A MITOCHONDRIAL KINASE CASCADE INDUCES ERK PHOSPHORYLATION OF A KEY CHOLESTEROL TRANSPORT PROTEIN

PODEROSO C . CONVERSO DP. DUARTE A, NEUMAN I , MALOBERTI P. CARRERAS M C, PODEROSO JJ, PODESTA EJ

Villa Carlos Paz, Cordoba

Congreso; XLIV Reunion Anual de la Sociedad Argentina de Investigación en Bioquímica y Biología Molecular (SAIB); 2008

ERKI/2 is known to be involved in hormone-stimulated steroid synthesis, but its exact roles and the underlying mechanisms remain elusive. ERKl/2 activation by cAMP results in a maximal steroidogenic rate. We have showed that temporal mitochondrial ERKl/2 activation is obligatory for PKA-mediated steroidogenesis through MEKl/2 phosphorylation in the murine Leydig MA-10 ceIl line. This cascade of events is strictly dependent on stimuli, hCG/cAMP/PKA leads to the phosphorylation of a constitutive mitochondrial MEKl/2 and ERKl/2 pool. ERK1 specificaIly co-precipitates with a 30kDa mitochondrial form of StAR which presents a basic-hydrophobic motif shared in several ERK substrates and mitochondrial 30kDa StAR interacts with VDAC (voltage-dependent anionic channel). ERKl/2 phosphorylates StAR at Ser232 only in the presence of cholesterol. Mutagenesis of Ser232 to Ala (S232A) inhibited in vitro StAR phosphorylation by active ERKl/2. Transient transfection of MA-10 ceIls with S232A reduced the yield of steroids. We show that StAR is a novel substrate ofmitochondrial ERK that is part of a multimeric kinase complex that regulates cholesterol transporto StAR phosphorylated at Ser232 may acquire additional negative charges and associate with VDAC promoting the retention of the mature form of 30kDa StAR in the outer mitochondrial membrane and to the formation of the multiprotein complex.