Recombinant human granulocyte‐macrophage colony‐stimulating factor induces secretion of autoinhibitory monokines by U‐937 cells

Abstract

Colony‐stimulating factors are required for survival proliferation, differentiation and functional activation of granulocytes, macrophages and their precursor cells. In the present report, however, we demonstrate antiproliferative activity of recombinant human (rh) granulocyte‐macrophage colony‐stimulating factor (GM‐CSF) on mono‐blast cell line U‐937 and provide evidence for the involvement of tumor necrosis factor alpha TNF‐α and interleukin 1 beta (IL 1β) in its growth inhibitory action. GM‐CSF (but not granulocyte CSF, G‐CSF or macrophage CSF, M‐CSF) suppressed DNA synthesis and self renewal of U‐937 cells. Similarly, medium conditioned by U‐937 cells in response to GM‐CSF (GM‐CSF U‐937‐CM) was able to reduce clonogenicity and [³H] thymidine uptake by U‐937 cells. Since neutralization of GM‐CSF present in GM‐CSF U‐937‐CM by monoclonal antibody to GM‐CSF did not abrogate the autoinhibitory activity present in GM‐CSF U‐937‐CM, we considered the possibility that other soluble molecules are released by U‐937 cells upon GM‐CSF stimulation. Neutralization by antibodies to IL1β and TNF‐α suggested that both monokines could be the antiproliferative principle operating in GM‐CSF U‐937‐CM. Moreover, employing IL 1β‐specific enzyme‐linked immunosorbent assay, TNF‐α specific radioimmunoassay, Northern analysis using a cloned TNF‐α‐specific cDNA and an oligonucleotide probe for IL 1β, we demonstrate GM‐CSF‐inducible IL 1β and TNF‐α gene expression by U‐937 cells at the mRNA and protein level. Although M‐CSF expression was induced under similar conditions, M‐CSF failed to inhibit growth of U‐937 cells.