Retinoid X receptor suppresses transformation by the v-myb oncogene

The v-myb oncogene of avian myeloblastosis virus causes acute monoblastic l eukemia in rico and transforms myelomonocytic cells in culture. Retinoids a re potent regulators of proliferation and differentiation in various cell t ypes, and they can initiate differentiation in certain types of leukemic ce lls, However, the BM2 v-myb-transformed chicken monoblastic cell Line is re sistant to retinoic acid treatment. We found that overexpression of the ret inoid X receptor confers sensitivity of BM2 cells to retinoic acid, resulti ng in induction of growth arrest and terminal differentiation, In contrast, the frequency of apoptosis was not affected by the retinoid X receptor in this cell type. We also demonstrated that suppression of transformation by v-Myb results from the negative effect of retinoid. X receptor on v-Myb tra nsactivation function, similar to that previously described for the retinoi c acid receptor, The retinoid X receptor-induced inhibition of transactivat ion by v-Myb seems to be enhanced by a cell type-specific factor(s), which is not required by retinoic acid receptor.