Steroidogenic acute regulatory protein mRNA expression in adrenal tumours

Abstract

The rate limiting step in steroidogenesis is cholesterol transport through the outer to the inner mitochondrial membrane and the cytochrome P450 side chain cleavage (P450scc) complex. The protein factor responsible for this transport, and as such necessary for regulating the acute production of steroids, has been identified and named the steroidogenic acute regulatory protein (StAR). We investigated the expression of StAR in functional and non-functional adrenal neoplasms and compared the expression with that of P450scc. Poly A RNA was extracted from normal adrenal glands (NAG, n ¼ 5), aldosterone producing adenomas (APA, n ¼ 4), cortisol producing adenomas (CPA, n ¼ 5), adrenocortical carcinomas (ACC, n ¼ 6) and non-functional adenomas (NFA, n ¼ 3), electrophoresed through a 1% agarose gel, blotted and hybridised with a PCR-generated cDNA labelled with [ 32 P]CTP. The blots were stripped and re-hybridised with a P450scc cDNA and a mouse b-actin probe. Compared with P450scc, StAR mRNA expression showed little variability in the magnitude of expression and did not correlate with the endocrine profiles (NAG: StAR 100 Ϯ 16%, P450scc 100 Ϯ 14%; APA: StAR 80 Ϯ 3%, P450scc 94 Ϯ 13%; CPA: StAR 71 Ϯ 10%, P450scc 109 Ϯ 15%; NFA: StAR 64 Ϯ 9.5%, P450scc 18 Ϯ 5%; means Ϯ S.E.M.). ACC expressed low levels of both genes probably as a result of dedifferentiation (StAR 29 Ϯ 9%, P450scc 46 Ϯ 18%). Incubation of the NCI-h295 tumour cell line with 10 nmol ACTH and 10 mmol forskolin induced an increase in the abundance of StAR and P450scc mRNA, demonstrating gene regulation by the cAMP protein kinase A pathway. Furthermore, we incubated the NCI-h295 tumour cell line with the adrenostatic compounds, aminoglutethimide and metyrapone. We could not detect an effect on the expression of StAR mRNA, whereas the expression of P450scc mRNA was significantly reduced. We conclude that, in contrast to P450scc, StAR seems to be evenly expressed in adrenocortical adenomas. Therefore, the endocrine activity of a given tumour cannot be explained by the abundance of StAR expression. In ACC, both StAR and P450scc expression is low, explaining the relatively inefficient steroid production of these tumours.

Regulation of steroid hormone biosynthesis enzymes and organic anion transporters by forskolin and DHEA-S treatment in adrenocortical cells

“…These results are in a good agreement with previously reported effects of forskolin stimulation in primary adrenal as well as in NCI-H295R cells (3,5,9,15). Stimulation of NCI-H295R cells with forskolin induced a 1.5-fold increase in StAR mRNA (21). Bird et al (4) reported an increase in the expression of CYP21A2, CYP17, CYP11A1, CYP11B1, and CYP11B2 enzymes by forskolin as well as by dibutyrylcAMP.…”

“…The protein responsible for this transport, and as such regulating the acute production of steroids, has been identified and named steroidogenic acute regulatory protein (StAR) (21).…”

Integrating Genetics and Genomics in Primary Aldosteronism

“…43 Despite its critical role, the expression of StAR shows only small variations among the different types of adrenal tumors, including APA, cortisolproducing adenomas, and nonfunctional adenomas, compared with normal adrenal. 37,44 Overexpression of the high-density lipoprotein scavenger receptor B1 suggests that cholesterol supply to the cell is increased through the high-density lipoprotein pathway; increases in adrenodoxin and P450 oxidoreductase indicate that additional electrons are provided via these 2 pathways to both mitochondrial P450 enzymes and enzymes located in the endoplasmic reticulum 38 (Table 1). Assié et al 38 showed that several genes involved in calcium signaling were differently expressed between control adrenal and APA, particularly the calcium effector calmodulin and genes encoding proteins involved in calcium storage, that is, the endoplasmic reticulum calreticulin and the calcium ATPase SERCA3.…”

Heterogeneity of Aldosterone-Producing Adenomas Revealed by a Whole Transcriptome Analysis

“…Whether the excess aldosterone in APA depends on aberrant StAR gene expression and/or upregulated activity by posttransductional mechanisms, as phosphorylation of regulatory residues, is unclear, because data in APA are limited and conflicting. 13,14 Hence, given the complexity of these molecular pathways, we used a whole transcriptome analysis approach to gain insight into the mechanisms causing aldosterone excess in APA.…”