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A High Resolution Method to Monitor Phosphorylation-dependent Activation of IRF3
Published on: January 24, 2016
PKCdelta-mediated IRS-1 Ser24 phosphorylation negatively regulates IRS-1 function.
Michael W Greene1, Mary S Ruhoff, Richard A Roth
1Bassett Research Institute, Mary Imogene Bassett Hospital, Cooperstown, NY 13326, USA. michael.greene@bassett.org <michael.greene@bassett.org>
Biochemical and Biophysical Research Communications
|September 15, 2006
Summary
Insulin receptor substrate-1 (IRS-1) Ser24 phosphorylation by PKCdelta acts as a negative regulator, inhibiting insulin signaling and cellular proliferation by impairing phosphatidylinositol-4,5-bisphosphate binding.
Area of Science:
- Molecular Biology
- Cell Signaling
- Biochemistry
Background:
- Insulin receptor substrate-1 (IRS-1) is crucial for insulin signaling, with its tyrosine phosphorylation regulated by both positive and negative mechanisms.
- Serine/threonine phosphorylation of IRS-1, particularly by Protein Kinase C (PKC), can disrupt insulin signaling pathways.
Purpose of the Study:
- To investigate the role of specific serine/threonine phosphorylation sites within the PH-PTB domains of human IRS-1.
- To determine if consensus PKC phosphorylation sites (Ser24, Ser58, Thr191) are involved in the negative regulation of insulin signaling.
Main Methods:
- Site-directed mutagenesis was used to create IRS-1 mutants where Ser24, Ser58, and Thr191 were replaced with Alanine (to block phosphorylation) or Glutamate (to mimic phosphorylation).
- These mutants were analyzed for their effects on insulin-stimulated IRS-1 tyrosine phosphorylation, cellular proliferation, and Akt activation.
- PKCdelta involvement was confirmed using catalytic domain mutants and RNA interference (RNAi).
- Phosphatidylinositol-4,5-bisphosphate binding assays were performed on mutated IRS-1 proteins.
Main Results:
- Mutating Ser24, Ser58, and Thr191 to Alanine (3A) abrogated the inhibitory effect of PKCdelta on IRS-1 tyrosine phosphorylation.
- Mutating these sites to Glutamate (3E) reduced insulin-stimulated IRS-1 tyrosine phosphorylation, cellular proliferation, and Akt activation.
- The Ser24 to Glutamate single mutant showed the most significant inhibition of insulin-stimulated IRS-1 tyrosine phosphorylation.
- PKCdelta-mediated phosphorylation at Ser24 was confirmed, and mutations at Ser24 impaired phosphatidylinositol-4,5-bisphosphate binding.
Conclusions:
- Serine 24 in IRS-1 is identified as a key negative regulatory phosphorylation site.
- PKCdelta-mediated phosphorylation of IRS-1 at Ser24 inhibits insulin signaling by disrupting phosphatidylinositol-4,5-bisphosphate binding.
- This finding provides mechanistic insight into how IRS-1 activity is downregulated in response to certain stimuli.
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