Role of Tumor Suppressor PTEN in Tumor Necrosis Factor α-Induced Inhibition of Insulin Signaling in Murine Skeletal Muscle C₂C₁₂ Cells

Abstract

In an attempt to clarify the role of phosphatase and tensin homologue deleted on chromosome 10 (PTEN) in muscle insulin resistance, we investigated the effect of PTEN on phosphoinositide 3 (PI3)-kinase/Akt related insulin signaling pathway in skeletal muscle-like C2C12 cells damaged by tumor necrosis factor-alpha (TNFalpha). C2C12 cells cultured with TNFalpha (10 ng/ml) for 1 h displayed a marked decrease of insulin-stimulated 2-[14C]-deoxy-D-glucose (2-DG) uptake in parallel with an elevation of PTEN mRNA and protein levels. However, pretreatment of PTEN antisense oligonucleotide (AS) (1 micromol/l for 3 days) for specific inhibition of PTEN expression in C2C12 cells abolished the TNFalpha-induced changes in 2-DG uptake. Similar pretreatment with PTEN AS, but not with sense oligonucleotide (1 micromol/l for 3 days), eliminated the ability of TNFalpha to impair insulin-stimulated signals including p85 regulatory subunit of PI3-kinase expression and the degree of Akt serine phosphorylation as well as protein expression in glucose transporter subtype 4. Data taken from cultured C2C12 cells emphasize the negative regulatory of muscle PI3-kinase/Akt signaling pathways as the major substrate of PTEN but also support the concept that PTEN contributes to the development of insulin resistance in skeletal muscle.

Deletion of Pten in Pancreatic β-Cells Protects Against Deficient β-Cell Mass and Function in Mouse Models of Type 2 Diabetes

“…Given PTEN′s role as a tumor suppressor in various cancer-prone tissues (16–18), we assessed for changes suggestive of cellular transformation and response to DNA-damaging stimuli such as gamma irradiation. Despite the significant increase in islet mass in both HFD-fed RIP cre + Pten fl/fl and RIP cre + Pten fl/fl Lepr db/db islets, intact islet integrity was observed even in the 9-month-old aged mice fed either HFD or on db/db background.…”

“…Given the well known tumorigenic effects of PTEN deletion in some tissues, we assessed for evidence of deregulated growth (16–18). PTEN deficient islets showed intact architecture and demonstrated intact DNA repair response to gamma irradiation as wild-type counterparts.…”

“…Phosphatase with tensin homology (PTEN) is a dual-specific phosphatase and a potent negative regulator of this pathway by its ability to dephosphorylate phosphatidylinosotol-3,4,5-triphosphate (PIP3) to phosphatidylinosotol-4,5-bisphosphate (PIP2), thereby effectively removing the critical secondary messenger of this signaling cascade (15,16). Although PTEN was first discovered as a tumor suppressor, recent studies have highlighted the important physiologic role of PTEN in metabolism (16–18). Tissue-targeted deletion of PTEN in liver, fat, or muscle lead to improved insulin sensitivity in these insulin-responsive tissues and protects mice from HFD-induced diabetes (19–22).…”

Toll-like receptor 4 modulates skeletal muscle substrate metabolism

“…NF-B is one such transcription factor and is known to stimulate the production of the cytokines TNF-␣, IL-6, and MCP1. Previous studies have found that these cytokines illicit a metabolic response in skeletal muscle, but the precise affect remains equivocal due to disparity in models, doses, and time course of treatments (1,5,9,15,21,23,34,41,42). One finding of the current work is that pharmacological blockade of NF-B either partially or completely prevents the changes in substrate metabolism in response to both low (50 pg/ml) and high (500 ng/ml) doses of LPS in C 2 C 12 muscle cells.…”

PPARγ inhibits NF-κB-dependent transcriptional activation in skeletal muscle

“…We used C 2 C 12 cells as an experimental model for skeletal muscle (25), as previous reports had demonstrated that insulin resistance (29) and atrophy (18) are induced by inflammatory stimuli in myotubes of this cell line. Moreover, it has been established that all three different PPAR proteins are present in C 2 C 12 cells (7).…”