Possible roles of N- and C-terminal unstructured tails of CPI-17 in regulating Ca2+ sensitization force of smooth muscle

J Smooth Muscle Res. 2022;58(0):22-33. doi: 10.1540/jsmr.58.22.


CPI-17 regulates the myosin phosphatase and mediates the agonist-induced contraction of smooth muscle. PKC and ROCK phosphorylate CPI-17 at Thr38 leading to a conformational change of the central inhibitory domain (PHIN domain). The N- and C-terminal tails of CPI-17 are predicted as unstructured loops and their sequences are conserved among mammals. Here we characterized CPI-17 N- and C-terminal unstructured tails using recombinant proteins that lack the potions. Recombinant CPI-17 proteins at a physiologic level (10 µM) were doped into beta-escin-permeabilized smooth muscle strips for Ca2+ sensitization force measurement. The ectopic full-length CPI-17 augmented the PDBu-induced Ca2+ sensitization force at pCa6.3, indicating myosin phosphatase inhibition. Deletion of N- and C-terminal tails of CPI-17 attenuated the extent of PDBu-induced Ca2+-sensitization force. The N-terminal deletion dampened phosphorylation at Thr38 by protein kinase C (PKC), and the C-terminal truncation lowered the affinity to the myosin phosphatase. Under the physiologic conditions, PKC and myosin phosphatase may recognize CPI-17 N-/C-terminal unstructured tails inducing Ca2+ sensitization force in smooth muscle cells.

Keywords: PP1; evolution; force development; myosin; protein kinase C (PKC).

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Calcium / metabolism
  • Mammals / metabolism
  • Muscle Contraction* / physiology
  • Muscle Proteins* / metabolism
  • Muscle, Smooth / metabolism
  • Myosin-Light-Chain Phosphatase / metabolism
  • Phosphoprotein Phosphatases / metabolism
  • Phosphoproteins / metabolism
  • Phosphorylation
  • Protein Kinase C / metabolism


  • Calcium
  • Muscle Proteins
  • Myosin-Light-Chain Phosphatase
  • Phosphoprotein Phosphatases
  • Phosphoproteins
  • Protein Kinase C