GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR GENE-EXPRESSION AND FUNCTION DURING TUMOR PROMOTION

Although recent evidence suggests that granulocyte-macrophage colony s timulating factor (GM-CSF) plays a role in cutaneous inflammation indu ced by topical exposure of phorbol ester tumor promoters to murine epi dermis, there is little information available on the temporal sequence of gene expression of this cytokine over the time course of tumor pro motion or about its function in this process. The goal of the present studies was to examine the potential role of GM-CSF in tumor promotion in SENCAR mice. Competitive reverse transcriptase polymerase chain re action (RT-PCR) studies demonstrated that a single topical application of 12-O-tetradecanoylphorbol-13-acetate (TPA; 2 mu g, 10 mu g) to the dorsal epidermis of SENCAR mouse skin stimulated a dose and time depe ndent GM-CSF gene expression that was upregulated at 1 h after TPA exp osure, peaked at 3 h and declined at 12 h. Although treatment with 7', 12'-dimethyl-benz[a]anthracene (DMBA) did not stimulate GM-CSF gene ex pression, GM-CSF gene expression was elevated in epidermal tissue isol ated from SENCAR mice treated with a single application of 10 nmol DMB A followed by multiple applications of 2 mu g TPA over a 1-22 week tim e course. Immunochemical and autoradiographic studies demonstrated tha t GM-CSF protein was produced by suprabasal keratinocytes, interfollic ular cells, nonproliferating papilloma cells and leukocytes within the dermis. Intraperitoneal injection of recombinant (r) GM-CSF into SENC AR mice at 2 h prior to topical application of 10 mu g TPA induced a s ignificant increase in epidermal keratinocyte proliferation, leukocyte infiltration into the dermis, hydroperoxide production by circulating neutrophils and chemotactic activity present within the plasma at 24 h compared to treatment with only 10 mu g TPA. Intravenous injection o f anti-GM-CSF antibodies significantly inhibited both local and system ic inflammatory events induced by topical application of TPA. The pres ent studies suggest that GM-CSF has a broad spectrum of activity with at least two target cell populations, epidermal keratinocytes within t he proliferative compartment and leukocytes.