Growth hormone receptor activity is stimulated by insulin-like growth factor binding protein 5 in rat osteosarcoma cells.

MC Slootweg, C Ohlsson, EJ Van Elk… - Growth …, 1996 - europepmc.org
MC Slootweg, C Ohlsson, EJ Van Elk, JC Netelenbos, DL Andress
Growth regulation, 1996europepmc.org
Osteoblast-like UMR-106.01 rat osteosarcoma cells express high affinity growth hormone
(GH) receptors (GHRs). Because osteoblasts secrete insulin-like growth factor binding
protein-5 (IGFBP-5), we evaluated whether it also modulates GH binding and GHR
expression in UMR cells. Human recombinant intact IGFBP-5 stimulated 125I-hGH binding
in a dose-dependent manner (dose range 300-3000 ng/ml), inducing an increase to 193.6+/-
2.1% of control binding at 3000 ng/ml (P< 0.001). Carboxy-truncated IGFBP-5 also …
Osteoblast-like UMR-106.01 rat osteosarcoma cells express high affinity growth hormone (GH) receptors (GHRs). Because osteoblasts secrete insulin-like growth factor binding protein-5 (IGFBP-5), we evaluated whether it also modulates GH binding and GHR expression in UMR cells. Human recombinant intact IGFBP-5 stimulated 125I-hGH binding in a dose-dependent manner (dose range 300-3000 ng/ml), inducing an increase to 193.6+/-2.1% of control binding at 3000 ng/ml (P< 0.001). Carboxy-truncated IGFBP-5 also stimulated GH binding but with less potency (125+/-2.7% of control at 3000 ng/ml, P< 0.01). GHRs identified by chemical crosslinking of 125I-hGH to cell monolayers increased after treatment with IGFBP-5 and decreased in response to insulin-like growth factor-I (IGF-I). GHR mRNA levels, as quantitated by a solution hybridization RNAse protection assay, increased up to 3 to 7-fold in a time-dependent manner by intact IGFBP-5 but not by carboxy-truncated IGFBP-5. An antiserum to IGFBP-5 reduced basal GH binding to 56.7+/-4.3% of control value at a concentration of 0.5%(P< 0.001), showing that IGFBP-5 produced by the cells is a strong regulator of GH binding. IGFBP-5 antiserum also decreased GH binding to 85.9+/-0.9% of IGFBP-5 stimulated value (P< 0.001), showing the specificity of IGFBP-5 stimulation. To determine whether the GHR upregulation was physiologically significant, cell proliferation was evaluated after coincubation of IGFBP-5 with low, non-stimulatory concentrations of GH. IGFBP-5 (1000 ng/ml) induced cell proliferation to 116.2+/-3.2% of control levels, and coincubation with hGH at 10 ng/ml induced an increase to 133.3+/-0.1% of control levels. We conclude that exogenous and endogenous IGFBP-5 upregulate GHR mRNA levels and GH binding and this interaction potentiates GH-stimulated mitogenesis in osteoblastic cells.
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