TY - JOUR

T1 - Role of adenosine 5'-monophosphate-activated protein kinase subunits in skeletal muscle mammalian target of rapamycin signaling

AU - Deshmukh, Atul S.

AU - Treebak, Jonas Thue

AU - Long, Yun Chau

AU - Viollet, Benoit

AU - Wojtaszewski, Jørgen F. P.

AU - Zierath, Juleen R.

N1 - CURIS 2008 5200 045

PY - 2008

Y1 - 2008

N2 - AMP-activated protein kinase (AMPK) is an important energy-sensing protein in skeletal muscle. Mammalian target of rapamycin (mTOR) mediates translation initiation and protein synthesis through ribosomal S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). AMPK activation reduces muscle protein synthesis by down-regulating mTOR signaling, whereas insulin mediates mTOR signaling via Akt activation. We hypothesized that AMPK-mediated inhibitory effects on mTOR signaling depend on catalytic alpha2 and regulatory gamma3 subunits. Extensor digitorum longus muscle from AMPK alpha2 knockout (KO), AMPK gamma3 KO, and respective wild-type (WT) littermates (C57BL/6) were incubated in the presence of 5-aminoimidazole-4-carboxamide-1-beta-d-ribonucleoside (AICAR), insulin, or AICAR plus insulin. Phosphorylation of AMPK, Akt, and mTOR-associated signaling proteins were assessed. Insulin increased Akt Ser473 phosphorylation (P < 0.01), irrespective of genotype or presence of AICAR. AICAR increased phosphorylation of AMPK Thr172 (P < 0.01) in WT but not KO mice. Insulin stimulation increased phosphorylation of S6K1 (Thr389), ribosomal protein S6 (Ser235/236), and 4E-BP1 (Thr37/46) (P < 0.01) in WT, AMPK alpha2 KO, and AMPK gamma3 KO mice. However, in WT mice, preincubation with AICAR completely inhibited insulin-induced phosphorylation of mTOR targets, suggesting mTOR signaling is blocked by prior AMPK activation. The AICAR-induced inhibition was partly rescued in extensor digitorum longus muscle from either alpha2 or gamma3 AMPK KO mice, indicating functional alpha2 and gamma3 subunits of AMPK are required for the reduction in mTOR signaling. AICAR alone was without effect on basal phosphorylation of S6K1 (Thr389), ribosomal protein S6 (Ser235/236), and 4E-BP1 (Thr37/46). In conclusion, functional alpha2 and gamma3 AMPK subunits are required for AICAR-induced inhibitory effects on mTOR signaling.

AB - AMP-activated protein kinase (AMPK) is an important energy-sensing protein in skeletal muscle. Mammalian target of rapamycin (mTOR) mediates translation initiation and protein synthesis through ribosomal S6 kinase 1 (S6K1) and eukaryotic initiation factor 4E-binding protein 1 (4E-BP1). AMPK activation reduces muscle protein synthesis by down-regulating mTOR signaling, whereas insulin mediates mTOR signaling via Akt activation. We hypothesized that AMPK-mediated inhibitory effects on mTOR signaling depend on catalytic alpha2 and regulatory gamma3 subunits. Extensor digitorum longus muscle from AMPK alpha2 knockout (KO), AMPK gamma3 KO, and respective wild-type (WT) littermates (C57BL/6) were incubated in the presence of 5-aminoimidazole-4-carboxamide-1-beta-d-ribonucleoside (AICAR), insulin, or AICAR plus insulin. Phosphorylation of AMPK, Akt, and mTOR-associated signaling proteins were assessed. Insulin increased Akt Ser473 phosphorylation (P < 0.01), irrespective of genotype or presence of AICAR. AICAR increased phosphorylation of AMPK Thr172 (P < 0.01) in WT but not KO mice. Insulin stimulation increased phosphorylation of S6K1 (Thr389), ribosomal protein S6 (Ser235/236), and 4E-BP1 (Thr37/46) (P < 0.01) in WT, AMPK alpha2 KO, and AMPK gamma3 KO mice. However, in WT mice, preincubation with AICAR completely inhibited insulin-induced phosphorylation of mTOR targets, suggesting mTOR signaling is blocked by prior AMPK activation. The AICAR-induced inhibition was partly rescued in extensor digitorum longus muscle from either alpha2 or gamma3 AMPK KO mice, indicating functional alpha2 and gamma3 subunits of AMPK are required for the reduction in mTOR signaling. AICAR alone was without effect on basal phosphorylation of S6K1 (Thr389), ribosomal protein S6 (Ser235/236), and 4E-BP1 (Thr37/46). In conclusion, functional alpha2 and gamma3 AMPK subunits are required for AICAR-induced inhibitory effects on mTOR signaling.

U2 - 10.1210/me.2007-0448

DO - 10.1210/me.2007-0448

M3 - Journal article

C2 - 18276828

VL - 22

SP - 1105

EP - 1112

JO - Molecular Endocrinology

JF - Molecular Endocrinology

SN - 0888-8809

IS - 5

ER -