Disulfide linkage of growth hormone (GH) receptors (GHR) reflects GH- induced GHR dimerization. Association of JAK2 with the GHR is enhanced by receptor dimerization

Academic Article

Abstract

  • The growth hormone (GH) receptor (GHR) binds GH in its extracellular domain and transduces activating signals via its cytoplasmic domain. Both GH- induced GHR dimerization and JAK2 tyrosine kinase activation are critical in initiation of GH signaling. We previously described a rapid GH-induced disulfide linkage of GHRs in human IM-9 cells. In this study, three GH- induced phenomena (GHR dimerization, GHR disulfide linkage, and enhanced GHR- JAK2 association) were examined biochemically and immunologically. By using the GH antagonist, G120K, and an antibody recognizing a dimerization- sensitive GHR epitope, we demonstrated that GH-induced GHR disulfide linkage reflects GH-induced GHR dimerization. GH, not G120K, promoted both GHR disulfide linkage and enhanced association with JAK2. Measures that diminished GH-dependent JAK2 and GHR tyrosine phosphorylation diminished neither GH-induced GHR disulfide linkage nor GH-enhanced GHR-JAK2 association. By using both transient and stable expression systems, we determined that cysteine 241 (an unpaired extracellular cysteine) was critical for GH-induced GHR disulfide linkage; however, GH-induced GHR dimerization, GHR-JAK2 interaction, and GHR, JAK2, and STAT5 tyrosine phosphorylation still proceeded when this cysteine residue was mutated. We conclude GH-induced GHR disulfide linkage is not required for GHR dimerization, and activation and GH-enhanced GHR-JAK2 association depends more on GHR dimerization than on GHR and/or JAK2 tyrosine phosphorylation.
  • Published In

    Digital Object Identifier (doi)

    Author List

  • Zhang Y; Jiang J; Kopchick JJ; Frank SJ
  • Start Page

  • 33072
  • End Page

  • 33084
  • Volume

  • 274
  • Issue

  • 46