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 P450(scc) (cholesterol side-chain cleavage enzyme), P450(C17) 
(17alpha-hydroxylase/17, 20-lyase), and P450(C21) (steroid 21-hydroxylase) gene 
increased in the transfected cells. The K-ras oncogene significantly increases 
cortisol secretion by normal adrenocortical cells.