OR09-05 Expression of SLC35F1 in the Plasma Membrane of Cells of Aldosterone Producing Cell Clusters (APCCs) and Its Possible Role in Aldosterone Synthesis

Abstract

Background Genetic mutations and histological appearances suggest that APCCs are precursors to some aldosterone producing adenomas (APA). They are hypothesised to contribute to post-operative non-cure and recurrence of primary aldosteronism (PA) but are currently undetectable pre-operatively. SLC35F1 is a possible nucleotide sugar transporter. On microarray it is highly expressed in APCCs, but not in the rest of the adrenal cortex (1). Our aim was to investigate the role of SLC35F1 in APCCs, determine its subcellular localisation and establish whether expression is consistent with pathological APCC subtypes (as suggested by recent evidence from in situ metabolomic studies (2)). Methods Comparative bioinformatic analysis of the SLC35F1 amino acid sequence was carried out. Ex vivo 4uM adrenal sections, from 6 PA patients in the MATCH study, were stained on serial sections with anti-CYP11B2 (Gomez-Sanchez) or anti-SLC35F1 (Novus NBP1-86755). In vitro, H295R cells were transfected with SLC35F1 cDNA. Subcellular localisation of SLC35F1-GFP was studied by comparison to organelle markers (golgin 97, RAB11, wheat germ agglutinin, calnexin and Tom20) using confocal microscopy. Overexpression and siRNA knock-down in H295R cells was correlated to aldosterone production. Results SLC35F1 is a decamembrane-spanning transporter molecule predicted to have a negatively charged pocket in the substrate binding site, implying a transport substrate with a positive charge. Strong staining of CYP11B2 in clusters of cells in adrenal cortex, consistent with APCCs, were present in all six adrenal glands (25 APCCs). Serial sections showed specific SLC35F1 staining of APCCs, in cytoplasm and plasma membrane. SLC35F1 staining was absent from normal cortex. 12 APCCs (48%) were SLC35F1-negative. Visualisation of transiently expressed SLC35F1 demonstrated localisation to the endoplasmic reticulum in H295R cells (Pearson’s coefficient r=0.758) with no plasma membrane localisation (r=-0.07). Preliminary transfection data suggest direct involvement in aldosterone production. Conclusions Expression of SLC35F1 in the plasma membrane and cytosol of APCC cells supports a role in pathological aldosterone production by APCCs. The inferred transport substrate of SLC35F1 is the NAD(P)(H) precursor, nicotinamide riboside, a positively-charged nucleotide sugar. If confirmed, the essential requirement for NAD(P)H in steroidogenesis, and heterogeneity of SLC35F1-staining in APCCs, is consistent with a metabolically active, possibly pathological, subtype of APCCs. Detection of SLC35F1 in vivo may therefore facilitate sub-classification of PA patients.1). Nishimoto et. al. PNAS. 2015 Aug 18;112(33):E4591-9. 2). Murakami et. al. 2019 Hypertension. In press.