Cell-specific ATP7A transport sustains copper-dependent tyrosinase activity in melanosomes

The degradation of TYR variants derived from Chinese OCA families is mediated by the ERAD and ERLAD pathway

Oculocutaneous albinism (OCA) is a genetically heterogeneous group of autosomal recessive disorders, which presents with decreased or absent pigmentation in the hair, skin, and eyes. OCA1, as a subtype of OCA, is caused by mutations in the tyrosinase gene (TYR). In this study, we performed in vitro functional analysis of eight TYR variants (one frameshift variant: c.929dupC (p.Arg311Lysfs*7); seven missense variants: c.896G>A (p.Arg299His), c.1234C>A (p.Pro412Thr), c.1169A>G (p.His390Arg), c.937C>A (p.Pro313Thr), c.636A>T (p.Arg212Ser), c.623 T>G (p.Leu208Arg), c.1325C>A (p.Ser442Tyr)) identified in Chinese OCA families. TYR plasmids were transfected into HEK 293 T cells to explore the effects of TYR variants on their processing, protein expression, activity, and degradation. The results showed that all eight variants caused TYR to be retained in the endoplasmic reticulum (ER), processing was blocked, and TYR activity almost disappeared; the frameshift variant caused the size of the TYR protein to be reduced by about 30KD, and the protein expression of the remaining seven missense variants was reduced; the ER-associated degradation (ERAD) pathway mediates the degradation of TYR variants that occur on the Tyrosinase copper-binding domain, while the degradation of TYR variants that are not located on that domain may be mediated by a new degradation pathway--ER-to-lysosome-associated degradation (ERLAD). In summary, TYR variants affected their protein processing and activity, and may also induce ER stress and trigger degradation through the ERLAD pathway in addition to the ERAD degradation pathway, providing new insights into the potential pathogenic mechanism for OCA1 caused by TYR variants.

Mammalian copper homeostasis: physiological roles and molecular mechanisms

In the past decade, evidence for the numerous roles of copper (Cu) in mammalian physiology has grown exponentially. The discoveries of Cu involvement in cell signaling, autophagy, cell motility, differentiation, and regulated cell death (cuproptosis) have markedly extended the list of already known functions of Cu, such as a cofactor of essential metabolic enzymes, a protein structural component, and a regulator of protein trafficking. Novel and unexpected functions of Cu transporting proteins and enzymes have been identified, and new disorders of Cu homeostasis have been described. Significant progress has been made in the mechanistic studies of two classic disorders of Cu metabolism, Menkes disease and Wilson's disease, which paved the way for novel approaches to their treatment. The discovery of cuproptosis and the role of Cu in cell metastatic growth have markedly increased interest in targeting Cu homeostatic pathways to treat cancer. In this review, we summarize the established concepts in the field of mammalian Cu physiology and discuss how new discoveries of the past decade expand and modify these concepts. The roles of Cu in brain metabolism and in cell functional speciation and a recently discovered regulated cell death have attracted significant attention and are highlighted in this review.

TRIM24-DTNBP1-ATP7A mediated astrocyte cuproptosis in cognition and memory dysfunction caused by Y2O3 NPs

Yttrium oxide nanoparticles (Y2O3 NPs), extensively utilized rare earth nanoparticles, exhibited a diverse range of applications across various fields, which leading to increased human exposure. Moreover, potential neurotoxic risks have been associated with their use, yet the underlying mechanism remains unclear. The present study aimed to investigate the effects of Y2O3 NPs on cognitive function in rats with a particular focus on elucidating the pivotal role played by astrocytes in this process. The results demonstrated that Y2O3 NPs induced cognitive and memory impairment in rats, copper (Cu) accumulation and cuproptosis of astrocytes as contributing factors. Furthermore, we elucidated that Y2O3 NPs induced astrocytes cuproptosis by inhibiting TRIM24/DTNBP1/ATP7A signaling pathway-mediated cellular Cu efflux. We provide, for the first time, the important involvement of astrocytes in Y2O3 NPs-induced neurotoxicity, elucidating that cuproptosis as the primary mode of cell death. These results offer valuable insights for the future safe application of rare earth nanoparticles in field of neurology.

Copper homeostasis and copper-induced cell death in tumor immunity: implications for therapeutic strategies in cancer immunotherapy

Copper is an important trace element for maintaining key biological functions such as cellular respiration, nerve conduction, and antioxidant defense. Maintaining copper homeostasis is critical for human health, and its imbalance has been linked to various diseases, especially cancer. Cuproptosis, a novel mechanism of copper-induced cell death, provides new therapeutic opportunities for metal ion regulation to interact with cell fate. This review provides insights into the complex mechanisms of copper metabolism, the molecular basis of cuproptosis, and its association with cancer development. We assess the role of cuproptosis-related genes (CRGs) associated with tumorigenesis, their importance as prognostic indicators and therapeutic targets, and the impact of copper homeostasis on the tumor microenvironment (TME) and immune response. Ultimately, this review highlights the complex interplay between copper, cuproptosis, and cancer immunotherapy.

Copper-Based Nanomedicines for Cuproptosis-Mediated Effective Cancer Treatment

The recent discovery of cuproptosis, a novel copper-ion-induced cell death pathway, has suggested the novel therapeutic potential for treating heterogeneous and drug-resistant cancers. Currently, copper ionophore-based therapeutics have been designed to treat cancers, utilizing copper ions as a strategic tool to impede tumor proliferation and promote cellular demise. However, limitations of copper ionophore-based therapies include nontargeted delivery of copper ions, low tumor accumulation, and short half-life. Strategies to enhance specificity involve targeting intracellular cuproptosis mechanisms using nanotechnology-based drugs. Additionally, the importance of exploring combination therapies cannot be overstated, as they are a key strategy in improving the efficacy of cancer treatments. Recent studies have reported the anticancer effects of nanomedicines that can induce cuproptosis of cancer both in vitro and in vivo. These cuproptosis-targeted nanomedicines could improve delivery efficiency with the pharmacokinetic properties of copper ion, resulting in increasing cuproptosis-based anticancer effects. This review will summarize the intricate nexus between copper ion and carcinogenesis, examining the pivotal roles of copper homeostasis and its dysregulation in cancer progression and fatality. Furthermore, we will introduce the latest advances in cuproptosis-targeted nanomedicines for cancer treatment. Finally, the challenges in cuproptosis-based nanomedicines will be discussed for future development directions.

Impaired cellular copper regulation in the presence of ApoE4

The strongest genetic risk factor for late-onset Alzheimer's disease (AD) is allelic variation of the APOE gene, with the following risk structure: ε4 > ε3 > ε2. The biochemical basis for this risk profile is unclear. Here, we reveal a new role for the APOE gene product, apolipoprotein E (ApoE) in regulating cellular copper homeostasis, which is perturbed in the AD brain. Exposure of ApoE target replacement (TR) astrocytes (immortalised astrocytes from APOE knock-in mice) to elevated copper concentrations resulted in exacerbated copper accumulation in ApoE4- compared to ApoE2- and ApoE3-TR astrocytes. This effect was also observed in SH-SY5Y neuroblastoma cells treated with conditioned medium from ApoE4-TR astrocytes. Increased intracellular copper levels in the presence of ApoE4 may be explained by reduced levels and delayed trafficking of the copper transport protein, copper-transporting ATPase 1 (ATP7A/Atp7a), potentially leading to impaired cellular copper export. This new role for ApoE in copper regulation lends further biochemical insight into how APOE genotype confers risk for AD and reveals a potential contribution of ApoE4 to the copper dysregulation that is a characteristic pathological feature of the AD brain.

Enhanced MC1R-signalling and pH modulation facilitate melanogenesis within late endosomes of BLOC-1-deficient melanocytes

Photoprotective melanins in the skin are synthesised by epidermal melanocytes within specialised lysosome-related organelles called melanosomes. Melanosomes coexist with lysosomes; thus, melanocytes employ specific trafficking machineries to ensure correct cargo delivery to either the endolysosomal system or maturing melanosomes. Mutations in some of the protein complexes required for melanogenic cargo delivery, such as biogenesis of lysosome-related organelles complex 1 (BLOC-1), result in hypopigmentation due to mistrafficking of cargo to endolysosomes. We show that hypopigmented BLOC-1-deficient melanocytes retain melanogenic capacity that can be enhanced by treatment with cAMP elevating agents despite the mislocalisation of melanogenic proteins. The melanin formed in BLOC-1-deficient melanocytes is not generated in melanosomes but rather within late endosomes/lysosomes to which some cargoes mislocalise. Although these organelles generally are acidic, a cohort of late endosomes/lysosomes have a sufficiently neutral pH to facilitate melanogenesis, perhaps due to mislocalised melanosomal transporters and melanogenic enzymes. Modulation of the pH of late endosomes/lysosomes by genetic manipulation or via treatment with lysosomotropic agents significantly enhances the melanin content of BLOC-1-deficient melanocytes. Our data suggest that upregulation of mistargeted cargoes can facilitate reprogramming of a subset of endolysosomes to generate some functions of lysosome-related organelles.

The metabolism of melanin synthesis-From melanocytes to melanoma

Melanin synthesis involves the successful coordination of metabolic pathways across multiple intracellular compartments including the melanosome, mitochondria, ER/Golgi, and cytoplasm. While pigment production offers a communal protection from UV damage, the process also requires anabolic and redox demands that must be carefully managed by melanocytes. In this report we provide an updated review on melanin metabolism, including recent data leveraging new techniques, and technologies in the field of metabolism. We also discuss the many aspects of melanin synthesis that intersect with metabolic pathways known to impact melanoma phenotypes and behavior. By reviewing the metabolism of melanin synthesis, we hope to highlight outstanding questions and opportunities for future research that could improve patient outcomes in pigmentary and oncologic disease settings.

Malignant Melanoma: An Overview, New Perspectives, and Vitamin D Signaling

Melanoma, originating through malignant transformation of melanin-producing melanocytes, is a formidable malignancy, characterized by local invasiveness, recurrence, early metastasis, resistance to therapy, and a high mortality rate. This review discusses etiologic and risk factors for melanoma, diagnostic and prognostic tools, including recent advances in molecular biology, omics, and bioinformatics, and provides an overview of its therapy. Since the incidence of melanoma is rising and mortality remains unacceptably high, we discuss its inherent properties, including melanogenesis, that make this disease resilient to treatment and propose to use AI to solve the above complex and multidimensional problems. We provide an overview on vitamin D and its anticancerogenic properties, and report recent advances in this field that can provide solutions for the prevention and/or therapy of melanoma. Experimental papers and clinicopathological studies on the role of vitamin D status and signaling pathways initiated by its active metabolites in melanoma prognosis and therapy are reviewed. We conclude that vitamin D signaling, defined by specific nuclear receptors and selective activation by specific vitamin D hydroxyderivatives, can provide a benefit for new or existing therapeutic approaches. We propose to target vitamin D signaling with the use of computational biology and AI tools to provide a solution to the melanoma problem.

Cuproptosis: unveiling a new frontier in cancer biology and therapeutics

Copper plays vital roles in numerous cellular processes and its imbalance can lead to oxidative stress and dysfunction. Recent research has unveiled a unique form of copper-induced cell death, termed cuproptosis, which differs from known cell death mechanisms. This process involves the interaction of copper with lipoylated tricarboxylic acid cycle enzymes, causing protein aggregation and cell death. Recently, a growing number of studies have explored the link between cuproptosis and cancer development. This review comprehensively examines the systemic and cellular metabolism of copper, including tumor-related signaling pathways influenced by copper. It delves into the discovery and mechanisms of cuproptosis and its connection to various cancers. Additionally, the review suggests potential cancer treatments using copper ionophores that induce cuproptosis, in combination with small molecule drugs, for precision therapy in specific cancer types.

Targeting cuproplasia and cuproptosis in cancer

Copper, an essential trace element that exists in oxidized and reduced forms, has pivotal roles in a variety of biological processes, including redox chemistry, enzymatic reactions, mitochondrial respiration, iron metabolism, autophagy and immune modulation; maintaining copper homeostasis is crucial as both its deficiency and its excess are deleterious. Dysregulated copper metabolism has a dual role in tumorigenesis and cancer therapy. Specifically, cuproplasia describes copper-dependent cell growth and proliferation, including hyperplasia, metaplasia and neoplasia, whereas cuproptosis refers to a mitochondrial pathway of cell death triggered by excessive copper exposure and subsequent proteotoxic stress (although complex interactions between cuproptosis and other cell death mechanisms, such as ferroptosis, are likely and remain enigmatic). In this Review, we summarize advances in our understanding of copper metabolism, the molecular machineries underlying cuproplasia and cuproptosis, and their potential targeting for cancer therapy. These new findings advance the rapidly expanding field of translational cancer research focused on metal compounds.

Alkyne-tagged SERS nanoprobe for understanding Cu+ and Cu2+ conversion in cuproptosis processes

Simultaneously quantifying mitochondrial Cu+ and Cu2+ levels is crucial for evaluating the molecular mechanisms of copper accumulation-involved pathological processes. Here, a series of molecules containing various diacetylene derivatives as Raman reporters are designed and synthesized, and the alkyne-tagged SERS probe is created for determination Cu+ and Cu2+ with high selectivity and sensitivity. The developed SERS probe generates well-separated distinguishable Raman fingerprint peaks with built-in corrections in the cellular silent region, resulting in accurate quantification of Cu+ and Cu2+. The present probe demonstrates high tempo-spatial resolution for real-time imaging and simultaneously quantifying mitochondrial Cu+ and Cu2+ with long-term stability benefiting from the probe assembly with designed Au-C≡C groups. Using this powerful tool, it is found that mitochondrial Cu+ and Cu2+ increase during ischemia are associated with breakdown of proteins containing copper as well as conversion of Cu+ and Cu2+. Meanwhile, we observe that parts of Cu+ and Cu2+ are transported out of neurons by ATPase. More importantly, cuproptosis in neurons is found including the oxidative stress process caused by the conversion of Cu+ to Cu2+, which dominates at the early stage (<9 h), and subsequent proteotoxic stress. Both oxidative and proteotoxic stresses contribute to neuronal death.

Structure and mechanism of the human copper transporting ATPases: Fitting the pieces into a moving puzzle

Human copper transporters ATP7B and ATP7A deliver copper to biosynthetic pathways and maintain copper homeostasis in the cell. These enzymes combine several challenges for structural biology because they are large low abundance membrane proteins with many highly mobile domains and long disordered loops. No method has yet succeeded in solving the structure of the complete fully functional protein. Still, X-ray crystallography, Cryo-EM and NMR helped to piece together a structure based model of the enzyme activity and regulation by copper. We review the structures of ATP7B and ATP7A with an emphasis on the mechanistic insights into the unique aspects of the transport function and regulation of the human copper ATPases that have emerged from more than twenty years of research.

Regulation of the apico-basolateral trafficking polarity of the homologous copper-ATPases ATP7A and ATP7B

The homologous P-type copper-ATPases (Cu-ATPases) ATP7A and ATP7B are the key regulators of copper homeostasis in mammalian cells. In polarized epithelia, upon copper treatment, ATP7A and ATP7B traffic from the trans-Golgi network (TGN) to basolateral and apical membranes, respectively. We characterized the sorting pathways of Cu-ATPases between TGN and the plasma membrane and identified the machinery involved. ATP7A and ATP7B reside on distinct domains of TGN in limiting copper conditions, and in high copper, ATP7A traffics to basolateral membrane, whereas ATP7B traverses common recycling, apical sorting and apical recycling endosomes en route to apical membrane. Mass spectrometry identified regulatory partners of ATP7A and ATP7B that include the adaptor protein-1 complex. Upon knocking out pan-AP-1, sorting of both Cu-ATPases is disrupted. ATP7A loses its trafficking polarity and localizes on both apical and basolateral surfaces in high copper. By contrast, ATP7B loses TGN retention but retained its trafficking polarity to the apical domain, which became copper independent. Using isoform-specific knockouts, we found that the AP-1A complex provides directionality and TGN retention for both Cu-ATPases, whereas the AP-1B complex governs copper-independent trafficking of ATP7B solely. Trafficking phenotypes of Wilson disease-causing ATP7B mutants that disrupts putative ATP7B-AP1 interaction further substantiates the role of AP-1 in apical sorting of ATP7B.

Augmenting MEK inhibitor efficacy in BRAF wild-type melanoma: synergistic effects of disulfiram combination therapy

BACKGROUND

MEK inhibitors (MEKi) were shown to be clinically insufficiently effective in patients suffering from BRAF wild-type (BRAF WT) melanoma, even if the MAPK pathway was constitutively activated due to mutations in NRAS or NF-1. Thus, novel combinations are needed to increase the efficacy and duration of response to MEKi in BRAF WT melanoma. Disulfiram and its metabolite diethyldithiocarbamate are known to have antitumor effects related to cellular stress, and induction of endoplasmic reticulum (ER) stress was found to synergize with MEK inhibitors in NRAS-mutated melanoma cells. Therefore, we investigated the combination of both therapeutics to test their effects on BRAF-WT melanoma cells and compared them with monotherapy using the MEKi trametinib.

METHODS

The effects of combined therapy with disulfiram or its metabolite diethyldithiocarbamate and the MEKi trametinib were evaluated in a series of BRAF-WT melanoma cell lines by measuring cell viability and apoptosis induction. Cytotoxicity was additionally assessed in 3D spheroids, ex vivo melanoma slice cultures, and in vivo xenograft mouse models. The response of melanoma cells to treatment was studied at the RNA and protein levels to decipher the mode of action. Intracellular and intratumoral copper measurements were performed to investigate the role of copper ions in the antitumor cytotoxicity of disulfiram and its combination with the MEKi.

RESULTS

Diethyldithiocarbamate enhanced trametinib-induced cytotoxicity and apoptosis induction in 2D and 3D melanoma culture models. Mechanistically, copper-dependent induction of oxidative stress and ER stress led to Janus kinase (JNK)-mediated apoptosis in melanoma cells. This mechanism was also detectable in patient-derived xenograft melanoma models and resulted in a significantly improved therapeutic effect compared to monotherapy with the MEKi trametinib.

CONCLUSIONS

Disulfiram and its metabolite represent an attractive pharmaceutical approach to induce ER stress in melanoma cells that potentiates the antitumor effect of MEK inhibition and may be an interesting candidate for combination therapy of BRAF WT melanoma.

Two High-Quality Cygnus Genome Assemblies Reveal Genomic Variations Associated with Plumage Color

As an exemplary model for examining molecular mechanisms responsible for extreme phenotypic variations, plumage color has garnered significant interest. The Cygnus genus features two species, Cygnus olor and Cygnus atratus, that exhibit striking disparities in plumage color. However, the molecular foundation for this differentiation has remained elusive. Herein, we present two high-quality genomes for C. olor and C. atratus, procured using the Illumina and Nanopore technologies. The assembled genome of C. olor was 1.12 Gb in size with a contig N50 of 26.82 Mb, while its counterpart was 1.13 Gb in size with a contig N50 of 21.91 Mb. A comparative analysis unveiled three genes (TYR, SLC45A2, and SLC7A11) with structural variants in the melanogenic pathway. Notably, we also identified a novel gene, PWWP domain containing 2A (PWWP2A), that is related to plumage color, for the first time. Using targeted gene modification analysis, we demonstrated the potential genetic effect of the PWWP2A variant on pigment gene expression and melanin production. Finally, our findings offer insight into the intricate pattern of pigmentation and the role of polygenes in birds. Furthermore, these two high-quality genome references provide a comprehensive resource and perspective for comparative functional and genetic studies of evolution within the Cygnus genus.

Role of copper and its complexes in cardiovascular diseases

Copper is a trace element essential for the maintenance of normal physiological functions in cardiovascular system, and its transport and metabolisms are regulated by various copper proteins such as copper-based enzymes, copper chaperones and copper transporters. The disturbance of copper level or abnormal expression of copper proteins are closely associated with the development of cardiovascular diseases such as atherosclerosis, hypertension, ischemic heart disease, myocardial hypertrophy and heart failure. Thus, intervention of copper ion signaling pathways is expected to be an effective measure for treating cardiovascular diseases. Some copper complexes, such as trientine, copper-aspirinate complex and copper (II) diethyldithiocarbamate, have been found to play a role in the prevention and treatment of cardiovascular diseases and possess potential prospects. Exploring the role of copper in maintaining normal cardiovascular status and the potential application of copper complexes in the treatment of cardiovascular diseases may lay a foundation for finding new targets for prevention and treatment of various cardiovascular diseases, and provide new ideas for clinical treatment of cardiovascular diseases.

Pallidin function in Drosophila surface glia regulates sleep and is dependent on amino acid availability

The Pallidin protein is a central subunit of a multimeric complex called biogenesis of lysosome-related organelles complex 1 (BLOC1) that regulates specific endosomal functions and has been linked to schizophrenia. We show here that downregulation of Pallidin and other members of BLOC1 in the surface glia, the Drosophila equivalent of the blood-brain barrier, reduces and delays nighttime sleep in a circadian-clock-dependent manner. In agreement with BLOC1 involvement in amino acid transport, downregulation of the large neutral amino acid transporter 1 (LAT1)-like transporters JhI-21 and mnd, as well as of TOR (target of rapamycin) amino acid signaling, phenocopy Pallidin knockdown. Furthermore, supplementing food with leucine normalizes the sleep/wake phenotypes of Pallidin downregulation, and we identify a role for Pallidin in the subcellular trafficking of JhI-21. Finally, we provide evidence that Pallidin in surface glia is required for GABAergic neuronal activity. These data identify a BLOC1 function linking essential amino acid availability and GABAergic sleep/wake regulation.

A genome-wide genetic screen uncovers determinants of human pigmentation

Skin color, one of the most diverse human traits, is determined by the quantity, type, and distribution of melanin. In this study, we leveraged the light-scattering properties of melanin to conduct a genome-wide screen for regulators of melanogenesis. We identified 169 functionally diverse genes that converge on melanosome biogenesis, endosomal transport, and gene regulation, of which 135 represented previously unknown associations with pigmentation. In agreement with their melanin-promoting function, the majority of screen hits were up-regulated in melanocytes from darkly pigmented individuals. We further unraveled functions of KLF6 as a transcription factor that regulates melanosome maturation and pigmentation in vivo, and of the endosomal trafficking protein COMMD3 in modulating melanosomal pH. Our study reveals a plethora of melanin-promoting genes, with broad implications for human variation, cell biology, and medicine.

Pigmentation and TYRP1 expression are mediated by zinc through the early secretory pathway-resident ZNT proteins

Tyrosinase (TYR) and tyrosinase-related proteins 1 and 2 (TYRP1 and TYRP2) are essential for pigmentation. They are generally classified as type-3 copper proteins, with binuclear copper active sites. Although there is experimental evidence for a copper cofactor in TYR, delivered via the copper transporter, ATP7A, the presence of copper in TYRP1 and TYRP2 has not been demonstrated. Here, we report that the expression and function of TYRP1 requires zinc, mediated by ZNT5-ZNT6 heterodimers (ZNT5-6) or ZNT7-ZNT7 homodimers (ZNT7). Loss of ZNT5-6 and ZNT7 function results in hypopigmentation in medaka fish and human melanoma cells, and is accompanied by immature melanosomes and reduced melanin content, as observed in TYRP1 dysfunction. The requirement of ZNT5-6 and ZNT7 for TYRP1 expression is conserved in human, mouse, and chicken orthologs. Our results provide novel insights into the pigmentation process and address questions regarding metalation in tyrosinase protein family.

A Comprehensive Review of Mammalian Pigmentation: Paving the Way for Innovative Hair Colour-Changing Cosmetics

The natural colour of hair shafts is formed at the bulb of hair follicles, and it is coupled to the hair growth cycle. Three critical processes must happen for efficient pigmentation: (1) melanosome biogenesis in neural crest-derived melanocytes, (2) the biochemical synthesis of melanins (melanogenesis) inside melanosomes, and (3) the transfer of melanin granules to surrounding pre-cortical keratinocytes for their incorporation into nascent hair fibres. All these steps are under complex genetic control. The array of natural hair colour shades are ascribed to polymorphisms in several pigmentary genes. A myriad of factors acting via autocrine, paracrine, and endocrine mechanisms also contributes for hair colour diversity. Given the enormous social and cosmetic importance attributed to hair colour, hair dyeing is today a common practice. Nonetheless, the adverse effects of the long-term usage of such cosmetic procedures demand the development of new methods for colour change. In this context, case reports of hair lightening, darkening and repigmentation as a side-effect of the therapeutic usage of many drugs substantiate the possibility to tune hair colour by interfering with the biology of follicular pigmentary units. By scrutinizing mammalian pigmentation, this review pinpoints key targetable processes for the development of innovative cosmetics that can safely change the hair colour from the inside out.

Overlapping Machinery in Lysosome-Related Organelle Trafficking: A Lesson from Rare Multisystem Disorders

Lysosome-related organelles (LROs) are a group of functionally diverse, cell type-specific compartments. LROs include melanosomes, alpha and dense granules, lytic granules, lamellar bodies and other compartments with distinct morphologies and functions allowing specialised and unique functions of their host cells. The formation, maturation and secretion of specific LROs are compromised in a number of hereditary rare multisystem disorders, including Hermansky-Pudlak syndromes, Griscelli syndrome and the Arthrogryposis, Renal dysfunction and Cholestasis syndrome. Each of these disorders impacts the function of several LROs, resulting in a variety of clinical features affecting systems such as immunity, neurophysiology and pigmentation. This has demonstrated the close relationship between LROs and led to the identification of conserved components required for LRO biogenesis and function. Here, we discuss aspects of this conserved machinery among LROs in relation to the heritable multisystem disorders they associate with, and present our current understanding of how dysfunctions in the proteins affected in the disease impact the formation, motility and ultimate secretion of LROs. Moreover, we have analysed the expression of the members of the CHEVI complex affected in Arthrogryposis, Renal dysfunction and Cholestasis syndrome, in different cell types, by collecting single cell RNA expression data from the human protein atlas. We propose a hypothesis describing how transcriptional regulation could constitute a mechanism that regulates the pleiotropic functions of proteins and their interacting partners in different LROs.

Type II phosphatidylinositol 4-kinases function sequentially in cargo delivery from early endosomes to melanosomes

Melanosomes are pigment cell-specific lysosome-related organelles in which melanin pigments are synthesized and stored. Melanosome maturation requires delivery of melanogenic cargoes via tubular transport carriers that emanate from early endosomes and that require BLOC-1 for their formation. Here we show that phosphatidylinositol-4-phosphate (PtdIns4P) and the type II PtdIns-4-kinases (PI4KIIα and PI4KIIβ) support BLOC-1-dependent tubule formation to regulate melanosome biogenesis. Depletion of either PI4KIIα or PI4KIIβ with shRNAs in melanocytes reduced melanin content and misrouted BLOC-1-dependent cargoes to late endosomes/lysosomes. Genetic epistasis, cell fractionation, and quantitative live-cell imaging analyses show that PI4KIIα and PI4KIIβ function sequentially and non-redundantly downstream of BLOC-1 during tubule elongation toward melanosomes by generating local pools of PtdIns4P. The data show that both type II PtdIns-4-kinases are necessary for efficient BLOC-1-dependent tubule elongation and subsequent melanosome contact and content delivery during melanosome biogenesis. The independent functions of PtdIns-4-kinases in tubule extension are downstream of likely redundant functions in BLOC-1-dependent tubule initiation.

The retinal pigmentation pathway in human albinism: Not so black and white

Albinism is a pigment disorder affecting eye, skin and/or hair. Patients usually have decreased melanin in affected tissues and suffer from severe visual abnormalities, including foveal hypoplasia and chiasmal misrouting. Combining our data with those of the literature, we propose a single functional genetic retinal signalling pathway that includes all 22 currently known human albinism disease genes. We hypothesise that defects affecting the genesis or function of different intra-cellular organelles, including melanosomes, cause syndromic forms of albinism (Hermansky-Pudlak (HPS) and Chediak-Higashi syndrome (CHS)). We put forward that specific melanosome impairments cause different forms of oculocutaneous albinism (OCA1-8). Further, we incorporate GPR143 that has been implicated in ocular albinism (OA1), characterised by a phenotype limited to the eye. Finally, we include the SLC38A8-associated disorder FHONDA that causes an even more restricted "albinism-related" ocular phenotype with foveal hypoplasia and chiasmal misrouting but without pigmentation defects. We propose the following retinal pigmentation pathway, with increasingly specific genetic and cellular defects causing an increasingly specific ocular phenotype: (HPS1-11/CHS: syndromic forms of albinism)-(OCA1-8: OCA)-(GPR143: OA1)-(SLC38A8: FHONDA). Beyond disease genes involvement, we also evaluate a range of (candidate) regulatory and signalling mechanisms affecting the activity of the pathway in retinal development, retinal pigmentation and albinism. We further suggest that the proposed pigmentation pathway is also involved in other retinal disorders, such as age-related macular degeneration. The hypotheses put forward in this report provide a framework for further systematic studies in albinism and melanin pigmentation disorders.

Triphenyltin exposure induced abnormal morphological colouration in adult male guppies (Poecilia reticulata)

Fish morphological colouration is essential for their survival and reproduction success; however, it is vulnerable to environmental factors, such as pollutants. Triphenyltin (TPT) is widespread in aquatic ecosystems, and its impacts on fish have been problematic. Therefore, the purpose of this study was to investigate the effects of TPT at environment-related concentrations (0, 1, 10 and 100 ng Sn/L) on morphological colouration in male guppies (Poecilia reticulata). The results showed that TPT exposure affected both orange/red and dark morphological colouration in guppies. The faded orange/red colouration might be related to the decrease of coloured pteridine and Pts (6-Pyruvoyltetrahydropterin Synthase) expression. In addition, TPT exposure induced melanogenesis, however, much melanin was distributed diffusely in the skin and did not seem to form a spot pattern, giving the fish a dull appearance. According to the skin transcriptional profiles, the changes of dark morphological colouration might be related to the changes in genes related to the functions of melanosome components (Gpnmb, Slc45a2 and Tyr), construction (Ap3d1, Fig4, Hps3, Hps5, Lyst, Rabggta, Txndc5 and Vps33a), and transport (Rab27a). Additionally, genes related to the regulation of melanogenesis (Atrn and Pomc) and system effects (Atox1, Atp6ap2, Atp6v1f, Atp6v1h, Rpl24, Rps19 and Rps20) might also be involved in the molecular mechanisms of abnormal morphological colouration induced by TPT. The present study provides crucial data on the molecular basis of abnormal morphological colouration in fish exposed to TPT and underscores the importance of toxicological studies of the effects of pollutants in aquatic environments on fish morphological colouration.

Polarized trafficking and copper transport activity of ATP7B: a mutational approach to establish genotype-phenotype correlation in Wilson disease

Mutation in ATP7B gene causes Wilson disease (WD) that is characterized by severe hepatic and neurological symptoms. ATP7B localizes at the trans-Golgi Network (TGN) transporting copper to copper-dependent enzymes and traffics in apically targeted vesicles upon intracellular copper elevation. To decode the cellular underpinnings of WD manifestation we investigated copper-responsive polarized trafficking and copper transport activity of fifteen WD causing point mutations in ATP7B. Amino-terminal mutations Gly85Val, Leu168Pro and Gly591Asp displayed TGN and sub-apical localization whereas, Leu492Ser mislocalized at the basolateral region. The actuator domain mutation Gly875Arg shows retention in the endoplasmic reticulum (ER), Ala874Val and Leu795Phe show partial targeting to TGN and post-Golgi vesicles. The Nucleotide-Binding Domain mutations His1069Gln and Leu1083Phe also display impaired targeting. The C-terminal mutations Leu1373Pro/Arg is arrested at ER but Ser1423Asn shows TGN localization. Transmembrane mutant Arg778Leu resides in ER and TGN while Arg969Gln is exclusively ER localized. Cellular Cu level does not alter the targeting of any of the studied mutations. Mutants that traffic to TGN exhibits biosynthetic function. Finally, we correlated cellular phenotypes with the clinical manifestation of the two most prevalent mutations; the early onset and more aggressive WD caused by Arg778Leu and the milder form of WD caused by mutation His1069Gln. This article is protected by copyright. All rights reserved.

Elesclomol elevates cellular and mitochondrial iron levels by delivering copper to the iron import machinery

Copper (Cu) and iron (Fe) are redox-active metals that serve as cofactors for many essential cellular enzymes. Disruption in the intracellular homeostasis of these metals results in debilitating and frequently fatal human disorders, such as Menkes disease and Friedreich's ataxia. Recently, we reported that an investigational anticancer drug, elesclomol (ES), can deliver Cu to critical mitochondrial cuproenzymes and has the potential to be repurposed for treatment of Cu deficiency disorders. Here, we sought to determine the specificity of ES and the ES-Cu complex in delivering Cu to cuproenzymes in different intracellular compartments. Using a combination of yeast genetics, subcellular fractionation, and inductively coupled plasma-mass spectrometry-based metal measurements, we showed that ES and ES-Cu treatment results in an increase in cellular and mitochondrial Fe content, along with the expected increase in Cu. Utilizing yeast mutants of Cu and Fe transporters, we demonstrate that ES-based elevation in cellular Fe levels is independent of the major cellular Cu importer, but is dependent on the Fe importer Ftr1 and its partner Fet3, a multicopper-oxidase. As Fet3 is metallated in the Golgi lumen, we sought to uncover the mechanism by which Fet3 receives Cu from ES. Using yeast knockouts of genes involved in Cu delivery to Fet3, we determined that ES can bypass Atx1, a metallochaperone involved in Cu delivery to the Golgi membrane Cu pump, Ccc2, but not Ccc2 itself. Taken together, our study provides a mechanism by which ES distributes Cu in cells and impacts cellular and mitochondrial Fe homeostasis.

KIF13A—A Key Regulator of Recycling Endosome Dynamics

Molecular motors of the kinesin superfamily (KIF) are a class of ATP-dependent motor proteins that transport cargo, including vesicles, along the tracks of the microtubule network. Around 45 KIF proteins have been described and are grouped into 14 subfamilies based on the sequence homology and domain organization. These motors facilitate a plethora of cellular functions such as vesicle transport, cell division and reorganization of the microtubule cytoskeleton. Current studies suggest that KIF13A, a kinesin-3 family member, associates with recycling endosomes and regulates their membrane dynamics (length and number). KIF13A has been implicated in several processes in many cell types, including cargo transport, recycling endosomal tubule biogenesis, cell polarity, migration and cytokinesis. Here we describe the recent advances in understanding the regulatory aspects of KIF13A motor in controlling the endosomal dynamics in addition to its structure, mechanism of its association to the membranes, regulators of motor activity, cell type-specific cargo/membrane transport, methods to measure its activity and its association with disease. Thus, this review article will provide our current understanding of the cell biological roles of KIF13A in regulating endosomal membrane remodeling.

Highly Sensitive and Specific Responses of Oyster Hemocytes to Copper Exposure: Single-Cell Transcriptomic Analysis of Different Cell Populations

Oyster hemocytes are the primary vehicles transporting and detoxifying metals and are regarded as important cells for the occurrence of colored oysters due to copper (Cu) contamination. However, its heterogeneous responses under Cu exposure have not been studied. Single-cell transcriptome profiling (scRNA-seq) provides high-resolution visual insights into tissue dynamics and environmental responses. Here, we used scRNA-seq to study the responses of different cell populations of hemocytes under Cu exposure in an estuarine oyster Crassostrea hongkongensis. The 1900 population-specific Cu-responsive genes were identified in 12 clusters of hemocytes, which provided a more sensitive technique for examining Cu exposure. The granulocyte, semigranulocyte, and hyalinocyte had specific responses, while the granulocyte was the most important responsive cell type and displayed heterogeneity responses of its two subtypes. In one subtype, Cu was transported with metal transporters and chelated with Cu chaperons in the cytoplasm. Excess Cu disturbed oxidative phosphorylation and induced reactive oxygen species production. However, in the other subtype, endocytosis was mainly responsible for Cu internalization, which was sequestered in membrane-bound granules. Collectively, our results provided the first mRNA expression profile of hemocytes in oysters and revealed the heterogeneity responses under Cu exposure.

Mahogunin Ring Finger 1 regulates pigmentation by controlling the pH of melanosomes in melanocytes and melanoma cells

Mahogunin Ring Finger 1 (MGRN1) is an E3-ubiquitin ligase absent in dark-furred mahoganoid mice. We investigated the mechanisms of hyperpigmentation in Mgrn1-null melan-md1 melanocytes, Mgrn1-KO cells obtained by CRISPR-Cas9-mediated knockdown of Mgrn1 in melan-a6 melanocytes, and melan-a6 cells depleted of MGRN1 by siRNA treatment. Mgrn1-deficient melanocytes showed higher melanin content associated with increased melanosome abundance and higher fraction of melanosomes in highly melanized maturation stages III-IV. Expression, post-translational processing and enzymatic activity of the rate-limiting melanogenic enzyme tyrosinase measured in cell-free extracts were comparable in control and MGRN1-depleted cells. However, tyrosinase activity measured in situ in live cells and expression of genes associated with regulation of pH increased upon MGRN1 repression. Using pH-sensitive fluorescent probes, we found that downregulation of MGRN1 expression in melanocytes and melanoma cells increased the pH of acidic organelles, including melanosomes, strongly suggesting a previously unknown role of MGRN1 in the regulation of melanosomal pH. Among the pH regulatory genes upregulated by Mgrn1 knockdown, we identified those encoding several subunits of the vacuolar adenosine triphosphatase V-ATPase (mostly Atp6v0d2) and a calcium channel of the transient receptor potential channel family, Mucolipin 3 (Mcoln3). Manipulation of expression of the Mcoln3 gene showed that overexpression of Mcoln3 played a significant role in neutralization of the pH of acidic organelles and activation of tyrosinase in MGRN1-depleted cells. Therefore, lack of MGRN1 led to cell-autonomous stimulation of pigment production in melanocytes mostly by increasing tyrosinase specific activity through neutralization of the melanosomal pH in a MCOLN3-dependent manner.

Establishment and Validation of Prognostic Nomograms Based on Serum Copper Level for Patients With Early-Stage Triple-Negative Breast Cancer

Background: Altered copper levels have been observed in several cancers, but studies on the relationship between serum copper and early-stage triple-negative breast cancer (TNBC) remain scare. We sought to establish a predictive model incorporating serum copper levels for individualized survival predictions. Methods: We retrospectively analyzed clinicopathological information and baseline peripheric blood samples of patients diagnosed with early-stage TNBC between September 2005 and October 2016 at Sun Yat-sen University Cancer Center. The optimal cut-off point of serum copper level was determined using maximally selected log-rank statistics. Kaplan-Meier curves were used to estimate survival probabilities. Independent prognostic indicators associated with survival were identified using multivariate Cox regression analysis, and subsequently, prognostic nomograms were established to predict individualized disease-free survival (DFS) and overall survival (OS). The nomograms were validated in a separate cohort of 86 patients from the original randomized clinical trial SYSUCC-001 (SYSUCC-001 cohort). Results: 350 patients were eligible in this study, including 264 in the training cohort and 86 in the SYSUCC-001 cohort. An optimal cut-off value of 21.3 μmol/L of serum copper was determined to maximally divide patients into low- and high-copper groups. After a median follow-up of 87.1 months, patients with high copper levels had significantly worse DFS (p = 0.002) and OS (p < 0.001) than those with low copper levels in the training cohort. Multivariate Cox regression analysis revealed that serum copper level was an independent factor for DFS and OS. Further, prognostic models based on serum copper were established for individualized predictions. These models showed excellent discrimination [C-index for DFS: 0.689, 95% confidence interval (CI): 0.621-0.757; C-index for OS: 0.728, 95% CI: 0.654-0.802] and predictive calibration, and were validated in the SYSUCC-001 cohort. Conclusion: Serum copper level is a potential predictive biomarker for patients with early-stage TNBC. Predictive nomograms based on serum copper might be served as a practical tool for individualized prognostication.

Elesclomol induces copper-dependent ferroptosis in colorectal cancer cells via degradation of ATP7A

Cancer cells reprogram their copper metabolism to adapt to adverse microenvironments, such as oxidative stress. The copper chelator elesclomol has been reported to have considerable anticancer efficacy, but the underlying mechanisms remain largely unknown. In this study, we found that elesclomol-mediated copper overload inhibits colorectal cancer (CRC) both in vitro and in vivo. Elesclomol alone promotes the degradation of the copper transporter copper-transporting ATPase 1 (ATP7A), which retards the proliferation of CRC cells. This property distinguishes it from several other copper chelators. Combinational treatment of elesclomol and copper leads to copper retention within mitochondria due to ATP7A loss, leading to reactive oxygen species accumulation, which in turn promotes the degradation of SLC7A11, thus further enhancing oxidative stress and consequent ferroptosis in CRC cells. This effect accounts for the robust antitumour activity of elesclomol against CRC, which can be reversed by the administration of antioxidants and ferroptosis inhibitors, as well as the overexpression of ATP7A. In summary, our findings indicate that elesclomol-induced copper chelation inhibits CRC by targeting ATP7A and regulating ferroptosis.

Imaging Cu2+ binding to charged phospholipid membranes by high-throughput second harmonic wide-field microscopy

The interaction of divalent copper ions (Cu²⁺) with cell membranes is crucial for a variety of physiological processes of cells, such as hormone synthesis and cellular energy production. These interactions would not be possible without membrane hydration. However, the role of water has not received a lot of attention in membrane studies. Here, we use high-throughput wide-field second harmonic (SH) microscopy to study the interaction between Cu²⁺ and hydrated freestanding Montal-Müller lipid membranes. The symmetric lipid membranes are composed of 1,2-diphytanoyl-sn-glycero-3-phosphocholine and either 1,2-diphytanoyl-sn-glycero-3-phosphate or 1,2-diphytanoyl-sn-glycero-3-phospho L-serine and are brought into contact with divalent Cu²⁺, which are added to one leaflet while maintaining the ionic strength balance. We observe transient domains of high SH intensity. In these areas, Cu²⁺ ions bind to the charged head groups, leading to charge neutralization on one side of the membrane. This exposes the ordered water at the non-interacting side of the membrane interface, which can be used to compute the interfacial membrane potential difference. We find that the domains of lipids with phosphatidic acid head groups display a higher interfacial membrane potential than those with phosphatidylserine head groups, which converts into higher dynamic electrostatic free energies and binding constants.

Melanosome Biogenesis in the Pigmentation of Mammalian Skin

Melanins, the main pigments of the skin and hair in mammals, are synthesized within membrane-bound organelles of melanocytes called melanosomes. Melanosome structure and function are determined by a cohort of resident transmembrane proteins, many of which are expressed only in pigment cells and localize specifically to melanosomes. Defects in the genes that encode melanosome-specific proteins or components of the machinery required for their transport in and out of melanosomes underlie various forms of ocular or oculocutaneous albinism, characterized by hypopigmentation of the hair, skin, and eyes and by visual impairment. We review major components of melanosomes, including the enzymes that catalyze steps in melanin synthesis from tyrosine precursors, solute transporters that allow these enzymes to function, and structural proteins that underlie melanosome shape and melanin deposition. We then review the molecular mechanisms by which these components are biosynthetically delivered to newly forming melanosomes-many of which are shared by other cell types that generate cell type-specific lysosome-related organelles. We also highlight unanswered questions that need to be addressed by future investigation.

Real-time Tracking and Sensing of Cu+ and Cu2+ with a Single SERS Probe in the Live Brain: Toward Understanding Why Copper Ions Were Increased upon Ischemia

The imbalance of Cu⁺ and Cu²⁺ in the brain is closely related to neurodegenerative diseases. However, it still lacks of effective analytical methods for simultaneously determining the concentrations of Cu⁺ and Cu²⁺ . Herein, we created a novel SERS probe (CuSP) to real-time track and accurately quantify extracellular concentrations of Cu⁺ and Cu²⁺ in the live brain. The present CuSP probe demonstrated specific ability for recognition of Cu⁺ and Cu²⁺ in a dual-recognition mode. Then, a microarray consisting of 8 CuSP probes with high tempo-spatial resolution and good accuracy was constructed for tracking and simultaneously biosensing of Cu⁺ and Cu²⁺ in the cerebral cortex of living brain. Using our powerful tool, it was found that that the concentrations of Cu²⁺ and Cu⁺ were increased by ≈4.26 and ≈1.80 times upon ischemia, respectively. Three routes were first discovered for understanding the mechanisms of the increased concentrations of Cu⁺ and Cu²⁺ during ischemia.

Genetics of non-syndromic and syndromic oculocutaneous albinism in human and mouse

Oculocutaneous albinism (OCA) is the most frequent presentation of albinism, a heterogeneous rare genetic condition generally associated with variable alterations in pigmentation and with a profound visual impairment. There are non-syndromic and syndromic types of OCA, depending on whether the gene product affected impairs essentially the function of melanosomes or, in addition, that of other lysosome-related organelles (LROs), respectively. Syndromic OCA can be more severe and associated with additional systemic consequences, beyond pigmentation and vision alterations. In addition to OCA, albinism can also be presented without obvious skin and hair pigmentation alterations, in ocular albinism (OA), and a related genetic condition known as foveal hypoplasia, optic nerve decussation defects, and anterior segment dysgenesis (FHONDA). In this review, we will focus only in the genetics of skin pigmentation in OCA, both in human and mouse, updating our current knowledge on this subject.

A BLOC-1-AP-3 super-complex sorts a cis-SNARE complex into endosome-derived tubular transport carriers

Membrane transport carriers fuse with target membranes through engagement of cognate vSNAREs and tSNAREs on each membrane. How vSNAREs are sorted into transport carriers is incompletely understood. Here we show that VAMP7, the vSNARE for fusing endosome-derived tubular transport carriers with maturing melanosomes in melanocytes, is sorted into transport carriers in complex with the tSNARE component STX13. Sorting requires either recognition of VAMP7 by the AP-3δ subunit of AP-3 or of STX13 by the pallidin subunit of BLOC-1, but not both. Consequently, melanocytes expressing both AP-3δ and pallidin variants that cannot bind their respective SNARE proteins are hypopigmented and fail to sort BLOC-1-dependent cargo, STX13, or VAMP7 into transport carriers. However, SNARE binding does not influence BLOC-1 function in generating tubular transport carriers. These data reveal a novel mechanism of vSNARE sorting by recognition of redundant sorting determinants on a SNARE complex by an AP-3-BLOC-1 super-complex.

ATP7A-Regulated Enzyme Metalation and Trafficking in the Menkes Disease Puzzle

Copper is vital for numerous cellular functions affecting all tissues and organ systems in the body. The copper pump, ATP7A is critical for whole-body, cellular, and subcellular copper homeostasis, and dysfunction due to genetic defects results in Menkes disease. ATP7A dysfunction leads to copper deficiency in nervous tissue, liver, and blood but accumulation in other tissues. Site-specific cellular deficiencies of copper lead to loss of function of copper-dependent enzymes in all tissues, and the range of Menkes disease pathologies observed can now be explained in full by lack of specific copper enzymes. New pathways involving copper activated lysosomal and steroid sulfatases link patient symptoms usually related to other inborn errors of metabolism to Menkes disease. Additionally, new roles for lysyl oxidase in activation of molecules necessary for the innate immune system, and novel adapter molecules that play roles in ERGIC trafficking of brain receptors and other proteins, are emerging. We here summarize the current knowledge of the roles of copper enzyme function in Menkes disease, with a focus on ATP7A-mediated enzyme metalation in the secretory pathway. By establishing mechanistic relationships between copper-dependent cellular processes and Menkes disease symptoms in patients will not only increase understanding of copper biology but will also allow for the identification of an expanding range of copper-dependent enzymes and pathways. This will raise awareness of rare patient symptoms, and thus aid in early diagnosis of Menkes disease patients.

Copper metabolism as a unique vulnerability in cancer

The last 25 years have witnessed tremendous progress in identifying and characterizing proteins that regulate the uptake, intracellular trafficking and export of copper. Although dietary copper is required in trace amounts, sufficient quantities of this metal are needed to sustain growth and development in humans and other mammals. However, copper is also a rate-limiting nutrient for the growth and proliferation of cancer cells. Oral copper chelators taken with food have been shown to confer anti-neoplastic and anti-metastatic benefits in animals and humans. Recent studies have begun to identify specific roles for copper in pathways of oncogenic signaling and resistance to anti-neoplastic drugs. Here, we review the general mechanisms of cellular copper homeostasis and discuss roles of copper in cancer progression, highlighting metabolic vulnerabilities that may be targetable in the development of anticancer therapies.

Melanosome transport and regulation in development and disease

Melanosomes are specialized membrane-bound organelles that synthesize and organize melanin, ultimately providing color to the skin, hair, and eyes. Disorders in melanogenesis and melanosome transport are linked to pigmentary diseases, such as Hermansky-Pudlak syndrome, Chediak-Higashi syndrome, and Griscelli syndrome. Clinical cases of these pigmentary diseases shed light on the molecular mechanisms that control melanosome-related pathways. However, only an improved understanding of melanogenesis and melanosome transport will further the development of diagnostic and therapeutic approaches. Herein, we review the current literature surrounding melanosomes with particular emphasis on melanosome membrane transport and cytoskeleton-mediated melanosome transport. We also provide perspectives on melanosome regulatory mechanisms which include hormonal action, inflammation, autophagy, and organelle interactions.

SLC45A2 protein stability and regulation of melanosome pH determine melanocyte pigmentation

SLC45A2 encodes a putative transporter expressed primarily in pigment cells. SLC45A2 mutations cause oculocutaneous albinism type 4 (OCA4) and polymorphisms are associated with pigmentation variation, but the localization, function, and regulation of SLC45A2 and its variants remain unknown. We show that SLC45A2 localizes to a cohort of mature melanosomes that only partially overlaps with the cohort expressing the chloride channel OCA2. SLC45A2 expressed ectopically in HeLa cells localizes to lysosomes and raises lysosomal pH, suggesting that in melanocytes SLC45A2 expression, like OCA2 expression, results in the deacidification of maturing melanosomes to support melanin synthesis. Interestingly, OCA2 overexpression compensates for loss of SLC45A2 expression in pigmentation. Analyses of SLC45A2- and OCA2-deficient mouse melanocytes show that SLC45A2 likely functions later during melanosome maturation than OCA2. Moreover, the light skin-associated SLC45A2 allelic F374 variant restores only moderate pigmentation to SLC45A2-deficient melanocytes due to rapid proteasome-dependent degradation resulting in lower protein expression levels in melanosomes than the dark skin-associated allelic L374 variant. Our data suggest that SLC45A2 maintains melanosome neutralization that is initially orchestrated by transient OCA2 activity to support melanization at late stages of melanosome maturation, and that a common allelic variant imparts reduced activity due to protein instability.

Membrane Transporters and Channels in Melanoma

Recent research has revealed that ion channels and transporters can be important players in tumor development, progression, and therapy resistance in melanoma. For example, members of the ABC family were shown to support cancer stemness-like features in melanoma cells, while several members of the TRP channel family were reported to act as tumor suppressors.Also, many transporter proteins support tumor cell viability and thus suppress apoptosis induction by anticancer therapy. Due to the high number of ion channels and transporters and the resulting high complexity of the field, progress in understanding is often focused on single molecules and is in total rather slow. In this review, we aim at giving an overview about a broad subset of ion transporters, also illustrating some aspects of the field, which have not been addressed in detail in melanoma. In context with the other chapters in this special issue on "Transportome Malfunctions in the Cancer Spectrum," a comparison between melanoma and these tumors will be possible.

Copper bioavailability is a KRAS-specific vulnerability in colorectal cancer

Despite its importance in human cancers, including colorectal cancers (CRC), oncogenic KRAS has been extremely challenging to target therapeutically. To identify potential vulnerabilities in KRAS-mutated CRC, we characterize the impact of oncogenic KRAS on the cell surface of intestinal epithelial cells. Here we show that oncogenic KRAS alters the expression of a myriad of cell-surface proteins implicated in diverse biological functions, and identify many potential surface-accessible therapeutic targets. Cell surface-based loss-of-function screens reveal that ATP7A, a copper-exporter upregulated by mutant KRAS, is essential for neoplastic growth. ATP7A is upregulated at the surface of KRAS-mutated CRC, and protects cells from excess copper-ion toxicity. We find that KRAS-mutated cells acquire copper via a non-canonical mechanism involving macropinocytosis, which appears to be required to support their growth. Together, these results indicate that copper bioavailability is a KRAS-selective vulnerability that could be exploited for the treatment of KRAS-mutated neoplasms.

The road to lysosome-related organelles: Insights from Hermansky-Pudlak syndrome and other rare diseases

Lysosome-related organelles (LROs) comprise a diverse group of cell type-specific, membrane-bound subcellular organelles that derive at least in part from the endolysosomal system but that have unique contents, morphologies and functions to support specific physiological roles. They include: melanosomes that provide pigment to our eyes and skin; alpha and dense granules in platelets, and lytic granules in cytotoxic T cells and natural killer cells, which release effectors to regulate hemostasis and immunity; and distinct classes of lamellar bodies in lung epithelial cells and keratinocytes that support lung plasticity and skin lubrication. The formation, maturation and/or secretion of subsets of LROs are dysfunctional or entirely absent in a number of hereditary syndromic disorders, including in particular the Hermansky-Pudlak syndromes. This review provides a comprehensive overview of LROs in humans and model organisms and presents our current understanding of how the products of genes that are defective in heritable diseases impact their formation, motility and ultimate secretion.

Elesclomol alleviates Menkes pathology and mortality by escorting Cu to cuproenzymes in mice

Loss-of-function mutations in the copper (Cu) transporter ATP7A cause Menkes disease. Menkes is an infantile, fatal, hereditary copper-deficiency disorder that is characterized by progressive neurological injury culminating in death, typically by 3 years of age. Severe copper deficiency leads to multiple pathologies, including impaired energy generation caused by cytochrome c oxidase dysfunction in the mitochondria. Here we report that the small molecule elesclomol escorted copper to the mitochondria and increased cytochrome c oxidase levels in the brain. Through this mechanism, elesclomol prevented detrimental neurodegenerative changes and improved the survival of the mottled-brindled mouse-a murine model of severe Menkes disease. Thus, elesclomol holds promise for the treatment of Menkes and associated disorders of hereditary copper deficiency.

Membrane transport proteins in melanosomes: Regulation of ions for pigmentation

Melanosomes are unique organelles in melanocytes that produce melanin, the pigment for skin, hair, and eye color. Tyrosinase is the essential and rate-limiting enzyme for melanin production, that strictly requires neutral pH for activity. pH maintenance is a result of the combinational function of multiple ion transport proteins. Thus, ion homeostasis in melanosomes is crucial for melanin synthesis. Defect of the ion transport system causes various pigmentation phenotypes, from mild effect to severe disorders such as albinism. In this review, we summarize the up-to-date knowledge of the ion transport system, such as transport function, structure, and the physiological roles and mechanisms of the ion transport proteins in melanosomes. In addition, we propose a model of melanosomal ion transport system-how the functional coupling of multiple transport proteins modulates and maintains ion homeostasis. We discuss melanin synthesis in terms of the ion transport system.

Exploring the Extended Biological Functions of the Human Copper Chaperone of Superoxide Dismutase 1

The human copper chaperone of SOD1 (designated as CCS) was discovered more than two decades ago. It is an important copper binding protein and a homolog of Saccharomyces cerevisiae LYS7. To date, no studies have systematically or specifically elaborated on the functional development of CCS. This review summarizes the essential information about CCS, such as its localization, 3D structure, and copper binding ability. An emphasis is placed on its interacting protein partners and its biological functions in vivo and in vitro. Three-dimensional structural analysis revealed that CCS is composed of three domains. Its primary molecular function is the delivery of copper to SOD1 and activation of SOD1. It has also been reported to bind to XIAP, Mia40, and X11α, and other proteins. Through these protein partners, CCS is implicated in several vital biological processes in vivo, such as copper homeostasis, apoptosis, angiogenesis and oxidative stress. This review is anticipated to assist scientists in systematically understanding the latest research developments of CCS for facilitating the development of new therapeutics targeting CCS in the future.

Topical treatment strategies to manipulate human skin pigmentation

Skin pigmentation is a result of melanin produced by melanocytes in the epidermis. Melanocyte activity, along with the type and distribution of melanins, is the main driver for diversity of skin pigmentation. Dark melanin acts to protect against the deleterious effects of ultraviolet (UV) radiation, including photo-aging and skin cancer formation. In turn, UV radiation activates skin melanocytes to induce further pigmentation (i.e., "tanning pathway"). The well-characterized MSH/MC1R-cAMP-MITF pathway regulates UV-induced melanization. Pharmacologic activation of this pathway ("sunless tanning") represents a potential strategy for skin cancer prevention, particularly in those with light skin or the "red hair" phenotype who tan poorly after UV exposure due to MC1R inactivating polymorphisms. Skin hyperpigmentation can also occur as a result of inflammatory processes and dermatological disorders such as melasma. While primarily of cosmetic concern, these conditions can dramatically impact quality of life of affected patients. Several topical agents are utilized to treat skin pigmentation disorders. Here, we review melanogenesis induced by UV exposure and the agents that target this pathway.