Paracrine stimulation of melanocytes by keratinocytes through basic fibroblast growth factor

Melanocytes cultured in the presence of keratinocytes survive for weeks without added basic fibroblast growth factor (bFGF) and cyclic-adenosine-monophosphate (cAMP), the two factors needed for their proliferation in vitro. We show here that the growth factor for melanocytes produced by human keratinocytes is bFGF because its activity can be abolished by neutralizing antibodies to bFGF and by a bFGF synthetic peptide that inhibits the binding of the growth factor to its receptor. The melanocyte mitogen in keratinocytes is cell-associated and increases after irradiation with ultraviolet B (UVB). Northern blots reveal bFGF gene transcripts in keratinocytes but not melanocytes. These studies demonstrate that bFGF elaborated by keratinocytes in vitro sustains melanocyte growth and survival, and they suggest that keratinocyte-derived bFGF is the natural growth factor for normal human melanocytes in vivo.