The Steroidogenic Acute Regulatory (StAR) protein as target for multiple kinases

PODEROSO, CECILIA; MALOBERTI, PAULA; DUARTE, ALEJANDRA; CASTILLA, ROCÍO; NEUMAN, ISABEL; PAZ, CRISTINA; CORNEJO MACIEL, FABIANA; PODESTÁ, ERNESTO J.

Current Topics in Steroid Reasearch

Reaserch Trends

Lugar: Kerala, India; Año: 2008 vol. 5 p. 35 - 49

0972-4788

The steroidogenic acute regulatory (StAR) protein was first identified as a cAMP dependent phosphoprotein that accumulates in steroidogenic tissues with the same stimulant, dose response, lag-time and translational dependence as the increase in steroid synthesis. The protein is synthesized in the cytosol and finally located in the mitochondria, the site of the rate-limiting step in steroid hormone biosynthesis. StAR was described as two short-lived precursor proteins, pp37 and pp32, of the mitochondrial mature phosphoprotein pp30. The transcription of the StAR gene increases in a PKA-dependent manner. Several sites for phosphorylation by cAMP dependent protein kinase (PKA) have been recognized in the sequence. Although StAR has been described as a phosphoprotein in systems working through cAMP independent mechanisms, the role of phosphorylation in the StAR protein function remains to be fully elucidated. Until now, only the phosphorylation of Ser194/195 in the murine, human and hamster proteins by PKA were identified as important in the regulation of StAR function. Recently, we demonstrated that a mitochondrial kinase complex (PKA, MEK1/2 and ERK1/2) is necessary to phosphorylate StAR and regulate its function. Due to the importance of having a whole view of the subject and the importance of StAR phosphorylation in controlling steroidogenesis, it seems important to compilate the literature and postulate future experiments to elucidate the role of protein phosphorylation of this target in different signaling transducing mechanisms triggered by different steroidogenic hormones. This review will focus in the role of different kinases on StAR phosphorylation and on its steroidogenic function.