A novel function of Prohibitin on melanosome transport in melanocytes

Acetylation-enhanced Sp1 transcriptional activity suppresses Mlph expression

Melanosome transport is regulated by major proteins, including Rab27a, Melanophilin (Mlph), and Myosin Va (Myo-Va), that form a tripartite complex. Mutation of these proteins causes melanosome aggregation around the nucleus. Among these proteins, Mlph is a linker between Rab27a and Myo-Va. There are some studies about the regulation of Mlph transcriptional expression. However, its regulation by post-translational modifications remains unclear. In this study, inhibition of HDACs by SAHA and TSA disrupted melanosome transport, causing melanosome aggregation. Specifically, we identified a novel mechanism in which HDAC5 regulates Mlph expression via Sp1. Knockdown of HDAC5 increased the acetylation of Sp1 and the binding to the Mlph promoter, thereby modulating its expression. This study highlights the crucial role of HDAC5 in melanosome transport through its interaction with Sp1. These findings suggest that HDAC5-mediated deacetylation is pivotal in the post-translational modification of melanosome transport, providing insights into the molecular mechanisms underlying this process.

An Overview of the Biological Complexity of Vitiligo

Vitiligo is a skin disease that affects all ethnicities and genders and is characterized by the loss of pigment essentially due to the selective loss of melanocytes. Although it is generally considered a systemic disease associated with polymorphisms in genes involved in the immune response, vitiligo is also considered an oxidative imbalance-associated disease. It represents a multifactorial pathology in which some genetic predisposition and epigenetic factors coupled with some critical biochemical and molecular pathways could play a pivotal role. The aim of this work was thus to review some of the fine cellular mechanisms involved in the etiopathogenesis of vitiligo, mainly focusing on the nonimmunological ones, extensively highlighted elsewhere. We took into consideration, in addition to oxidative stress, both the cause and the hallmark of the pathology, some less investigated aspects such as the role of epigenetic factors, e.g., microRNAs, of receptors of catecholamines, and the more recently recognized role of the mitochondria. Sex differences associated with vitiligo have also been investigated starting from sex hormones and the receptors through which they exert their influence. From literature analysis, a picture seems to emerge in which vitiligo can be considered not just a melanocyte-affecting disease but a systemic pathology that compromises the homeostasis of a complex tissue such as the skin, in which different cell types reside playing multifaceted physiological roles for the entire organism. The exact sequence of cellular and subcellular events associated with vitiligo is still a matter of debate. However, the knowledge of the individual biological factors implicated in vitiligo could help physicians to highlight useful innovative markers of progression and provide, in the long run, new targets for more tailored treatments based on individual manifestations of the disease.

Mitochondria-Melanocyte cellular interactions: An emerging mechanism of vitiligo pathogenesis

Mitochondria has emerged as a potential modulator of melanocyte function other than just meeting its cellular ATP demands. Mitochondrial DNA defects are now an established cause of maternal inheritance diseases. Recent cellular studies have highlighted the mitochondrial interaction with other cellular organelles that lead to disease conditions such as in Duchenne muscular dystrophy, where defective mitochondria was found in melanocytes of these patients. Vitiligo, a depigmentory ailment of the skin, is another such disorder whose pathogenesis is now found to be associated with mitochondria. The complete absence of melanocytes at the lesioned site in vitiligo is a fact; however, the precise mechanism of this destruction is still undefined. In this review we have tried to discuss and link the emerging facts of mitochondrial function or its inter- and intra-organellar communications in vitiligo pathogenesis. Mitochondrial close association with melanosomes, molecular involvement in melanocyte-keratinocyte communication and melanocyte survival are new paradigm of melanogenesis that could ultimately account for vitiligo. This definitely adds the new dimensions to our understanding of vitiligo, its management and designing of future mitochondrial targeted therapy for vitiligo.

Study on the Role of Mitophagy Receptor PHB2 in Doubly Uniparental Inheritance of Hyriopsis cumingii

In bivalves, the heterogeneity of mitochondrial DNA and its unique mode of transmission have been the focus of attention, which is called doubly uniparental inheritance (DUI). Prohibitin-2 (phb2) is a mitochondrial inner membrane protein that is a key mitophagy receptor for parental mitochondrial removal. Hyriopsis cumingii is a freshwater bivalve in China, the full-length cDNA of H. cumingii phb2 (named Hcphb2) is 2917 bp and encodes a total of 300 amino acids, a highly conserved sequence. Hcphb2 was highly expressed in the ovary. In the gonadal tissues of 5- to 8-month-old female mussels, the expression level of Hcphb2 continued to significantly increase. After Hcphb2 siRNA interference in 6-month-old female mussels, the expression of M-COII, a marker gene on M-type mitochondria, showed a considerable increase (p < 0.05). In contrast, the expression of autophagosome formation and maturation-related genes, atg4b, atg5, atg12, and atg16l, in the ATG family genes was significantly decreased (p < 0.01). Subcellular localization showed that Hcphb2 appeared in spermatogonia, spermatocyte, spermatid, and sperm, and its location changes synchronize with the behavior of M-type mitochondria location changes in DUI species. And it was found that miR-184 negatively regulated Hcphb2. The above results suggest that the mitochondrial autophagy receptor gene Hcphb2 may be associated with the degradation of M-type mitochondria in the freshwater mussel. This process requires multiple genes to participate, of which Hcphb2 and autophagy genes are only some of those that may play a role.

Melanin: a unifying theory of disease as exemplified by Parkinson's, Alzheimer's, and Lewy body dementia

Melanin, a ubiquitous dark pigment, plays important roles in the immune system, including scavenging reactive oxygen species formed in response to ultraviolet radiation absorption, absorbing metals, thermal regulation, drug uptake, innate immune system functions, redox, and energy transduction. Many tissue types, including brain, heart, arteries, ovaries, and others, contain melanin. Almost all cells contain precursors to melanin. A growing number of diseases in which there is a loss of melanin and/or neuromelanin are increasingly thought to have infectious etiologies, for example, Alzheimer's disease (AD), Parkinson's disease (PD), Lewy Body Dementia (LBD), and vitiligo. AD, PD, LBD, and vitiligo have been linked with herpesvirus, which enters melanosomes and causes apoptosis, and with gut dysbiosis and inflammation. Herpesvirus is also linked with gut dysbiosis and inflammation. We theorize that under normal healthy states, melanin retains some of the energy it absorbs from electromagnetic radiation, which is then used to fuel cells, and energy from ATP is used to compliment that energy supply. We further theorize that loss of melanin reduces the energy supply of cells, which in the case of AD, PD, and LBD results in an inability to sustain immune system defenses and remove the plaques associated with the disease, which appear to be part of the immune system's attempt to eradicate the pathogens seen in these neurodegenerative diseases. In addition, in an attempt to explain why removing these plaques does not result in improvements in cognition and mood and why cognitions and moods in these individuals have ebbs and flows, we postulate that it is not the plaques that cause the cognitive symptoms but, rather, inflammation in the brain resulting from the immune system's response to pathogens. Our theory that energy retained in melanin fuels cells in an inverse relationship with ATP is supported by studies showing alterations in ATP production in relationship to melanin levels in melanomas, vitiligo, and healthy cells. Therefore, alteration of melanin levels may be at the core of many diseases. We propose regulating melanin levels may offer new avenues for treatment development.

PHB promotes bladder cancer cell epithelial-mesenchymal transition via the Wnt/β-catenin signaling pathway

As a member of PHB (prohibitin1) family, PHB plays important roles in many cancers, but its property in bladder carcinoma aggressiveness is unknown. This research was to explore the function and potential mechanism of PHB in bladder carcinoma in vivo and in vitro. The invasive abilities of cancer cell were determined by transwell and wound-healing assays. The function of PHB was confirmed by gene knockdown and overexpression methods. Further in vivo confirmation was performed in a nude mouse model with lung metastasis. The relationship of PHB and β-catenin was confirmed by immunoprecipitation and immunofluorescence staining assays. The protein expression of epithelial-mescenchymal transition (EMT) and Wnt/β-catenin signaling pathway was tested by immunofluorescence staining and western blotting assay. The depletion of PHB prevented bladder cancer cell invasiveness and inhibited EMT. Contrarily，the abilities of bladder carcinoma cells migration and invasion in vitro as well as metastasis in vivo were enhanced when the PHB overexpressed unnormally. Importantly, the β-catenin was identified to be bound by PHB and β-catenin knockdown reduced the cancer cell migration, invasion and EMT in PHB overexpressing cells. In addition, PHB stabilized β-catenin by inhibiting its ubiqutin-mediated degradation thus leading to increased Wnt/β-catenin signaling. These observations indicate that PHB could promote bladder cancer aggressiveness by binding with β-catenin to prevent the degradation of β-catenin and the localized invasive bladder cancer patients with PHB overexpression should take more aggressive postsurgical adjuvant anticancer therapies.

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.

The genetic basis and potential molecular mechanism of yellow-albino northern snakehead (Channa argus)

Body colour is an important economic trait for commercial fishes. Recently, a new colour morph displaying market-favoured yellow skin (termed as yellow-mutant, YM) of northern snakehead (Channa argus) was discovered in China. We confirmed that YM snakehead is an albino with complete loss of melanin in the skin and eyes by histological and ultrastructural observations, and inherited as a recessive Mendelian trait. By applying genomic analysis approaches, in combination with gene knockdown and rescue experiments, we suggested a non-sense mutation in slc45a2 (c.383G > A) is the causation for the YM snakehead. Notably, significantly higher levels of key melanogenesis genes (tyr, tyrp1, dct and pmel) and phospho-MITF protein were detected in YM snakehead than those in wild-type individuals, and the underlying mechanism was further investigated by comparative transcriptomic analysis. Results revealed that differential expressed genes involved in pathways like MAPK, WNT and calcium signalling were significantly induced in YM snakehead, which might account for the increased amount of melanogenesis elements, and presumably be stimulated by fibroblast-derived melanogenic factors in a paracrine manner. Our study clarified the genetic basis of colour variation in C. argus and provided the preliminary clue indicating the potential involvement of fibroblasts in pigmentation in fish.

Candidate pigmentation genes related to feather color variation in an indigenous chicken breed revealed by whole genome data

Chicken plumage color is an inheritable phenotype that was naturally and artificially selected for during domestication. The Baicheng You chicken is an indigenous Chinese chicken breed presenting three main feather colors, lavender, black, and yellow plumages. To explore the genetic mechanisms underlying the pigmentation in Baicheng You chickens, we re-sequenced the whole genome of Baicheng You chicken with the three plumage colors. By analyzing the divergent regions of the genome among the chickens with different feather colors, we identified some candidate genomic regions associated with the feather colors in Baicheng You chickens. We found that EGR1, MLPH, RAB17, SOX5, and GRM5 genes were the potential genes for black, lavender, and yellow feathers. MLPH, GRM5, and SOX5 genes have been found to be related to plumage colors in birds. Our results showed that EGR1 is a most plausible candidate gene for black plumage, RAB17, MLPH, and SOX5 for lavender plumage, and GRM5 for yellow plumage in Baicheng You chicken.

The function of prohibitins in mitochondria and the clinical potentials

Prohibitins (PHBs) are a class of highly evolutionarily conserved proteins that widely distribute in prokaryotes and eukaryotes. PHBs function in cell growth and proliferation or differentiation, regulating metabolism and signaling pathways. PHBs have different subcellular localization in eukaryotes, but they are mainly located in mitochondria. In the mitochondria, PHBs stabilize the structure of the mitochondrial membrane and regulate mitochondrial autophagy, mitochondrial dynamics, mitochondrial biogenesis and quality control, and mitochondrial unfolded protein response. PHBs has shown to be associated with many diseases, such as mitochondria diseases, cancers, infectious diseases, and so on. Some molecule targets of PHBs can interfere with the occurrence and development of diseases. Therefore, this review clarifies the functions of PHBs in mitochondria, and provides a summary of the potential values in clinics.

Regulation of Melanophilin (Mlph) gene expression by the glucocorticoid receptor (GR)

Mlph plays a crucial role in regulating skin pigmentation through the melanosome transport process. Although Mlph is a major component involved in melanosome transport, the mechanism that regulates the expression of the Mlph gene has not been identified. In this study, we demonstrate that Mlph expression is regulated by the glucocorticoid receptor (GR). Alteration of GR activity using a specific GR agonist or antagonist only regulated the expression of Mlph among the 3 key melanosome transport proteins. Translocation of GR from the cytosol into the nucleus following Dex treatment was confirmed by separating the cytosol and nuclear fractions and by immunofluorescence staining. In ChIP assays, Dex induced GR binding to the Mlph promoter and we determined that Dex induced the GR binding motif on the Mlph promoter. Our findings contribute to understanding the regulation of Mlph expression and to the novel role of GR in Mlph gene expression.

PHB2 promotes tumorigenesis via RACK1 in non-small cell lung cancer

Background: Lung cancer has the highest mortality rate among cancers worldwide, with non-small cell lung cancer (NSCLC) the most common type. Increasing evidence shows that PHB2 is highly expressed in other cancer types; however, the effects of PHB2 in NSCLC are currently poorly understood.

Method: PHB2 expression and its clinical relevance in NSCLC tumor tissues were analyzed using a tissue microarray. The biological role of PHB2 in NSCLC was investigated in vitro and in vivo using immunohistochemistry and immunofluorescence staining, gene expression knockdown and overexpression, cell proliferation assay, flow cytometry, terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay, wound healing assay, Transwell assay, western blot analysis, qRT-PCR, coimmunoprecipitation, and mass spectrometry analysis.

Results: Our major finding is that PHB2 facilitates tumorigenesis in NSCLC by interacting with and stabilizing RACK1, which further induces activation of downstream tumor-promoting effectors. PHB2 was found to be overexpressed in NSCLC tumor tissues, and its expression was correlated with clinicopathological features. Furthermore, PHB2 overexpression promoted proliferation, migration, and invasion, whereas PHB2 knockdown enhanced apoptosis in NSCLC cells. The stimulating effect of PHB2 on tumorigenesis was also verified in vivo. In addition, PHB2 interacted with RACK1 and increased its expression through posttranslational modification, which further induced activation of the Akt and FAK pathways.

Conclusions: Our results reveal the effects of PHB2 on tumorigenesis and its regulation of RACK1 and RACK1-associated proteins and downstream signaling in NSCLC. We believe that the crosstalk between PHB2 and RACK1 provides us with a great opportunity to design and develop novel therapeutic strategies for NSCLC.

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.

Rab GTPases: Key players in melanosome biogenesis, transport, and transfer

Melanosomes are specialized intracellular organelles that produce and store melanin pigments in melanocytes, which are present in several mammalian tissues and organs, including the skin, hair, and eyes. Melanosomes form and mature stepwise (stages I-IV) in melanocytes and then are transported toward the plasma membrane along the cytoskeleton. They are subsequently transferred to neighboring keratinocytes by a largely unknown mechanism, and incorporated melanosomes are transported to the perinuclear region of the keratinocytes where they form melanin caps. Melanocytes also extend several dendrites that facilitate the efficient transfer of the melanosomes to the keratinocytes. Since the melanosome biogenesis, transport, and transfer steps require multiple membrane trafficking processes, Rab GTPases that are conserved key regulators of membrane traffic in all eukaryotes are crucial for skin and hair pigmentation. Dysfunctions of two Rab isoforms, Rab27A and Rab38, are known to cause a hypopigmentation phenotype in human type 2 Griscelli syndrome patients and in chocolate mice (related to Hermansky-Pudlak syndrome), respectively. In this review article, I review the literature on the functions of each Rab isoform and its upstream and downstream regulators in mammalian melanocytes and keratinocytes.

A Third MLPH Variant Causing Coat Color Dilution in Dogs

Altered melanosome transport in melanocytes, resulting from variants in the melanophilin (MLPH) gene, are associated with inherited forms of coat color dilution in many species. In dogs, the MLPH gene corresponds to the D locus and two variants, c.-22G > A (d¹) and c.705G > C (d²), leading to the dilution of coat color, as described. Here, we describe the independent investigations of dogs whose coat color dilution could not be explained by known variants, and who report a third MLPH variant, (c.667_668insC) (d³), which leads to a frameshift and premature stop codon (p.His223Profs*41). The d³ allele is found at low frequency in multiple dog breeds, as well as in wolves, wolf-dog hybrids, and indigenous dogs. Canids in which the d³ allele contributed to the grey (dilute) phenotype were d¹/d³ compound heterozygotes or d³ homozygotes, and all non-dilute related dogs had one or two D alleles, consistent with a recessive inheritance. Similar to other loci responsible for coat colors in dogs, this, alongside likely additional allelic heterogeneity at the D locus, or other loci, must be considered when performing and interpreting genetic testing.