Changes in promoter utilization in human and mouse c-myc genes upon transformation induction in temperature-sensitive cell lines

Publisher Website
Google Scholar
Abstract
We have previously reported accelerated transcription and rapid accumulation of c‐myc mRNAs upon induction of transformation in a temperature‐sensitive mouse cell line (Gallant et al., 1989, Oncogene Res., 4:39–46). Here we have used both mouse and human cell lines transformed with a temperature‐sensitive mutant of the Simian virus 40 (SV40) virus to investigate whether a shift in promoter utilization within the c‐myc gene locus is part of a general mechanism that deregulates c‐myc expression during transformation induction. We devised a simple and sensitive method using reverse transcription followed by radioactive polymerase chain reaction (RT‐PCR) to measure the relative change in c‐myc mRNAs arising from each of the four known promoters. We show that a three to fivefold increase in c‐myc transcripts from the P1 and P3 promoters occurs in both human and mouse cell lines within 30 min of the shift to the permissive temperature. The major P2‐initiated transcripts are not significantly effected. However, exon 3‐containing RNAs increase more gradually up to 24 h postinduction and P1 and P3 transcripts, while remaining elevated, still contribute relatively little to the total c‐myc RNA population. These and other results, demonstrating a transient activation of P1 and P3 promoters, suggest an indirect role of the minor transcripts in the deregulated expression of the c‐myc gene in transformed cells.