53(val 135), which lack E1A, underwent growth arrest at the permissive temperature for wild-type p53. p53-dependent growth arrest, however, could be relieved by E1A expression. Thus, H-ras alone was insufficient and cooperation of H-ras and E1A was required to override growth suppression by p53. Our data further suggest that two complementary growth signals from E1A plus H-ras can rescue cell death and thus permit transformation.

Constitutive Raf-1 kinase activity in breast cancer cells induces both estrogen-independent growth and apoptosis

“…It is well established that several oncogenes, including Ras, Raf, Src and Abl, can cooperate to protect against or rescue cells from apoptosis (Lin et al, 1995;White et al, 1994;Cortez et al, 1995;. In the 32D.3 hemopoietic cell line, Raf has been shown to physically interact with the apoptosis inhibitor Bcl-2 and in this manner cooperates with Bcl-2 to inhibit apoptosis (Wang et al, 1994).…”

Deregulation of p53/p21Cip1/Waf1 pathway contributes to polyploidy and apoptosis of E1A+cHa-ras transformed cells after γ-irradiation

“…E1A+E1B19kD transformants expressing the wild type p53 reveal a p53-dependent block at G1/S boundary of the cell cycle (Sabbatini et al, 1995). In contrast, E1A+cHa-ras-transformed cells are unable to be arrested at G1/S by over-expression of wild type p53 (Lin et al, 1995).…”

“…High e ciency of foci formation in the presence of Ad5-E1A can be achieved when E1A cooperates with genes that suppress the programmed cell death allowing the E1A expression at high levels (Lin et al, 1995;Sabbatini et al, 1995). Among these genes, the viral genes E1B19kD and E1B55kD, cellular gene bcl2 and oncogenic cHa-ras that are complementing with E1A to fully transform cells of di erent origin.…”

Novel small GTPase M-Ras participates in reorganization of actin cytoskeleton

“…Primary functions of Ras family members are to control cell growth, di erentiation, transformation and apoptosis (Bollag and McCormick, 1991;Lowy and Willumsen, 1993;Lin et al, 1995;Wang et al, 1995;Trent et al, 1996), whereas those of Rho family members are to regulate organization of the actin cytoskeleton (Hall, 1994;Takai et al, 1995;Narumiya, 1996). Typically, microinjection of RhoA, Rac1 and Cdc42 into cultured ®broblasts induces the actin stress ®bers, membrane ru es (lamellipodia), and microspikes (®lopodia), respectively, as well as the focal complexes associated with these structures Nishiyama et al, 1994;Kozma et al, 1995;Nobes and Hall, 1995).…”