ERK2-Mediated Phosphorylation of Transcriptional Coactivator Binding Protein PIMT/NCoA6IP at Ser298 Augments Hepatic Gluconeogenesis

Abstract

PRIP-Interacting protein with methyl transferase domain (PIMT) serves as a molecular bridge between CREB-binding protein (CBP)/ E1A binding protein p300 (Ep300) -anchored histone acetyl transferase and the Mediator complex sub-unit1 (Med1) and modulates nuclear receptor transcription. Here, we report that ERK2 phosphorylates PIMT at Ser298 and enhances its ability to activate PEPCK promoter. We observed that PIMT is recruited to PEPCK promoter and adenoviral-mediated over-expression of PIMT in rat primary hepatocytes up-regulated expression of gluconeogenic genes including PEPCK. Reporter experiments with phosphomimetic PIMT mutant (PIMTS298D) suggested that conformational change may play an important role in PIMT-dependent PEPCK promoter activity. Overexpression of PIMT and Med1 together augmented hepatic glucose output in an additive manner. Importantly, expression of gluconeogenic genes and hepatic glucose output were suppressed in isolated liver specific PIMT knockout mouse hepatocytes. Furthermore, consistent with reporter experiments, PIMTS298D but not PIMTS298A augmented hepatic glucose output via up-regulating the expression of gluconeogenic genes. Pharmacological blockade of MAPK/ERK pathway using U0126, abolished PIMT/Med1-dependent gluconeogenic program leading to reduced hepatic glucose output. Further, systemic administration of T4 hormone to rats activated ERK1/2 resulting in enhanced PIMT ser298 phosphorylation. Phosphorylation of PIMT led to its increased binding to the PEPCK promoter, increased PEPCK expression and induction of gluconeogenesis in liver. Thus, ERK2-mediated phosphorylation of PIMT at Ser298 is essential in hepatic gluconeogenesis, demonstrating an important role of PIMT in the pathogenesis of hyperglycemia.

Co-activator binding protein PIMT mediates TNF-α induced insulin resistance in skeletal muscle via the transcriptional down-regulation of MEF2A and GLUT4

“…In our previous study utilizing liver specific PIMT knockout mice, we have demonstrated that PIMT augments hepatic gluconeogenesis, an important aspect of glucose homeostasis 49 . Thus, to further explore the functional role of PIMT in glucose metabolism, we studied the involvement of PIMT in glucose homeostatic mechanisms in skeletal muscle.…”

“…Recently, we have shown that 1) PIMT deficiency in the liver impaired hepatic gluconeogenesis 2) ERK2-mediated phosphorylation of PIMT at Ser 298 is essential for hepatic gluconeogenesis 3) Hyperthyroidism induces PIMT Ser 298 phosphorylation and enhances PEPCK expression resulting hyperglycemia in rats 49 . These findings pointed towards an important role for PIMT/phospho PIMT in glucose homeostasis prompting us to systematically characterize the functional implications of PIMT in skeletal muscle tissue, a key metabolic tissue involved in glucose metabolism.…”

ERK1/2 pathway is involved in renal gluconeogenesis inhibition under conditions of lowered NADPH oxidase activity

“…However, there is some recent evidence that lowered phosphorylation of ERK1/2 might also result in the attenuation of this process in liver [32,33]. Thus, it seems likely that the involvement of the ERK1/2 pathway in the control of gluconeogenesis is a more universal, not only a kidneyspecific, regulatory mechanism.…”

PnTgs1-like expression during reproductive development supports a role for RNA methyltransferases in the aposporous pathway

“…PIMT has been proposed to serve as a molecular bridge between HAT- and non-HAT-containing transcriptional complexes and to control nuclear receptor-mediated transcription. Moreover, ERK2 phosphorylation at Ser 298 of PIMT/TGS1 activates transcriptional activity at some promoters, suggesting a direct role for signal transduction pathways in modulating transcription [ 38 ].…”

“…In S. cerevisiae , these alterations consist of cold-sensitive splicing defects, growth delay at low temperatures, loss of nucleolar structural organization, pre-rRNA processing deficiency, and meiotic failure after aberrant splicing of key regulators [ 29 , 31 , 35 ]. In mammals, PIMT/TGS1 loss of function leads to alteration of cell cycle progression, embryo lethality, and increased hepatic gluconeogenesis [ 38 - 40 ]. In Drosophila , embryo lethality in the early pupal stage has been reported [ 41 ].…”