title: Multidrug resistance decreases with mutations of melanosomal regulatory genes.
abstract: Whereas resistance to chemotherapy has long impeded effective treatment of metastatic melanoma, the mechanistic basis of this resistance remains unknown. One possible mechanism of drug resistance is alteration of intracellular drug distribution either by drug efflux or sequestration into intracellular organelles. Melanomas, as well as primary melanocytes from which they arise, have intracellular organelles, called melanosomes, wherein the synthesis and storage of the pigment melanin takes place. In this study, comparisons of congenic cells with and without functional molecules regulating melanosome formation show that sensitivity to the chemotherapeutic agent cis-diaminedichloroplatinum II (cis-platin) significantly increases with the mutation of genes regulating melanosome formation, concomitant disruption of melanosome morphology, and loss of mature melanosomes. Absence of the melanosomal structural protein gp100/Pmel17 causes increased cis-platin sensitivity. Independent mutations in three separate genes that regulate melanosome biogenesis (Dtnbp1, Pldn, Vps33a) also result in increased cis-platin sensitivity. In addition, a mutation of the gene encoding the integral melanosomal protein tyrosinase, resulting in aberrant melanosome formation, also causes increased cis-platin sensitivity. Furthermore, sensitivity to agents in other chemotherapeutic classes (e.g., vinblastine and etoposide) also increased with the mutation of Pldn. In contrast, a mutation in another melanosomal regulatory gene, Hps1, minimally affects melanosome biogenesis, preserves the formation of mature melanosomes, and has no effect on cis-platin or vinblastine response. Together, these data provide the first direct evidence that melanosomal regulatory genes influence drug sensitivity and that the presence of mature melanosomes likely contributes to melanoma resistance to therapy.
authors.affiliation: Department of Dermatology, University of California-San Francisco, San Francisco, California, USA.
authors.forename: Tong
authors.initials: T
authors.lastname: Xie
authors.forename: Thuyen
authors.initials: T
authors.lastname: Nguyen
authors.forename: Melanie
authors.initials: M
authors.lastname: Hupe
authors.forename: Maria L
authors.initials: ML
authors.lastname: Wei
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D002352:Carrier Proteins / Q000235:genetics / Q000378:metabolism; D002945:Cisplatin / Q000494:pharmacology; D018432:Drug Resistance, Multiple; D019008:Drug Resistance, Neoplasm; D005809:Genes, Regulator; D006367:HeLa Cells; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins / Q000235:genetics / Q000378:metabolism; D008544:Melanocytes / Q000187:drug effects / Q000378:metabolism / Q000502:physiology; D008545:Melanoma / Q000188:drug therapy* / Q000235:genetics* / Q000378:metabolism; D008546:Melanoma, Experimental / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism; D020460:Melanosomes / Q000235:genetics* / Q000378:metabolism; D008562:Membrane Glycoproteins / Q000172:deficiency / Q000378:metabolism; D051379:Mice; D008810:Mice, Inbred C57BL; D014442:Monophenol Monooxygenase / Q000235:genetics / Q000378:metabolism; D009154:Mutation; D014407:Tumor Cells, Cultured; D058951:gp100 Melanoma Antigen
chemical_list: D000970:Antineoplastic Agents; C400284:BLOC1S6 protein, human; C513476:Bloc1s6 protein, mouse; D002352:Carrier Proteins; D047908:Intracellular Signaling Peptides and Proteins; D037102:Lectins; D008562:Membrane Glycoproteins; C548637:PMEL protein, human; C548642:Pmel protein, mouse; D058951:gp100 Melanoma Antigen; D014442:Monophenol Monooxygenase; D002945:Cisplatin