PROTEIN-KINASE-C INHIBITS TRANSCRIPTION FROM THE RNA-POLYMERASE-III PROMOTER OF THE HUMAN C-MYC GENE

The c-myc promoter has a unique characteristic showing both RNA polyme rase II (pol II) and RNA polymerase III (pol III) activities. Previous studies demonstrated that activating PKC results in upregulation of c -myc expression from its pol II promoter. However, how PKC activation affects expression from the pol III promoter of the c-myc gene is not well understood. This study examines the effect of PKC on the pol III transcription from the c-myc gene by using an in vitro system. We repo rt the inhibition of the c-myc pol III transcript by activating PKC. F urther, either a phosphocellulose fraction of HeLa whole cell extract (WCE) enriched for transcription factor TF IIIB, or recombinant TATA-b ox binding protein could restore the inhibited c-myc pol III transcrip tion under conditions that activate PKC. A role has been proposed for the c-myc pol III transcript in the regulation of c-myc gene expressio n. Therefore, this report discusses the significance of the downregula tion of c-myc expression from its pol III promoter and the possible in terplay between the pol II and pol III promoters of this gene. (C) 199 8 Elsevier Science Ireland Ltd.