Amino Acid Starvation of MCF7 Cells Induces the Expression of PKCn in a 5'UTR-Dependent Manner

Protein Kinase C is a family of phospholipid dependent serine/threonine kinases that are involved in a wide variety of cellularprocesses, including membrane receptor signal transduction, cellproliferation and differentiation. The members of the PKC familydiffer from one another in their primary structure, tissue distribu-tion, subcellular localization and their activation signals. The novelPKCgisoform is implicated in differentiation, proliferation, secre-tion and apoptosis. We have recently reported that PKCgis locali-zed in the golgi, ER and nuclear envelope and translocates to thenuclear envelope upon PMA activation and serum-starvation. Herewe report for the first time that the expression of PKCgis inducedupon amino acids starvation in MCF7 cells. The mRNA increase,measured using quantitative Real Time PCR, could only partiallyexplain our data. Thus, we explored the regulation of PKCgat thetranslational level. Analysis of the human 5’UTR (untranslatedregion) of PKCgrevealed that it is especially long, GC rich andcontains two uORFs (upstream open reading frames). Since5¢UTRs are known translational regulators we have examined whe-ther the 5’UTR of PKCgplays a role in its induction followingamino acids starvation. We cloned the 5¢UTR of PKCgupstreamto a luciferase reporter gene and demonstrated that its induction is5¢UTR dependent. Moreover, site-directed mutagenesis of each ofthe uATGs of the two uORF’s enhanced expression of a luciferasereporter gene, suggesting that the basal expression of PKCgisrepressed due to its uATGs. Our data demonstrate unique transla-tional regulation of the PKCgisoform under stress induced byamino acids starvation.