Demonstration of type I and type II somatomedin receptors on bovine growth plate chondrocytes

J Orthop Res. 1988;6(6):817-26. doi: 10.1002/jor.1100060605.

Abstract

The chondrocytes of the epiphyseal growth plate are the presumed target cells for hormones regulating skeletal growth. The somatomedins, a family of low molecular weight peptides, are thought to play a stimulatory role in this regulation. The cellular actions of the somatomedins are themselves determined by binding to specific receptors on target cells. Previous studies have characterized a specific receptor for somatomedin-C (Sm-C) or insulin-like growth factor I (IGF-I) on bovine growth plate chondrocytes (GPCs). We now report the characterization of a second type of somatomedin receptor on these cells that is more specific for another class of somatomedin represented by multiplication-stimulating activity (MSA) or rat insulin-like growth factor II (rIGF-II). Binding of [125I]MSA/rIGF-II to isolated GPCs was time dependent and saturable. Unlabeled Mr 7,100 MSA/rIGF-II and Sm-C/IGF-I were approximately equipotent in competing with [125I]MSA/rIGF-II for binding, while Mr 8,600 MSA/rIGF-II was an order of magnitude less potent. Low levels of competition by insulin appeared in some studies at concentrations of 10(-7) M and higher, suggesting displacement of [125I]MSA/rIGF-II binding to the Sm-C/IGF-I receptor. In affinity-labeling studies, [125I]MSA/rIGF-I labeled a complex of Mr greater than 300,000 (unreduced) and of Mr 140,000 (reduced), consistent with a type I somatomedin receptor composed of disulfide-linked subunits. [125I]MSA/rIGF-II labeled a Mr 240,000 moiety (unreduced) and Mr 260,000 (reduced), consistent with a type II somatomedin receptor. Both affinity-labeling and kinetic data revealed cross-binding of MSA/rIGF-II and insulin with the type I receptor and of Sm-C/IGF-I with the type II receptor. In contrast, the type II receptor did not recognize insulin. These data suggest a complex pattern of graded specificity of these receptors for their ligands. These data are consistent with the hypothesis that IGF-II as well as Sm-C/IGF-I participate in the stimulation of skeletal growth.

Publication types

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

MeSH terms

  • Affinity Labels / metabolism
  • Animals
  • Autoradiography
  • Binding Sites
  • Cartilage / cytology
  • Cartilage / ultrastructure
  • Cattle
  • Electrophoresis, Polyacrylamide Gel
  • Growth Plate / cytology
  • Growth Plate / metabolism
  • Growth Plate / ultrastructure*
  • Insulin-Like Growth Factor I / metabolism
  • Insulin-Like Growth Factor II / metabolism
  • Iodine Radioisotopes
  • Receptor, Insulin / analysis*
  • Receptor, Insulin / metabolism
  • Receptors, Somatomedin

Substances

  • Affinity Labels
  • Iodine Radioisotopes
  • Receptors, Somatomedin
  • Insulin-Like Growth Factor I
  • Insulin-Like Growth Factor II
  • Receptor, Insulin