Lin, H.a d , Li, N.b , He, H.a d , Ying, Y.a d , Sunkara, S.a c , Luo, L.b , Lv, N.b , Huang, D.b , Luo, Z.a d AMPK inhibits the stimulatory effects of TGF-β on Smad2/3 activity, cell migration, and epithelial-to-mesenchymal transition

摘要

AMP-activated protein kinase (AMPK), an important downstream effector of the tumor suppressor liver kinase 1 (LKB1) and pharmacologic target ofmetformin, is well known to exert a preventive and inhibitory effect on tumorigenesis; however, its role in cancer progression and metastasis has not been well characterized. The present study investigates the potential roles of AMPK in inhibiting cancer-cell migration and epithelialto-mesenchymal transition (EMT) by regulating the canonical transforming growth factor ?(TGF-? signaling pathway, an important promoting factor for cancer progression. Our results showed that activation of AMPK bymetformin inhibited TGF-?induced Smad2/3 phosphorylation in cancer cells in a dosedependent manner. The effect of metformin is dependent on the presence of LKB1. A similar effect was obtained by expressing a constitutive active mutant of AMPK? subunit, whereas the expression of a dominant negative mutant of AMPK? or ablation of AMPK?subunits greatly enhanced TGF-?stimulation of Smad2/3 phosphorylation. As a consequence, expression of genes downstream of Smad2/3, including plasminogen activator inhibitor-1, fibronectin, and connective tissue growth factor, was suppressed by metformin in a LKB1-dependent fashion. In addition, metformin blocked TGF-?induced inteleukin-6 expression through both LKB1-dependent and -independent mechanisms. Our results also indicate that activation of LKB1/AMPK inhibits TGF-?stimulated cancer cell migration. Finally, TGF-?induction of EMT was inhibited by phenformin and enhanced by knockdown of LKB1 expression with shRNA. Together, our data suggest that AMPK could be a drug target for controlling cancer progression and metastasis.