Regulation of skeletal muscle insulin-stimulated signaling through the MEK-REDD1-mTOR axis

Biochem Biophys Res Commun. 2017 Jan 22;482(4):1067-1072. doi: 10.1016/j.bbrc.2016.11.159. Epub 2016 Nov 29.


Recent findings in adipocytes suggest that mitogen-activated protein kinase (MAPK)/extracellular-regulated signaling kinase (ERK) kinase 1/2 (MEK1/2) signaling regulates regulated in development and DNA damage 1 (REDD1) protein expression. Similarly, our previous work show that a lack of REDD1 protein expression, and associated hyperactive basal mechanistic target of rapamycin (mTOR) signaling, limits skeletal muscle's response to insulin. Therefore, we sought to determine: 1) if MEK1/2 inhibition is sufficient to reduce REDD1 protein expression and subsequently insulin receptor substrate-1 (IRS-1) tyrosine phosphorylation via negative feedback of hyperactive mTOR in REDD1 wild-type (WT) mice and 2) if rapamycin-mediated mTOR inhibition is sufficient to improve IRS-1 tyrosine phosphorylation in REDD1 knockout (KO) mice. REDD1 WT mice were injected with 10 mg/kg BW of the MEK1/2 non-competitive inhibitor, PD184352, 3 h prior to acute insulin treatment. In separate studies, REDD1 KO mice were injected with 5 mg/kg BW of the mTOR inhibitor, rapamycin, 3 h prior to acute insulin treatment. Following the inhibitor treatment period, markers of insulin signaling activation (IRS-1 Y1222, MEK1/2 S217/221, ERK1/2 T202/Y204), REDD1, and mTOR signaling activation (S6K1 T389, rpS6 S240/244) were examined in skeletal muscle collected before and after a 10 min insulin treatment. PD184352 treatment reduced MEK/ERK phosphorylation and REDD1 protein expression, independent of insulin. This reduction in REDD1 protein expression was associated with elevated basal S6K1 and rpS6 phosphorylation and reduced insulin stimulated IRS-1 phosphorylation. Conversely, rapamycin inhibited S6K1 and rpS6 activation, and significantly improved insulin -stimulated activation of IRS-1 and MEK1/2 in KO mice. These data support that REDD1 is required for normal insulin-stimulated signaling, and that a subtle balance exists between MEK1/2, REDD1, and mTOR for the proper regulation of insulin signaling.

Keywords: Insulin signaling; PD184352; REDD1; Rapamycin; Skeletal muscle.

MeSH terms

  • Animals
  • Benzamides / chemistry
  • Insulin / metabolism*
  • MAP Kinase Kinase 1 / metabolism*
  • MAP Kinase Kinase 2 / metabolism*
  • Mice
  • Mice, Knockout
  • Muscle, Skeletal / metabolism*
  • Phosphorylation
  • Signal Transduction
  • Sirolimus / chemistry
  • TOR Serine-Threonine Kinases / metabolism
  • Transcription Factors / genetics
  • Transcription Factors / metabolism*


  • 2-(2-chloro-4-iodophenylamino)-N-cyclopropylmethoxy-3,4-difluorobenzamide
  • Benzamides
  • Ddit4 protein, mouse
  • Insulin
  • Transcription Factors
  • mTOR protein, mouse
  • TOR Serine-Threonine Kinases
  • MAP Kinase Kinase 1
  • MAP Kinase Kinase 2
  • Map2k1 protein, mouse
  • Map2k2 protein, mouse
  • Sirolimus