Overexpression of glutathione-S-transferase A1 in benign adrenocortical adenomas from patients with Cushing's syndrome

Benign adrenocortical adenoma is a major primary cause of Cushing's syndrom e. Although numerous studies have been performed, the molecular mechanism o f adrenocortical adenoma is yet to be elucidated. In this study we endeavor ed to identify genes differentially regulated in adrenocortical adenoma by suppression PCR-based complementary DNA (cDNA) subtractive hybridization. T he cDNA population in atrophied nontumorous adrenal gland adjacent to the a denoma was subtracted from that in the adenoma. Then adenoma-specific cDNAs were amplified by PCR. We cloned several cDNAs that are selectively up-reg ulated in the adenoma, one of which was identified to encode glutathione-S- transferase A1 (GSTA1). Northern blot analysis revealed that GSTA1 messenge r ribonucleic acid was abundantly expressed in the adenoma compared with th at in the adjacent atrophied nontumorous gland. Western blot analysis and i mmunohistochemistry showed high expression of GSTA1 also at the protein lev el. In concordance with this finding, GST activity was significantly higher in the adenoma than in the adjacent atrophied nontumorous gland. To clarif y the role of GSTA1 in adrenocortical cells, GST activity in the H295R huma n adrenocortical cell line was inhibited by ethacrynic acid. Inhibition of GSTs interfered with proliferation of the cells. We, therefore, hypothesize that overexpression of GSTA1 in adrenocortical adenomas might be involved in the growth of tumor cells. We also speculate that this overexpression mi ght be an adaptive response to excess cortisol production.