G. Xu et al., PROTEIN-KINASE-C INHIBITS TRANSCRIPTION FROM THE RNA-POLYMERASE-III PROMOTER OF THE HUMAN C-MYC GENE, Cancer letters, 123(2), 1998, pp. 199-205
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.