Bcl-2 and CrmA have different effects on transformation, apoptosis and the stability of I kappa B-alpha in chicken spleen cells transformed by temperature-sensitive v-Rel oncoproteins.

The retroviral oncoprotein v-Rel is a member of the Rel/ NF-kappa B family of transcription factors. We have previously characterized two v-Rel mutants (v-G37E and v-R273H) that are temperature-sensitive (ts) for transformation and immortalization of chicken spleen cells in vitro. We have now constructed vectors for the co-expression of wild-type or ts mutant v-Rel proteins and the anti-apoptosis proteins Bcl-2 or CrmA. The formation of v-Rel-transformed colonies is enhanced in the presence of overexpressed Bcl-2. Moreover, co-expression of Bcl-2 suppresses apoptosis that is induced when ts v-Rel-transformed cells are shifted to the non-permissive temperature. However, co-expression of Bcl-2 in these cells does not affect ts functions of v-Rel, such as DNA binding and stabilization of I kappa B-alpha. In contrast, co-expression of CrmA does not suppress apoptosis, but does block an amino-terminal proteolysis of I kappa B-alpha that occurs in ts v-G37E-transformed cells shifted to the nonpermissive temperature, indicating that an ICE-like protease activity is not involved in apoptosis in these cells but is involved in proteolysis of I kappa B-alpha. In addition, CrmA can block cycloheximide-induced amino-terminal processing of I kappa B-alpha in spleen cells transformed by wild-type v-Rel. In summary, these results suggest that v-Rel immortalizes chicken spleen cells through a pathway that involves the Bcl-2 family of proteins, and suggest that one pathway of proteolysis of I kappa B-alpha involves an ICE-like protease.