The Effect of α‐MSH on the Attachment of Human Melanocytes to Laminin and Fibronectin: Evidence for Specific α‐MSH Receptors on These Cells a

Although it has been reported that a-melanocyte-stimulating hormone (a-MSH) fails to influence melanogenesis in cultured human melanocytes,l this does not preclude the hormone from having other effects on these cells. Since extracellular matrix (ECM) may regulate melanogenesis in human melanocytes,* we have investigated the effects of a-MSH on the attachment of human melanocytes to laminin (LM) and fibronectin (FN). Cells were cultured in MCDB 153 supplemented with various growth factors and 0.5-1% fetal calf serum. Three days prior to the assay, the medium was adjusted to 1 mM Ca2+ * M a-MSH. Cell fattening and an increase in dendricity were observed within 12 h of the addition of a-MSH. Tissue culture wells were preincubated with LM or FN, bovine serum albumin, or phosphate buffer alone. Cell adherence in serum-free medium at 2 h was quantitated either by prelabeling the cells with 3H-thymidine,3 or by staining adherent cells with crystal vi01et.~ Both methods produced a similar trend of results. Treatment with a-MSH significantly increased attachment to LM and FN ( p < 0.05 in each case for the data in FIGURE I) . These observations imply that human melanocytes have a-MSH receptors that are functional at the level of signal transduction. The presence of specific a-MSH binding sites was confirmed using 1251-Nle4~Phe7 a-MSH': the mean K , value was 4.9 x lo-" M and there was a mean of 700 binding sites/cell (FIGURE 2 ) . The present results demonstrate that human melanocytes express MSH receptors. Binding of a-MSH to its receptor would appear to alter both melanocyte morphology and the interaction of the cells with ECM proteins. While the effect on morphology may involve alterations to the cytoskeleton, the effects on attachment suggest an action on the LM and FN receptors, the VLA proteins of the integrin family. The latter could represent either an increase in the numbers of LM and FN receptors or a change in the specificity or affinity of the integrin for its ligand.' Since integrins act as a transmembrane bridge between the extracellular matrix and the cytoskeleton, these effects of a-MSH on morphology and attachment may