The role of protein kinase C in the regulation of serotonin-2A receptor expression

We have investigated in C6 glioma cells the involvement of protein kinase C (PKC) in the regulation of serotonin-(2A) receptor (5-HT2A receptor) expre ssion by agonist treatment. Comparison of the time-courses of agonist-induc ed downregulation of receptor number and mRNA indicate that a decrease in t he number of 5-HT2A receptor binding sites in response to serotonin (5-HT) treatment is preceded by a decrease in 5-HT2A receptor mRNA. This decrease in 5-HT2A receptor mRNA as a result of agonist exposure was not due to a ch ange in the stability or half-life of the transcript. Pretreatment of cells with the PKC inhibitor bisindolylmaleimide blocked the decrease in 5-HT2A receptor mRNA levels, and attenuated the down-regulation of 5-HT2A receptor binding sites induced by treatment with 5-HT. Experiments performed with t he PKC inhibitors calphostin C and Go 6976 confirmed that PKC was involved in the regulation of 5-HT2A receptor mRNA by agonist and implicate the conv entional subgroup of PKC isoforms. Western blot analysis, using isoform-spe cific anti-PKC antibodies showed that under our culture conditions C6 gliom a cells express the conventional isoforms PKC alpha PKC gamma, as well as t he novel isoforms PKC delta, PKC E, and the atypical isoforms PKC h and PKC L. Upon treatment with 5-HT for 10 min levels of the conventional isoforms PKC alpha and PKC gamma increased in the nuclear fraction. Taken together, our results implicate PKC alpha and/or PKC gamma in the regulation of 5-HT 2A mRNA receptor and binding sites in response to agonist treatment.