Identification in chicken macrophages of a set of proteins related to, but distinct from, the chicken cellular c‐ets‐encoded protein p54c‐ets.

Using an antiserum to a bacterially expressed polypeptide corresponding to 56 amino acids of v‐ets, we previously identified in chicken tissues a protein of 54 kd (p54c‐ets) which shares extensive sequence homology to the v‐ets‐encoded domain of the E26‐transforming protein p135gag‐myb‐ets and is thus apparently encoded by the c‐ets proto‐oncogene. We report here that the anti‐ets serum specifically identifies in chicken cells a second set of proteins of 60 kd (p60), 62 kd (p62) and 64 kd (p64) which appear to be highly related to each other but display only a limited domain of homology with p54c‐ets and p135gag‐myb‐ets and are thus probably encoded by a gene(s) partially related to, but different from c‐ets. In contrast to p54c‐ets which is expressed at high levels in chicken lymphoid tissues, prominent syntheses of p62 and p64 were found in both normal and transformed chicken macrophages but not in avian cells corresponding to immature stages of the myeloid differentiation pathway. These observations together with the fact that differentiation of avian myeloblastosis virus‐transformed myeloblasts into macrophage‐like cells after treatment with 12‐O‐tetradecanoylphorbol‐13‐acetate is accompanied by the synthesis of p62 and p64 suggest a role for these proteins in chicken macrophage differentiation or function. Induction of differentiation of human leukemia cell lines HL60 and U937 into macrophages is also accompanied by the increased synthesis of c‐ets‐encoded 68 kd, 62 kd and 58 kd proteins.