RESUMO
BACKGROUND: Gs alpha gene mutation, that constitutively increases intracellular cAMP, is found in some acromegalic patients. It was demonstrated that increased intracellular cAMP levels suppress the expression of rat TRH receptor (TRH-R) mRNA. We previously demonstrated that transient expression of a mutant Gs alpha gene suppress the rat TRH-R gene expression in the cultured rat growth hormone-secreting tumor cell line (GH3), whereas TRH-R gene expression in adenomas with Gs alpha gene mutation (gsp oncogene) did not differ from that in tumors without the mutation. The discrepancy suggests the possibilities that the effect of permanent expression of mutant Gs alpha gene on TRH-R gene expression is different from that of transient expression of the mutant gene and hypothalamic hormones including TRH regulate the gene expression. METHODS: We investigated whether permanent expression of the mutant-type Gs alpha does not suppress the TRH receptor gene expression in GH3 cells, and whether TRH suppresses the gene expression by using reverse transcription-polymerase chain reaction (RT-PCR) and in vitro transcription. RESULTS: Permanent expression of a mutant-type Gs alpha increased basal cAMP levels up to 1.7-fold relative to the controls, whereas the wild-type cell line did not show increased cAMP levels. Permanent expression of a mutant-type Gs alpha increased TRH receptor mRNA level up to 2.8 fold compared with the controls. Treatment of the permanently transfected GH3 cells with TRH suppressed TRH-R gene expression more prominently compared to the wild type GH3 cells. CONCLUSION: These results suggest that permanent expression of mutant Gs alpha enhances the expression of TRH-R in GH-secreting pituitary tumors with gsp oncogene, but the gene expression may also be regulated by other factors including TRH.