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Activated H-ras rescues E1A-induced apoptosis and cooperates with E1A to overcome p53-dependent growth arrest
H J Lin1, V Eviner, G C Prendergast
1Center for Advanced Biotechnology and Medicine, Rutgers University, Piscataway, New Jersey 08854, USA.
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.
Insights
Activated Harvey-ras (H-ras) suppresses programmed cell death (apoptosis) induced by adenovirus E1A and wild-type p53, enabling cell proliferation. Cooperation between H-ras and E1A is required to overcome p53-mediated growth suppression for cell transformation.
Area of Science:
- Oncogenes and Tumor Suppressors
- Cell Cycle Regulation
- Apoptosis Pathways
Background:
- Adenovirus E1A oncogene stimulates cell proliferation but induces p53-mediated apoptosis, preventing transformation of primary baby rat kidney (BRK) cells.
- Inhibitors of apoptosis, such as adenovirus E1B 19K or Bcl-2, and dominant-negative p53 mutants, can overcome E1A-induced apoptosis and permit cell transformation.
- Activated Harvey-ras (H-ras) cooperates with E1A to transform BRK cells, suggesting a role in overcoming E1A-induced apoptosis.
Purpose of the Study:
- To investigate the mechanism by which activated H-ras overcomes E1A-induced apoptosis and p53-mediated growth arrest.
- To compare the mechanisms of H-ras, E1B 19K, and Bcl-2 in regulating apoptosis and cell cycle progression.
- To determine the requirement for H-ras and E1A cooperation in overriding p53-dependent growth suppression.
Main Methods:
- Utilized baby rat kidney (BRK) cells for transformation assays.
- Introduced oncogenes such as adenovirus E1A, activated H-ras, and apoptosis inhibitors (E1B 19K, Bcl-2).
- Employed temperature-sensitive murine mutant p53 (val 135) to study p53-dependent growth arrest and rescue.
Main Results:
- Activated H-ras suppressed apoptosis induced by E1A and wild-type p53, allowing DNA synthesis and cell proliferation.
- Unlike E1B 19K and Bcl-2, H-ras permitted proliferation despite high levels of wild-type p53, indicating a distinct mechanism.
- H-ras alone was insufficient to override p53-mediated growth suppression; cooperation with E1A was necessary.
- E1A expression relieved p53-dependent growth arrest in cells transformed with H-ras and mutant p53.
Conclusions:
- H-ras employs a mechanism distinct from E1B 19K and Bcl-2 to regulate apoptosis and cell cycle progression.
- Cooperation between H-ras and E1A provides complementary growth signals that rescue cells from death and enable transformation.
- Two distinct oncogenic signals, H-ras and E1A, are required to overcome p53-mediated growth suppression and achieve cell transformation.