Author : Phani Kumar Talasila
Publisher :
ISBN 13 :
Total Pages : 80 pages
Book Rating : 4.:/5 (835 download)
Book Synopsis Novel Thyroid Hormone Target Genes in the Liver, and Their Roles in Thyroid Hormone Signaling and Physiology by : Phani Kumar Talasila
Download or read book Novel Thyroid Hormone Target Genes in the Liver, and Their Roles in Thyroid Hormone Signaling and Physiology written by Phani Kumar Talasila and published by . This book was released on 2012 with total page 80 pages. Available in PDF, EPUB and Kindle. Book excerpt: Thyroid hormone plays a critical role in growth, development and energy metabolism. The identification of novel target genes of thyroid hormone would greatly inform our complete understanding of T3 physiology. I have studied two genes, SGK1 (serum and glucocorticoid inducible kinase1), and ANGPTL4 (Angiopoietin like protein-4) as the potential target genes of thyroid hormone in the liver. SGK1, a component of the PI-3 kinase pathway, is ubiquitously expressed and plays a role in numerous physiological functions. Previous studies in our lab showed T3-mediated induction of SGK1, and also a PI-3kinase dependent phosphorylation of SGK1 by T3. As T3 induces and activates SGK1, I speculated that SGK1 might be contributing to T3- mediated transcription of its target genes. Dual luciferase assays following SGK1 activity inhibition by GSK650394 and T3 treatment, showed a dose-dependent decrease in the activity of the DR4 and CPT1alpha promoters. Also, real time PCRs performed following SGK1 activity inhibition and T3 treatment, showed a decreased induction of endogenous T3-target genes like G6P, PEPCK, and CPT1alpha suggesting that SGK1 is a modulator of transcriptional activity of T3. ANGPTL4 is expressed mainly in metabolic tissues like liver and adipose tissue. ANGPTL4 inhibits LPL activity, and the role of thyroid hormone in regulation of LPL has led me to hypothesize that T3 regulates ANGPTL4. My studies showed that T3 induces ANGTPL4 mRNA and protein. I have also looked at the role of PGC1alpha, a transcriptional co-activator, in the T3 regulation of ANGPTL4. PGC1alpha overexpression not only enhanced T3 induction of ANGPTL4, but also induced ANGPTL4 expression even in the absence of T3. However, T3 did not induce PGC1alpha which is contrary to the observations in rat livers. LPL assays using fluorescence based substrate DGGR were performed to look for the functional significance of T3 induction of ANGPTL4. The concentrated conditioned media samples from HepG2 cells treated with vehicle/T3 after ANGPTL4 siRNA knockdown were used for the LPL assays. However, there was no difference in LPL activities among the treatment samples at 8 hours or 24 hours. Thus, I have identified SGK1, a novel T3 target gene as a transcriptional modulator of T3 signaling, and ANGPTL4 as a novel T3 target gene in the liver, and signified the role of PGC1alpha in the T3 regulation of ANGPTL4.