ABSTRACT
This study examined the effect of GHRP-6,a known GHSs receptor agonist,on the phosphorylation of cAMP-responsive clement-binding protein(CREB)and the underly mechanism.GH3 cells were cultured and subjected to different treatments as follows: GHRP-6,GHRP-6 plus GHRH,phorbol ester(PMA),an activator of PKC,alone or in combination with GHRP-6,G(o)6983,a general inhibitor of PKCs,in the presence or absence of GHRP-6,rottlerin,an inhibitor of PKCs,alone or plus GHRP-6.The cells were transiently transfected with PKCσ-specific siRNA and then treated with GHRP-6.GH level was measured by enzyme-linked immunosorbent assay(ELISA).The expression of phosphor-CREB,PKCσ,PKCθ and phosphor-PKCσ was determined by Western blotting.The results showed that GHRP-6 stimulated GH secretion in both time-and dose-dependent manners and enhanced the effect of GHRH on GH secretion.GHRP-6 was also found to induce CREB phosphorylation.Moreover,GH secretion was enhanced by the PKC activator PMA and reduced by the PKC inhibitors(G(o)6983,rottlerin)and knockdown of PKCσ.PKCσ could be activated by GHRP-6.It is concluded that PKC,especially PKCσ,mediates CREB phosphorylation and GHRP-6-induced GH secretion.