STEM-CELL FACTOR, A NOVEL CUTANEOUS GROWTH-FACTOR FOR MAST-CELLS AND MELANOCYTES

Mechanisms affecting mast cell and melanocyte growth and function are still poorly understood. This report summarizes the current state of k nowledge on a recently described growth factor for both these cell typ es and for primitive haematopoietic stem cells. Stem cell factor (SCF) , also named mast cell growth factor or kit-ligand, has only recently been cloned and has been shown to be encoded on human chromosome 12. I t may be of specific importance in cutaneous physiology and pathology since it is produced by several cell types in the skin (e.g. fibroblas ts, keratinocytes, endothelial cells) and since it affects melanocyte and mast cell growth, survival, secretion and adhesion as well as migr ation into tissues. Defects in the genes encoding for the SCF receptor (c-kit-protein) have been shown to be responsible for human piebaldis m. A pathogenetic role in mastocytosis has recently been proposed, but remains to be proven. SCF receptor expression is decreased on cells o f some malignant cell lines compared to their physiological counterpar ts, making it unlikely that SCF is a key factor in malignant transform ation and cellular hyperproliferation. In haematopoiesis, SCF acts pri marily in concert with other growth factors, and we show here that alo ne in serum-free culture it has no effect on mast cell growth. Further more, there is evidence that besides SCF, additional mast cell growth factors are secreted by fibroblasts and keratinocytes, suggesting a co mplex orchestration of several growth factors in the regulation of cut aneous growth and differentiation in which SCF plays only one part.