Pathways from senescence to melanoma: focus on MITF sumoylation

Cellular senescence: mechanisms and relevance to cancer and aging

Cellular senescence is an irreversible cell cycle arrest induced by stresses such as telomere shortening and oncogene activation. It acts as a tumor suppressor mechanism that prevents the proliferation of potentially tumorigenic cells. Paradoxically, senescent stromal cells that arise in the tumor microenvironment have been shown to promote tumor progression. In addition, senescent cells that accumulate in vivo over time are thought to contribute to aging and age-related diseases. These deleterious effects of senescent cells involve the secretion of bioactive molecules such as inflammatory cytokines and chemokines, a phenomenon known as the senescence-associated secretory phenotype. While the role of cellular senescence in vivo is becoming increasingly clear, the intracellular signaling pathways that induce the expression of senescent phenotypes are not fully understood. In this review, we outline senescence-associated signaling pathways and their relevance to cancer and aging.

Unravelling tumour cell diversity and prognostic signatures in cutaneous melanoma through machine learning analysis

Melanoma, a highly malignant tumour, presents significant challenges due to its cellular heterogeneity, yet research on this aspect in cutaneous melanoma remains limited. In this study, we utilized single-cell data from 92,521 cells to explore the tumour cell landscape. Through clustering analysis, we identified six distinct cell clusters and investigated their differentiation and metabolic heterogeneity using multi-omics approaches. Notably, cytotrace analysis and pseudotime trajectories revealed distinct stages of tumour cell differentiation, which have implications for patient survival. By leveraging markers from these clusters, we developed a tumour cell-specific machine learning model (TCM). This model not only predicts patient outcomes and responses to immunotherapy, but also distinguishes between genomically stable and unstable tumours and identifies inflamed ('hot') versus non-inflamed ('cold') tumours. Intriguingly, the TCM score showed a strong association with TOMM40, which we experimentally validated as an oncogene promoting tumour proliferation, invasion and migration. Overall, our findings introduce a novel biomarker score that aids in selecting melanoma patients for improved prognoses and targeted immunotherapy, thereby guiding clinical treatment decisions.

DNA damage remodels the MITF interactome to increase melanoma genomic instability

Since genome instability can drive cancer initiation and progression, cells have evolved highly effective and ubiquitous DNA damage response (DDR) programs. However, some cells (for example, in skin) are normally exposed to high levels of DNA-damaging agents. Whether such high-risk cells possess lineage-specific mechanisms that tailor DNA repair to the tissue remains largely unknown. Using melanoma as a model, we show here that the microphthalmia-associated transcription factor MITF, a lineage addition oncogene that coordinates many aspects of melanocyte and melanoma biology, plays a nontranscriptional role in shaping the DDR. On exposure to DNA-damaging agents, MITF is phosphorylated at S325, and its interactome is dramatically remodeled; most transcription cofactors dissociate, and instead MITF interacts with the MRE11-RAD50-NBS1 (MRN) complex. Consequently, cells with high MITF levels accumulate stalled replication forks and display defects in homologous recombination-mediated repair associated with impaired MRN recruitment to DNA damage. In agreement with this, high MITF levels are associated with increased single-nucleotide and copy number variant burdens in melanoma. Significantly, the SUMOylation-defective MITF-E318K melanoma predisposition mutation recapitulates the effects of DNA-PKcs-phosphorylated MITF. Our data suggest that a nontranscriptional function of a lineage-restricted transcription factor contributes to a tissue-specialized modulation of the DDR that can impact cancer initiation.

Mechanisms of Melanoma Progression and Treatment Resistance: Role of Cancer Stem-like Cells

Melanoma is the third most common type of skin cancer, characterized by its heterogeneity and propensity to metastasize to distant organs. Melanoma is a heterogeneous tumor, composed of genetically divergent subpopulations, including a small fraction of melanoma-initiating cancer stem-like cells (CSCs) and many non-cancer stem cells (non-CSCs). CSCs are characterized by their unique surface proteins associated with aberrant signaling pathways with a causal or consequential relationship with tumor progression, drug resistance, and recurrence. Melanomas also harbor significant alterations in functional genes (BRAF, CDKN2A, NRAS, TP53, and NF1). Of these, the most common are the BRAF and NRAS oncogenes, with 50% of melanomas demonstrating the BRAF mutation (BRAFV600E). While the successful targeting of BRAFV600E does improve overall survival, the long-term efficacy of available therapeutic options is limited due to adverse side effects and reduced clinical efficacy. Additionally, drug resistance develops rapidly via mechanisms involving fast feedback re-activation of MAPK signaling pathways. This article updates information relevant to the mechanisms of melanoma progression and resistance and particularly the mechanistic role of CSCs in melanoma progression, drug resistance, and recurrence.

Cellular senescence in skin-related research: Targeted signaling pathways and naturally occurring therapeutic agents

Despite the growing interest by researchers into cellular senescence, a hallmark of cellular aging, its role in human skin remains equivocal. The skin is the largest and most accessible human organ, reacting to the external and internal environment. Hence, it is an organ of choice to investigate cellular senescence and to target root-cause aging processes using senolytic and senomorphic agents, including naturally occurring plant-based derivatives. This review presents different aspects of skin cellular senescence, from physiology to pathology and signaling pathways. Cellular senescence can have both beneficial and detrimental effects on the skin, indicating that both prosenescent and antisenescent therapies may be desirable, based on the context. Knowledge of molecular mechanisms involved in skin cellular senescence may provide meaningful insights for developing effective therapeutics for senescence-related skin disorders, such as wound healing and cosmetic skin aging changes.

Disulfidptosis-related classification patterns and tumor microenvironment characterization in skin cutaneous melanoma

Aim

To identify distinct disulfidptosis-molecular subtypes and develop a novel prognostic signature.

Methods/materials

We integrated into this study multiple SKCM transcriptomic datasets from the Cancer Genome Atlas database and Gene Expression Omnibus dataset. The consensus clustering algorithm was applied to categorize SKCM patients into different DRG subtypes.

Results

Three distinct DRG subtypes were identified, which were correlated to different clinical outcomes and signaling pathways. Then, a disulfidptosis-relaed signature and nomogram were constructed, which could accurately predict the individual OS of patients with SKCM. The high-risk group was less sensitive to immunotherapy than the low-risk group.

Conclusion

The signature can assist healthcare professionals in making more accurate and individualized treatment choices for patients with SKCM.

The Cross Talk between Cellular Senescence and Melanoma: From Molecular Pathogenesis to Target Therapies

Melanoma is a malignant skin tumor that originates from melanocytes. The pathogenesis of melanoma involves a complex interaction that occurs between environmental factors, ultraviolet (UV)-light damage, and genetic alterations. UV light is the primary driver of the skin aging process and development of melanoma, which can induce reactive oxygen species (ROS) production and the presence of DNA damage in the cells, and results in cell senescence. As cellular senescence plays an important role in the relationship that exists between the skin aging process and the development of melanoma, the present study provides insight into the literature concerning the topic at present and discusses the relationship between skin aging and melanoma, including the mechanisms of cellular senescence that drive melanoma progression, the microenvironment in relation to skin aging and melanoma factors, and the therapeutics concerning melanoma. This review focuses on defining the role of cellular senescence in the process of melanoma carcinogenesis and discusses the targeting of senescent cells through therapeutic approaches, highlighting the areas that require more extensive research in the field.

Identification of anoikis-related subtypes and development of risk stratification system in skin cutaneous melanoma

Background

Anoikis, a form of apoptosis induced by cell detachment, plays a key role in cancer metastasis. However, the potential roles of anoikis-related genes (ARGs) in assessing the prognosis of skin cutaneous melanoma (SKCM) and the tumor microenvironment (TME) remain unclear.

Methods

The data from TCGA corresponding to transcriptomic expression patterns for patients with SKCM were downloaded and utilized to screen distinct molecular subtypes by a non-negative matrix factorization algorithm. The prognostic signature was constructed by least absolute shrinkage and selection operator (LASSO) Cox regression and was validated in SKCM patients from the GEO cohort. Moreover, the relationship of the ARG_score with prognosis, tumor-infiltrating immune cells, gene mutation, microsatellite instability (MSI), and immunotherapy efficacy.

Results

We screened 100 anoikis-related differentially expressed genes between SKCM tissues and normal skin tissues, which could divide all patients into three different subtypes with significantly distinct prognosis and immune cell infiltration. Then, an anoikis-related signature was developed based on subtype-related DEGs, which could classify all SKCM patients into low and high ARG_score groups with differing overall survival (OS) rates. ARG_score was confirmed to be a strong independent prognostic indicator for SKCM patients. By combining ARG_score with clinicopathological features, a nomogram was constructed, which could accurately predict the individual OS of patients with SKCM. Moreover, low ARG_score patients presented with higher levels of immune cell infiltration, TME score, higher tumor mutation burden, and better immunotherapy responses.

Conclusions

Our comprehensive analysis of ARGs in SKCM provides important insights into the immunological microenvironment within the tumor of SKCM patients and helps to forecast prognosis and the response to immunotherapy in SKCM patients, thereby making it easier to tailor more effective treatment strategies to individual patients.

[Translated article] Modern Concepts in Melanocytic Tumors

The advent of molecular pathology has fueled unprecedented advances in the diagnosis and understanding of melanocytic tumors. These advances, however, have also generated concepts that may be difficult to grasp for clinical practitioners, who are not always conversant with the array of genetic techniques employed in the laboratory. These same practitioners, however, are being increasingly called on to provide treatments that are often based on the latest molecular findings for melanocytic tumors. We review the most recent concepts in the pathway classification of melanocytic tumors, including intermediate lesions known as melanocytomas. We examine the genetic and molecular techniques used to study these tumors, look at where they overlap, and discuss their limitations and some of the most difficult-to-interpret results.

The journey from melanocytes to melanoma

Over the past decade, melanoma has led the field in new cancer treatments, with impressive gains in on-treatment survival but more modest improvements in overall survival. Melanoma presents heterogeneity and transcriptional plasticity that recapitulates distinct melanocyte developmental states and phenotypes, allowing it to adapt to and eventually escape even the most advanced treatments. Despite remarkable advances in our understanding of melanoma biology and genetics, the melanoma cell of origin is still fiercely debated because both melanocyte stem cells and mature melanocytes can be transformed. Animal models and high-throughput single-cell sequencing approaches have opened new opportunities to address this question. Here, we discuss the melanocytic journey from the neural crest, where they emerge as melanoblasts, to the fully mature pigmented melanocytes resident in several tissues. We describe a new understanding of melanocyte biology and the different melanocyte subpopulations and microenvironments they inhabit, and how this provides unique insights into melanoma initiation and progression. We highlight recent findings on melanoma heterogeneity and transcriptional plasticity and their implications for exciting new research areas and treatment opportunities. The lessons from melanocyte biology reveal how cells that are present to protect us from the damaging effects of ultraviolet radiation reach back to their origins to become a potentially deadly cancer.

DNA damage-induced interaction between a lineage addiction oncogenic transcription factor and the MRN complex shapes a tissue-specific DNA Damage Response and cancer predisposition

Since genome instability can drive cancer initiation and progression, cells have evolved highly effective and ubiquitous DNA Damage Response (DDR) programs. However, some cells, in skin for example, are normally exposed to high levels of DNA damaging agents. Whether such high-risk cells possess lineage-specific mechanisms that tailor DNA repair to the tissue remains largely unknown. Here we show, using melanoma as a model, that the microphthalmia-associated transcription factor MITF, a lineage addition oncogene that coordinates many aspects of melanocyte and melanoma biology, plays a non-transcriptional role in shaping the DDR. On exposure to DNA damaging agents, MITF is phosphorylated by ATM/DNA-PKcs, and unexpectedly its interactome is dramatically remodelled; most transcription (co)factors dissociate, and instead MITF interacts with the MRE11-RAD50-NBS1 (MRN) complex. Consequently, cells with high MITF levels accumulate stalled replication forks, and display defects in homologous recombination-mediated repair associated with impaired MRN recruitment to DNA damage. In agreement, high MITF levels are associated with increased SNV burden in melanoma. Significantly, the SUMOylation-defective MITF-E318K melanoma predisposition mutation recapitulates the effects of ATM/DNA-PKcs-phosphorylated MITF. Our data suggest that a non-transcriptional function of a lineage-restricted transcription factor contributes to a tissue-specialised modulation of the DDR that can impact cancer initiation.

Leveraging a cuproptosis-based signature to predict the prognosis and drug sensitivity of cutaneous melanoma

Immunotherapy is a vital treatment for patients with cutaneous melanoma (CM), but effective predictors to guide clinical immunotherapy are lacking. Cuproptosis is a newly discovered mode of cell death related to tumorigenesis. Exploring the relationship between the mode of cuproptosis and the effect of immunotherapy on CM could better guide clinical management. We clustered all patients with CM in the Cancer Genome Atlas (TCGA) database based on cuproptosis-related genes (CRGs). Prognosis, immunotherapeutic effect, tumor microenvironment score, expression of CD274, CTLA4, and PDCD1, and abundance of CD8 + T infiltration in group A were higher than in group B. Using a combination of LASSO and COX regression analysis, we identified 10 molecules significant to prognosis from differentially expressed genes between the two groups and constructed a cuproptosis-related scoring system (CRSS). Compared with the American Joint Committee on Cancer (AJCC) staging system, CRSS more accurately stratified CM patient risk and guided immunotherapy. CRSS successfully stratified risk and predicted the effect of immunotherapy in 869 patients with eight CM immunotherapy datasets and multiple other tumor immunotherapy cohorts. The nomogram model, which combined AJCC stage and CRSS, greatly improved the ability and accuracy of prognosis prediction. In general, our cuproptosis-related scoring system and nomogram model accurately stratified risk in CM patients and effectively predicted prognosis and the effect of immunotherapy in CM patients.

Modern Concepts in Melanocytic Tumors

The advent of molecular pathology has fueled unprecedented advances in the diagnosis and understanding of melanocytic tumors. These advances, however, have also generated concepts that may be difficult to grasp for clinical practitioners, who are not always conversant with the array of genetic techniques employed in the laboratory. These same practitioners, however, are being increasingly called on to provide treatments that are often based on the latest molecular findings for melanocytic tumors. We review the most recent concepts in the pathway classification of melanocytic tumors, including intermediate lesions known as melanocytomas. We examine the genetic and molecular techniques used to study these tumors, look at where they overlap, and discuss their limitations and some of the most difficult-to-interpret results.

A unique hyperdynamic dimer interface permits small molecule perturbation of the melanoma oncoprotein MITF for melanoma therapy

Microphthalmia transcription factor (MITF) regulates melanocyte development and is the "lineage-specific survival" oncogene of melanoma. MITF is essential for melanoma initiation, progression, and relapse and has been considered an important therapeutic target; however, direct inhibition of MITF through small molecules is considered impossible, due to the absence of a ligand-binding pocket for drug design. Here, our structural analyses show that the structure of MITF is hyperdynamic because of its out-of-register leucine zipper with a 3-residue insertion. The dynamic MITF is highly vulnerable to dimer-disrupting mutations, as we observed that MITF loss-of-function mutations in human Waardenburg syndrome type 2 A are frequently located on the dimer interface and disrupt the dimer forming ability accordingly. These observations suggest a unique opportunity to inhibit MITF with small molecules capable of disrupting the MITF dimer. From a high throughput screening against 654,650 compounds, we discovered compound TT-012, which specifically binds to dynamic MITF and destroys the latter's dimer formation and DNA-binding ability. Using chromatin immunoprecipitation assay and RNA sequencing, we showed that TT-012 inhibits the transcriptional activity of MITF in B16F10 melanoma cells. In addition, TT-012 inhibits the growth of high-MITF melanoma cells, and inhibits the tumor growth and metastasis with tolerable toxicity to liver and immune cells in animal models. Together, this study demonstrates a unique hyperdynamic dimer interface in melanoma oncoprotein MITF, and reveals a novel approach to therapeutically suppress MITF activity.

Loss of SUMO-specific protease 2 causes isolated glucocorticoid deficiency by blocking adrenal cortex zonal transdifferentiation in mice

SUMOylation is a dynamic posttranslational modification, that provides fine-tuning of protein function involved in the cellular response to stress, differentiation, and tissue development. In the adrenal cortex, an emblematic endocrine organ that mediates adaptation to physiological demands, the SUMOylation gradient is inversely correlated with the gradient of cellular differentiation raising important questions about its role in functional zonation and the response to stress. Considering that SUMO-specific protease 2 (SENP2), a deSUMOylating enzyme, is upregulated by Adrenocorticotropic Hormone (ACTH)/cAMP-dependent Protein Kinase (PKA) signalling within the zona fasciculata, we generated mice with adrenal-specific Senp2 loss to address these questions. Disruption of SENP2 activity in steroidogenic cells leads to specific hypoplasia of the zona fasciculata, a blunted reponse to ACTH and isolated glucocorticoid deficiency. Mechanistically, overSUMOylation resulting from SENP2 loss shifts the balance between ACTH/PKA and WNT/β-catenin signalling leading to repression of PKA activity and ectopic activation of β-catenin. At the cellular level, this blocks transdifferentiation of β-catenin-positive zona glomerulosa cells into fasciculata cells and sensitises them to premature apoptosis. Our findings indicate that the SUMO pathway is critical for adrenal homeostasis and stress responsiveness.

Clinical significance and immune landscape of KIR2DL4 and the senescence-based signature in cutaneous melanoma

Senescence is an effective barrier to tumor progression. Mutations that inhibit senescence and promote cell division are mandatory for the development of cancer. Therefore, it is particularly important to explore the differences between cutaneous melanoma (CM) patients with severe and mild degrees of senescence. We clustered all the patients with CM in the Cancer Genome Atlas (TCGA) database based on all the genes of the senescence pathway in the cellAge and MSigDB database. The prognosis, immunotherapy effect, tumor microenvironment score, NRAS mutation rate, expression of CD274, CTLA4, and PDCD1, and abundance of CD8+ T and NK cell infiltration in the younger group of patients (YG) were higher than those in the older group (OG). Compared with the American Joint Committee on Cancer (AJCC) stage, the risk scoring system stratified the risk of CM patients and guided immunotherapy more accurately. The nomogram model, which combined the AJCC stage and risk score, greatly improved the ability and accuracy of prognosis prediction. As KIR2DL4 is the core molecule in the risk scoring system (RSS), knocking down the KIR2DL4 of human NK cells in vitro can inhibit the cytotoxicity of NK cells and can also inhibit the secretion of tumor necrosis factor-α and interferon-γ by NK cells. In contrast, upregulation of KIR2DL4 can activate the MEK/ERK signaling pathway, which is the activation pathway of NK cells. OurRSS and nomogram model can accurately stratify the risk of CM patients and effectively predict the effect of immunotherapy and prognosis in CM patients.

Identification of distinct genomic features reveals frequent somatic AHNAK and PTEN mutations predominantly in primary malignant melanoma presenting in the ureter

BACKGROUND

Primary malignant melanoma of the ureter is extremely rare. Genetic variants to the increased risk of developing the disease have not yet been investigated.

METHODS

Tumour mutation profiling for primary malignant melanoma of the ureter was performed by whole-exome sequencing. Immunohistochemistry was performed to verify histopathological features and the variants of predisposing genes and driver mutation genes. Furthermore, we conducted a literature review and Surveillance, Epidemiology and End Result-based study by searching public databases.

RESULTS

We identified 38 somatic single nucleotide variants and 9 somatic insertions and deletions (INDELs) in tumour specimens. After filtering with the Cancer Gene Census database, seven predisposing genes and two driver mutation genes were identified. Moreover, the immunohistochemical profile showed that tumour cells were positive for Melan-A, melanoma gp100 human melanoma black 45 (HMB45), S100 beta and P53. The expression levels of two driver mutation genes (phosphatase and tensin homolog (PTEN) and desmoyokin (AHNAK) and five predisposing genes (AT-rich interaction domain 1B (ARID1B), catalase, eukaryotic translation initiation factor 4 gamma 3 (EIF4G3), ANK3 and collagen type I) were significantly downregulated in tumour tissues compared to paracancerous tissues. In the literature review and Surveillance, Epidemiology and End Results-based study, patients with primary malignant melanoma of the urinary tract had worse clinical outcomes than patients with primary urothelial carcinoma after 1:2 propensity score matching (P = 0.010). Additionally, Cox multivariate analysis for patients with primary malignant melanoma of the urinary tract indicated that distant metastasis (hazard ratio = 1.185; P = 0.044) was an independent predictor for overall survival, and tumour focality (hazard ratio = 0.602; P = 0.017) and non-surgery (hazard ratio = 0.434; P = 0.003) were independent factors for tumour progression.

CONCLUSIONS

Our study is the first to provide evidence that the distinct phenotypes of primary malignant melanoma of the ureter may be due to different genetic variations. The prognosis of primary malignant melanoma of the urinary tract was poorer than that of primary urothelial carcinoma of the urinary tract.

Detection of Cellular Senescence in Human Primary Melanocytes and Malignant Melanoma Cells In Vitro

Detection and quantification of senescent cells remain difficult due to variable phenotypes and the absence of highly specific and reliable biomarkers. It is therefore widely accepted to use a combination of multiple markers and cellular characteristics to define senescent cells in vitro. The exact choice of these markers is a subject of ongoing discussion and usually depends on objective reasons such as cell type and treatment conditions, as well as subjective considerations including feasibility and personal experience. This study aims to provide a comprehensive comparison of biomarkers and cellular characteristics used to detect senescence in melanocytic systems. Each marker was assessed in primary human melanocytes that overexpress mutant BRAFV600E, as it is commonly found in melanocytic nevi, and melanoma cells after treatment with the chemotherapeutic agent etoposide. The combined use of these two experimental settings is thought to allow profound conclusions on the choice of senescence biomarkers when working with melanocytic systems. Further, this study supports the development of standardized senescence detection and quantification by providing a comparative analysis that might also be helpful for other cell types and experimental conditions.

Genodermatoses associated with melanocytic nevi

Though melanocytic nevi are ubiquitous in the general population, they can also be key cutaneous manifestations of genetic syndromes. We describe genodermatoses associated with melanocytic nevi and discuss their clinical characteristics, cutaneous manifestations, underlying genetics, and, if applicable, guidelines for when genetic testing should be performed. We categorized these genodermatoses based on their association with congenital nevi, acquired nevi, or nevi whose first appearance is unknown. In many cases, the distinctive morphology or distribution of melanocytic nevi can be an important clue that an underlying genetic syndrome is present, allowing both the patient as well as family members to be screened for the more serious complications of their genetic disorder and receive education on potential preventative measures. As we continue to advance our understanding of how various genotypes give rise to the wide spectrum of phenotypes observed in these genodermatoses, we shall be able to better stratify risk and tailor our screening methods to clinically manage the heterogeneous manifestations of genodermatoses among these patients.

Pannexin 1 binds β-catenin to modulate melanoma cell growth and metabolism

Melanoma is the most aggressive skin malignancy with increasing incidence worldwide. Pannexin1 (PANX1), a member of the pannexin family of channel-forming glycoproteins, regulates cellular processes in melanoma cells including proliferation, migration, and invasion/metastasis. However, the mechanisms responsible for coordinating and regulating PANX1 function remain unclear. Here, we demonstrated a direct interaction between the C-terminal region of PANX1 and the N-terminal portion of β-catenin, a key transcription factor in the Wnt pathway. At the protein level, β-catenin was significantly decreased when PANX1 was either knocked down or inhibited by two PANX1 blockers, Probenecid and Spironolactone. Immunofluorescence imaging showed a disrupted pattern of β-catenin localization at the cell membrane in PANX1-deficient cells, and transcription of several Wnt target genes, including MITF, was suppressed. In addition, a mitochondrial stress test revealed that the metabolism of PANX1-deficient cells was impaired, indicating a role for PANX1 in the regulation of the melanoma cell metabolic profile. Taken together, our data show that PANX1 directly interacts with β-catenin to modulate growth and metabolism in melanoma cells. These findings provide mechanistic insight into PANX1-mediated melanoma progression and may be applicable to other contexts where PANX1 and β-catenin interact as a potential new component of the Wnt signaling pathway.

Targeted Therapy in Melanoma and Mechanisms of Resistance

The common mutation BRAFV600 in primary melanomas activates the mitogen-activated protein kinase/extracellular-signal-regulated kinase (MAPK/ERK) pathway and the introduction of proto-oncogene B-Raf (BRAF) and mitogen-activated protein kinase kinase (MEK) inhibitors (BRAFi and MEKi) was a breakthrough in the treatment of these cancers. However, 15–20% of tumors harbor primary resistance to this therapy, and moreover, patients develop acquired resistance to treatment. Understanding the molecular phenomena behind resistance to BRAFi/MEKis is indispensable in order to develop novel targeted therapies. Most often, resistance develops due to either the reactivation of the MAPK/ERK pathway or the activation of alternative kinase signaling pathways including phosphatase and tensin homolog (PTEN), neurofibromin 1 (NF-1) or RAS signaling. The hyperactivation of tyrosine kinase receptors, such as the receptor of the platelet-derived growth factor β (PDFRβ), insulin-like growth factor 1 receptor (IGF-1R) and the receptor for hepatocyte growth factor (HGF), lead to the induction of the AKT/3-phosphoinositol kinase (PI3K) pathway. Another pathway resulting in BRAFi/MEKi resistance is the hyperactivation of epidermal growth factor receptor (EGFR) signaling or the deregulation of microphthalmia-associated transcription factor (MITF).

WNT5A-Induced Activation of the Protein Kinase C Substrate MARCKS Is Required for Melanoma Cell Invasion

WNT5A is a well-known mediator of melanoma cell invasion and metastasis via its ability to activate protein kinase C (PKC), which is monitored by phosphorylation of the endogenous PKC substrate myristoylated alanine-rich c-kinase substrate (MARCKS). However, a possible direct contribution of MARCKS in WNT5A-mediated melanoma cell invasion has not been investigated. Analyses of melanoma patient databases suggested that similar to WNT5A expression, MARCKS expression appears to be associated with increased metastasis. A relationship between the two is suggested by the findings that recombinant WNT5A (rWNT5A) induces both increased expression and phosphorylation of MARCKS, whereas WNT5A silencing does the opposite. Moreover, WNT5A-induced invasion of melanoma cells was blocked by siRNA targeting MARCKS, indicating a crucial role of MARCKS expression and/or its phosphorylation. Next, we employed a peptide inhibitor of MARCKS phosphorylation that did not affect MARCKS expression and found that it abolished WNT5A-induced melanoma cell invasion. Similarly, rWNT5A induced the accumulation of phosphorylated MARCKS in membrane protrusions at the leading edge of melanoma cells. Our results demonstrate that WNT5A-induced phosphorylation of MARCKS is not only an indicator of PKC activity but also a crucial regulator of the metastatic behavior of melanoma and therefore an attractive future antimetastatic target in melanoma patients.

The Genetics of Human Skin and Hair Pigmentation

Human skin and hair color are visible traits that can vary dramatically within and across ethnic populations. The genetic makeup of these traits-including polymorphisms in the enzymes and signaling proteins involved in melanogenesis, and the vital role of ion transport mechanisms operating during the maturation and distribution of the melanosome-has provided new insights into the regulation of pigmentation. A large number of novel loci involved in the process have been recently discovered through four large-scale genome-wide association studies in Europeans, two large genetic studies of skin color in Africans, one study in Latin Americans, and functional testing in animal models. The responsible polymorphisms within these pigmentation genes appear at different population frequencies, can be used as ancestry-informative markers, and provide insight into the evolutionary selective forces that have acted to create this human diversity.

A conserved role for transcription factor sumoylation in binding-site selection

Large numbers of eukaryotic transcription factors (TFs) are modified by SUMO post-translational modifications. Whereas the effect of TF sumoylation on the expression of target genes is largely context-dependent, it is not known whether the modification has a common function in regulating TFs throughout eukaryotic species. Here, I highlight four studies that used genome-wide chromatin-immunoprecipitation analysis (ChIP-seq) to examine whether sumoylation affects the selection of sites on the genome that are bound by human and yeast TFs. The studies found that impairing sumoylation led to deregulated binding-site selection for all four of the examined TFs. Predominantly, compared to wild-type forms, the sumoylation-deficient forms of the TFs bound to numerous additional non-specific sites, pointing to a common role for the modification in restricting TF binding to appropriate sites. Evidence from these studies suggests that TF sumoylation influences binding-site selection by modulating protein-protein interactions with other DNA-binding TFs, or by promoting conformational changes in the TFs that alter their DNA-binding specificity or affinity. I propose a model in which, prior to their sumoylation, TFs initially bind to chromatin with reduced specificity, which leads to spurious binding but also ensures that all functional sites become bound. Once the TFs are bound to DNA, sumoylation then acts to increase specificity and promotes release of the TFs from non-specific sites. The similar observations from these four genome-wide studies across divergent species suggest that binding-site selection is a general and conserved function for TF sumoylation.

WIPI1, BAG1, and PEX3 Autophagy-Related Genes Are Relevant Melanoma Markers

ROS and oxidative stress may promote autophagy; on the other hand, autophagy may help reduce oxidative damages. According to the known interplay of ROS, autophagy, and melanoma onset, we hypothesized that autophagy-related genes (ARGs) may represent useful melanoma biomarkers. We therefore analyzed the gene and protein expression of 222 ARGs in human melanoma samples, from 5 independent expression databases (overall 572 patients). Gene expression was first evaluated in the GEO database. Forty-two genes showed extremely high ability to discriminate melanoma from nevi (63 samples) according to ROC (AUC ≥ 0.85) and Mann-Whitney (p < 0.0001) analyses. The 9 genes never related to melanoma before were then in silico validated in the IST online database. BAG1, CHMP2B, PEX3, and WIPI1 confirmed a strong differential gene expression, in 355 samples. A second-round validation performed on the Human Protein Atlas database showed strong differential protein expression for BAG1, PEX3, and WIPI1 in melanoma vs control samples, according to the image analysis of 80 human histological sections. WIPI1 gene expression also showed a significant prognostic value (p < 0.0001) according to 102 melanoma patients' survival data. We finally addressed in Oncomine database whether WIPI1 overexpression is melanoma-specific. Within more than 20 cancer types, the most relevant WIPI1 expression change (p = 0.00002; fold change = 3.1) was observed in melanoma. Molecular/functional relationships of the investigated molecules with melanoma and their molecular/functional network were analyzed via Chilibot software, STRING analysis, and gene ontology enrichment analysis. We conclude that WIPI1 (AUC = 0.99), BAG1 (AUC = 1), and PEX3 (AUC = 0.93) are relevant novel melanoma markers at both gene and protein levels.

BRN2, a POUerful driver of melanoma phenotype switching and metastasis

The POU domain family of transcription factors play a central role in embryogenesis and are highly expressed in neural crest cells and the developing brain. BRN2 is a class III POU domain protein that is a key mediator of neuroendocrine and melanocytic development and differentiation. While BRN2 is a central regulator in numerous developmental programs, it has also emerged as a major player in the biology of tumourigenesis. In melanoma, BRN2 has been implicated as one of the master regulators of the acquisition of invasive behaviour within the phenotype switching model of progression. As a mediator of melanoma cell phenotype switching, it coordinates the transition to a dedifferentiated, slow cycling and highly motile cell type. Its inverse expression relationship with MITF is believed to mediate tumour progression and metastasis within this model. Recent evidence has now outlined a potential epigenetic switching mechanism in melanoma cells driven by BRN2 expression that induces melanoma cell invasion. We summarize the role of BRN2 in tumour cell dissemination and metastasis in melanoma, while also examining it as a potential metastatic regulator in other tumour models.

Naturally-Occurring Canine Invasive Urothelial Carcinoma: A Model for Emerging Therapies

The development of targeted therapies and the resurgence of immunotherapy offer enormous potential to dramatically improve the outlook for patients with invasive urothelial carcinoma (InvUC). Optimization of these therapies, however, is crucial as only a minority of patients achieve dramatic remission, and toxicities are common. With the complexities of the therapies, and the growing list of possible drug combinations to test, highly relevant animal models are needed to assess and select the most promising approaches to carry forward into human trials. The animal model(s) should possess key features that dictate success or failure of cancer drugs in humans including tumor heterogeneity, genetic-epigenetic crosstalk, immune cell responsiveness, invasive and metastatic behavior, and molecular subtypes (e.g., luminal, basal). While it may not be possible to create these collective features in experimental models, these features are present in naturally-occurring InvUC in pet dogs. Naturally occurring canine InvUC closely mimics muscle-invasive bladder cancer in humans in regards to cellular and molecular features, molecular subtypes, biological behavior (sites and frequency of metastasis), and response to therapy. Clinical treatment trials in pet dogs with InvUC are considered a win-win scenario; the individual dog benefits from effective treatment, the results are expected to help other dogs, and the findings are expected to translate to better treatment outcomes in humans. This review will provide an overview of canine InvUC, the similarities to the human condition, and the potential for dogs with InvUC to serve as a model to predict the outcomes of targeted therapy and immunotherapy in humans.

Regulation of melanocyte stem cell behavior by the niche microenvironment

Somatic stem cells are regulated by their niches to maintain tissue homeostasis and repair throughout the lifetime of an organism. An excellent example to study stem cell/niche interactions is provided by the regeneration of melanocytes during the hair cycle and in response to various types of injury. These processes are regulated by neighboring stem cells and multiple signaling pathways, including WNT/β-catenin, KITL/KIT, EDNs/EDNRB, TGF-β/TGF-βR, α-MSH/MC1R, and Notch signaling. In this review, we highlight recent studies that have advanced our understanding of the molecular crosstalk between melanocyte stem cells and their neighboring cells, which collectively form the niche microenvironment, and we focus on the question of how McSCs/niche interactions shape the responses to genotoxic damages and mechanical injury.