title: NDRG2 promotes myoblast proliferation and caspase 3/7 activities during differentiation, and attenuates hydrogen peroxide - But not palmitate-induced toxicity.
abstract: The function of the stress-responsive N-myc downstream-regulated gene 2 (NDRG2) in the control of myoblast growth, and the amino acids contributing to its function, are not well characterized. Here, we investigated the effect of increased NDRG2 levels on the proliferation, differentiation and apoptosis in skeletal muscle cells under basal and stress conditions. NDRG2 overexpression increased C2C12 myoblast proliferation and the expression of positive cell cycle regulators, cdk2, cyclin B and cyclin D, and phosphorylation of Rb, while the serine/threonine-deficient NDRG2, 3A-NDRG2, had less effect. The onset of differentiation was enhanced by NDRG2 as determined through the myogenic regulatory factor expression profiles and myocyte fusion index. However, the overall level of differentiation in myotubes was not different. While NDRG2 up-regulated caspase 3/7 activities during differentiation, no increase in apoptosis was measured by TUNEL assay or through cleavage of caspase 3 and PARP proteins. During H2O2 treatment to induce oxidative stress, NDRG2 helped protect against the loss of proliferation and ER stress as measured by GRP78 expression with 3A-NDRG2 displaying less protection. NDRG2 also attenuated apoptosis by reducing cleavage of PARP and caspase 3 and expression of pro-apoptotic Bax while enhancing the pro-survival Bcl-2 and Bcl-xL levels. In contrast, Mcl-1 was not altered, and NDRG2 did not protect against palmitate-induced lipotoxicity. Our findings show that NDRG2 overexpression increases myoblast proliferation and caspase 3/7 activities without increasing overall differentiation. Furthermore, NDRG2 attenuates H2O2-induced oxidative stress and specific serine and threonine amino acid residues appear to contribute to its function in muscle cells.
authors.affiliation: Centre for Physical Activity and Nutrition Research (C-PAN), School of Exercise and Nutrition Sciences, Faculty of Health, Deakin University, Melbourne, Australia.
authors.forename: Kimberley J
authors.initials: KJ
authors.lastname: Anderson
authors.affiliation: Centre for Physical Activity and Nutrition Research (C-PAN), School of Exercise and Nutrition Sciences, Faculty of Health, Deakin University, Melbourne, Australia.
authors.forename: Aaron P
authors.initials: AP
authors.lastname: Russell
authors.affiliation: Centre for Physical Activity and Nutrition Research (C-PAN), School of Exercise and Nutrition Sciences, Faculty of Health, Deakin University, Melbourne, Australia.
authors.forename: Victoria C
authors.initials: VC
authors.lastname: Foletta
keywords: Acta1, skeletal muscle alpha-actin; Akt, thymoma viral proto-oncogene; Apoptosis; Bax, Bcl-2-associated X protein; Bcl-2, B cell leukemia/lymphoma 2; Bcl-xL, Bcl-2-like 1; Caspase, apoptosis-related cysteine peptidase; Cdk, cyclin-dependent kinase; Ckm, muscle creatine kinase; Differentiation; ER stress; ER, endoplasmic reticulum; GRP78, glucose-regulated protein 78; H2O2, hydrogen peroxide; Lipotoxicity; MRFs, myogenic regulatory factors; Mcl-1, myeloid cell leukemia 1; Myf5, myogenic factor 5; Myh7, myosin, heavy polypeptide 7; MyoD, myogenic differentiation; Myoblast; Myotube; NDRG2; NDRG2, N-myc downstream-regulated gene 2; Oxidative stress; PA, palmitate; PARP, poly (ADP-ribose) polymerase family, member; PKCθ, protein kinase C theta; Proliferation; Rb, retinoblastoma; SGK1, serum- and glucocorticoid-inducible kinase 1; p21, p21 waf1/cip1; p27, p27 kip1