Specific cellular microenvironments for spatiotemporal regulation of StAR and steroid synthesis.

For many years, research in the field of steroid synthesis has aimed to understand the regulation of the rate-limiting step of steroid synthesis, i.e. the transport of cholesterol from the outer to the inner mitochondrial membrane, and identify the protein involved in the conversion of cholesterol into pregnenolone. The extraordinary work by B Clark, J Wells, S R King, and D M Stocco eventually identified this protein and named it steroidogenic acute regulatory protein (StAR). The group's finding was also one of the milestones in understanding the mechanism of nonvesicular lipid transport between organelles. A notable feature of StAR is its high degree of phosphorylation. In fact, StAR phosphorylation in the acute phase is required for full steroid biosynthesis. As a contribution to this subject, our work has led to the characterization of StAR as a substrate of kinases and phosphatases and as an integral part of a mitochondrion-associated multiprotein complex, essential for StAR function and cholesterol binding and mitochondrial transport to yield maximum steroid production. Results allow us to postulate the existence of a specific cellular microenvironment where StAR protein synthesis and activation, along with steroid synthesis and secretion, are performed in a compartmentalized manner, at the site of hormone receptor stimulation, and involving the compartmentalized formation of the steroid molecule-synthesizing complex.

New insights into signal transduction pathways in adrenal steroidogenesis: role of mitochondrial fusion, lipid mediators, and MAPK phosphatases.

Hormone-receptor signal transduction has been extensively studied in adrenal gland. Zona glomerulosa and fasciculata cells are responsible for glucocorticoid and mineralocorticoid synthesis by adrenocorticotropin (ACTH) and angiotensin II (Ang II) stimulation, respectively. Since the rate-limiting step in steroidogenesis occurs in the mitochondria, these organelles are key players in the process. The maintenance of functional mitochondria depends on mitochondrial dynamics, which involves at least two opposite events, i.e., mitochondrial fusion and fission. This review presents state-of-the-art data on the role of mitochondrial fusion proteins, such as mitofusin 2 (Mfn2) and optic atrophy 1 (OPA1), in Ang II-stimulated steroidogenesis in adrenocortical cells. Both proteins are upregulated by Ang II, and Mfn2 is strictly necessary for adrenal steroid synthesis. The signaling cascades of steroidogenic hormones involve an increase in several lipidic metabolites such as arachidonic acid (AA). In turn, AA metabolization renders several eicosanoids released to the extracellular medium able to bind membrane receptors. This report discusses OXER1, an oxoeicosanoid receptor which has recently arisen as a novel participant in adrenocortical hormone-stimulated steroidogenesis through its activation by AA-derived 5-oxo-ETE. This work also intends to broaden knowledge of phospho/dephosphorylation relevance in adrenocortical cells, particularly MAP kinase phosphatases (MKPs) role in steroidogenesis. At least three MKPs participate in steroid production and processes such as the cellular cycle, either directly or by means of MAP kinase regulation. To sum up, this review discusses the emerging role of mitochondrial fusion proteins, OXER1 and MKPs in the regulation of steroid synthesis in adrenal cortex cells.

Acyl-CoA synthetase-4 is implicated in drug resistance in breast cancer cell lines involving the regulation of energy-dependent transporter expression.

Acyl-CoA synthetase-4 (ACSL4) is an enzyme implicated in estrogen receptor α (ERα) negative regulation and hormone therapy resistance in breast cancer. In addition, ACSL4 has been associated to certain types of hormone resistance in prostate cancer. Chemotherapeutic treatment of disseminated breast cancer is usually faced with therapy resistance associated to ATP-binding cassette (ABC) transporter expression, which detect and eject anti-cancer drugs from cells. In this context, the aim of the present work was to study the role of ACSL4 in anti-cancer drug resistance and the involvement of ABC transporters in the underlying mechanisms. To this end, we used MCF-7 Tet-Off/ACSL4 and MDA-MB-231 mock cells, which overexpress ACSL4, and control line MCF-7 Tet-Off empty vector, MDA-MB-231 shRNA ACSL4 and MDA-MB-231 wild type cells. Assays were conducted on cell viability (MTT), cell proliferation (BrdU), drug efflux (flow cytometry), ACSL4-responsive drug resistance ABC transporter genes (RNA-Seq), transporter mRNA expression, protein levels and signaling pathway participation (real-time PCR and Western blot). Higher survival rates upon chemotherapeutic treatment were obtained in MCF-7 Tet-Off/ACSL4 and MDA-MB-231 mock cells, an effect counteracted by doxycycline- or shRNA-induced ACSL4 inhibition, respectively. A synergic effect of ACSL4 inhibitor triacsin C and chemotherapeutic drugs was observed on the inhibition of MDA-MB-231 wild type cell proliferation. MCF-7 Tet-Off/ACSL4 cells showed greater doxorubicin, Hoechst 33342 and calcein AM efflux. In contrast, MDA-MB-231 shRNA ACSL4 cells evidenced inhibition of chemotherapeutic drug efflux. ABCG2, ABCC4, and ABCC8 were identified as ACSL4-responsive drug resistance genes whose expression was increased in MCF-7 Tet-Off/ACSL4 cells but inhibited in MDA-MB-231 shRNA ACSL4 cells. Further cell survival assays in the presence of Ko 143 and Ceefourin 1, inhibitors of ABCG2 and ABCC4, respectively, upon chemotherapeutic treatment showed greater participation of ABCG2 in anti-cancer drug resistance in cells overexpressing ACSL4. In addition, ACSL4 inhibition and chemotherapeutic treatment combined with rapamycin-induced mTOR inhibition synergically inhibited proliferation and reduced ABCG2 expression in cells overexpressing ACSL4. In sum, ACSL4 may be regarded as a novel therapeutic target regulating the expression of transporters involved in anticancer drug resistance through the mTOR pathway to restore drug sensitivity in tumors with poor prognosis for disease-free and overall survival.