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

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 α and β chains of the GM‐CSF receptor (GMR). Immunocytochemistry showed that serum‐starved hOB cells express both GM‐CSF and GMRα 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. J Cell Physiol 170:35–46, 1997 © 1997 Wiley‐Liss, Inc.