Melanocyte stimulating hormone activation of tyrosinase in B16 mouse melanoma cells Evidence for a differential induction of two distinct isoenzymes

Tyrosinase induction in murine malignant melanocytes by alpha MSH is well known, but its molecular basis has not been characterized. Treatment of B16 melanoma cells with theophylline or alpha MSH mediates a larger induction of tyrosine hydroxylase than of dopa oxidase activity in total cell extracts, and in the melanosomal and microsomal fractions. No evidence for the modulation of a tyrosinase effector was found. SDS-PAGE and specific activity stain demonstrated two forms of tyrosinase, with different degrees of induction by theophylline. These results agree with the recent proposal that two tyrosinases, encoded by different genes, are present in murine melanocytes.

Serum ceruloplasmin in melanoma patients

We have studied the serum ceruloplasmin levels as a possible diagnostic factor or marker for detection, diagnosis and follow-up of patients with melanoma. Ceruloplasmin concentration was determined in 64 melanoma patients (MP) and in 37 healthy persons (HP) by nephelometry. We found a mean value of 29.85 +/- 5.47 mg/dl in MP and 26.10 +/- 5.22 mg/dl in HP. A significant increase in the levels of serum ceruloplasmin was observed in MP in comparison to those in HP (P = 0.0011). In order to check whether this test could discriminate between MP and HP, a complete statistical Receiver Operating Characteristic (ROC) curve analysis was performed. The cut-off value was 25.10 mg/dl. The area under the curve was 0.689. According to these results, the test could discriminate adequately between the two groups.

Melanization stimulating factors in the integument of the Mugil cephalus and Dicertranchus labrax

The pigment pattern expression resides in the chromatoblasts of the embryonic skin. The differentiation of these chromatoblasts is influenced by specific local factors such a melanization inhibiting factor (MIF) and a melanization-stimulating factor (MSF). We reveal the presence of these factors by means of a series of experiments on the skin of the marine species of fish Dicertranchus labrax and Mugil cephalus, each with different pigment pattern, the former having a light skin and the latter a darker one. Media conditioned by exposure to dorsal and/or ventral skin, stimulates the melanization of Xenopus laevis neural crest cells throughout a 3 day assay period. Similarly conditioned culture media tested on B16-F10 murine malignant melanocytes, revealed a considerable influence in enzymatic activities: dopachrome tautomerase (DCT), tyrosine hydroxylase and dopa oxidase. The use of media in a dose response basis suggests that the conditioned media may contain both melanophore stimulating and inhibiting factors. The results obtained may actually reflect the resultant activity of the two factors present.

Whole blood glutathione peroxidase activity in melanoma patients

We have studied whole blood glutathione peroxidase activity as a possible diagnostic factor or marker for detection and diagnosis of patients with melanoma. This activity was determined in 40 melanoma patients (MP) and in 40 healthy persons (HP) using an enzymatic method. We found a mean value of 17.90+/-6.82 units/ml in MP and 27.07+/-14.35 units/ml in HP. A very significant decrease in whole blood glutathione peroxidase activity was observed in MP in comparison to the enzymatic activity in HP (P = 0.0005). In order to check whether this test could discriminate between MP and HP, a complete statistical Receiver Operating Characteristic (ROC) curve analysis was performed. The cut-off value was 14.26 units/ml. The area under the curve was 0.737. According to these results, the test could discriminate adequately between both groups. However, the high specificity and low sensitivity values associated with that cut-off value would make this test a very valuable tool for confirming the detection, rather than for primary screening.

Serum sialic acid in malignant melanoma patients: an ROC curve analysis

We have studied the total serum sialic acid as a possible diagnostic factor for the prognosis of patients with melanoma. The sialic acid concentration was determined in the sera of fifty melanoma patients (MP) and forty healthy persons (HP), by using an enzymatic method. We found a mean value of 67.52 +/- 17.32 mg/dl in MP and 57.11 +/- 12.98 mg/dl in HP (p < 0.005). In order to check whether this test could discriminate adequately between MP and HP, a complete statistical Receiver Operating Characteristic (ROC) curve analysis was performed. The cut-off value was 62.39 mg/dl. The area under the curve was 0.661. According to these results, the test could discriminate between both groups. However, due to the rise of sialic acid-rich acute-phase proteins in inflammatory processes, determination of total serum sialic acid would be more useful for diagnosis of melanoma stage and prognosis rather than for early detection and screening.

Serum tyrosine hydroxylase activity is increased in melanoma patients. An ROC curve analysis

We have studied the serum tyrosine hydroxylase activity of tyrosinase, the key enzyme in the melanogenesis via, as a possible diagnostic factor or marker for detection, prognosis and follow-up of patients with melanoma. This activity was determined in 30 melanoma patients (MP) and in 30 healthy persons (HP) by using a radiometric method. We found mean values of 10.8+/-3.0 and 7.65+/-2.32 mU/l for serum tyrosine hydroxylase activity in MP and HP, respectively. A very significant increase in serum tyrosine hydroxylase activity was observed in MP in comparison to the enzymatic activity in HP (P < 0.00001). Although these data seem very conclusive, we wanted to know whether this test could discriminate adequately between MP and HP. In order to reach this aim, a complete statistical study was performed by using receiver operating characteristic (ROC) curve analysis. The cut-off value obtained was 8.47 mU/l. According to our results and after analytical treatment of the data, we can confirm that evaluation of tyrosine hydroxylase activity in serum could be a quick and reliable diagnostic method for detection, prognosis and follow-up in melanoma patients.

Serum zinc levels are increased in melanoma patients

We studied the levels of serum copper and zinc as possible diagnostic factors or markers for the early detection of patients with melanoma. Levels were determined in 35 melanoma patients at various clinical stages and in 39 healthy persons. Measurements were performed by atomic absorption spectroscopy using 5100-PC-Perkin-Elmer equipment. We found that serum copper levels were very similar in the melanoma patients and the healthy individuals, the medium values being 118.32 +/- 25.32 micrograms/dl and 117.94 +/- 28.01 micrograms/dl, respectively. Therefore, no significant differences were observed with regard to copper levels. On the other hand, we obtained a medium value of 82.32 +/- 25.38 micrograms/dl for serum zinc levels in the melanoma patients and 56.72 +/- 11.79 micrograms/dl in the healthy persons, which represents a very significant increase in the serum levels of zinc in melanoma patients (P < 0.0001). A receiver operating characteristic (ROC) curve statistical analysis was also performed; the cut-off value obtained was 60.9 micrograms/dl. According to our results, zinc is increased in 86.5% of melanoma patients. Although further investigations are needed to assess its value in prognosis and follow-up, evaluation of serum zinc level could be a good tool to check for the presence of melanoma.

The amphibian melanization inhibiting factor (MIF) blocks the alpha-MSH effect on mouse malignant melanocytes

We have found that a melanization inhibitory factor (MIF) extracted from the ventral skin of Rana forreri has a slight inhibitory effect on the activity levels of tyrosinase and dopachrome tautomerase in B16/F10 and Cloudman S-91 murine melanoma cell lines. Furthermore, this factor appears to block the effects of alpha-MSH on these enzymatic activities. However, MIF treatment does not affect the melanogenic action of theophylline on the same cells, suggesting that MIF acts proximal to MSH-mediated cAMP formation, possibly by interaction with the MSH receptor. In this way, we show that this amphibian factor has biological activity on mammalian melanocytes. This suggests the existence of mammalian counterparts of amphibian MIF in the mouse integument that might regulate epidermal melanocytes. These peptides might be related to the agouti protein, as they share similar mechanisms of action. The interaction of different peptides with the MSH receptor would be a complex but general mechanism responsible for many mammalian coat color variants.

Molecular mechanism for catalysis by a new zinc-enzyme, dopachrome tautomerase

Dopachrome tautomerase (DCT; EC 5.3.3.12) catalyses the conversion of L-dopachrome into 5,6-dihydroxyindole-2-carboxylic acid in the mammalian eumelanogenic biosynthetic pathway. This enzyme, also named TRP2, belongs to a family of three metalloenzymes termed the tyrosinase-related proteins (TRPs). It is well known that tyrosinase has copper in its active site. However, the nature of the metal ion in the active site of DCT is under discussion. Whereas theoretical predictions based on similarity between the protein sequences of the TRPs suggest the presence of copper, the different inhibition pattern of DCT with some metal chelators compared with that of tyrosinase suggests that the nature of the metal ion could differ. Direct estimations of the metal content in purified DCT preparations show the presence of around 1.5 Zn atoms/molecule and the absence of copper. Apoenzyme preparation by treatment of DCT with cyanide or o-phenanthroline followed by reconstitution experiments of tautomerase activity in the presence of different ions confirmed that the metal cofactor for the DCT active site is zinc. Our results are consistent with Zn2+ chelation by the highly conserved histidine residues homologous to the histidines at the classical copper-binding sites in tyrosinase. This finding accounts for the reaction catalysed by DCT, i.e. a tautomerization, versus the copper-mediated oxidations catalysed by tyrosinase. Based on the predicted tetrahedrical coordination of the zinc ions in the enzyme active site, a molecular mechanism for the catalysis of L-dopachrome tautomerization is proposed. From the present data, the existence of additional ligands for metal ions other than zinc in the DCT molecule, such as the proposed cysteine iron-binding sites, cannot be completely ruled out. However, if such sites exist, they could be subsidiary binding sites, whose function would be likely to stabilize the protein.

Effect of penicillin-streptomycin and other antibiotics on melanogenic parameters in cultured B16/F10 melanoma cells

Penicillin and streptomycin, the most widely used antibiotics in mammalian cell cultures, caused a moderate stimulation in dopa oxidase and tyrosine hydroxylase activities, but a slight inactivation in the dopachrome tautomerase activity of B16/F10 melanoma cells at the routine concentration (100 units/ml penicillin and 100 micrograms/ml streptomycin) used for preventing bacterial growth in cultured animal cells. At these concentrations, tyrosinase activities and melanin content augmented with time during the first 24-48 hr. The opposite effect acted on cell viability. After withdrawal of the antibiotics from the culture medium, the recovery of melanogenic parameters to normal values was fully reached after few hours (around 10), and it was already noticeable as soon as 4 hr after removal. Other antibiotics used in cell culture, like kanamycin, gentamicin, and the antimicotic nystatin, exerted similar low effects at the recommended concentrations, always lower than two-fold and thus lower than those reported for amphotericin B. Taking into account these relatively low effects, and the high risk of contamination of mammalian cells culture without antibiotics, penicillin and streptomycin may still be routinely used in experiments leading to explore the melanogenic activity of malignant melanocytes in culture, unless very precise studies and strict conditions were needed.

Melanization stimulating activity in the skin of the gilthead porgy, Sparus auratus

The presence of a melanization-stimulating factor (MSF) was discovered in dorsal and/or ventral skin of Sparus auratus. Skin from this marine species was used to condition Steinberg's balanced salt solution (BSS), which was subsequently tested with the neural tube assay. BBS conditioned by dorsal and/or ventral skin of S. auratus at 25% and 50% concentrations had a profound stimulatory effect on the percentage of melanization of neural crest cells throughout the 3-day assay period. In some cases 90% melanization occurred within the first 24 hr. Such stimulated cells showed a doubling of the number of dendrites per cell. To assess the effects of MSF on other indices of melanization, dorsal and/or ventral skin was used to condition MEM used in the culture of B16-F10 murine melanoma cells. During the first 24 hr, B16-F10 murine melanoma cells responded to conditioned media by demonstrating a considerable increase in activities of tyrosine hydroxylase, dopa oxidase, and dopachrome tautomerase, but no effect was observed on melanin content. In contrast, melanin content increased after 48 hr of incubation, whereas the enzymatic activities were inhibited during this period. It seems that MSF activity, expressed in several ways, may be present generally among marine species.

Effect of amphotericin B on dopachrome tautomerase activity and other melanogenic parameters in cultured B16/F10 melanoma cells

The antifungal reagent Fungizone (amphotericin B and deoxycholate) caused an activation in dopachrome tautomerase and dopa oxidase activities of B16/F10 melanoma cells at the routine concentration (2.5 micrograms/ml) used for preventing molds and yeast growth in cultures of animal cells. However, higher amphotericin B concentrations caused a significant cell death and the inhibition of enzymatic activities. At the optimal concentration of Fungizone, the enzymatic activities and melanin content were augmented as incubation time increased. The detergent sodium deoxycholate alone exerted no effect on these melanogenic parameters, eliminating the possibility that this detergent was partially responsible for melanogenic modifications produced by Fungizone. After withdrawal of Fungizone from the reaction medium, the recovery of melanogenic parameters to normal values was slower for DCT than for tyrosinase. The behavior of dopa oxidase was very similar to that reported by Johnson and Bagnara (Pigment Cell Res. 3, 173-175) for tyrosine hydroxylase.

Alpha-MSH and other melanogenic activators mediate opposite effects on tyrosinase and dopachrome tautomerase in B16/F10 mouse melanoma cells

alpha-MSH was found to decrease the recently characterized dopachrome tautomerase activity in cultures of B16/F10 mouse melanoma cells. Other stimulating agents of melanogenesis, like dibutyryl cyclic AMP, 3-isobutyl-1-methylxanthine, theophylline, retinol, and retinoic acid, caused the same effect. The grade of inhibition depended on the nature of the agent and the time of exposure. In all cases, both melanin production and tyrosinase activity were activated by these treatments, although the grade of tyrosine hydroxylase and dopa oxidase stimulation was different. Moreover, no correlation among the intensities of dopachrome tautomerase inhibition and tyrosinase activation by the tested agents could be obtained. The significance of these results in the regulation of mammalian melanogenesis is discussed.