Induction of proto-oncogenes during 3-deazaadenosine-stimulated differentiation of 3T3-L1 fibroblasts to adipocytes: mimicry of insulin action.

3-Deazaadenosine (DZA) mimicked the molecular action of insulin in the induction of 3T3-L1 fibroblasts to differentiate into adipocytes. The molecular effects of DZA were compared with insulin, which served as a positive control, on the expression of proto-oncogenes during the initial stage of differentiation of 3T3-L1 fibroblasts. Treatment of confluent 3T3-L1 fibroblasts with DZA or insulin produced a rapid but-transient expression of mRNA for proto-oncogenes c-fos and c-jun within 30-60 min. The mRNA of c-myc increased for 2 h and then decreased 4 h after treatment. Electrophoretic mobility shift assays showed a heightened increase in the appearance of transcription factors AP-1 and AP-2. The increase was detectable as early as 1 h after the treatment with either DZA or insulin and was maintained for 6 h. 3T3-L1 cells stably transfected with the promotor of c-fos linked to a CAT reporter gene showed an increase in CAT activity in response to DZA in a time- and dose-dependent manner. In cells stably transfected with antisense c-fos, neither DZA nor insulin was able to induce a differentiation response. The early transcription of c-fos, c-jun, and c-myc proto-oncogenes and the increased expression of transcription factors AP-1 and AP-2, induced by DZA and insulin, appear to be crucial events in the differentiation of the 3T3-L1 fibroblasts to adipocytes.