Thyroid Hormone and Glucocorticoid-Dependent Regulation of Mig6 gene, an Inhibitor of the Erbb Receptor Family, in Mouse Hippocampal Neurons

Presentation Number: SUN 263
Date of Presentation: April 2nd, 2017

Pia Dano Bagamasbad*, Vincent Isidor Jarel Alihan, Chromewell Agustin Mojica and Jose Ezekiel Clemente Espina
University of the Philippines Diliman, Quezon City, Philippines

Abstract

Thyroid hormones (TH) and glucocorticoids (GC) are known to act synergistically in regulating animal tissue remodeling and development, particularly of the central nervous system. These hormones mediate their actions by binding to their cognate nuclear hormone receptors which function as ligand-activated transcription factors. Although several studies have examined the individual actions of TH and GC on neuronal development, relatively little is known on the mechanisms of how TH and GC interact to synergistically influence neuronal morphology and function. Previous microarray studies identified the Mitogen-inducible gene 6 (Mig6) to be synergistically upregulated by TH and GC in mouse hippocampal neuronal cells. Mig6 is an immediate early response gene whose expression is induced by a wide array of stimulus including growth factors, hormones, and stress. It encodes for an adaptor protein that functions as a feedback inhibitor of ERBB receptor family including Epidermal Growth Factor Receptor (EGFR) and HER2, which are critical players in cell proliferation, migration, and survival. In cortical neurons, overexpression of Mig6 has been shown to suppress growth factor- associated cell migration and neurite growth.  To validate the microarray data and gain insight into the molecular mechanism behind the hormone-dependent regulation of Mig6 in the brain, mouse neuronal hippocampal (HT-22) cells were treated with TH, GC and TH plus GC, followed by total RNA extraction, reverse transcription (RT) and, pre-mRNA and mRNA expression analysis using SYBR Green quantitative PCR (qPCR). Hormone treatments were also done in the presence of a protein synthesis inhibitor cycloheximide (CHX) to determine if Mig6 is a direct target of thyroid hormone receptor (TR) and glucocorticoid receptor (GR) action. Gene expression analysis showed that GC can induce Mig6 pre-mRNA and mRNA expression. In addition, GC-dependent pre-mRNA induction persisted even in the presence of CHX indicating that Mig6 is a direct target of GR, and the effect of GR can be observed at the level of transcription. Results also showed that TH does not induce Mig6 pre-mRNA and mRNA expression and, TH does not enhance the effect of GC on Mig6 gene transcription. However, when measuring Mig6 mRNA levels in the presence of CHX, a synergistic effect of TH and GC was observed suggesting TH may influence Mig6 expression by promoting mRNA stability. In silico analysis using the publicly available ENCODE data identified a 600 bp putative enhancer element containing GC and TH response elements located 20 kb upstream of the Mig6 transcription start site. Collectively, results from this study support the concept of synergistic modulation of Mig6 expression by GC and TH and suggest that Mig6 may be a key mediator of GC and TH effects on neuronal development.

 

Nothing to Disclose: PDB, VIJA, CAM, JECE