CAMP AND PROTEIN-KINASE-C ELEVATE LH-BETA MESSENGER-RNA LEVELS BY ACTIVATING TRANSCRIPTION RATHER THAN STABILIZING MESSENGER-RNA IN RAT PITUITARY-CELLS

The mechanisms by which GnRH modulates synthesis of LH beta subunit an d release of LH from the pituitary gonadotropes are not clearly unders tood. However, GnRH actions in the pituitary gonadotropes have been su ggested to be mediated by the PKC- and/or cAMP-dependent pathways. Thu s, in the present study we have examined 1) whether the activations of either the PKC- and/or cAMP-dependent signaling cascades could elevat e the levels of LH beta mRNA, and if so, 2) whether this increase of L H beta mRNA level is the result of transcriptional activation or the r esult of suppressing the turnover of LH beta mRNA. In the present expe riment, the activators of protein kinase C and the adenylate cyclase, PMA (5 nM) and forskolin (10 mu M) respectively, have elevated the ste ady state levels of LH beta mRNA significantly by 18 h at the specific concentrations shown in the parenthesis. Subsequently, we have determ ined whether the elevation of LH beta mRNA levels by either PMA or for skolin is due to the new synthesis of LH beta mRNA or the suppression of LH beta mRNA turnover. Result showed that the ability of PMA or for skolin to elevate the LH beta mRNA levels was suppressed by the additi on of actinomycin D, an inhibitor of transcription. Result further sho wed that the turnover of LH beta mRNA was not suppressed either by PMA or forskolin. These results indicate that the activation of PKC as we ll as the elevation of cAMP by GnRH leads to the increase in the level s of LH beta mRNA by stimulating the new synthesis of LH beta mRNA ins tead of increasing the stability of pre-existing LH beta mRNA.