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cAMP counter-regulates insulin-mediated protein phosphatase-2A inactivation in rat skeletal muscle cells

N Begum1, L Ragolia

  • 1Diabetes Research Laboratory, Winthrop University Hospital, Mineola, New York 11501, USA. diabetes96@aol.com

The Journal of Biological Chemistry
|December 6, 1996
PubMed

Insights

Insulin rapidly inactivates protein phosphatase-2A (PP-2A) by increasing its tyrosine phosphorylation. Cyclic adenosine monophosphate (cAMP) agonists counteract this effect, decreasing PP-2A phosphorylation and restoring its activity.

Area of Science:

  • Cellular signaling pathways
  • Enzyme regulation
  • Molecular biology

Background:

  • Insulin signaling is crucial for glucose metabolism.
  • Protein phosphatase-2A (PP-2A) plays a key role in dephosphorylation.
  • Recent studies indicated insulin inactivates PP-2A.

Purpose of the Study:

  • To investigate the mechanism of insulin-induced PP-2A inactivation.
  • To explore the counter-regulation of PP-2A by cAMP agonists.
  • To identify signaling pathways involved in PP-2A regulation.

Main Methods:

  • Incubation of L6 myotubes with insulin and/or cAMP agonists.
  • Measurement of PP-2A activity.
  • Immunoprecipitation and Western blotting to assess tyrosine phosphorylation of PP-2A catalytic subunit.
  • Use of inhibitors: sodium orthovanadate, wortmannin, and rapamycin.

Main Results:

  • Insulin treatment rapidly inhibited PP-2A activity and increased its catalytic subunit's tyrosine phosphorylation.
  • (Sp)-cAMP pretreatment blocked insulin's inhibitory effect and reduced tyrosine phosphorylation.
  • Sodium orthovanadate mimicked insulin's effect on PP-2A phosphorylation when cells were pretreated with (Sp)-cAMP.
  • Wortmannin and rapamycin inhibited insulin-mediated PP-2A inactivation.

Conclusions:

  • Insulin signaling inactivates PP-2A through increased tyrosine phosphorylation.
  • cAMP agonists counteract insulin's effect by decreasing PP-2A phosphorylation, likely via an activated phosphatase.
  • Phosphatidylinositol 3-kinase and 70-kDa S6 kinase pathways are implicated in insulin-mediated PP-2A regulation.

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