SIGNIFICANCE OF STEROIDOGENIC ENZYMES IN THE PATHOGENESIS OF HYPERFUNCTIONING AND NON-HYPERFUNCTIONING ADRENAL-TUMOR

To elucidate the mechanisms of abnormal steroid production in hyperfunctioning and non-hyperfunctioning adrenal tumors, we examined both the activities and amounts of steroidogenic cytochromes P450 in the tumor and non-tumor portions of these adrenals at the posttranslational (protein) level. Adrenals from 5 patients with primary aldosteronism, 5 with Cushing's syndrome, I with deoxycorticosterone (DOC)-producing adenoma, 10 with non-hyperfunctioning adrenal adenoma, and 5 subjects with normal control adrenals (obtained from patients with renal cell carcinoma) were used in our studies. Activities of P450scc, P45011 beta and P450aldo, and P450C21 and P-45017 alpha were assayed in a reconstituted enzyme system using 20 alpha-hydroxycholesterol, DOC, and progesterone, respectively, and the substrate and the extracted products were analyzed by HPLC. Enzyme amounts were determined by immunoblot analysis with anti-bovine P450scc, P45011 beta, and P450C21 IgG, and anti-porcine P45017 alpha IgG. Human P450aldo was only detected in the tumor portion of primary aldosteronism adrenals, with both activities and amounts of other P-450s similar to those in the non-tumor portion of primary aldosteronism and normal controls. In Cushing's syndrome, both activities and amounts of P45017 alpha and P450C21 were significantly increased in the tumor compared with those in the non-tumor portion of Cushing's syndrome and normal controls. In DOC-producing adenoma, both activities and amounts of P45017 alpha and P45011 beta in the tumor portion of the adenoma decreased compared with normal control, while those of other P450s were similar to normal controls. On the other hand, steroidogenic enzymes including P450scc, P45011 beta, P450aldo, P45017 alpha, and P450C21 in the non-hyperfunctioning adenomas were not different from those of normal controls. These results demonstrate that overexpression of P450aldo in primary aldosteronism, overexpression of P45017 alpha and P450C21 in Cushing's syndrome, and underexpression of P45017 alpha and P45011 beta in DOC-producing adenoma may play some role in the pathogenesis of these three kinds of hyperfunctioning adrenal tumors. Conversely, incidentally discovered non-hyperfunctioning adrenal adenomas possess a normal synthetic system for adrenocortical steroids, and mechanisms other than abnormal expression of steroidogenic enzymes presumably underlie tumorigenesis.