Degradation of alpha‐melanocyte stimulating hormone (alpha‐MSH) by CALLA/endopeptidase 24. 11 expressed by human melanoma cells in culture

Abstract

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.

Immunosuppressive effects of corticotropin and melanotropin and their possible significance in human immunodeficiency virus infection.

“…In addition, blockage of MSH degradation by phosphoramidon (Fig. 3) is consistent with NEP activity (23 (33), but their failure to find induction of POMC mRNA after infection may be due to differences in the length of infection time.…”

Bacterial lipopolysaccharide (LPS) and interleukin 1 (IL-1) exert multiple physiological effects in the tilapia Oreochromis mossambicus (Teleostei)

“…In mammals alternative processing of A C T H 1-39 to ACTHi-24 has been demonstrated in lymphocytes si mulated by LPS (Smith et al 1990). Degradation of authentic a-MSH by endopeptidase 24.11, which is I esent on the surface of pre-B lymphocytes, could also \ Id alternative immunoreactive forms of a-MSH >eschodt- Lanckman et al 1990). These are of interest, because regulation of interrenal cortisol production in 1 Icosts by a-MSH appears extremely sensitive to modifications of the molecule, such as alterations of the e iin length and the degree of acetylation (Ranee and 1 ker 1981).…”

Induction of autocrine factor inhibiting cell motility from murine B16-Bl6 melanoma cells by ?-melanocyte stimulating hormone

“…Since ␣-MSH is of small size (Mr: 1664,9), it may have been included in the fraction (M r Յ 3 kDa). However, it is unlikely that ␣-MSH remained intact in CM, because ␣-MSH is rapidly degraded to small fragments by endopeptidase 24.11 on the surface of melanoma cells in culture (Deschodt-Lanckman et al, 1990). In addition, ␣-MSH at 10 Ϫ6 M is inactivated by trypsin digestion (data not shown), while the fraction (M r Յ 3 kDa) was insensitive to trypsin.…”