ENDOCRINOLOGY AND REPRODUCTION RESEARCH BRANCH

Kevin Catt, MD, PhD, Chief

The Endocrinology and Reproduction Research Branch (ERRB) investigates the molecular and cellular mechanisms of reproductive hormone action, the structure-function properties and signaling pathways of peptide hormone receptors, and the roles of phosphorylation and sulfonation in metabolic regulation and signal transduction.

Tamas Balla leads the Unit on Molecular Signal Transduction, whose studies on phospholipid signaling revealed that PH domains, which bind to phosphoinositides, regulate signaling proteins and recognize inositol lipids in the context of other protein components, accounting for the domains' highly specific inhibition of PI(3,4,5)P3-mediated cellular responses. Localization of PH domains that recognize PI(4)P, the lipid product of PI 4-kinases, is determined by both PI(4)P and Golgi proteins. Investigations of these PH domains revealed that type-III PI 4-kinases are largely responsible for PI(4)P synthesis in the plasma membrane.

Kevin Catt's group, the Section on Hormonal Regulation, investigates the structure-function properties and signaling pathways of peptide hormone receptors and the roles of autocrine regulation and G protein switching in episodic GnRH secretion. Angiotensin AT1 receptors and GnRH receptors were found to activate EGF receptor-mediated MAP kinase signaling in hepatic and neuronal cells via liberation of HB-EGF. In addition to such GPCR-induced transactivation of a receptor tyrosine kinase, the group identified a reciprocal mechanism in which EGF receptor activation stimulates AT1 receptor phosphorylation.

Studies conducted by the Molecular Endocrinology Section, which is led by Maria Dufau, on orphan receptor-mediated silencing of LH receptor gene transcription have demonstrated that COUP-TFI/EAR3 bound to DNA perturbs communication between the Sp1/Sp3 complex and TFIIB, reducing recruitment of RNA Pol II. This mechanism operates in repressive/ inductive receptor states during the ovarian cycle. A novel gonadotropin-regulated RNA helicase (GRTH/Ddx25) was found in Leydig and germ cells. Testosterone increases GRTH expression at the transcriptional level and promotes utilization of one of three ATG codons in both cell types.

The Section on Metabolic Regulation, led by Kuo-Ping Huang, discovered that neurogranin, a neuronal calmodulin (CaM)-binding protein, enhances hippocampus-dependent learning and memory by promoting calcium-mediated signaling. Neurogranin modulates synaptic responses by sequestering CaM and regulating free Ca2+ and Ca2+/CaM. NMDA receptor- mediated calcium influx triggers the stimulation of PKC, Ca2+/CaM kinases, adenylyl cyclases, and NO synthase. The phosphorylation and oxidation of neurogranin participate in the regulation of Ca2+- and Ca2+/CaM-dependent neuronal signaling in the hippocampus to promote the enhanced synaptic plasticity that underlies learning and memory.

 
Stanko Stojilkovic's group, the Section on Cellular Signaling, studies nucleotide-gated receptor channels and cyclic nucleotide-controlled channels expressed in anterior pituitary cells and their roles in calcium signaling and hormone secretion. The group identified residues critical for nucleotide binding to recombinant nucleotide receptors as well as the impact of receptor-ATP affinity on C-terminal domain-controlled receptor desensitization. The group also characterized dependence of guanylyl cyclase activity on intracellular calcium, nitric oxide, and phosphorylation by protein kinase C and of cyclic nucleotide-gated channel activity on basal and receptor-stimulated adenylyl/guanylyl cyclases.

Charles Strott's group, the Section on Steroid Regulation, studies the SULT2 subfamily of cytosolic sulfotransferases that sulfoconjugate DHEA (SULT2A1), pregnenolone (SALT2B1a), and cholesterol (SALT2B1b). SULT2B1b is exclusively expressed in keratinocytes, where it is confined to epidermal granular cells, and in platelets. SULT2B1a is selectively expressed in the central nervous system, where pregnenolone sulfate is important in learning and memory. Comparison of the 3-D structures of SULT2B1 isoforms and SULT2A1 has yielded new insights into the molecular basis of substrate selectivity.