Comparative RT-PCR analysis of SOCS-1, cyclin D1, RB1, and HPRT expression. RT-PCR using specific primer pairs to detect the expression of the indicated genes was performed on RNA extracts derived from MedB-1 cells cultured in complete medium or cultured for 5 days in medium supplemented with 20 μM Tyrphostin AG490 or 10 μM 5-aza-deoxycytosine (5-aza-dC) and on RNA from MedB-1 cells transiently transfected with a SOCS-1 expression plasmid. AG490 slightly decreases cyclin D1 expression, and 5-aza-dC induces RB1 expression. Wild-type SOCS-1 induces RB1 expression and abolishes cyclin D1 transcription.