Degradation of alpha-melanocyte stimulating hormone (alpha-MSH) by CALLA/endopeptidase 24.11 expressed by human melanoma cells in culture.
The common acute lymphoblastic leukemia antigen (CALLA) is identical to human endopeptidase 24.11 (E-24.11) and is expressed on certain human melanoma lines. This work was conducted in order to investigate whether alpha-melanocyte-stimulating hormone (alpha-MSH) could be a substrate for E-24.11, its degradation leading to the negative alpha-MSH radiobinding assay results observed with some CALLA-positive cell lines. We used 3 human melanoma cell lines (GLL-19, Mel Juso and G361) which lack receptors to alpha-MSH and express CALLA, and, as a control, one CALLA-negative melanoma cell line (HBL) with specific receptors for alpha-MSH. Radioimmunoassays give evidence that alpha-MSH was degraded in the presence of the 4 melanoma cell lines and that disappearance of the peptide was significantly reduced by phosphoramidon in 2 lines (GLL-19 and G361). Upon incubation of alpha-MSH with GLL-19 and G361 cell membranes, 3 degradation products were completely abolished in the presence of phosphoramidon. Amino acid content analysis of alpha-MSH fragments produced by purified E-24.11 permitted identification of 6 peptide bonds in the sequence of alpha-MSH susceptible to cleavage by the enzyme. It is concluded that alpha-MSH is a substrate in vitro for purified E-24.11 and for the enzyme present on the human melanoma cell lines GLL-19 and G361, expressing a high level of endopeptidase activity. However, hydrolysis of alpha-MSH by this enzyme does not seem to represent the main factor responsible for the apparent absence of receptors for the hormone on some cell lines.
Deschodt-Lanckman
M
M
Laboratoire Pluridisciplinaire de Recherche Expérimentale Biomédicale, Faculté de Médecine, Université Libre de Bruxelles, Belgium.
Vanneste
Y
Y
Loir
B
B
Michel
A
A
Libert
A
A
Ghanem
G
G
Lejeune
F
F
D000595:Amino Acid Sequence; D000943:Antigens, Differentiation / Q000096:biosynthesis / Q000378:metabolism*; D000951:Antigens, Neoplasm / Q000096:biosynthesis / Q000378:metabolism*; D000954:Antigens, Surface / Q000096:biosynthesis / Q000378:metabolism*; D006801:Humans; D008545:Melanoma / Q000201:enzymology*; D008969:Molecular Sequence Data; D015260:Neprilysin / Q000096:biosynthesis / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D000521:alpha-MSH / Q000032:analysis / Q000378:metabolism*
D000943:Antigens, Differentiation; D000951:Antigens, Neoplasm; D000954:Antigens, Surface; D000521:alpha-MSH; D015260:Neprilysin