Over-expression of NYGGF4 (PID1) inhibits glucose transport in skeletal myotubes by blocking the IRS1/PI3K/AKT insulin pathway.

INTRODUCTION: Defects in insulin-stimulated glucose uptake in muscle are the important early events in the pathogenesis of insulin resistance. NYGGF4 (also named PID1) is a recently discovered gene which is suggested to be associated with obesity-associated insulin resistance. In this study, we aimed to investigate the effects of NYGGF4 on glucose uptake and insulin signaling in rat skeletal muscle cells. METHODS: Rat L6 myoblasts were transfected with either an empty vector or an NYGGF4-expressing vector and induced to differentiate into mature L6 skeletal myotubes. Glucose uptake was determined by measuring uptake of 2-deoxy-d-[(3)H] glucose. Immunoblotting was performed to detect the translocation of insulin-sensitive glucose transporter 4 (GLUT4). Immunoblotting was also used to measure phosphorylation and total protein levels of the insulin signaling proteins including insulin receptor (IR), insulin receptor substrate 1 (IRS1), Akt, extracellular signal-regulated kinase 1 and 2 (ERK1/2), p38, and c-Jun-N-terminal kinase (JNK). RESULTS: NYGGF4 over-expression in L6 skeletal myotubes reduced insulin-stimulated glucose uptake and impaired insulin-stimulated GLUT4 translocation. It also diminished insulin-stimulated tyrosine phosphorylation of IRS1 and serine phosphorylation of Akt without affecting the phosphorylation of IR, ERK1/2, p38, or JNK. CONCLUSIONS: Over-expression of NYGGF4 inhibits glucose transport in skeletal myotubes by blocking the IRS1/PI3K/AKT insulin pathway. These observations highlight the potential role of NYGGF4 in glucose homeostasis and the development of insulin resistance in obesity.