Melanogenic Regulatory Factors in Coated Vesicles from Melanoma Cells

Chakraborty, Ashok; Mishima, Yutaka; Inazu, Mizuho; Hatta, Susumu; Ichihashi, Masamitsu

doi:10.1111/1523-1747.ep12319736

Cited by 44 publications

(23 citation statements)

References 18 publications

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“…The Sephadex G-100 column used was not calibrated, but it is clear that DHICA/melanins obtained in the presence of DCT are smaller than the DHI/melanins function of the ratio between DCT and tyrosinase activities. In agreement with this, the subcellular distribution of DCT matched perfectly that of a hypothetical indole-blocking activity, when both activities were measured independently in different melanocyte organelles [24].…”

Section: L-dopa a L-dopachromesupporting

confidence: 79%

“…Chakraborty et al [24] found that tyrosinase, DC'T and DHICA cocxist in coated vesicles of malignant melanocytes, but melanin is not formed in this compartment. This was explained in terms of the presence of the indole-blocking factor, which could prevent the incorporation of DHICA to melanin.…”

Section: L-dopa a L-dopachromementioning

confidence: 99%

“…Some authors still assume the existence of three factors different from tyrosinase, and the distribution of such activities in melanosomes and coated vesicles from malignant melanocytes has been reported [24]. Furthermore, an enzyme similar to mammalian DCT, isolated from insect cuticles, which catalyzes the decarboxylative transformation of L-dopachrome to DHI, has also been described Therefore, it should be interesting to clarify how many proteins with a catalytic activity different from tyrosinase are actually needed to account for the available data on melanin composition and regulation of mammalian melanogenesis.…”

mentioning

confidence: 99%

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Regulation of the final phase of mammalian melanogenesis

Aroca

Solano

Salinas

et al. 1992

European Journal of Biochemistry

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The regulation of the final steps of the melanogenesis pathway, after ~-2-carboxy-2,3-dihydroindole-5,h-quinonc (dopachrome) formation, is studied. It is shown that both tyrosinase and dopachrome tautomerase are involved in the process. In vivo, it seems that tyrosinase is involved in the regulation of the amount of melanin formed, whereas dopachrome tautomerase is mainly involved in the size, structure and composition of melanin, by regulating to the incorporation of 5,6-dihydroxyindole-2-carboxylic acid (DHICA) into the polymer. Moreover, using ~-3,4-dihydroxyphenylalanine (dopa) and related compounds, it was shown that the presence of dopachrome tautomerase mediates an initial acceleration of melanogenesis since L-dopachrome is rapidly transformed to DHICA, but that melanin formation is inhibited because of the stability of this carboxylated indole compared to 5,6-dihydroxyindole (DHI), its decarboxylated counterpart obtained by spontaneous decarboxylation of L-dopachrome. Using L-dopa methyl ester as a precursor of melanogenesis, it is shown that this carboxylated indole does not polymerize in the absence of DHI, even in the presence of tyrosinase. However, it is incorporated into the polymer in the presence of both tyrosinase and DHI. Thus, this study suggests that DHI is essential for melanin formation, and the rate of polymerization depends on the ratio between DHICA and DHI in the medium. In the melanosome, this ratio should be regulated by the ratio between the activities of dopachrome tautomerase and tyrosinase.In mammals, melanin pigmentation results from the biosynthetic and secretory activity of specialized cells called melanocytes. The main biological function of melanin is in protection against ultraviolet radiation [l], but another possible role for this pigment is to act as a scavenger of cytotoxic agents, such as amines, free radicals and metal ions, preventing undesirable cellular processes [2, 31.The early key steps in the melanogenic pathway, the 0-hydroxylation of c-Tyr to ~-3,4-dihydroxyphenylalanine (dopa) and the oxidation of L-Dopa to L-dopaquinone, are catalyzed by tyrosinase [4, 51. Until 1980, it was believed that the reactions subsequent L-dopaquinone in the pathway leading to melanin, the Raper-Mason pathway, were spontaneous and proceeded through a series of unstable intermediates, such as (2-carboxy-2,3-dihydroindole-5,6-quinone) (Ldopachrome), 5,6-dihydroxyindole (DHI) and 5,6-indolequinone (IndQu) [4-61. However. the content of carboxylic Correspondence to F. Solano,

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Section: L-dopa a L-dopachromesupporting

confidence: 79%

Section: L-dopa a L-dopachromementioning

confidence: 99%

mentioning

confidence: 99%

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Regulation of the final phase of mammalian melanogenesis

Aroca

Solano

Salinas

et al. 1992

European Journal of Biochemistry

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“…1990), and indole blocking factor (Chakraborty et al, 1989). These findings point to an important role for coated vesicles in the initiation of melanogenesis.…”

mentioning

confidence: 76%

Structural/functional relationships between internal and external MSH receptors: Modulation of expression in Cloudman melanoma cells by UVB radiation

Chakraborty

Orlow

Bolognia

et al. 1991

Journal Cellular Physiology

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Expression of internal receptors for MSH is an important criterion for responsiveness to MSH by Cloudman melanoma cells (Orlow et al: J. Cell. Physiol., 142:129-136, 1990). Here, we show that internal and external receptors for MSH are of identical molecular weights (50-53 kDa) and share common antigenic determinants, indicating a structural relationship between the 2 populations of molecules. The internal receptors co-purified with a sub-cellular fraction highly enriched for small vesicles, many of which were coated. Ultraviolet B light (UVB) acted synergistically with MSH to increase tyrosinase activity and melanin content of cultured Cloudman melanoma cells, consistent with previous findings in the skin of mice and guinea pigs (Bolognia et al: J. Invest. Derm., 92:651-656, 1989). Preceding the rise in tyrosinase activity in cultured cells, UVB elicited a decrease in internal MSH binding sites and a concomitant increase in external sites. The time frame for the UVB effects on MSH receptors and melanogenesis, 48 hours, was similar to that for a response to solar radiation in humans. Together, the results indicate a key role for MSH receptors in the induction of melanogenesis by UVB and suggest a potential mechanism of action for UVB: redistribution of MSH receptors with a resultant increase in cellular responsiveness to MSH.

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“…A vesicle-enriched fraction was isolated (adaptation of Chakraborty et al, 1989) following 24 hr incubation in either HT or LT. Cells were washed twice with cold PBS, scraped into MES buffer (0 .…”

Section: Isolation Of a Vesicle-enriched Fractionmentioning

confidence: 99%