Protein kinase C activation selectively increases mRNA levels for one of the regulatory subunits (RIα) of cAMP-dependent protein kinases in HT-29 cells

Abstract

We have examined the effect of the protein kinase C activator, TPA, on mRNA levels for subunits of cAMP-dependent protein kinases in the human colonic cancer cell line HT-29, subline m2. Messenger RNA for the regulatory subunit, RIα, of cAMP-dependent protein kinases was shown to be present and regulated by TPA. Other mRNAs for subunits of cAMP-dependent protein kinases (RIβ,RIIα,RIIβ,Cα,Cβ) were also present in these cells, but revealed no or only minor changes upon TPA stimulation. When HT-29 cells were cultured in the presence of 10 nM TPA for various time periods, a biphasic response was observed in RIα mRNA levels with a maximal increase (approximately 4 fold) after 24 hours. TPA stimulated RIα mRNA increased in a concentration-dependent manner and maximal response (4–8 fold) was seen at 3–10 nM. The TPA-induced increase in RIα mRNA was not obtained when cells were incubated with TPA together with the protein kinase C inhibitors, staurosporine or H7. The cAMP-analog 8-CPTcAMP alone induced RIα mRNA levels 50% more than TPA. Combined treatment with TPA (10 nM) and 8-CPTcAMP (0.1 mM) gave an increase in RIα mRNA similar to TPA. These results demonstrate an interaction between the protein kinase C pathway and mRNA levels for the RIα subunit of cAMP-dependent protein kinases in HT-29 cells.