Post-transcriptional regulation of the gonadotropin-releasing hormone gene in GT1-7 cells

GT1-7 cells respond to treatment with the phorbol ester, phorbol 12-myristate 13-acetate (PMA), with an inhibition of transcription of the proGnRH gene and decreases in GnRH mRNA levels, However, the timing of this decrease in GnRH mRNA levels suggests that a decrease in GnRH mRNA stability may be involved in addition to an inhibition of transcription of the proGnRH gene, To address this possibility, we treated GT1-7 cells with 100 nM PMA for 4 h and then monitored GnRH mRNA levels over time after blockade of GnRH gene transcription with DRB. PMA treatment caused GnRH mRNA half-life to decrease from 30 to 11 h, Then, to verify this observation, we examined changes in GnRH mRNA poly (A) tail length, which may be a reflection of mRNA turnover, following treatment of GT1-7 cells with PMA or vehicle for 0, 4, 8 or 24 h. The poly (A) tail was removed from half of the GT1 cytoplasmic RNA sample by digestion with RNase H and the difference in GnRH mRNA size with and without RNase H treatment was determined by Northern hybridization. PMA treatment (4 and 8 h) resulted in a significant decrease in the length of the GnRH mRNA poly (A) tail, consistent with a decrease in GnRH mRNA stability. This finding suggests that GnRH mRNA turnover is inducible by substances such as PMA. Our study indicates that a change in mRNA stability is one of a multiplicity of levels at which GnRH gene expression is regulated.