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Logesh R, Prasad SR, Chipurupalli S, Robinson N, Mohankumar SK. Natural tyrosinase enzyme inhibitors: A path from melanin to melanoma and its reported pharmacological activities. Biochim Biophys Acta Rev Cancer 2023; 1878:188968. [PMID: 37657683 DOI: 10.1016/j.bbcan.2023.188968] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 01/18/2023] [Revised: 08/15/2023] [Accepted: 08/15/2023] [Indexed: 09/03/2023]
Abstract
The skin containing melanin pigment acts as a protective barrier and counteracts the UVR and other environmental stressors to maintain or restore disrupted cutaneous homeostasis. The production of melanin pigment is dependent on tyrosine levels. L-tyrosine and L-dihydroxyphenylalanine (L-DOPA) can serve both as a substrates and intermediates of melanin synthetic pathway and as inducers and positive regulators of melanogenesis. The biosynthesis of melanin is stimulated upon exposure to UVR, which can also stimulate local production of hormonal factors, which can stimulate melanoma development by altering the chemical properties of eu- and pheomelanin. The process of melanogenesis can be altered by several pathways. One involves activation of POMC, with the production of POMC peptides including MSH and ACTH, which increase intracellular cAMP levels, which activates the MITF, and helps to stimulate tyrosinase (TYR) expression and activity. Defects in OCA1 to 4 affects melanogenic activity via posttranslational modifications resulting in proteasomal degradation and reducing pigmentation. Further, altering, the MITF factor, helps to regulate the expression of MRGE in melanoma, and helps to increase the TYR glycosylation in ER. CRH stimulates POMC peptides that regulate melanogenesis and also by itself can stimulate melanogenesis. The POMC, P53, ACTH, MSH, MC1R, MITF, and 6-BH4 are found to be important regulators for pigmentation. Melanogenesis can affect melanoma behaviour and inhibit immune responses. Therefore, we reviewed natural products that would alter melanin production. Our special focus was on targeting melanin synthesis and TYR enzyme activity to inhibit melanogenesis as an adjuvant therapy of melanotic melanoma. Furthermore, this review also outlines the current updated pharmacological studies targeting the TYR enzyme from natural sources and its consequential effects on melanin production.
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Affiliation(s)
- Rajan Logesh
- Department of Pharmacognosy, JSS College of Pharmacy, JSS Academy of Higher Education and Research, Mysuru 570015, Karnataka, India.
| | - Sagar Rajendra Prasad
- Department of Pharmacognosy, Varadaraja Institute of Pharmaceutical Education and Research, Tumkur 572102, Karnataka, India
| | - Sandhya Chipurupalli
- Department of Pharmacology, JSS College of Pharmacy, JSS Academy of Higher Education and Research, Ooty, India
| | - Nirmal Robinson
- Cellular Stress and Immune Response Laboratory, Centre for Cancer Biology, University of South Australia, Adelaide, Australia
| | - Suresh Kumar Mohankumar
- Pharmacy, Swansea University Medical School, Singleton Park, Swansea University, Wales SA2 8PP, United Kingdom
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Lee S, Choi H, Park Y, Jung HJ, Ullah S, Choi I, Kang D, Park C, Ryu IY, Jeong Y, Hwang Y, Hong S, Chun P, Moon HR. Urolithin and Reduced Urolithin Derivatives as Potent Inhibitors of Tyrosinase and Melanogenesis: Importance of the 4-Substituted Resorcinol Moiety. Int J Mol Sci 2021; 22:ijms22115616. [PMID: 34070680 PMCID: PMC8199067 DOI: 10.3390/ijms22115616] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/27/2021] [Revised: 05/17/2021] [Accepted: 05/22/2021] [Indexed: 12/17/2022] Open
Abstract
We previously reported (E)-β-phenyl-α,β-unsaturated carbonyl scaffold ((E)-PUSC) played an important role in showing high tyrosinase inhibitory activity and that derivatives with a 4-substituted resorcinol moiety as the β-phenyl group of the scaffold resulted in the greatest tyrosinase inhibitory activity. To examine whether the 4-substituted resorcinol moiety could impart tyrosinase inhibitory activity in the absence of the α,β-unsaturated carbonyl moiety of the (E)-PUSC scaffold, 10 urolithin derivatives were synthesized. To obtain more candidate samples, the lactone ring in synthesized urolithins was reduced to produce nine reduced urolithins. Compounds 1c (IC50 = 18.09 ± 0.25 μM), 1h (IC50 = 4.14 ± 0.10 μM), and 2a (IC50 = 15.69 ± 0.40 μM) had greater mushroom tyrosinase-inhibitory activities than kojic acid (KA) (IC50 = 48.62 ± 3.38 μM). The SAR results suggest that the 4-substituted resorcinol motif makes an important contribution to tyrosinase inhibition. To investigate whether these compounds bind to human tyrosinase, a human tyrosinase homology model was developed. Docking simulations with mushroom and human tyrosinases showed that 1c, 1h, and 2a bind to the active site of both tyrosinases with higher binding affinities than KA. Pharmacophore analyses showed that two hydroxyl groups of the 4-substituted resorcinol entity act as hydrogen bond donors in both mushroom and human tyrosinases. Kinetic analyses indicated that these compounds were all competitive inhibitors. Compound 2a inhibited cellular tyrosinase activity and melanogenesis in α-MSH plus IBMX-stimulated B16F10 melanoma cells more strongly than KA. These results suggest that 2a is a promising candidate for the treatment of skin pigment disorders, and show the 4-substituted resorcinol entity importantly contributes to tyrosinase inhibition.
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Affiliation(s)
- Sanggwon Lee
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Heejeong Choi
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Yujin Park
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Hee Jin Jung
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Sultan Ullah
- Department of Molecular Medicine, The Scripps Research Institute, Jupiter, FL 33458, USA;
| | - Inkyu Choi
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Dongwan Kang
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Chaeun Park
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Il Young Ryu
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Yeongmu Jeong
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - YeJi Hwang
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Sojeong Hong
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
| | - Pusoon Chun
- College of Pharmacy and Inje Institute of Pharmaceutical Sciences and Research, Inje University, Gimhae 50834, Korea;
| | - Hyung Ryong Moon
- College of Pharmacy, Pusan National University, Busan 46241, Korea; (S.L.); (H.C.); (Y.P.); (H.J.J.); (I.C.); (D.K.); (C.P.); (I.Y.R.); (Y.J.); (Y.H.); (S.H.)
- Correspondence: ; Tel.: +82-51-510-2815; Fax: +82-51-513-6754
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Inhibitory effects of N-(acryloyl)benzamide derivatives on tyrosinase and melanogenesis. Bioorg Med Chem 2019; 27:3929-3937. [DOI: 10.1016/j.bmc.2019.07.034] [Citation(s) in RCA: 12] [Impact Index Per Article: 2.4] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2019] [Revised: 07/09/2019] [Accepted: 07/19/2019] [Indexed: 01/03/2023]
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Falletta P, Bagnato P, Bono M, Monticone M, Schiaffino MV, Bennett DC, Goding CR, Tacchetti C, Valetti C. Melanosome-autonomous regulation of size and number: the OA1 receptor sustains PMEL expression. Pigment Cell Melanoma Res 2014; 27:565-79. [PMID: 24650003 DOI: 10.1111/pcmr.12239] [Citation(s) in RCA: 18] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/05/2013] [Accepted: 03/17/2014] [Indexed: 12/21/2022]
Abstract
Little is known as to how cells ensure that organelle size and number are coordinated to correctly couple organelle biogenesis to the demands of proliferation or differentiation. OA1 is a melanosome-associated G-protein-coupled receptor involved in melanosome biogenesis during melanocyte differentiation. Cells lacking OA1 contain fewer, but larger, mature melanosomes. Here, we show that OA1 loss of function reduces both the basal expression and the α-melanocyte-stimulating hormone/cAMP-dependent induction of the microphthalmia-associated transcription factor (MITF), the master regulator of melanocyte differentiation. In turn, this leads to a significant reduction in expression of PMEL, a major melanosomal structural protein, but does not affect tyrosinase and melanin levels. In line with its pivotal role in sensing melanosome maturation, OA1 expression rescues melanosome biogenesis, activates MITF expression and thereby coordinates melanosome size and number, providing a quality control mechanism for the organelle in which resides. Thus, resident sensor receptors can activate a transcriptional cascade to specifically promote organelle biogenesis.
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Affiliation(s)
- Paola Falletta
- Department of Experimental Medicine, University of Genoa, Genoa, Italy
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Role of the ubiquitin proteasome system in regulating skin pigmentation. Int J Mol Sci 2009; 10:4428-4434. [PMID: 20057953 PMCID: PMC2790116 DOI: 10.3390/ijms10104428] [Citation(s) in RCA: 31] [Impact Index Per Article: 2.1] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/03/2009] [Revised: 09/29/2009] [Accepted: 10/09/2009] [Indexed: 11/16/2022] Open
Abstract
Pigmentation of the skin, hair and eyes is regulated by tyrosinase, the critical rate-limiting enzyme in melanin synthesis by melanocytes. Tyrosinase is degraded endogenously, at least in part, by the ubiquitin proteasome system (UPS). Several types of inherited hypopigmentary diseases, such as oculocutaneous albinism and Hermansky-Pudlak syndrome, involve the aberrant processing and/or trafficking of tyrosinase and its subsequent degradation which can occur due to the quality-control machinery. Studies on carbohydrate modifications have revealed that tyrosinase in the endoplasmic reticulum (ER) is proteolyzed via ER-associated protein degradation and that tyrosinase degradation can also occur following its complete maturation in the Golgi. Among intrinsic factors that regulate the UPS, fatty acids have been shown to modulate tyrosinase degradation in contrasting manners through increased or decreased amounts of ubiquitinated tyrosinase that leads to its accelerated or decelerated degradation by proteasomes.
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Ando H, Kondoh H, Ichihashi M, Hearing VJ. Approaches to Identify Inhibitors of Melanin Biosynthesis via the Quality Control of Tyrosinase. J Invest Dermatol 2007; 127:751-61. [PMID: 17218941 DOI: 10.1038/sj.jid.5700683] [Citation(s) in RCA: 247] [Impact Index Per Article: 14.5] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 02/07/2023]
Abstract
Tyrosinase, a copper-containing glycoprotein, is the rate-limiting enzyme critical for melanin biosynthesis in specialized organelles termed melanosomes that are produced only by melanocytic cells. Inhibitors of tyrosinase activity have long been sought as therapeutic means to treat cutaneous hyperpigmentary disorders. Multiple potential approaches exist that could control pigmentation via the regulation of tyrosinase activity, for example: the transcription of its messenger RNA, its maturation via glycosylation, its trafficking to melanosomes, as well as modulation of its catalytic activity and/or stability. However, relatively little attention has been paid to regulating pigmentation via the stability of tyrosinase, which depends on its processing and maturation in the endoplasmic reticulum and Golgi, its delivery to melanosomes and its degradation via the ubiquitin-proteasome pathway and/or the endosomal/lysosomal system. Recently, it has been shown that carbohydrate modification, molecular chaperone engagement, and ubiquitylation all play pivotal roles in regulating the degradation/stability of tyrosinase. While such processes affect virtually all proteins, such effects on tyrosinase have immediate and dramatic consequences on pigmentation. In this review, we classify melanogenic inhibitory factors in terms of their modulation of tyrosinase function and we summarize current understanding of how the quality control of tyrosinase processing impacts its stability and melanogenic activity.
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Affiliation(s)
- Hideya Ando
- Laboratory of Cell Biology, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892, USA
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Wang N, Hebert DN. Tyrosinase maturation through the mammalian secretory pathway: bringing color to life. ACTA ACUST UNITED AC 2006; 19:3-18. [PMID: 16420243 DOI: 10.1111/j.1600-0749.2005.00288.x] [Citation(s) in RCA: 167] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/24/2023]
Abstract
Tyrosinase has been extensively utilized as a model substrate to study the maturation of glycoproteins in the mammalian secretory pathway. The visual nature of its enzymatic activity (melanin production) has facilitated the identification and characterization of the proteins that assist it becoming a functional enzyme, localized to its proper cellular location. Here, we review the steps involved in the maturation of tyrosinase from when it is first synthesized by cytosolic ribosomes until the mature protein reaches its post-Golgi residence in the melanosomes. These steps include protein processing, covalent modifications, chaperone binding, oligomerization, and trafficking. The disruption of any of these steps can lead to a wide range of pigmentation disorders.
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Affiliation(s)
- Ning Wang
- Program in Molecular and Cellular Biology, Department of Biochemistry and Molecular Biology, University of Massachusetts, Amherst, MA, USA
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Ando H, Watabe H, Valencia JC, Yasumoto KI, Furumura M, Funasaka Y, Oka M, Ichihashi M, Hearing VJ. Fatty acids regulate pigmentation via proteasomal degradation of tyrosinase: a new aspect of ubiquitin-proteasome function. J Biol Chem 2004; 279:15427-33. [PMID: 14739285 DOI: 10.1074/jbc.m313701200] [Citation(s) in RCA: 102] [Impact Index Per Article: 5.1] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/06/2022] Open
Abstract
Fatty acids are common components of biological membranes that are known to play important roles in intracellular signaling. We report here a novel mechanism by which fatty acids regulate the degradation of tyrosinase, a critical enzyme associated with melanin biosynthesis in melanocytes and melanoma cells. Linoleic acid (unsaturated fatty acid, C18:2) accelerated the spontaneous degradation of tyrosinase, whereas palmitic acid (saturated fatty acid, C16:0) retarded the proteolysis. The linoleic acid-induced acceleration of tyrosinase degradation could be abrogated by inhibitors of proteasomes, the multicatalytic proteinase complexes that selectively degrade intracellular ubiquitinated proteins. Linoleic acid increased the ubiquitination of many cellular proteins, whereas palmitic acid decreased such ubiquitination, as compared with untreated controls, when a proteasome inhibitor was used to stabilize ubiquitinated proteins. Immunoprecipitation analysis also revealed that treatment with fatty acids modulated the ubiquitination of tyrosinase, i.e. linoleic acid increased the amount of ubiquitinated tyrosinase whereas, in contrast, palmitic acid decreased it. Furthermore, confocal immunomicroscopy showed that the colocalization of ubiquitin and tyrosinase was facilitated by linoleic acid and diminished by palmitic acid. Taken together, these data support the view that fatty acids regulate the ubiquitination of tyrosinase and are responsible for modulating the proteasomal degradation of tyrosinase. In broader terms, the function of the ubiquitin-proteasome pathway might be regulated physiologically, at least in part, by fatty acids within cellular membranes.
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Affiliation(s)
- Hideya Ando
- Laboratory of Cell Biology, NCI, National Institutes of Health, Bethesda, Maryland 20892, USA.
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Ancans J, Thody AJ. Activation of melanogenesis by vacuolar type H(+)-ATPase inhibitors in amelanotic, tyrosinase positive human and mouse melanoma cells. FEBS Lett 2000; 478:57-60. [PMID: 10922469 DOI: 10.1016/s0014-5793(00)01795-6] [Citation(s) in RCA: 39] [Impact Index Per Article: 1.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/18/2022]
Abstract
In this study, we describe the activation of melanogenesis by selective vacuolar type H(+)-ATPase inhibitors (bafilomycin A1 and concanamycin A) in amelanotic human and mouse melanoma cells which express tyrosinase but show no melanogenesis. Addition of the inhibitors activated tyrosinase within 4 h, and by 24 h the cells contained measurable amounts of melanin. These effects were not inhibited by cycloheximide (2 microgram/ml) which is consistent with a post-translational mechanism of activation. Our findings suggest that melanosomal pH could be an important and dynamic factor in the control of melanogenesis in mammalian cells.
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Affiliation(s)
- J Ancans
- Department of Biomedical Sciences, University of Bradford, BD7 1DP, Bradford, UK
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Mason RS, Pryke AM, Ranson M, Thomas HE, Posen S. Human melanoma cells: functional modulation by calciotropic hormones. J Invest Dermatol 1988; 90:834-40. [PMID: 2836516 DOI: 10.1111/1523-1747.ep12462072] [Citation(s) in RCA: 20] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/02/2023]
Abstract
Four human melanoma cell lines were examined for their responsiveness to the hormones 1,25-dihydroxyvitamin D3 (1,25[OH]2D3), calcitonin, and parathyroid hormone (1-34). Cells from each of the 4 lines contained high affinity binding sites for 1,25(OH)2D3. At high cell densities, binding of 1,25(OH)2D3 was diminished due to a decrease in receptor number with no apparent change in affinity. Preincubation with 1,25(OH)2D3 (10(-10) to 10(-8) M) increased tyrosinase activity 1.3- to 3.2-fold and 25-hydroxyvitamin D3-24-hydroxylase activity 1.4- to 10-fold. Human calcitonin (0.82 to 82.5 ng/well) raised the intracellular concentration of cyclic adenosine monophosphate 1.4- to 9.4-fold. Tyrosinase activity increased in response to calcitonin in 2 of the cell lines, decreased in the third, and showed no change in the fourth. Human parathyroid hormone (1-34) in concentrations of 1 to 10 ng/ml produced no significant changes in cyclic adenosine monophosphate accumulation, cell numbers, or tyrosinase activity in any of the cell lines. This study indicates that the phenotype of human melanoma cells can be modulated by the calciotropic hormones 1,25(OH)2D3 and calcitonin.
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Affiliation(s)
- R S Mason
- Endocrine Unit, Royal North Shore Hospital, Sydney, New South Wales, Australia
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Nordenberg J, Wasserman L, Beery E, Aloni D, Malik H, Stenzel KH, Novogrodsky A. Growth inhibition of murine melanoma by butyric acid and dimethylsulfoxide. Exp Cell Res 1986; 162:77-85. [PMID: 3079593 DOI: 10.1016/0014-4827(86)90427-1] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.9] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/04/2023]
Abstract
Treatment of B16-F10 melanoma cells with dimethylsulfoxide (DMSO) or butyric acid (BA) inhibits cell growth and delays tumor appearance in syngeneic mice. Both agents induce morphological changes in these cells. Treatment of melanoma cells with DMSO results in a marked increase in tyrosinase activity and melanin content. BA, on the other hand, does not increase melanin content and decreases tyrosinase activity. The data show that there are marked differences in the effect of DMSO and BA on melanin biosynthesis, whereas both agents inhibit cell growth and cause a delay in tumor appearance. These findings indicate that decreased proliferation of melanoma cells and induction of melanin biosynthesis are not necessarily associated phenomena.
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Słomiński A, Bomirski A, Scisłowski PW, Zołnierowicz S. Effects of actinomycin D and cycloheximide on the increase in tyrosinase activity of hamster amelanotic melanoma cells in vitro. Biosci Rep 1984; 4:1059-64. [PMID: 6442169 DOI: 10.1007/bf01116699] [Citation(s) in RCA: 10] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023] Open
Abstract
Tyrosinase activity in the Ab hamster amelanotic melanoma cells cultured in serum-free Eagle's MEM increased 3 times after 6 h of primary cell culture. This increase was inhibited completely by cycloheximide, while actinomycin D had no effect on this process. After 24 h of culture in MEM with calf serum, further increase of the tyrosinase activity was inhibited by both cycloheximide and actinomycin D. The data presented may indicate that the increase of tyrosinase activity in the primary cell culture of the Ab melanoma is due initially to the unblocking of translation and later to the activation of transcription of the gene controlling the enzyme.
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Saeki H, Oikawa A. Stimulation of tyrosinase activity of cultured melanoma cells by lysosomotropic agents. J Cell Physiol 1983; 116:93-7. [PMID: 6406524 DOI: 10.1002/jcp.1041160114] [Citation(s) in RCA: 33] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/20/2023]
Abstract
The tyrosinase (EC 1.14.18.1) activity of cell-free extracts (TyH) of B16 melanoma cells cultured in the presence of 5 to 10 mM ammonium chloride was considerably higher than that of cells from control cultures. This increase in TyH in the presence of ammonium chloride seemed to be due to de novo synthesis of the enzyme, because it was inhibited by 1 microgram/ml of cycloheximide. In the presence of the latter, however, ammonium chloride did increase the tyrosinase activity of living cells in culture (TyC) resulting in about threefold increase in the TyC/TyH ratio, a measure of the extent of tyrosinase reaction exerted by the enzyme present in living cells. This higher TyC/TyH ratio induced by ammonium chloride was also observed in the absence of cycloheximide. Similar increases in TyH, TyC, and TyC/TyH occurred in the presence of methylamine or ethylamine instead of ammonium chloride, but not in the presence of tetraethylammonium chloride, and also in culture medium of higher pH. The apparently similar effects of lysosomotropic bases and medium of higher pH on the TyC/TyH ratio suggest that there are some mechanisms that control the intramelanosomal pH lower than the cytoplasmic pH.
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