Identification of leukemia inhibitory factor as a potent mast cell growth-enhancing factor produced by mouse keratinocyte cell line, KCMH-1

Inoculation of KCMH-1 cells, a keratinocyte-derived cell line established f rom a chemically induced skin tumor, into the skin of mice results in accum ulation of mast cells around the resulting tumors, The conditioned medium o f KCMH-1 cells enhances the growth of mast cells in vitro when they are cul tured in the presence of NIH/3T3 fibroblasts, suggesting an important role for keratinocytes in mast cell hyperplasia in the skin, The aim of this stu dy was to identify this mast cell growth-enhancing factor (MCGEF) by screen ing a KCMH-1 cDNA library. We first established a polyclonal antibody raise d against the partially purified factor obtained from KCMH-1-conditioned me dium which neutralized the MCGEF activity in KCMH-1-conditioned medium. Exp ression cloning of 1 X 10(6) cDNAs from the KCMH-1 cDNA library led to 16 c DNAs, One of these cloned cDNAs was found to be leukemia inhibitory factor (LIF). Both LIF produced by COS cells and the recombinant protein obtained commercially showed MCGEF activity when added to mast cell/fibroblast cocul tures, MCGEF activity in KCMH-1-conditioned medium was completely neutraliz ed by an anti-LIE monoclonal antibody, These results suggest that MCGEF pro duced by KCMH-1 cells is identical to LIF.