Presentation Type

Poster

Title of Abstract

A Role for AU-Rich Binding Proteins in Thyroid Hormone Mediated Stablization of Hepatic HMG-CoA Reductase mRNA

Abstract

Increased expression of hepatic HMG-CoA reductase (HMGR) in response to thyroid hormone (T3) treatment involves mRNA stabilization in addition to increased transcription. With several other genes, mRNA stabilization is mediated by binding of proteins to AU-rich elements (AREs) in their 3’-untranslated regions. The 3’-untranslated region of HMGR contains several AU-rich sequences including the ARE sequence AUUUUUAUUUAUUCA at +3118 to +3132. The question of whether T3 increases the expression of any of the known AU-rich RNA-binding proteins was investigated. Western blotting analysis showed that hepatic HUR, AUF-1, TIA-1, AUH, KSRP, TIAR and hnRNP I levels were increased by T3 treatment. On the other hand TTP and Nucleolin levels were markedly decreased. In vivo electroporation experiments revealed that siRNAs to TTP completely eliminated HMGR transcription. siRNAs to HUR, TIA-1 and AUF-1 significantly reduced transcription and siRNAs to AUH modestly reduced transcription of HMGR. The ARE sequence, AUUUUUAUUUAUUCA was biotinylated and used in RNA mobility shift analysis (RMSA) studies with liver cytosol or microsomes from hypothyroid (hypophysectomized) or T3-treated rats. Increased binding to the probe was observed with liver microsomal preparations from T3-treated rats.

Categories

Biomedical Sciences

Research Type

Research Assistant

Mentor Information

Dr. Gene Ness

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A Role for AU-Rich Binding Proteins in Thyroid Hormone Mediated Stablization of Hepatic HMG-CoA Reductase mRNA

Increased expression of hepatic HMG-CoA reductase (HMGR) in response to thyroid hormone (T3) treatment involves mRNA stabilization in addition to increased transcription. With several other genes, mRNA stabilization is mediated by binding of proteins to AU-rich elements (AREs) in their 3’-untranslated regions. The 3’-untranslated region of HMGR contains several AU-rich sequences including the ARE sequence AUUUUUAUUUAUUCA at +3118 to +3132. The question of whether T3 increases the expression of any of the known AU-rich RNA-binding proteins was investigated. Western blotting analysis showed that hepatic HUR, AUF-1, TIA-1, AUH, KSRP, TIAR and hnRNP I levels were increased by T3 treatment. On the other hand TTP and Nucleolin levels were markedly decreased. In vivo electroporation experiments revealed that siRNAs to TTP completely eliminated HMGR transcription. siRNAs to HUR, TIA-1 and AUF-1 significantly reduced transcription and siRNAs to AUH modestly reduced transcription of HMGR. The ARE sequence, AUUUUUAUUUAUUCA was biotinylated and used in RNA mobility shift analysis (RMSA) studies with liver cytosol or microsomes from hypothyroid (hypophysectomized) or T3-treated rats. Increased binding to the probe was observed with liver microsomal preparations from T3-treated rats.