Lipin1 Regulates Steroidogenic Factor-1 Function and Steroidogenic Gene Expression in Human Adrenocortical Cells

Program: Abstracts - Orals, Featured Poster Presentations, and Posters
Session: SAT 358-380-Steroid Hormone Biosynthesis & Metabolism
Saturday, June 15, 2013: 1:45 PM-3:45 PM
Expo Halls ABC (Moscone Center)

Poster Board SAT-360
Andres Betancourt-Torres*1 and Marion B Sewer2
1Univ. of Cal. San Diego, La Jolla, CA, 2Univ. of Cal., San Diego, La Jolla, CA
Lipins (LPINs) are a family of proteins that have PA phosphatase enzymatic activity, thereby converting PA to DAG.  These lipid phosphatases also act as coregulators of gene transcription and have been shown to interact with varied nuclear receptors, including the peroxisome proliferator-activated receptor and hepatic nuclear receptor-4.  We have previously shown that PA is a ligand for the nuclear receptor steroidogenic factor-1 (SF-1) and that steroidogenic gene expression and cortisol biosynthesis in the adrenal cortex is dependent on nuclear PA production.  Nuclear PA concentrations are rapidly increased in response to cAMP in the H295R human adrenocortical cell line.  Given the key role that PA production plays in controlling the transactivation potential of SF-1 transactivation and the established role of LPIN1 as a coregulator of nuclear receptors, we sought to define the function of LPIN1 in regulating the capacity of adrenocortical cells to produce cortisol.  Transient transfection assays using the CYP17A1 promoter fused to the luciferase gene revealed that LPIN1 attenuated the ability of SF-1 to stimulate CYP17A1 reporter gene activity.  To further assess the functional significance of LPIN1 in the adrenal cortex, we generated a stable cell line where the expression of LPIN1 was silenced and assessed the effect of LPIN1 suppression on steroidogenic gene expression.  We hypothesized that silencing LPIN1 would increase the nuclear concentrations of PA and result in an increase in the basal and cAMP-stimulated expression of all genes required for cortisol biosynthesis.  Unexpectedly we found that LPIN1 knockdown cells exhibited a significant decrease in the basal expression of CYP17A1 mRNA and protein and completely abrogated cAMP-dependent CYP17A1 mRNA and protein expression.  In contrast, silencing LPIN1 resulted in an increase in the cAMP-stimulated expression of CYP11B1, while the constitutive and cAMP-stimulated mRNA and protein expression of steroidogenic acute regulatory protein (StAR) was reduced in the LPIN1 knockdown cell line.  Collectively, these studies identify LPIN1 as a novel regulator of SF-1 function and steroidogenic capacity in the human adrenal cortex.

Nothing to Disclose: AB, MBS

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Sources of Research Support: NIH Grant DK084178 awarded to MBS