Local presentation of Steel factor increases expression of c-kit immunoreactive interstitial cells of Cajal in culture

The binding of Steel factor (SF) to c-kit initiates a signaling pathway essential for development and maintenance of interstitial cells of Cajal (ICC). Soluble and membrane-bound isoforms of SF are expressed in the gastrointestinal tract, but the role for either isoform in supporting ICC development is unknown. The aim of this study was to determine the role of SF in supporting ICC in culture. ICC were cultured from dissociated mouse jejunum and grown with fibroblast cell lines that produced either soluble, membrane-bound or membrane-restricted SF. ICC were identified and counted by c-kit immunoreactivity. The number of c-kit immunoreactive cells was greater in the coculture system compared with cultures grown without SF-producing fibroblasts. All forms of SF-producing fibroblasts increased ICC number in culture but physical separation of the fibroblasts from the c-kit immunoreactive cells, the addition of exogenous SF to the culture medium, or fibroblast-conditioned media did not. These results are consistent with the hypothesis that the membrane-bound form of SF preferentially contributes to expression of c-kit-positive ICC under cell culture conditions.