Regulated expression and mechanism of action of the steroidogenic acute regulatory protein.

Format:

Book

Thesis/Dissertation

Author/Creator:

Kallen, Caleb Benjamin.

Contributor:

Strauss, Jerome F., III, advisor.

University of Pennsylvania.

Language:

English

Subjects (All):

Cytology.

Molecular biology.

0307.

0379.

Penn dissertations--Cell and molecular biology.

Cell and molecular biology--Penn dissertations.

Local Subjects:

Penn dissertations--Cell and molecular biology.

Cell and molecular biology--Penn dissertations.

0307.

0379.

Physical Description:

100 pages

Contained In:

Dissertation Abstracts International 62-02B.

System Details:

Mode of access: World Wide Web.

text file

Summary:

Stimulation of steroid-producing cells of the gonads and adrenals with trophic hormone (LH and ACTH, respectively) produces a marked increase in steroid hormone synthesis within minutes. The rate-limiting step in this acute steroidogenic response is the transport of cholesterol from the outer to the inner mitochondrial membrane, where the first committed step in steroid synthesis is performed by the side-chain cleavage enzyme system (P450scc), resulting in the production of pregnenolone. This process of cholesterol translocation is blocked by inhibitors of protein synthesis (i.e., cycloheximide) indicating that the effect of trophic hormones, acting through the intermediacy of cAMP, most likely involves the de novo synthesis of a protein that is rapidly inactivated. The recently identified Steroidogenic A&barbelow;cute R&barbelow;egulatory protein (StAR) appears to be the most likely candidate for the "labile" protein: (1) StAR is synthesized in response to cAMP and it disappears rapidly in the presence of inhibitors of protein synthesis; (2) StAR has an N-terminal targeting sequence that directs the protein to the mitochondria; (3) StAR protein is expressed almost exclusively in steroid-producing cells, its presence is correlated with steroid hormone production, and lack of functional StAR causes the autosomal recessive disease congenital lipoid adrenal hyperplasia (lipoid CAH), characterized by markedly impaired gonadal and adrenal steroid hormone synthesis. We show that StAR import by mitochondria is not essential to its steroidogenesis enhancing activity, and, more likely, represents a means of rapidly inactivating StAR. Truncation mutations and site-directed mutations in StAR demonstrated that the C-terminus of the protein contains the functionally important domains. Further, we demonstrate potent steroidogenic activity of recombinant StAR protein on mitochondria isolated from bovine corpus luteum using protein that lacks the mitochondrial targeting sequence. These observations confirm that StAR import is not essential for its steroidogenic activity and suggest that StAR acts directly on the outer mitochondrial membrane and in the absence of intermediary cytosolic factors. Finally, we show that StAR functions as a cholesterol transfer protein that does not require a protein "receptor" or co-factor, suggesting that StAR acts directly on lipids of the outer mitochondrial membrane to promote cholesterol translocation.

Notes:

Thesis (Ph.D. in Cell and Molecular Biology) -- University of Pennsylvania, 2001.

Source: Dissertation Abstracts International, Volume: 62-02, Section: B, page: 0698.

Supervisor: Jerome F. Strauss, III.

Local Notes:

School code: 0175.

ISBN:

9780493129686

Access Restriction:

Restricted for use by site license.