ONCOGENIC TRANSFORMATION-INDUCED BY THE QIN PROTEIN IS CORRELATED WITH TRANSCRIPTIONAL REPRESSION

The retroviral oncogene gin codes for a protein that belongs to the fa mily of the winged helix transcription factors, The viral Qin protein, v-Qin, differs from its cellular counterpart, c-qin, by functioning a s a stronger transcriptional repressor and a more efficient inducer of tumors, This observation suggests that repression may be important in tumorigenesis, To test this possibility, chimeric proteins were const ructed in which the Qin DNA-binding domain was fused to either a stron g repressor domain (derived from the Drosophila Engrailed protein) or a strong activator domain (from the herpes simplex virus VP16 protein) , The chimeric transcriptional repressor, Qin-Engrailed, transformed c hicken embryo fibroblasts in culture and induced sarcomas in young chi ckens, The chimeric activator, Qin-VP16, failed to transform cells in vitro or in vivo and caused cellular resistance to oncogenic transform ation by Qin, These data support the conclusion that the Qin protein i nduces oncogenic transformation by repressing the transcription of gen es which function as negative growth regulators or tumor suppressors.