Significantly Increased Cortisol Secretion in Normal Adrenocortical Cells Transfected withK-rasMutants Derived from Human Functional Adrenocortical Tumors

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Abstract
Our previous study showed that the mutation hotspots of the K-ras proto-oncogene in human functional adrenocortical tumors are in codons 15, 16, 18, and 31, thus differing from the sites in other tumors. In addition, analyzing the K-Ras protein by a recombinant DNA technique showed that the activity of endogenic GTPase and the GTPase-activating protein (GAP)-binding ability were significantly decreased in patients with these tumors. The aim of this study was to understand whether those K-ras mutants, which were found only in human adrenocortical tumors, play an important role in these tumors. Thus, the mutant K-ras cDNA was constructed with mammalian expression vectors and transfected into normal adrenocortical cells. The amount of cortisol secreted by the transfected cells was 20 to 30 times that of normal cells. Furthermore, Northern blot analysis revealed that the expression of the three steroidogenesis-related genes P450scc (cholesterol side-chain cleavage enzyme), P450C17 (17α-hydroxylase/17, 20-lyase), and P450C21 (steroid 21-hydroxylase) gene increased in the transfected cells. The K-ras oncogene significantly increases cortisol secretion by normal adrenocortical cells.

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