The mitogenic effect of parathyroid hormone is associated with E2F-dependent activation of cyclin-dependent kinase 1 (cdc2) in osteoblast precursors

J Bone Miner Res. 1997 Oct;12(10):1596-605. doi: 10.1359/jbmr.1997.12.10.1596.

Abstract

Injections of parathyroid hormone (PTH) have been reported to stimulate skeletal accretion through increased bone formation in several species, and osteoblast proliferation is a critical component of bone formation. However, the biological mechanisms of PTH-stimulated bone cell proliferation are largely unknown. In this study, we demonstrated that PTH stimulates proliferation of the osteoblast precursor cell line, TE-85, in association with increasing cdc2 protein levels and its kinase activity. cdc2 antisense oligonucleotides blocked PTH-induced DNA synthesis and cell cycle progression. Analysis of the time course of PTH-stimulated cdc2 message levels demonstrated that cdc2 mRNA levels were increased 1.5- to 4-fold between 3-18 h following release from cell synchronization. Transfections of TE-85 cells with a series of cdc2 promoter-luciferase deletion constructs revealed PTH stimulation of the cdc2 promoter. Promoter constructs containing a mutation in the E2F binding site were not stimulated by PTH. Gel mobility shift assays demonstrated increased free E2F levels in TE-85 nuclear extracts in response to PTH. Furthermore, the ratios of hyperphosphorylated to hypophosphorylated forms of Rb protein were increased by PTH treatment. These results demonstrate that PTH-stimulated cdc2 expression was associated with TE-85 cell proliferation and that the mechanism of stimulating cdc2 gene expression involved increasing the levels of free E2F.

Publication types

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

MeSH terms

  • CDC2 Protein Kinase / biosynthesis*
  • CDC2 Protein Kinase / genetics
  • CDC2 Protein Kinase / metabolism*
  • Carrier Proteins*
  • Cell Cycle / drug effects
  • Cell Cycle Proteins*
  • Cell Division / drug effects
  • DNA / biosynthesis
  • DNA-Binding Proteins / biosynthesis
  • E2F Transcription Factors
  • Enzyme Activation / drug effects
  • Humans
  • Mitogens / pharmacology*
  • Mutation / drug effects
  • Mutation / genetics
  • Oligonucleotides, Antisense / pharmacology
  • Osteoblasts / drug effects*
  • Osteosarcoma
  • Parathyroid Hormone / pharmacology*
  • Promoter Regions, Genetic
  • RNA, Messenger / metabolism
  • Retinoblastoma-Binding Protein 1
  • Transcription Factor DP1
  • Transcription Factors / biosynthesis*
  • Transfection
  • Tumor Cells, Cultured / drug effects

Substances

  • Carrier Proteins
  • Cell Cycle Proteins
  • DNA-Binding Proteins
  • E2F Transcription Factors
  • Mitogens
  • Oligonucleotides, Antisense
  • Parathyroid Hormone
  • RNA, Messenger
  • Retinoblastoma-Binding Protein 1
  • Transcription Factor DP1
  • Transcription Factors
  • DNA
  • CDC2 Protein Kinase