KERATINOCYTE EXTRACELLULAR MATRIX-MEDIATED REGULATION OF NORMAL HUMANMELANOCYTE FUNCTIONS

Active roles of cell-cell interaction between melanocytes and neighbor ing keratinocytes for the regulation of melanocyte functions in the sk in have been suggested. We examined substantial regulatory mechanisms of keratinocyte extracellular matrix (kECMs) for normal human melanocy te functions without direct cell-cell contact, We specially devised kE CMs from proliferating or differentiating keratinocytes and further tr eated them with environmental stimulus ultraviolet B (UVB) for skin pi gmentary system. Normal human melanocytes (NHM) were cultured on the v arious keratinocyte ECMs and initially the effects of the kECMs upon m elanocyte morphology (dendrite formation and extension), growth, melan in production and expressions of pigmentation-associated protein (MEL- 5) and proliferation-associated protein (proliferating cell nuclear an tigen; PCNA/cyclin) were studied. Then we compared the effects of thes e cell-matrix interactions with those of direct melanocyte-keratinocyt e, cell-cell contact in co-culture on melanocyte functions. Melanocyte s cultured on any types of the kECMs that were tested significantly ex tended dendrites more than that on plastic cell culture dish without k ECM (control). Melanocytes cultured on the kECM prepared from UVB irra diated differentiating keratinocytes resulted in 219% increase in the number of dendrites. The growth of melanocytes on kECMs was also stimu lated up to 280% of control. The kECM produced by proliferating kerati nocytes had a more significant effect on the growth than kECM from dif ferentiating keratinocytes. This melanocyte growth stimulating effect was decreased with kECM from UVB treated differentiating keratinocytes . The melanin content per melanocyte was constant on any of the kECMs. Expression of pigmentation-associated protein detected by monoclonal antibody, MEL-5, was not changed on the kECM, while it was increased i n melanocytes in co-culture with keratinocytes. Expression of PCNA/cyc lin in melanocytes cultured on kECMs was generally downregulated on kE CM and in co-culture compared to that in a control culture. We demonst rated that the kECMs play important roles in the melanocyte morphology and proliferation. These observations suggest that environmental (WE) and physiological (Ca++) stimuli can regulate melanocyte functions th rough the keratinocyte extracellular matrix in vivo.