Title : The
receptor for
alpha-melanotropin of mouse and human melanoma cells
Abstract :
- Application of a potent alpha-melanotropin photoaffinity label
- The melanotropin ( MSH ) receptor of mouse B16-F1 melanoma cells was characterized by photoaffinity cross-linking, using a potent alpha- MSH photolabel, [norleucine4, D- phenylalanine7 , 1'-(2-nitro-4-azidophenylsulfenyl)- tryptophan9 ] -alpha-melanotropin (Naps- MSH )
- Its monoiodinated form, 125I-Naps- MSH , displayed a approximately 6.5-fold higher biological activity than alpha-MSH
- Scatchard analysis of the saturation curves with 125I-Naps- MSH revealed approximately 20,000 receptors/B16-F1 cell and an apparent KD of approximately 0.3 nM
- Analysis of the cross-linked MSH receptor by sodium dodecyl sulfate-polyacrylamide gel electrophoresis showed that a photolabeled band of approximately 45 kDa occurs in B16-F1, B16- F10 , and Cloudman S91 mouse melanoma, as well as in human D10 and 205 melanoma but not in non-melanoma cells
- The labeled 45-kDa protein had an isoelectric point of 4.5-4.9 as determined by two-dimensional gel electrophoresis
- Treatment of the labeled 45-kDa protein of B16-F1 cell membranes by neuraminidase shifted the band to approximately 42 kDa
- A similar band of about 42 kDa was also observed after receptor labeling of B16-W4 cells, a cell line with a decreased number of terminal N-linked neuraminyl residues
- These results indicate that the labeled 45-kDa glycoprotein contains terminal sialic acid residues, explaining the low pI of this protein , and that it is characteristic for melanoma cells and hence part of the MSH receptor