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OBJECTIVE
Phosphorylation of two members of the TBC1 domain family of proteins, Akt substrate of 160 kDa (AS160, also known as TBC1D4) and TBC1D1, has been implicated in the regulation of glucose transport in skeletal muscle. Insulin-stimulated phosphorylation (measured using the phospho-Akt substrate [PAS] antibody) of AS160 and TBC1D1 appears to occur in an Akt-dependent manner, but the kinases responsible for contraction-stimulated PAS-AS160 and PAS-TBC1D1 remain unclear. AMP-activated protein kinase (AMPK) and Akt, both activated by contraction, can each phosphorylate AS160 and TBC1D1 in cell-free assays.METHODS
To evaluate the roles of AMPK and Akt on insulin- or contraction-stimulated PAS-AS160, PAS-TBC1D1, and glucose transport, rat epitrochlearis was incubated with and without compound C (inhibitor of AMPK) or Wortmannin (inhibitor of phosphatidylinositol [PI] 3-kinase, which is upstream of Akt) before and during insulin stimulation or contraction.RESULTS
Insulin-stimulated glucose transport and phosphorylation of both AS160 and TBC1D1 were completely inhibited by Wortmannin. Wortmannin eliminated contraction stimulation of phospho-Ser(21/9)glycogen synthase kinase 3alpha/beta (pGSK3; Akt substrate) and PAS-AS160 but did not significantly alter pAMPK, phospho-Ser79acetyl CoA carboxylase (pACC; AMPK substrate), PAS-TBC1D1, or glucose transport in contraction-stimulated muscle. Compound C completely inhibited contraction-stimulated pACC and PAS-TBC1D1 and partially blocked glucose transport, but it did not significantly alter pAkt, pGSK3, or PAS-AS160.CONCLUSIONS
These data suggest that 1) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt-dependent manner, 2) contraction stimulates PAS-AS160 (but not PAS-TBC1D1 or glucose transport) in a PI 3-kinase/Akt-dependent manner, and 3) contraction stimulates PAS-TBC1D1 and glucose transport (but not PAS-AS160) in an AMPK-dependent manner.
AS160 → Insulin: " Insulin stimulated phosphorylation ( measured using the phospho-Akt substrate [ PAS ] antibody ) of AS160 and TBC1D1 appears to occur in an Akt dependent manner, but the kinases responsible for contraction stimulated PAS-AS160 and PAS-TBC1D1 remain unclear "
PAS-TBC1D1 — Akt: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160, PAS-TBC1D1 , and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
PAS-TBC1D1 — AMPK: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160, PAS-TBC1D1 , and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
PAS-AS160 — Akt: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160 , PAS-TBC1D1, and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
PAS-AS160 — AMPK: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160 , PAS-TBC1D1, and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
insulin- — Akt: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160, PAS-TBC1D1, and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
insulin- — AMPK: " To evaluate the roles of AMPK and Akt on insulin- or contraction stimulated PAS-AS160, PAS-TBC1D1, and glucose transport, rat epitrochlearis was incubated with and without compound C ( inhibitor of AMPK ) or Wortmannin ( inhibitor of phosphatidylinositol [ PI] 3-kinase, which is upstream of Akt ) before and during insulin stimulation or contraction "
TBC1D1 → Insulin: " Insulin stimulated glucose transport and phosphorylation of both AS160 and TBC1D1 were completely inhibited by Wortmannin "
AS160 → Insulin: " Insulin stimulated glucose transport and phosphorylation of both AS160 and TBC1D1 were completely inhibited by Wortmannin "
PAS-TBC1D1 → AS160: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "
PAS-TBC1D1 — 3-kinase/Akt: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "
PAS-TBC1D1 — PI 3-kinase/Akt: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "
PAS-TBC1D1 — AMPK: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "
PAS-AS160 — 3-kinase/Akt: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "
PAS-AS160 — PI 3-kinase/Akt: " These data suggest that 1 ) insulin stimulates glucose transport and phosphorylation of AS160 and TBC1D1 in a PI 3-kinase/Akt dependent manner, 2 ) contraction stimulates PAS-AS160 ( but not PAS-TBC1D1 or glucose transport ) in a PI 3-kinase/Akt dependent manner, and 3 ) contraction stimulates PAS-TBC1D1 and glucose transport ( but not PAS-AS160 ) in an AMPK dependent manner "