Steroid hormones are key regulators of a diverse array of physiological processes, including sodiumhomeostasis, reproduction, and the development of secondary sex characteristics. These molecules allowtissues to respond in a coordinated manner to changes in the internal and external environments byfunctioning as ligands for both nuclear and plasma membrane receptors. Because steroid hormones controlthe expression of numerous genes in virtually all cell types, steroidogenic cells utilize multiple mechanisms thatensure tight control of the synthesis of these molecules. A major goal of our research is to understand themechanisms by which the pituitary-derived hormone adrenocorticotropin (ACTH) regulates cortisol productionby the adrenal cortex. Our research has identified an integral role lipid ligands in regulating the transactivationpotential of the nuclear receptor steroidogenic factor-1 (SF-1). Further, we have found that signaling moleculessuch as ACTH direct temporally distinct and reversible post-translational modifications (PTMs) of severalnuclear proteins, including SF-1. These PTMs serve as master regulators of protein function by controlling theability of modified proteins to participate in varied nuclear processes, including transcription and splicing. Wepropose that ACTH controls steroid hormone biosynthesis by modulating the PTM of target proteins, thusfacilitating the assembly of distinct protein-protein, protein-DNA, and protein-RNA complexes. This researchproject will test the central hypothesis that activation of the ACTH signaling cascade promotes the PTMof multiple proteins that regulate the transcription and splicing of CYP17. Further, signal-dependentPTMs of SF-1 and coregulatory proteins such as p54nrb, modulate the differential assembly of proteincomplexes that facilitate the coupling of multiple nuclear processes, including repression, transcriptionalinitiation, ligand synthesis, transcript elongation and termination, and RNA processing.
Specific Aim 1 willdetermine the mechanism by which p54nrb bridges transcription and splicing by employing massspectrometric proteomic approaches to analyze of protein complexes and PTMs of p54nrb. These studies willalso define how ACTH/cAMP-stimulated PTM regulates the ability of the p54nrb to control varied nuclearprocesses.
Specific Aim 2 will define the mechanism by which p21-activated kinases (PAK) controlsteroid hormone production in the human adrenal cortex. Substrate trapping and coupled with massspectrometric, microscopic, and biochemical approaches will be used to identify novel PAK targets andelucidate the functional significance of PAK-catalyzed phosphorylation on protein function and steroidogeniccapacity.
Specific Aim 3 will define the parameters that control ligand-dependent modulation of SF-1function. SF-1 is predominantly localized in the nucleus, thus localized nuclear synthesis of lipid ligands isrequired to promote optimal steroidogenic gene expression. We propose that ACTH/cAMP signaling regulatesSF-1 transactivation potential by triggering PTMs that regulate occupancy of the receptor's ligand bindingpocket. Mass spectrometric analysis of PTMs and ligands will define the relationship between signal-dependent stabilization of the interactions between SF-1 and ligand and SF-1 and coregulatory proteins.
Understanding how genes are regulated in cells that make steroid hormones will provide insight into themechanisms by which pathophysiological concentrations of cortisol and adrenal androgens are produced. Thiswork will provide insight into multiple endocrine disorders; including adrenal hyperplasia; polycystic ovarysyndrome; and Cushing's disease.
|Lu, Jia Yang; Sewer, Marion B (2015) p54nrb/NONO regulates cyclic AMP-dependent glucocorticoid production by modulating phosphodiesterase mRNA splicing and degradation. Mol Cell Biol 35:1223-37|
|Li, Donghui; Dammer, Eric B; Sewer, Marion B (2012) Resveratrol stimulates cortisol biosynthesis by activating SIRT-dependent deacetylation of P450scc. Endocrinology 153:3258-68|
|Li, Donghui; Sewer, Marion B (2010) RhoA and DIAPH1 mediate adrenocorticotropin-stimulated cortisol biosynthesis by regulating mitochondrial trafficking. Endocrinology 151:4313-23|
|Sewer, Marion B; Jagarlapudi, Srinath (2009) Complex assembly on the human CYP17 promoter. Mol Cell Endocrinol 300:109-14|