Inhibition of melanosome transfer from melanocytes to keratinocytes by lectins and neoglycoproteins in an in vitro model system

We propose that some of the critical molecules involved in the transfer of melanosomes from melanocytes to keratinocytes include plasma membrane lecti ns and their glycoconjugates, To investigate this mechanism, co-cultures of human melanocytes and keratinocytes derived from neonatal foreskins were e stablished. The process of melanosome transfer was assessed by two experime ntal procedures, The first involved labeling melanocyte cultures with the f luorochrome CFDA, Labeled melanocytes were subsequently co-cultured with ke ratinocytes, and the transfer of fluorochrome assessed visually by confocal microscopy and quantitatively by Row cytometry, The second investigative a pproach involved co-culturing melanocytes with keratinocytes, and processin g the co-cultures after 3 days for electron microscopy to quantitate the nu mbers of melanosomes in keratinocytes, Results from these experimental appr oaches indicate significant transfer of dye or melanosomes from melanocytes to keratinocytes that increased with time of co-culturing. Using these mod el systems, we subsequently tested a battery of lectins and neoglycoprotein s for their effect in melanosome transfer. Addition of these selected molec ules to co-cultures inhibited transfer of fluorochrome by approximately 15- 44% as assessed by Row cytometry, and of melanosomes by 67-93% as assessed by electron microscopy, Therefore, our results suggest the roles of selecte d lectins and glycoproteins in melanosome transfer to keratinocytes in the skin.