Increased level of p27 subunit of proteasomes and its co-localization with tyrosinase in amelanotic melanoma cells indicate its direct role in the regulation of melanin biosynthesis

Abstract

Proteasomes have been shown to be involved in the regulation of melanin biosynthesis in melanoma cells. Here we report on the correlation between proteasome subunits and Tyrosinase (Tyr) activity in different cell phenotypes, and thereby regulation of melanin biosynthesis in B16F10 mouse melanoma cells. Our results indicated that the quantity of proteasome subunit p27 is higher and that of the enzyme Tyr and its activity are lower in amelanotic melanoma cells, while the reverse is true in melanotic melanoma cells. Proteasome subunit p27, compared to another subunit p31, shows increased co-localization with Tyr and Tyrosinase related protein 1 (Trp1) in amelanotic cells to a greater extent than that in melanotic cells. On exposure to cycloheximide, increased Tyr degradation was seen in amelanotic cells, as indicated by increased co-localization of p27 and Tyr. Further, exposure of amelanotic melanoma cells with proteasome-specific inhibitor MG132 resulted in an increased Tyr activity, increased levels of Tyr and Trp1, leading to increased melanin synthesis. These results therefore suggest that proteasomes, particularly p27 subunit, are directly involved in the regulation of melanin biosynthesis in mouse melanoma cells.

p38 Regulates Pigmentation via Proteasomal Degradation of Tyrosinase

“…Tyrosinase and TRP-1 are degraded endogenously at least in part by proteasomes (52, 58 -60), which are multicatalytic protease complexes that selectively degrade intracellular proteins. Previously, Ando et al (58) reported that fatty acids, the major components of cell membranes, are able to regulate the proteasomal degradation of tyrosinase by relative increases or decreases in ubiquitinated tyrosinase (59,60). Consistently, we demonstrated that, in B16 cells and in NHM, p38 modulates melanogenic enzyme abundance, reinforcing the concept that post-transcriptional regulation might play a crucial role in the melanogenic pathway.…”

Glycosylation of tyrosinase is a determinant of melanin production in cultured melanoma cells

“…The majority of MMs produce melanin, and the degree of melanin synthesis differs for each type of cultured cell line (4)(5)(6). For example, MNT-1 cells were demonstrated to be highly pigmented MMs (4); however, SK-Mel-28 cells were not able to produce melanin due to a mutation in the endocytic pathway that affected the endosomal trafficking of tyrosinase (5).…”

“…For example, MNT-1 cells were demonstrated to be highly pigmented MMs (4); however, SK-Mel-28 cells were not able to produce melanin due to a mutation in the endocytic pathway that affected the endosomal trafficking of tyrosinase (5). In addition, B16F10 cells were pigmented; whereas amelanotic melanoma was not pigmented, due to the increased expression of proteasome subunit p27 (6).…”