The insulin receptor substrate (IRS-1) is a PEST protein that is susceptible to calpain degradation in vitro

Biochem Biophys Res Commun. 1993 Oct 29;196(2):767-72. doi: 10.1006/bbrc.1993.2315.


The insulin receptor substrate 1 (IRS-1) contains at least 11 sequence motifs that are rich in proline (P), glutamic acid (E), serine (S), and threonine (T), i.e., PEST regions. Proteins with PEST regions turn over rapidly. IRS-1 is degraded rapidly in vivo upon exposure of 3T3-L1 adipocytes to insulin. The intracellular, calcium-dependent, neutral proteases known as calpains are one possible mechanism by which IRS-1 may be degraded. To begin to investigate this possibility, purified exogenous calpain was shown to degrade IRS-1 in cell-free extracts from basal and insulin-treated cells and rat recombinant IRS-1 in vitro. Only two proteolytic fragments could be detected. One had a mol wt of approximately 79 kDa, arising from the C-terminus end, and the second had a mol wt of approximately 90 kDa arising from near the N-terminus, possibly a product of the same cleavage event, since the mol wt of IRS-1 from insulin-treated cells was approximately 170 kDa. These results suggest that IRS-1 may serve as a substrate for calpain in vivo, accounting for its rapid degradation.

Publication types

  • Research Support, Non-U.S. Gov't
  • Research Support, U.S. Gov't, P.H.S.

MeSH terms

  • 3T3 Cells
  • Adipocytes / cytology
  • Adipocytes / drug effects
  • Adipocytes / metabolism*
  • Amino Acid Sequence
  • Animals
  • Calcium / pharmacology
  • Calpain / metabolism*
  • Cell Differentiation
  • Humans
  • Insulin / pharmacology
  • Insulin Receptor Substrate Proteins
  • Kinetics
  • Mice
  • Molecular Sequence Data
  • Phosphoproteins / chemistry
  • Phosphoproteins / metabolism*
  • Rats
  • Recombinant Proteins
  • Software
  • Substrate Specificity


  • IRS1 protein, human
  • Insulin
  • Insulin Receptor Substrate Proteins
  • Irs1 protein, mouse
  • Irs1 protein, rat
  • Phosphoproteins
  • Recombinant Proteins
  • Calpain
  • Calcium