Human keratinocyte locomotion: the effect of selected cytokines

Epidermal growth factor (EGF) and basic fibroblast growth factor (bFGF) are two powerful mitogens for human keratinocytes that also have been shown to promote the healing of in vivo wounds. Transforming growth factor-beta (TGF-beta) markedly inhibits human keratinocyte proliferation and growth and yet has been shown to promote wound healing. Using a migration assay that evaluates pure cell locomotion independently from cell proliferation, we examined the influence of EGF, bFGF, and TGF-B on human keratinocyte locomotion. Although these agents had profound influences upon the growth potential of keratinocytes in parallel thymidine incorporation assays, they had no significant effect upon keratinocyte locomotion when cells were apposed to either tissue culture plastic or a collagen substratum. In contrast, we found that bovine pituitary extract (BPE), a poorly defined mitogen that is commonly used in keratinocyte cultures, could stimulate keratinocyte locomotion when the cells were apposed to a collagen substrate. These studies demonstrate that i) keratinocyte locomotion and proliferation operate by completely independent mechanisms, ii) the positive effects upon wound healing by EGF, bFGF, and TGF-beta are not due to a direct promotion of keratinocyte locomotion, and iii) that one or more components of BPE are capable of directly promoting keratinocyte locomotion on collagen.