Steroidogenic acute regulatory protein (StAR) retains activity in the absence of its mitochondrial import sequence: Implications for the mechanism of StAR action

Futoshi Arakane, Teruo Sugawara, Hideaki Nishino, Zhiming Liu, John A. Holt, Debkumar Pain, Douglas M. Stocco, Walter L. Miller, Jerome F. Strauss

Research output: Contribution to journalArticlepeer-review

257 Scopus citations

Abstract

Steroidogenic acute regulatory protein (StAR) plays a critical role in steroid hormone biosynthesis, presumably by facilitating the delivery of cholesterol to P450scc in the inner mitochondrial membranes. StAR is synthesized as a 37-kDa preprotein that is processed to a 30-kDa mature form by cleavage of an N-terminal mitochondrial import sequence. To identify structural features required for StAR biological activity, we mutated the human StAR cDNA, including the deletion of N- and C-terminal sequences, and examined the ability of the mutants to promote steroidogenesis and enter the mitochondria of transfected COS-1 cells. Deletion of up to 62 residues from the N terminus (N-62) did not significantly affect steroidogenesis-enhancing activity. The N-terminal deletion mutants were associated with mitochondria- enriched fractions, but import and processing were progressively impaired with increasing length of the deletion. Immunogold electron microscopy and in vitro import assays showed that the active N-62 mutant was not imported into the mitochondria. Removal of the 28 C-terminal amino acids (C-28) inactivated StAR. Deletion of the C-terminal 10 amino acids (C-10) reduced steroidogenic activity by 53%, while truncation of the last 4 amino acids had no effect. The C-28 mutant StAR was not efficiently imported into mitochondria or processed, whereas some of the C-10 mutant was processed, indicating that import had occurred. We conclude that in the COS-1 cell system used, StAR does not need to enter into mitochondria to stimulate steroidogenesis and that residues in the C terminus are essential for steroidogenesis-enhancing activity. These findings imply that StAR acts via C-terminal domains on the outside of the mitochondria.

Original languageEnglish (US)
Pages (from-to)13731-13736
Number of pages6
JournalProceedings of the National Academy of Sciences of the United States of America
Volume93
Issue number24
DOIs
StatePublished - Nov 26 1996
Externally publishedYes

All Science Journal Classification (ASJC) codes

  • General

Fingerprint

Dive into the research topics of 'Steroidogenic acute regulatory protein (StAR) retains activity in the absence of its mitochondrial import sequence: Implications for the mechanism of StAR action'. Together they form a unique fingerprint.

Cite this