Inhibition of ataxia telangiectasia mutated (ATM) prevents the prolonged increase in phosphorylation of Akt substrate of 160 kDa (AS160) subsequent to activation of the AMP‐activated protein kinase (AMPK)

We hypothesized that activation of AMPK would result in a lingering increase in AS160 phosphorylation (P‐AS) and that inhibition of ATM, a reported regulator of AMPK and Akt, would prevent this effect. L6 myotubes were incubated for 30 min with DMSO (vehicle) or the ATM inhibitor KU55933 (KU) at a concentration (1 μM) that would inhibit ATM but would be unlikely to interfere with the related kinases PI3K or mTOR. Then, myotubes were incubated 60 min ± 2 mM AICAR (an AMPK activator) and ± KU, after which cells were incubated 1 h ± KU, then 1 h without additives, and finally 20 min ± 100 nM insulin. There was a ~40% increase in AMPK phosphorylation (P‐AMPK) immediately after 1 h of AICAR treatment, but this had worn off by 140 min later. In myotubes not exposed to KU, P‐AS tended to be elevated by ~70% in myotubes previously exposed to AICAR. Insulin also tended to increase P‐AS by about 2‐fold, and effects of insulin and prior exposure to AICAR tended to be more than additive. KU caused an overall elevation in P‐AS, but prevented any further effects of insulin or prior exposure to AICAR on P‐AS. KU increased Akt phosphorylation (P‐Akt, S473 and T308) in the absence of insulin but did not interfere with insulin‐stimulated increases in P‐Akt. Previous exposure to KU depressed P‐AMPK by about 40%. It appears that exposure to an AMPK activator leads to long‐term elevation of P‐AS, and ATM may play some role in this effect. NIH DK08437 supported this work.