BCL-2 AND CRMA HAVE DIFFERENT EFFECTS ON TRANSFORMATION, APOPTOSIS AND THE STABILITY OF I-KAPPA-B-ALPHA IN CHICKEN SPLEEN-CELLS TRANSFORMEDBY TEMPERATURE-SENSITIVE V-REL ONCOPROTEINS

The retroviral oncoprotein v-Rel is a member of the Rel/ NF-kappa B fa mily of transcription factors, We have previously characterized two v- Rel mutants (v-G37E and v-R273H) that are temperature-sensitive (ts) f or transformation and immortalization of chicken spleen cells in vitro . We have now constructed vectors for the co-expression of wild-type o r ts mutant v-Rel proteins and the anti-apoptosis proteins Bcl-2 or Cr mA. The formation of v-Rel-transformed colonies is enhanced in the pre sence of overexpressed Bcl-2, Moreover, coexpression of Bcl-2 suppress es apoptosis that is induced when ts v-Rel-transformed cells are shift ed to the nonpermissive temperature. However, co-expression of Bcl-2 i n these cells does not affect ts functions of v-Rel, such as DNA bindi ng and stabilization of I kappa B-alpha. In contrast, coexpression of CrmA does not suppress apoptosis, but does block an amino-terminal pro teolysis 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 bloc k cycloheximide-induced amino-terminal processing of I kappa B-alpha i n spleen cells transformed by wild-type v-Rel. In summary, these resul ts suggest that v-Rel immortalizes chicken spleen cells through a path way that involves the Bcl-2 family of proteins, and suggest that one p athway of proteolysis of I kappa B-alpha involves an ICE-like protease .