Comparison of TRPs from murine and human malignant melanocytes.

Most of our knowledge of the mammalian tyrosinase related protein (TRP) activities is derived from studies using murine melanoma models, such as B16 or Cloudman S-91 melanocytes. Owing to the high degree of homology between the murine and human enzymes, it has been assumed that their kinetic behaviour could be similar. However, the protein sequences at the metal binding sites of the murine and human enzymes show some differences of possible functional relevance.

Immunoreactive alpha-melanotropin as an autocrine effector in human melanoma cells.

Melanotropin is a peptide having several functions, including the stimulation of melanogenesis and the modulation of proliferation of melanocytes and melanoma cells. It acts through binding to high-affinity receptors of the melanocortin-1 subtype, exclusively expressed in cells of the melanocytic lineage. Elevated levels of immunoreactive alpha-melanotropin were previously reported in melanoma cell lines, tumours and plasma from patients with melanoma.

Cysteine deprivation promotes eumelanogenesis in human melanoma cells.

Melanocytic cells can produce two types of pigment, pheomelanin or eumelanin. We used two types of human melanoma cell lines to explore the regulation of pigmentation by biochemical and enzymatic studies. These two cell lines were previously designated as either pheomelanotic or of mixed type when cultured in a medium rich in cysteine.

Tyrosinase and related proteins in mammalian pigmentation.

Tyrosinase is the key enzyme in pigment synthesis, initiating a cascade of reactions which convert the amino acid tyrosine to the melanin biopolymer. Two other tyrosinase-related proteins (TRP) are known, TRP-1 (probably DHICAoxidase) and TRP-2 (DOPAchrome tautomerase). These proteins show about 40% homology, and recent results have indicated that the genes might be derived from a common ancestor.

African origin of an intragenic deletion of the human P gene in tyrosinase positive oculocutaneous albinism.

Oculocutaneous albinism (OCA) is a genetically heterogeneous hypopigmentation disorder. One of the two major autosomal recessive forms involves the tyrosinase gene (OCA1), while the other form (OCA2) has recently been associated with alterations of the P gene on chromosome 15. OCA2 is about twice as common as OCA1 in African and African-American populations.

Molecular characterization of a human tyrosinase-related-protein-2 cDNA. Patterns of expression in melanocytic cells.

Pigmentation in mammals is under complex genetic control. Amongst the genes involved in this process, those encoding tyrosinase and the tyrosinase-related-proteins 1 and 2 have been well characterized and share a number of features. Recently, the murine tyrosinase-related-protein-2 gene was shown to encode dopachrome-tautomerase activity and was mapped to the slaty locus.

Glutathione depletion increases tyrosinase activity in human melanoma cells.

The aim of the present work was to estimate the effect of intracellular glutathione depletion on melanogenesis in human melanoma cells. We determined tyrosine hydroxylation activity, the rate-limiting step of the pathway, and 14C-melanin formation, an assay reflecting the global eumelanogenic pathway. Intracellular glutathione was depleted by treatment with buthionine-S-sulfoximine, a well-known inhibitor of gamma-glutamylcysteine synthetase.

TRP-1 expression correlates with eumelanogenesis in human pigment cells in culture.

We have investigated the relationship in human cultured normal and malignant melanocytes between the accumulation of mRNAs encoding tyrosinase and tyrosinase-related protein-1 (TRP-1), the activity of tyrosinase and the presence of melanin. Tyrosinase mRNA correlates with tyrosinase activity and with the presence of pheomelanin, eumelanin or both melanin types. In contrast TRP-1 mRNA is only detectable in cells containing eumelanin, which suggests a role for TRP-1 in the eumelanin synthesis pathway.

Partial characterization of IR-alpha-MSH peptides found in melanoma tumors.

Our previous work indicated that IR-alpha-MSH (immunoreactive alpha-melanocyte-stimulating hormone) plasma levels are three times as high in melanoma patients with progressing disease than in disease-free patients, and that the melanoma tumor itself may be the source of IR-alpha-MSH. Further identification of the material in tumor extracts has been carried out in this study, and the results presented here show that the immunoreactivity is associated with a major fraction of about 16 kDa and another of 5-9 kDa. Significant amounts of the immunoreactive material were also found in human melanoma cells but not in culture supernatants.

Studies on factors influencing human plasma alpha-MSH.

The various physiological effects of alpha-MSH, mainly on the CNS and on pigmentation in animal models, are well documented in the literature. Only a few investigators have confirmed similar properties in the human. However, the possible physiopathological role played by this hormone in human melanoma is still poorly defined.