THE V-REL ONCOPROTEIN BLOCKS APOPTOSIS AND PROTEOLYSIS OF I-KAPPA-B-ALPHA IN TRANSFORMED CHICKEN SPLEEN-CELLS

The v-Rel oncoprotein of the avian Rev-T retrovirus malignantly transf orms chicken spleen cells in vivo and in vitro. We previously describe d two temperature-sensitive (ts) mutants of v-Rel (v-G37E and v-R273H) that show a ts ability to transform chicken spleen cells and to bind to DNA in vitro. We now show that spleen cell lines transformed by ts v-Rel proteins at the permissive temperature undergo apoptosis when ce lls are shifted to the nonpermissive temperature. The levels of most p roteins (including v-Rel, p53, c-Myc, Rb and Bcl-2) do not change in t hese cells even at advanced stages of apoptosis, However, the chicken I kappa B-alpha protein (also called p40), which is in a complex with v-Rel in transformed cells, is degraded when ts v-Rel-transformed cell s are shifted to the nonpermissive temperature. In v-R273H-transformed cells, p40 is degraded without the appearance of proteolytic intermed iates. In contrast, in v-G37E-transformed cells, p40 is cleaved to an intermediate species that is missing approximately 3-4 kDa from its am ino terminus, This truncated form of p40 is found in a detergent-insol uble fraction and can also be detected in wild-type v-Rel-transformed cells that are induced to undergo apoptosis by treatment with cyclohex imide, Both ts v-Rel proteins are ts for interaction with p40 in vitro . The results reported here indicate that v-Rel blocks a normal pathwa y of programmed cell death and that I kappa B-alpha can undergo multip le degradative pathways, which can be induced by alterations in the st ructure of the Rel protein to which it is bound.