Regulation of insulin-like growth factor binding protein-5 messenger ribonucleic acid expression and protein availability in rat osteoblast-like cells

Endocrinology. 1993 Jun;132(6):2525-30. doi: 10.1210/endo.132.6.7684979.


PTH treatment of UMR 106-01 rat osteosarcoma cells increased 20- to 100-fold medium levels of a discrete insulin-like growth factor binding protein (IGFBP) with M(r) of 29K. Northern analysis of UMR cellular RNA hybridized with a specific IGFBP-5 complementary DNA probe indicated a 6.0-kilobase transcript induced within 2 h in PTH-treated cells. IGFBP-5 messenger RNA (mRNA) abundance was maximal around 6 h and remained elevated after 24 h of treatment. Another rat osteosarcoma cell line (ROS 17/2.8) did not express IGFBP-5 mRNA and did not secrete 29K IGFBP. Induction of IGFBP-5 mRNA by PTH was blocked when RNA synthesis in UMR cells was inhibited by actinomycin D (Bu)2cAMP mimicked the effect of PTH on IGFBP-5 mRNA expression and protein secretion. In addition, a monoclonal antibody against IGF-I (Sm 1.2) inhibited the PTH-induced increase in medium IGFBP-5 without influencing IGFBP-5 transcript levels. Direct addition of IGF-I to UMR cell cultures increased medium IGFBP-5 levels approximately 14-fold, with a modest effect on IGFBP-5 mRNA levels. Studies comparing IGF-I, IGF-II, different IGF-I analogs, and insulin indicated that the predominant IGF effect on IGFBP-5 accumulation was type I IGF receptor independent. Thus, in UMR 106-01 cells, PTH and IGF-I increase extracellular concentrations of IGFBP-5 via distinct but coordinate mechanisms; PTH acts primarily to induce IGFBP-5 mRNA expression through a cAMP-mediated mechanism, and IGF-I appears to interact directly with IGFBP-5 protein to promote its accumulation.

Publication types

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

MeSH terms

  • Animals
  • Biological Availability
  • Blotting, Northern
  • Blotting, Western
  • Carrier Proteins / genetics*
  • Carrier Proteins / metabolism*
  • Insulin-Like Growth Factor Binding Protein 5
  • Osteoblasts / metabolism*
  • Parathyroid Hormone / pharmacology
  • RNA, Messenger / metabolism*
  • Rats
  • Somatomedins / pharmacology
  • Tumor Cells, Cultured


  • Carrier Proteins
  • Insulin-Like Growth Factor Binding Protein 5
  • Parathyroid Hormone
  • RNA, Messenger
  • Somatomedins