The role of the StAR protein in steroidogenesis: challenges for the future.

The steroidogenic acute regulatory or StAR protein has been shown to be instrumental in the acute regulation of steroid hormone biosynthesis through its action in mediating cholesterol transfer to the inner mitochondrial membrane and the cholesterol side chain cleavage enzyme system. Since the time of its cloning in 1994, a number of studies have been performed which underscore the important role that this protein plays in steroidogenesis. While it is now quite apparent that StAR fulfills the criteria for the acute regulator as proposed by early studies, several crucial areas remain poorly understood. This list is topped by the so far intractable nature of the mechanism of action of StAR in transferring cholesterol to the P450scc enzyme. A second area which should prove to be of great interest is that of further understanding the regulation of the StAR gene which, like many genes, is quite complex. Lastly, with the recent demonstration of StAR being present in the brain, determining if StAR has a role in the synthesis of neurosteroids should prove to be of great importance.