Endogenous GM-CSF is involved as an autocrine growth factor for human osteoblastic cells

Abstract

Granulocyte-macrophage colony-stimulating factor (GM-CSF) is an important modulator of hematopoietic cells. However, the role of GM-CSF in nonhematopoietic cells remains unclear. We have determined whether GM-CSF is an autocrine mitogenic factor for human osteoblastic (hOB) cells. We found by reverse transcriptase-polymerase chain reaction (RT-PCR) that hOB cells express constitutively both GM-CSF and the alpha and beta chains of the GM-CSF receptor (GMR). Immunocytochemistry showed that serum-starved hOB cells express both GM-CSF and GMR alpha chain. Recombinant human (rh) GM-CSF induces a dose-dependent stimulation of hOB cell proliferation, showing that hOB cells have functional GMRs. A specific neutralizing GM-CSF antibody decreased the basal growth rate and suppressed cell proliferation induced by media conditioned by hOB cells, indicating that GM-CSF released by hOB cells is biologically active. Treatment of hOB cells with GM-CSF antisense (AS) oligonucleotide inhibited the endogenous GM-CSF production as shown by ELISA and immunocytochemistry, whereas a random (R) sequence had no effect. AS oligonucleotides markedly inhibited hOB cell growth reversibly, whereas R oligonucleotides had no effect. AS was more effective than the anti-GM-CSF antibody, and the addition of rhGM-CSF did not rescue the inhibitory effect of AS on cell growth. The findings that human osteoblastic cells produce GM-CSF and express functional GMR constitutively and that suppression of endogenous GM-CSF results in inhibition of cell growth demonstrate that GM-CSF is involved as an autocrine growth factor for human osteoblastic cells.