Metformin Sensitizes Insulin Signaling Through AMPK-Mediated PTEN Down-Regulation in Preadipocyte 3T3-L1 Cells Soo Kyung Lee, 1 Jung Ok Lee, 1 Ji Hae Kim, 1 Su Jin Kim, 1 Ga Young You, 1 Ji Wook Moon, 1 Jin Hee Jung, 1 Sun Hwa Park, 1 Kyung-Ok Uhm, 2 Ji Man Park, 3 Pann-Ghill Suh, 3 and Hyeon Soo Kim 1 * 1 Department of Anatomy, Korea University College of Medicine, Seoul, Korea 2 Department of Alzheimer’s Disease Research, National Institute for Geriatrics and Gerontology, Morioka, Obu, Aichi 474-8522, Japan 3 School of Nano-Bioscience & Chemical Engineering, Ulsan National Institute of Science and Technology, Ulsan 689-798, Republic of Korea ABSTRACT Insulin resistance is the primary cause responsible for type 2 diabetes. Phosphatase and tensin homolog (PTEN) plays a negative role in insulin signaling and its inhibition improves insulin sensitivity. Metformin is a widely used insulin-sensitizing drug; however, the mechanism by which metformin acts is poorly understood. To gain insight into the role of PTEN, we examined the effect of metformin on PTEN expression. Metformin suppressed the expression of PTEN in an AMP-activated protein kinase (AMPK)-dependent manner in preadipocyte 3T3-L1 cells. Knock-down of PTEN potentiated the increase in insulin-mediated phosphorylation of Akt/ERK. Metformin also increased the phosphoryla- tion of c-Jun N-terminal kinase (JNK)-c-Jun and mammalian target of rapamycin (mTOR)-p70S6 kinase pathways. Both pharmacologic inhibition and knock-down of AMPK blocked metformin-induced phosphorylation of JNK and mTOR. Knock-down of AMPK recovered the metformin-induced PTEN down-regulation, suggesting the involvement of AMPK in PTEN regulation. PTEN promoter activity was suppressed by metformin and inhibition of mTOR and JNK by pharmacologic inhibitors blocked metformin-induced PTEN promoter activity suppression. These findings provide evidence for a novel role of AMPK on PTEN expression and thus suggest a possible mechanism by which metformin may contribute to its beneficial effects on insulin signaling. J. Cell. Biochem. 112: 1259–1267, 2011. ß 2010 Wiley-Liss, Inc. KEY WORDS: ADIPOCYTE; AMPK; INSULIN; METFORMIN; PTEN M etformin is an oral anti-diabetic drug of the biguanide class. Metformin originates from the French lilac (Galega officinalis), a plant known to reduce the symptoms of diabetic mellitus [Despres, 2003; Bailey and Day, 2004; Bailey, 2008; Kooy et al., 2009]. Among the known actions of metformin are an increase in insulin sensitivity in muscles and liver [Borst and Snellen, 2001; Teranishi et al., 2007], a decrease in hepatic glucose production [He et al., 2009], an increase in peripheral glucose utilization [Yoshida et al., 2009], positive effects on insulin receptor expression and tyrosine kinase activity [Wiernsperger, 1999; Pryor et al., 2000; Wang et al., 2007], and lipolysis and oxidative stress in adipose tissue [Abbasi et al., 1998; Anedda et al., 2008]. The precise molecular mechanisms which determine the effect of metformin are unknown. AMP-activated protein kinase (AMPK) is a phylogenetically conserved intracellular energy sensor that plays a central role in the regulation of glucose and lipid metabolism. AMPK, a heterotrimeric complex comprised of a catalytic subunit and two regulatory Journal of Cellular Biochemistry ARTICLE Journal of Cellular Biochemistry 112:1259–1267 (2011) 1259 Abbreviations used: ACCacetyl-CoA carboxylaseAICAR5-aminoimidazole-4-carboxy-amide-1-D-ribofuranosi- deAMPKAMP-activated protein kinasePTENphosphatase and tensin homologmTORmammalian target of rapamy- cinJNKc-Jun N-terminal kinase Grant sponsor: Korea Healthcare Technology R & D Project, Ministry of Health & Welfare, Republic of Korea R1009171. *Correspondence to: Hyeon Soo Kim, MD, PhD, 126-1, Anam-dong 5-ga, Seongbuk-gu, Seoul 136-701, Korea. E-mail: anatomykim@korea.ac.kr Received 20 April 2010; Accepted 8 December 2010  DOI 10.1002/jcb.23000  ß 2010 Wiley-Liss, Inc. Published online 29 December 2010 in Wiley Online Library (wileyonlinelibrary.com).