Protein arginine methyltransferase 1 regulates hepatic glucose production in a FoxO1-dependent manner

Abstract

Postprandial insulin plays a critical role in suppressing hepatic glucose production to maintain euglycemia in mammals. Insulin-dependent activation of protein kinase B (Akt) regulates this process, in part, by inhibiting FoxO1-dependent hepatic gluconeogenesis by direct phosphorylation and subsequent cytoplasmic exclusion. Previously, it was demonstrated that protein arginine methyltransferase 1 (PRMT1)-dependent arginine modification of FoxO1 interferes with Akt-dependent phosphorylation, both in cancer cells and in the Caenorhabditis elegans model, suggesting that this additional modification of FoxO1 might be critical in its transcriptional activity. In this study, we attempted to directly test the effect of arginine methylation of FoxO1 on hepatic glucose metabolism. The ectopic expression of PRMT1 enhanced messenger RNA levels of FoxO1 target genes in gluconeogenesis, resulting in increased glucose production from primary hepatocytes. Phosphorylation of FoxO1 at serine 253 was reduced with PRMT1 expression, without affecting the serine 473 phosphorylation of Akt. Conversely, knockdown of PRMT1 promoted an inhibition of FoxO1 activity and hepatic gluconeogenesis by enhancing the phosphorylation of FoxO1. In addition, genetic haploinsufficiency of Prmt1 reduced hepatic gluconeogenesis and blood-glucose levels in mouse models, underscoring the importance of this factor in hepatic glucose metabolism in vivo. Finally, we were able to observe an amelioration of the hyperglycemic phenotype of db/db mice with PRMT1 knockdown, showing a potential importance of this protein as a therapeutic target for the treatment of diabetes. Conclusion: Our data strongly suggest that the PRMT1-dependent regulation of FoxO1 is critical in hepatic glucose metabolism in vivo. (HEPATOLOGY 2012;56:1546-1556 P ancreatic insulin is a major anabolic hormone to maintain glucose homeostasis. Activation of insulin signaling upon feeding conditions promotes glucose uptake in muscle and fat cells by the protein kinase B (Akt)-dependent translocation of the Glut4 glucose transporter to the plasma membrane. [1][2][3] Furthermore, the Akt pathway is critical in reducing glucose production from the liver not only by the promotion of glycogen synthesis, but also by the inhibition of gluconeogenesis at the transcriptional level. [4][5][6][7] Among the transcription factors that are critical in regulating gluconeogenic genes (e.g., phosphoenol pyruvate carboxykinase [PEPCK], or glucose-6-phosphatase catalytic subunit [G6Pase]), FoxO1 is most tightly linked with the insulin/Akt-dependent regulation of hepatic glucose metabolism. 8,9

O-GlcNAc Modification of the runt-Related Transcription Factor 2 (Runx2) Links Osteogenesis and Nutrient Metabolism in Bone Marrow Mesenchymal Stem Cells

“…We observed methylation at Arg386 that occurs within close proximity to phosphorylation at Ser388 (59). Recent studies demonstrate mutually exclusive functions for protein arginine methyltransferase (PRMT)-mediated methylation of FOXO1 at Arg248 and Arg250, which antagonizes its AKT-mediated phosphorylation at Ser253 and nuclear export (63,64). It is therefore possible that sites of methylation and phosphorylation may interact to influence Runx2 function.…”

“…Arg386 occurs in close proximity to Ser388, which in murine type II Runx2 is targeted by the MAP3K mixed-lineage kinase 3 (MLK3), an upstream regulator of ERK1/2-and p38MAPK-mediated Runx2 activation (59). This raises the possibility of functional regulation of Runx2 phosphorylation by proximal methylation, which has been described on other transcription factors such as FoxO1 (63,64). …”

S-Adenosylmethionine-dependent Protein Methylation Is Required for Expression of Selenoprotein P and Gluconeogenic Enzymes in HepG2 Human Hepatocytes

“…This strengthens the association between ADMA-producing co-activators and gluconeogenic enzyme expression. While this manuscript was in review, another group published results demonstrating the essential role of PRMT1 in regulation of gluconeogenic enzymes and hepatic glucose output (45).…”

“…5B). When lysates from POA-treated cells were probed by Western blot for the presence of ADMA, a decrease in signal was noted for some proteins (25-35 kDa) but not for others (45)(46)(47)(48)(49)(50)(51)(52)(53)(54)(55)(56)(57)(58)(59)(60). The identity of the proteins altered by POA treatment was not further characterized.…”

Prmt7 Deficiency Causes Reduced Skeletal Muscle Oxidative Metabolism and Age-Related Obesity

“…Among these, Prmt1, -4, and -5 are relatively well studied and known to play critical roles in various biological processes. Recent studies have shown that Prmt1 and Prmt5 are involved in regulation of hepatic gluconeogenesis through inhibition of FOXO (33) or through activation of CREB (34). In addition, Prmt1 has been shown to methylate PGC-1a and thereby stimulates the nuclear receptormediated expression of mitochondrial genes in nonmuscle cells (35).…”