Abstract LB-25: Activation of AMPK by ATM in reponse to AICAR and metformin

Abstract

Abstract AMPK is an AMP-activated protein kinase that plays a key role in regulating cellular energy homeostasis. Metabolic stress, such as heat shock and glucose starvation, causes energy deficiency in the cell and leads to elevated levels of intracellular AMP. This results in the phosphorylation and activation of AMPK. LKB1, a tumor suppressor, has been known as an upstream kinase of AMPK. We found that in response to treatment with 5-aminoimidazole-4-carboxamide-1-b-4-ribofuranoside (AICAR), a LKB1-null cancer cell line, HeLa, still exhibited AMPK phosphorylation. This indicates the existence of an LKB1-independent AMPK protein kinase. ATM is a protein kinase that is deficient in the disease ataxia telangiectasia (A-T). We measured the activation of AMPK by AICAR in the normal mouse embryo fibroblast (MEF) cell line, A29, and the MEF cell line lacking the ATM protein, A38. In A38 cells, the level of AICAR-induced AMPK phosphorylation was dramatically lower than that found in A29 cells. Furthermore, phosphorylation of AMPK in HeLa and A29 cells was inhibited by an ATM specific inhibitor, KU-55933. Our results demonstrate that AICAR treatment could lead to phosphorylation of AMPK in an ATM-dependent and LKB1-independent manner. Similar to the results of AICAR treatment, our work also revealed that the metformin-induced phosphorylation of AMPK in A38 cells is significantly lower than that in A29 cells. We also examined the effect of ATM on AMPK in rat hepatoma cell line H4IIE. Inhibition of ATM by KU-55933 dramatically reduced the phosphorylation of AMPK in response to metformin in this cell line. Thus, ATM may act as a potential AMPK kinase in response to both AICAR and metformin treatment. Metformin is the most commonly prescribed pharmaceutical drug for type 2 diabetes (T2D). In addition, patients with T2D or obesity/insulin resistance who take metformin have reduced rates of cancer occurrence, including breast cancer. However, the mechanism underlying metformin's effect on cancer prevention and/or treatment is unclear (Nature, New & views, Feb. 2011; Science, News Focus, Jan. 2012). While ATM acts as a sensor of DNA damage by controlling cell cycle progression, it also has glucose regulatory function. Our results put ATM as a novel player in the AMPK signaling pathway in response to metformin. These findings provide new insights into the mechanisms by which metformin functions as a preventive and/or therapeutic agent for cancer. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 103rd Annual Meeting of the American Association for Cancer Research; 2012 Mar 31-Apr 4; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2012;72(8 Suppl):Abstract nr LB-25. doi:1538-7445.AM2012-LB-25