C-MYC DEREGULATION DURING TRANSFORMATION INDUCTION - INVOLVEMENT OF 7SK RNA

The process of oncogenic transformation has been widely studied but is still poorly understood. We have focused on the mechanism of deregula tion of the c-myc gene during transformation of a temperature-sensitiv e SV40-transformed mouse cell line. Run-on transcription assays showed that the two c-myc minor promoters, P1 and P3, are transiently activa ted following induction of transformation and that peak activation of both promoters is preceded by a large increase in transcription of a s mall RNA (7SK). To test the possibility that this RNA might participat e in promoter activation, we transfected cells with sense and antisens e oligodeoxynucleotides corresponding to different regions of the 7SK RNA predicted to be accessible within the RNP particle. Out of 14 olig os tested, inhibition of activation of P1 and/or P3 was observed with four antisense oligonucleotides corresponding to looped regions in the putative 7SK secondary structure. To identify c-myc promoter sequence s which might serve as targets for 7SK activity, we carried out mobili ty-shift assays with either whole or 7SK-depleted cell extracts. The C T element of the c-myc promoter formed a 7SK-dependent complex which c ould be competed only with the same antisense 7SK oligo that suppresse d P1 and P3 activation in vivo. Taken together these results suggest t hat 7SK RNP participates in transformation-dependent c-myc deregulatio n. (C) 1997 Wiley-Liss, Inc.