title: Mitochondrial fusion and ERK activity regulate steroidogenic acute regulatory protein localization in mitochondria.
abstract: The rate-limiting step in the biosynthesis of steroid hormones, known as the transfer of cholesterol from the outer to the inner mitochondrial membrane, is facilitated by StAR, the Steroidogenic Acute Regulatory protein. We have described that mitochondrial ERK1/2 phosphorylates StAR and that mitochondrial fusion, through the up-regulation of a fusion protein Mitofusin 2, is essential during steroidogenesis. Here, we demonstrate that mitochondrial StAR together with mitochondrial active ERK and PKA are necessary for maximal steroid production. Phosphorylation of StAR by ERK is required for the maintenance of this protein in mitochondria, observed by means of over-expression of a StAR variant lacking the ERK phosphorylation residue. Mitochondrial fusion regulates StAR levels in mitochondria after hormone stimulation. In this study, Mitofusin 2 knockdown and mitochondrial fusion inhibition in MA-10 Leydig cells diminished StAR mRNA levels and concomitantly mitochondrial StAR protein. Together our results unveil the requirement of mitochondrial fusion in the regulation of the localization and mRNA abundance of StAR. We here establish the relevance of mitochondrial phosphorylation events in the correct localization of this key protein to exert its action in specialized cells. These discoveries highlight the importance of mitochondrial fusion and ERK phosphorylation in cholesterol transport by means of directing StAR to the outer mitochondrial membrane to achieve a large number of steroid molecules per unit of StAR.
authors.affiliation: Institute of Biomedical Investigations (INBIOMED, UBA-CONICET), Department of Biochemistry, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.
authors.forename: Alejandra
authors.initials: A
authors.lastname: Duarte
authors.affiliation: Institute of Biomedical Investigations (INBIOMED, UBA-CONICET), Department of Biochemistry, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.
authors.forename: Ana Fernanda
authors.initials: AF
authors.lastname: Castillo
authors.affiliation: Institute of Biomedical Investigations (INBIOMED, UBA-CONICET), Department of Biochemistry, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.
authors.forename: Ernesto J
authors.initials: EJ
authors.lastname: Podestá
authors.affiliation: Institute of Biomedical Investigations (INBIOMED, UBA-CONICET), Department of Biochemistry, School of Medicine, University of Buenos Aires, Buenos Aires, Argentina.
authors.forename: Cecilia
authors.initials: C
authors.lastname: Poderoso
mesh_terms: D000818:Animals; D002460:Cell Line; D000242:Cyclic AMP / Q000378:metabolism; D017868:Cyclic AMP-Dependent Protein Kinases / Q000378:metabolism; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D020558:GTP Phosphohydrolases / Q000378:metabolism; D005786:Gene Expression Regulation; D008297:Male; D051379:Mice; D008928:Mitochondria / Q000201:enzymology / Q000378:metabolism*; D063154:Mitochondrial Dynamics / Q000235:genetics; D008954:Models, Biological; D010750:Phosphoproteins / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D021381:Protein Transport; D012333:RNA, Messenger / Q000235:genetics / Q000378:metabolism; D013256:Steroids / Q000096:biosynthesis; D014158:Transcription, Genetic; D000098682:Steroidogenic Acute Regulatory Protein
chemical_list: D010750:Phosphoproteins; D012333:RNA, Messenger; D013256:Steroids; D000098682:Steroidogenic Acute Regulatory Protein; D010768:Phosphoserine; D000242:Cyclic AMP; D017868:Cyclic AMP-Dependent Protein Kinases; D048049:Extracellular Signal-Regulated MAP Kinases; D020558:GTP Phosphohydrolases; C488751:Mfn2 protein, mouse