Granulocyte
-colony-stimulating factor (G-CSF), a hematopoietic cytokine, regulates the proliferation and differentiation of granulocytic progenitor cells and functionally activated mature neutrophils. G-CSF also affects nonhematopoietic tumor cells by the binding of G-CSF to its specific receptor (G-CSFR) on the cells. In this study, we investigated the effect of G-CSF on the invasive potential of head-and-neck carcinoma cells, and explored the intracellular events initiated by the binding of G-CSF in tumor cells. In vitro treatment of head-and-neck-carcinoma cell lines, IMC-2, IMC-3, KB, Ca9-22, SCCKN and SCCTF, with recombinant G-CSF (rG-CSF) significantly augmented their invasive potential in dose-and time-dependent manners. Among these cancer cells, IMC-2, IMC-3, KB and Ca9-22 cells produced little G-CSF, while large amounts of G-CSF were produced by SCCKN and SCCTF cell lines. Anti-G-CSF antibody (Ab) abrogated the rG-CSF-enhanced invasiveness to the control level of that in untreated cancer cell lines. Immunocytochemical staining and Western blotting using anti-G-CSFR monoclonal antibody (MAb) revealed the expression of G-CSFR on head-and-neck-cancer cell lines exhibiting the enhancement of invasive activity by rG-CSF. IMC-2 cells, having the highest invasive ability among the cell lines used, showed augmentation of G-CSFR expression on stimulation with rG-CSF. Furthermore, stimulation of IMC-2 cells with rG-CSF induced rapid activation of tyrosine-phosphorylated JAK1, suggesting that the G-CSF signal may be transduced into the cells through G-CSFR. Moreover, the gelatinolytic activity of IMC-2 cells was enhanced by stimulation of rG-CSF, and the enhanced invasiveness was inhibited on addition of the tissue inhibitors of metalloproteinases (TIMPs). These results suggest that exogenous rG-CSF may increase the risk of metastasis and/or local recurrence in patients with G-CSFR-positive head-and-neck squamous-cell carcinoma, via an invasive mechanism.