Biomedical subjects
Publications and source records attributed to A Slominski.
Expression of mRNA hybridizable to murine POMC cDNA, and immunoreactivity specific for POMC derived peptide, beta-endorphin, are reported for the first time in one murine and two hamster melanoma lines. The apparent sizes of POMC mRNA transcript were 3.5, 1.5 and 1 kb. It is suggested that POMC gene expression may be involved in the autoregulation of the melanoma phenotype at the cellular and tissue levels.
Exposure of hamster amelanotic melanoma cells to L-tyrosine caused a time-dependent increase of tyrosinase protein concentrations, tyrosinase activity and level of cell pigmentation. In contrast, Northern blot analysis using mouse tyrosinase cDNA showed a steady level of tyrosinase mRNA. Thus in hamster melanoma cells the stimulation of intracellular tyrosinase concentration by L-tyrosine is mediated mainly via a posttranscriptional mechanism.
Crosslinking of [14C]L-tyrosine to at least five hamster melanoma cell surface proteins is reported. This effect was abolished by addition of nonradioactive L-tyrosine, L-phenylalanine, or L-dopa, but not by D-tyrosine, tyramine, dopamine, norepinephrine, or epinephrine. The above proteins can be purified by tyrosine-affinity chromatography. They have molecular weights different from proteins staining for dopa oxidase and proteins that bind anti-tyrosinase antibody in Western blots. It is suggested that they may be a hithergo unrecognized part of the cellular apparatus governing melanogenesis.
Exposure of hamster amelanotic melanoma cells to L-dihydroxyphenylalanine (L-DOPA) resulted in a time dependent increase of cell pigmentation, tyrosinase concentration and activity with peak after 24 hours. Northern blot analysis showed a small but reproducible increase of tyrosinase mRNA after 3 hours and a decrease below the control level after 9 hours. After 24 and 48 hours tyrosinase mRNA was undetectable. It is suggested that L-DOPA or its oxidation products can stimulate intracellular tyrosinase concentration and regulate tyrosinase mRNA level both in positive and negative fashion.
In C57 Bl-6 mice, melanogenesis is strictly coupled to the growth phase of the hair cycle (anagen). To further study this phenomenon of concerted developmental and pigmentary activity, we followed the sequence of tyrosinase (key enzyme of melanogenesis) expression and activity and the presence of the melanosomal protein gp 75 during the development of traumatically induced anagen follicles (days 0 = telogen, and days 1-12, after anagen induction studied). In addition to performing Northern and Western blots for tyrosinase, tyrosine hydroxylase activity (THA) and dopa oxidase activity (DOA) were measured. On day 0, DOA was undetectable, and THA was very low. On days 1 and 2, both activities were undetectable; starting from day 3, they increased rapidly, reaching a plateau on days 8 and 12. DO-positive proteins had apparent molecular weights (MW) of 66-68 kD (days 3-12), 72-74 kD (days 5-12), and 130 kD (days 8 and 12). Western blotting emphasized proteins of MW 66-68 kD (tyrosinase), and 73-75 kD (gp 75); tyrosinase was undetectable on day 0, but already present on days 1 and 2; it increased by day 5 and had reached a plateau on days 8 and 12; gp 75 was undetectable on days 0-2; it was present on day 3, increased by day 5, and reached a plateau on days 8 and 12. Northern blot analysis revealed high levels of tyrosinase mRNA on days 5 and 8, low levels on days 1-3, and none on day 0. These data suggest a highly regulated, time frame-restricted, differential pattern of tyrosinase transcription, translation, and enzyme activity during the different stages of the developing murine anagen follicle, possibly as a result of complex interactions between follicular melanocytes and their environment.
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The stimulation of melanogenesis by L-tyrosine in hamster melanoma is several-fold higher than that by norepinephrine, epinephrine, clonidine and isoproterenol and absent in the case of tyramine dopamine and phenylephrine. Therefore, the melanogenic effect of L-tyrosine in hamster melanoma follows a different pathway than that linked to the activation of dopaminergic and adrenergic receptors.
Some amino acids have bioregulatory functions, which far exceed those of precursors for proteins or of substrates for specific enzymes. Two of these amino acids, L-tyrosine and L-dopa, are precursors to melanin and catecholamines. In vertebrates, they can act as inducers and regulators of the melanogenic apparatus and of MSH receptors--two quite complex functions that could hardly be performed by mere substrates. Focussing on the pigmentary system as a study model, we therefore explore the hypothesis that L-tyrosine and L-dopa act as hormone-like bioregulators in mammals, with melanocytes regulating tyrosine and dopa activity via their metabolic consumption.
The glycosphingolipid compositions of Bomirski melanomas at different stages of differentiation, including Ab amelanotic melanoma (fast growing), Ma melanotic melanoma (slow growing), and MI hypomelanotic melanoma (slow growing), were studied. The total concentration of lipid-bound sialic acid in Ab amelanotic melanoma was found to be much lower than those in Ma and MI melanomas (0.8 micrograms versus 1.4 micrograms and 1.4 micrograms/mg of dry tissue, respectively). The ganglioside patterns in melanoma tissues were composed mainly of three components, which were confirmed as NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer (GM3), acetyl1-9-O-NeuAc alpha 2-8NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer (9-O-acetyl-GD3), and NeuAc alpha 2-8NeuAc alpha 2-3Gal beta 1-4Glc beta 1-1'Cer(GD3) by structural analysis and monoclonal antibody detections. However, the relative ratios of these gangliosides expressed in the different types of melanomas were completely different. The MI melanoma tissues contained GM3 as the predominant species (greater than 90% of the total gangliosides) with very little of GD3 and 9-O-acetyl-GD3 gangliosides (less than 2% of the total gangliosides). In contrast, Ab amelanotic melanomas contained mainly 9-O-acetyl-GD3 (greater than 27%) and GD3 (greater than 51%) with lesser amounts of GM3. However, Ma melanoma had intermediate levels of GM3, GD3, and 9-O-acetyl GD3. The MI and Ma melanomas also contained monohexosylceramide (GL1) (about 60% as Gal beta 1-1'Cer and 40% as Glc beta 1-1'Cer in Ma and 30% as Gal beta 1-1'Cer and 70% as Glc beta 1-1'Cer in MI) and Gal beta 1-4Glc beta 1-1'Cer as the predominant neutral glycosphingolipid species. In contrast, Ab melanoma tissues contained more GalNAc beta 1-3GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc beta 1-1'Cer (Gb5), Gal alpha 1-4Gal beta 1-4Glc beta 1-1'Cer (Gb3), and GalNAc beta 1-3Gal alpha 1-4Gal beta 1-4Glc beta 1-1'Cer (Gb4) than MI and Ma melanomas. Our data suggest that the expression of glycosphingolipids in hamster melanoma cells may be closely related to cell growth and the degree of differentiation, with slow growing, highly differentiated cells expressing GM3 and GL1, and fast growing, undifferentiating cells having a preponderance of GD3, 9-O-acetyl-GD3, Gb5, Gb3, and Gb4.
L-tyrosine, a precurosr to melanin, has recently been shown to be a regulator of the melanogenic pathway in some cultured melanoma cell lines. In this paper we demonstrated that L-tyrosine, besides increasing binding capacity for MSH, decreased cooperativity between MSH receptors and increased the level of tyrosinase induction by MSH. Apparently, regulation of MSH receptor activity by L-tyrosine involves specific changes in the interactions between the receptors and modification of the cellular responsiveness to MSH.
In cultured amelanotic hamster melanoma cells L-tyrosine induces melanogenesis. This induction involves an increase in intracellular concentration of proteins precipitated by polyclonal anti-tyrosinase antibodies, and stimulation of the Vmax of tyrosinase activity. Therefore it is suggested that in hamster melanoma cells L-tyrosine induces synthesis of tyrosinase and melanogenesis related proteins.
A new unifying hypothesis for the aetiology of vitiligo is proposed, in which we postulate that the final destruction of melanocytes in vitiligo results from a cascade of reactions initiated by a disregulation of melanogenesis, caused by activation of the melatonin receptor. These events result in the high and uncontrolled production of free radicals and toxic products of melanogenesis which sequentially damage or destroy melanocytes and keratinocytes, provoke an autoimmune response against exposed intracellular or altered cell surface antigens, and increase the propensity of melanocytes to undergo malignant transformation.
In Bomirski Ab amelanotic hamster melanoma cells, L-tyrosine and/or L-dopa induce increases in tyrosinase activity as well as synthesis of melanosomes and melanin. L-tyrosine also modifies melanocyte-stimulating hormone (MSH) binding. In this paper we show that in the Bomirski amelanotic melanoma system MSH and agents that raise intracellular cyclic AMP induce dendrite formation, inhibit cell growth, and cause substantial increases in tyrosinase activity without inducing melanin synthesis. Tyrosinase activity is detected only in broken cell preparations, or cytochemically in fixed cells. In the continued absence of mature melanosomes, the induced enzyme remains in elements of the trans-Golgi reticulum. Comparative measurements of cyclic AMP in amelanotic and tyrosine-induced melanotic cells show similar basal levels. L-tyrosine and L-dopa have little or no effect, whereas MSH may cause a 1000% peak increase in cyclic AMP levels both in amelanotic and melanotic cells. None of these agents influences cyclic GMP or inositol trisphosphate (InsP3) levels. In agreement with the InsP3 assays, phorbol ester (TPA) has no effect on melanization, tyrosinase activity or cell proliferation. In conclusion, in the Bomirski amelanotic melanoma, MSH induces only partial cell differentiation associated with raised levels of cyclic AMP. Induction of melanosome synthesis and melanization by L-tyrosine or L-dopa appear to follow pathways unrelated to cyclic AMP, cyclic GMP or InsP3.
Bomirski Ab amelanotic melanoma cells have recently been shown to undergo striking phenotypic changes when precursors of the melanogenic pathway, L-tyrosine and L-dopa, are added to the culture medium. The changes include increased tyrosinase activity and de novo synthesis of melanosomes and melanin. L-tyrosine and L-dopa appeared to elicit these responses through separate but overlapping regulatory pathways. Here we show an additional effect of L-tyrosine: stimulation of MSH binding capacity. Cells cultured for 24-48 hours in the presence of 200 microM L-tyrosine display a 3-4 fold increase in their ability to bind 125I-beta-MSH. L-dopa did not stimulate MSH binding under the same conditions. In control experiments neither L-tyrosine nor L-dopa had any effect on insulin binding. The amelanotic cells respond to MSH with increased dendrite formation, increased tyrosinase activity without melanin production, and decreased growth rate.
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Explore the source record for details and available documents.
Explore the source record for details and available documents.