PTEN and melanomagenesis

Differences of clinical features, prognosis and genetic mutations in Chinese patients with malignant melanoma and additional primary tumours

BACKGROUND

The differences in the clinical features, prognosis and genetic mutations in Chinese patients with malignant melanoma (MM) and additional primary tumours remain unclear.

METHODS

A retrospective analysis was conducted on patients with malignancies in Fujian Cancer Hospital from January 2007 to September 2022, end follow-up in September 2023. Clinical data were gathered, survival analysis was performed, and genetic mutations were detected.

RESULTS

There were 58 of 1223 melanoma patients with melanoma and additional primary tumours, an incidence of 4.74%. Acral MM was the most common subtype (26/58), 23 (39.66%) patients had concomitant digestive tumours. Patients who had MM as their first primary tumour (MMFP) had shorter tumour occurrence intervals (9.93 vs. 57.78 months, p = .008) but longer melanoma survival (MM-OS) than the non-MMFP group (100.43 vs. 18.93 months, p = .015). Patients with cancer family histories were more likely to have pathogenic and likely pathogenic (P/LP) mutations (2/5 vs. 4/25). The somatic BRAF gene mutation was frequently observed in MM tissue (8/19, 42.11%). Three patients had whole-genome doubling and microsatellite instability-high (MSI-H). The COSMIC2 signature 3 was significantly higher in the P/LP group.

CONCLUSIONS

The frequency of MM and additional primary tumours is about 5% in Chinese populations. Patients with melanoma diagnosed first have longer melanoma survival. Digestive system tumours were the most concomitant; a digestive examination is advisable, especially for those with an expected overall survival (OS) greater than 10 months. Meanwhile, patient's family cancer history should be followed up in detail, along with completion of germline P/LP mutation and somatic mutation testing, all of which may provide valuable support for further treatment.

Cell Death Modalities in Therapy of Melanoma

Melanoma, one of the most lethal cancers, demands urgent and effective treatment strategies. However, a successful therapeutic approach requires a precise understanding of the mechanisms underlying melanoma initiation and progression. This review provides an overview of melanoma pathogenesis, identifies current pathogenic factors contributing to mortality, and explores targeted therapy and checkpoint inhibitor therapy. Furthermore, we examine melanoma classification and corresponding therapies, along with advancements in various cell death mechanisms for melanoma treatment. We also discuss the current treatment status along with some drawbacks encountered during research stages such as resistance and metastasis.

Interferon regulatory factor 4 modulates epigenetic silencing and cancer-critical pathways in melanoma cells

Interferon regulatory factor 4 (IRF4) was initially identified as a key controller in lymphocyte differentiation and function, and subsequently as a dependency factor and therapy target in lymphocyte-derived cancers. In melanocytes, IRF4 takes part in pigmentation. Although genetic studies have implicated IRF4 in melanoma, how IRF4 functions in melanoma cells has remained largely elusive. Here, we confirmed prevalent IRF4 expression in melanoma and showed that high expression is linked to dependency in cells and mortality in patients. Analysis of genes activated by IRF4 uncovered, as a novel target category, epigenetic silencing factors involved in DNA methylation (DNMT1, DNMT3B, UHRF1) and histone H3K27 methylation (EZH2). Consequently, we show that IRF4 controls the expression of tumour suppressor genes known to be silenced by these epigenetic modifications, for instance cyclin-dependent kinase inhibitors CDKN1A and CDKN1B, the PI3-AKT pathway regulator PTEN, and primary cilium components. Furthermore, IRF4 modulates activity of key downstream oncogenic pathways, such as WNT/β-catenin and AKT, impacting cell proliferation and survival. Accordingly, IRF4 modifies the effectiveness of pertinent epigenetic drugs on melanoma cells, a finding that encourages further studies towards therapeutic targeting of IRF4 in melanoma.

Non-coding RNAs: Emerging biomarkers and therapeutic targets in ulcerative colitis

Ulcerative colitis (UC) is a persistent inflammatory condition affecting the colon's mucosal lining, leading to chronic bowel inflammation. Despite extensive research, the precise molecular mechanisms underlying UC pathogenesis remain elusive. NcRNAs form a category of functional RNA molecules devoid of protein-coding capacity. They have recently surfaced as pivotal modulators of gene expression and integral participants in various pathological processes, particularly those related to inflammatory disorders. The diverse classes of ncRNAs, encompassing miRNAs, circRNAs, and lncRNAs, have been implicated in UC. It highlights their involvement in key UC-related processes, such as immune cell activation, epithelial barrier integrity, and the production of pro-inflammatory mediators. ncRNAs have been identified as potential biomarkers for UC diagnosis and monitoring disease progression, offering promising avenues for personalized medicine. This approach may pave the way for novel, more specific treatments with reduced side effects, addressing the current limitations of conventional therapies. A comprehensive understanding of the interplay between ncRNAs and UC will advance our knowledge of the disease, potentially leading to more effective and personalized treatments for patients suffering from this debilitating condition. This review explores the pivotal role of ncRNAs in the context of UC, shedding light on their possible targets for diagnosis, prognosis, and therapeutic interventions.

Antioxidant mechanisms of mesenchymal stem cells and their therapeutic potential in vitiligo

Vitiligo is a skin pigmentation disorder caused by melanocyte damage or abnormal function. Reac-tive oxygen species Reactive oxygen species can cause oxidative stress damage to melanocytes, which in turn induces vitiligo. Traditional treatments such as phototherapy, drugs, and other methods of treatment are long and result in frequent recurrences. Currently, mesenchymal stem cells (MSCs) are widely used in the research of various disease treatments due to their excellent paracrine effects, making them a promising immunoregulatory and tissue repair strategy. Furthermore, an increasing body of evi-dence suggests that utilizing the paracrine functions of MSCs can downregulate oxidative stress in the testes, liver, kidneys, and other affected organs in animal models of certain diseases. Addition-ally, MSCs can help create a microenvironment that promotes tissue repair and regeneration in are-as with oxidative stress damage, improving the disordered state of the injured site. In this article, we review the pathogenesis of oxidative stress in vitiligo and promising strategies for its treatment.

Phenotypic and Dermoscopic Patterns of Familial Melanocytic Lesions: A Pilot Study in a Third-Level Center

Cutaneous melanoma is a highly aggressive skin cancer. It is estimated that 5% to 10% of the underlying mutations are hereditary and responsible for familial (or hereditary) melanoma. These patients are prone to the early development and higher risk of multiple melanomas. In recent years, an increasing number of genes have been identified thanks to genetic testing, allowing the subsequent surveillance of individuals at risk, yet it is still difficult to predict the presence of these mutations on a clinical basis. In this scenario, specific phenotypic and dermoscopic features could help clinicians in their identification. The aim of this work has been to correlate mutations to prevalent dermoscopic patterns, paving the way for reference models useful in clinical practice. In our cohort, out of 115 patients referred to genetic counseling for melanoma, 25 tested positive (21.7%) for critical mutations: CDKN2A (n = 12), MITF (n = 3), BAP1 (n = 1), MC1R (n = 3), PTEN (n = 1), TYR (n = 2), OCA2 (n = 1), and SLC45A2 (n = 2). The phenotype profiles obtained through the digital acquisition, analysis, and description of both benign and malignant pigmented lesions showed a predominance of the type II skin phenotype, with an elevated mean total nevus number (182 moles, range 75-390). As for dermoscopic features, specific mutation-related patterns were described in terms of pigmentation, areas of regression, and vascular structures. Although further studies with larger cohorts are needed, our work represents the beginning of a new approach to the study and diagnosis of familial melanoma, underlining the importance of clinical and dermoscopic patterns, which may constitute a reference model for each gene, enabling comparison.

Resistance to Molecularly Targeted Therapies in Melanoma

Malignant melanoma is the most aggressive type of skin cancer with invasive growth patterns. In 2021, 106,110 patients are projected to be diagnosed with melanoma, out of which 7180 are expected to die. Traditional methods like surgery, radiation therapy, and chemotherapy are not effective in the treatment of metastatic and advanced melanoma. Recent approaches to treat melanoma have focused on biomarkers that play significant roles in cell growth, proliferation, migration, and survival. Several FDA-approved molecular targeted therapies such as tyrosine kinase inhibitors (TKIs) have been developed against genetic biomarkers whose overexpression is implicated in tumorigenesis. The use of targeted therapies as an alternative or supplement to immunotherapy has revolutionized the management of metastatic melanoma. Although this treatment strategy is more efficacious and less toxic in comparison to traditional therapies, targeted therapies are less effective after prolonged treatment due to acquired resistance caused by mutations and activation of alternative mechanisms in melanoma tumors. Recent studies focus on understanding the mechanisms of acquired resistance to these current therapies. Further research is needed for the development of better approaches to improve prognosis in melanoma patients. In this article, various melanoma biomarkers including BRAF, MEK, RAS, c-KIT, VEGFR, c-MET and PI3K are described, and their potential mechanisms for drug resistance are discussed.

Mesenchymal stem cells promote human melanocytes proliferation and resistance to apoptosis through PTEN pathway in vitiligo

Background

Vitiligo is an acquired chronic and recurrent skin disease that causes a depigmentation disorder, resulting in selective destruction of melanocytes (MC). However, the mechanism that leads to melanocyte dysfunction and death remains unclear.

Methods

We performed RNA sequencing, immunohistochemistry, and immunoblotting to characterize the patterns of phosphatase and tensin homolog (PTEN)/phosphatidylinositol 3 kinase (PI3K)/protein kinase B (AKT) pathway activation in vitiligo. We also cocultured primary melanocytes with mesenchymal stem cells (MSCs) in a Transwell system to explore how MSCs inhibit the PTEN/PI3K/AKT pathway in melanocytes.

Results

We identified that vitiligo normal-lesional junction skin presented with high expression of PTEN, which led to the inhibition of AKT phosphorylation (p-AKT) at S^-473. Furthermore, PTEN overexpression led to oxidative stress-induced apoptosis in melanocytes. Coculturing with MSCs enhanced the cell proliferation of human melanocytes and repressed PTEN expression, which inhibited oxidative stress-induced apoptosis.

Conclusion

We report that vitiligo patients present with high PTEN expression, which may play a role in the impairment of melanocytes. Furthermore, our study provides evidence that MSCs target the PTEN/PI3K/AKT pathway to regulate cell proliferation and apoptosis in human melanocytes, indicating that MSCs may serve as a promising therapy for vitiligo.

Comprehensive Analysis of PTEN in Primary Cutaneous Melanoma

Phosphatase and tensin homologue (PTEN) is a tumour suppressor gene implicated in tumorigenesis of melanoma, with distinct cytoplasmic and nuclear functions. Cytoplasmic PTEN negatively regulates the PI3K/AKT/mTOR signalling pathway, while nuclear PTEN works as a tumour suppressor. Clinical data suggest that the loss of PTEN function in melanoma is associated with aggressive tumour behaviour. We performed a comprehensive analysis of PTEN in 112 primary cutaneous melanomas including immunohistochemical (IHC), fluorescent in situ hybridization (FISH), next-generation sequencing (NGS), and epigenetic analysis. The goal of our study was to: (a) correlate PTEN expression with selected clinico-pathological variables, and assess its prognostic significance; (b) correlate molecular aberrations with PTEN expression to consider the utility of immunohistochemical analysis of PTEN protein expression for screening PTEN genetic alterations; (c) review the literature and evaluate the PTEN expression level in melanoma with respect to possible therapeutic targeting. Our results showed that PTEN molecular alterations were present in 4/20 (20 %) cases with a loss of expression, 3/11 (27 %) cases with clonal-like expression, and 1/81 (1 %) cases with positive PTEN expression. No PTEN promoter methylation was found in any of the cases. Even though the value of our observation is limited by the low number of cases fully evaluated by IHC (112 cases), FISH (19 cases) and NGS (30 cases), our data suggest that IHC is not an appropriate method for the screening of PTEN genetic alterations. Our survival analysis suggests that patients with positive cytoplasmic PTEN expression show better disease-free survival (P < 0.05).

Cantharidin inhibits melanoma cell proliferation via the miR‑21‑mediated PTEN pathway

Cantharidin (CTD) is an active component isolated from the blister beetle that has been demonstrated to exert antitumor effects on multiple types of cancer. The current study aimed to investigate whether the potential inhibitory effects of CTD exist in human melanoma cells and to assess the underlying antitumor mechanisms of CTD. Using the Cell Counting Kit‑8 assay, it was demonstrated that CTD treatment reduced A375 cell proliferation significantly in a dose‑dependent manner. The colony formation assay demonstrated that CTD treatment could decrease the number of A375 cell colonies. Using subcutaneous xenograft tumor models, it was also demonstrated that CTD retarded solid tumor growth significantly. Furthermore, CTD treatment could induce A375 cell apoptosis, as detected by Annexin V‑fluorescein isothiocyanate/propidium iodide staining and western blot analysis. Notably, CTD treatment reduced microRNA (miR)‑21 expression and enhanced phosphatase and tensin homolog (PTEN) protein expression levels in A375 cells. Furthermore, overexpressing miR‑21 in A375 cells with the miR‑21 agomir blocked the antitumor effect of CTD both in vitro and in vivo. Finally, it was demonstrated that the inhibitory effects of CTD on A375 cells may be regulated by attenuating miR‑21‑mediated PTEN suppression. Based on these observations, it was suggested that CTD be used as a novel anti‑proliferation agent of human melanoma via targeting the miR‑21‑PTEN signaling pathway.

MicroRNA-30a-3p overexpression improves sepsis-induced cell apoptosis in vitro and in vivo via the PTEN/PI3K/AKT signaling pathway

The aim of the present study was to explain the mechanism of miR-30a-3p overexpression in sepsis-induced cell apoptosis in vitro and in vivo. For the in vitro cell experiments, H9c2 cells were divided into three groups, including the untreated normal control (NC), lipopolysaccharide (LPS)-treated and miRNA (treated with LPS and transfection with miRNA-30a-3p) groups. The cell proliferation and apoptosis were evaluated by MTT assay and flow cytometry, respectively. The relative protein expression levels were measured by western blot assay. In the in vivo experiment, a sepsis rat model was established by intraperitoneal injection of LPS. Sprague Dawley rats were divided into three groups, including the NC, LPS-injected and miRNA (in which model rats were injected with miR-30a-3p vector at the caudal vein) groups. The myocardial morphology in different groups was observed by hematoxylin and eosin staining. In addition, tissue apoptosis and protein expression levels were evaluated by TUNEL and western blot assay, respectively. The results of cell experiments indicated that the cell proliferation rate was significantly increased and the cell apoptosis rate was significantly downregulated in the miR-30a-3p group compared with the LPS group (both P<0.05). The relative protein expression of phosphatase and tensin homolog (PTEN) was markedly decreased in the miRNA group compared with the LPS group, while the levels of phosphoinositide 3-kinase (PI3K) and protein kinase B (AKT) were significantly increased in the miRNA group (all P<0.05). In the in vivo experiments, the myocardial morphology of the miRNA group was improved compared with that of the LPS group. Compared with the LPS group, cell apoptosis in the miRNA group was significantly downregulated (P<0.05), while the relative protein levels (PTEN, PI3K and AKT) in the tissues were also significantly altered (P<0.05). In conclusion, miR-30a-3p overexpression may improve the sepsis-induced cell apoptosis in vitro and in vivo via the PTEN/PI3K/AKT signaling pathway.

Effect of operating room care combined with home care for the postoperative rehabilitation and prognosis of gastric cancer patients with low PTEN gene expression

The aim of the present study was to analyze the effect of operating room (OR) care combined with home care on postoperative rehabilitation and prognosis of gastric cancer patients with low PTEN gene expression. Ninety-six gastric cancer patients with low PTEN gene expression, who underwent surgical treatment in our hospital were recruited. PTEN expression was measured by semi-quantitative polymerase chain reaction. Participants were randomized into the observation and control groups, with 48 cases each. Participants in the two groups received the same preoperative examination, gastric cancer surgery, postoperative drug therapy, and general care, while observation group participants were provided more comprehensive OR care combined with home care. After 1 year of home care, the self-rating anxiety scale (SAS) and Hamilton anxiety scale (HAMA) scores, rehabilitation status, overall quality of life, and Family Adaptability and Cohesion Scale were applied to compare postoperative rehabilitation and prognosis status in both groups. Data were statistically analyzed. Patients were followed up for 3 years, and survival time was analyzed. The operative time and bleeding volume between the two groups were not significantly different (p>0.05). The time of extubation and postoperative recovery time in the observation group were shorter than in the control group (p<0.01). The postoperative SAS and HAMA scores in both groups were significantly decreased compared with those preoperatively (p<0.01). Additionally, these scores were significantly lower in the observation than in the control group (p<0.01). The rehabilitation status of body function in the observation group was better than in the control group (p<0.01). Regarding the overall quality of life score and family adaptability and cohesion score, the observation group was better than the control group (p<0.01). In conclusion, OR care combined with home care was effective for the care of gastric cancer patients with low PTEN expression. Improving patient mood and mental state played a positive role in postoperative rehabilitation and prognosis.

Inhibition of the PI3K-Akt-mTOR signaling pathway in T lymphocytes in patients with active tuberculosis

OBJECTIVES

To investigate PI3K-Akt-mTOR signaling pathway changes and the proliferation of FoxP3⁺T_reg cells in patients with active tuberculosis.

METHODS

We isolated PBMCs and CD4⁺CD25⁺FoxP3⁺T_reg cells from peripheral blood collected from patients with active tuberculosis and healthy controls. We compared the proportion and MFI of PI3K-Akt-mTOR pathway components and PTEN by flow cytometry using specific cell-surface and intracellular markers. Moreover, we detected the specific secretory proteins ESAT-6 and Ag85B, cytokines IL-10, TGF-β1 and IL-35 in serum by ELISA.

RESULTS

Compared with healthy controls, the proportions of CD3⁺Akt⁺, CD3⁺p-Akt⁺, CD3⁺mTOR⁺, CD3⁺p-mTOR⁺ and CD3⁺PTEN⁺ cells, in the T lymphocyte population of patients with active tuberculosis, were decreased (p<0.05), while CD3⁺FoxP3⁺ cells were increased (p=0.013). Similarly, for CD4⁺CD25⁺FoxP3⁺T_reg cells, the proportions of Akt⁺ cells, p-Akt⁺ cells, mTOR⁺ cells, p-mTOR⁺ cells and PTEN⁺ cells were decreased (p<0.05) in patients with active tuberculosis. Compared with healthy controls, the levels of ESAT-6 and Ag85B were higher in patients with active tuberculosis (p<0.001). Levels of IL-10 and TGF-β1 were higher (p<0.001), whereas the level of IL-35 was lower (p<0.001).

CONCLUSION

The PI3K-Akt-mTOR signaling pathway in T lymphocytes and CD4⁺CD25⁺FoxP3⁺T_reg cells was inhibited, which could explain why M.tuberculosis can induce FoxP3⁺T_reg cell to expand.

A large-scale RNAi screen identifies LCMR1 as a critical regulator of Tspan8-mediated melanoma invasion

Melanoma is the deadliest form of skin cancer owing to its proclivity to metastasise, and recently developed therapies have not yielded the expected results, because almost all patients relapse. Therefore, understanding the molecular mechanisms that underlie early invasion by melanoma cells is crucial to improving patient survival. We have previously shown that, whereas the Tetraspanin 8 protein (Tspan8) is undetectable in normal skin and benign lesions, its expression arises with the progression of melanoma and is sufficient to increase cell invasiveness. Therefore, to identify Tspan8 transcriptional regulators that could explain the onset of Tspan8 expression, thereby conferring an invasive phenotype, we performed an innovative RNA interference-based screen, which, for the first time, identified several Tspan8 repressors and activators, such as GSK3β, PTEN, IQGAP1, TPT1 and LCMR1. LCMR1 is a recently identified protein that is overexpressed in numerous carcinomas; its expression and role, however, had not previously been studied in melanoma. The present study identified Tspan8 as the first LCMR1 target that could explain its function in carcinogenesis. LCMR1 modulation was sufficient to positively regulate endogenous Tspan8 expression, with concomitant in vitro phenotypic changes such as loss of melanoma cell-matrix adherence and increase in invasion, and Tspan8 expression promoted tumourigenicity in vivo. Moreover, LCMR1 and Tspan8 overexpression were shown to correlate in melanoma lesions, and both proteins could be downregulated in vitro by vemurafenib. In conclusion, this study highlights the importance of Tspan8 and its regulators in the control of early melanoma invasion and suggests that they may be promising new therapeutic targets downstream of the RAF-MEK-ERK signalling pathway.

Indole-3-carbinol (I3C) analogues are potent small molecule inhibitors of NEDD4-1 ubiquitin ligase activity that disrupt proliferation of human melanoma cells

The HECT domain-containing E3 ubiquitin ligase NEDD4-1 (Neural precursor cell Expressed Developmentally Down regulated gene 4-1) is frequently overexpressed in human cancers and displays oncogenic-like properties through the ubiquitin-dependent regulation of multiple protein substrates. However, little is known about small molecule enzymatic inhibitors of HECT domain-containing ubiquitin ligases. We now demonstrate that indole-3-carbinol (I3C), a natural anti-cancer phytochemical derived from cruciferous vegetables such as cabbage and broccoli, represents a new chemical scaffold of small molecule enzymatic inhibitors of NEDD4-1. Using in vitro ubiquitination assays, I3C, its stable synthetic derivative 1-benzyl-I3C and five novel synthetic analogues were shown to directly inhibit NEDD4-1 ubiquitination activity. Compared to I3C, which has an IC50 of 284μM, 1-benzyl-I3C was a significantly more potent NEDD4-1 enzymatic inhibitor with an IC50 of 12.3μM. Compounds 2242 and 2243, the two indolecarbinol analogues with added methyl groups that results in a more nucleophilic benzene ring π system, further enhanced potency with IC50s of 2.71μM and 7.59μM, respectively. Protein thermal shift assays that assess small ligand binding, in combination with in silico binding simulations with the crystallographic structure of NEDD4-1, showed that each of the indolecarbinol compounds bind to the purified catalytic HECT domain of NEDD4-1. The indolecarbinol compounds inhibited human melanoma cell proliferation in a manner that generally correlated with their effectiveness as NEDD4-1 enzymatic inhibitors. Taken together, we propose that I3C analogues represent a novel set of anti-cancer compounds for treatment of human melanomas and other cancers that express indolecarbinol-sensitive target enzymes.

MicroRNA-21 activation of Akt via PTEN is involved in the epithelial-mesenchymal transition and malignant transformation of human keratinocytes induced by arsenite

MicroRNAs are involved in the epithelial-mesenchymal transition (EMT) and malignant transformation of cells. However, the molecular mechanisms remain unclear. In seeking new biomarkers of chemical exposure in the risk assessment of arsenite-induced skin cancer, the function of microRNA-21 (miR-21) in the regulation of serine/threonine kinase (Akt) activation was investigated. Akt suppresses phosphatase and tensin homolog (PTEN) and is involved in neoplastic and metastatic properties of arsenite-transformed human keratinocyte (T-HaCaT) cells. In HaCaT cells, arsenite caused an increase of miR-21 levels and a decrease of PTEN, which activated Akt signaling and induced the EMT. On inhibiting miR-21, the levels of PTEN were increased, and activation of Akt was blocked. Knock-down of PTEN by siRNA enhanced the activation of Akt. The effects of an miR-21 inhibitor on Akt activation were antagonized by PTEN siRNA. In T-HaCaT cells, blocking the activation of Akt by LY294002 inhibited the EMT. Moreover, the effects of an miR-21 mimic on the EMT and the neoplastic capacity, invasion, and metastasis of T-HaCaT cells were antagonized by LY294002. T-HaCaT transfected with PTEN plasmids showed decreased Akt activation and E-cadherin expression and increased vimentin levels. Thus, activation of Akt, controlled by miR-21/PTEN, is involved in the EMT, and thereby affects the neoplastic, invasion, and migratory capacities of T-HaCaT cells. The results point to the potential use of miR-21 as a biomarker for skin cancer and as a target for cancer prevention and treatment.

Truncating PREX2 mutations activate its GEF activity and alter gene expression regulation in NRAS-mutant melanoma

PREX2 (phosphatidylinositol-3,4,5-triphosphate-dependent Rac-exchange factor 2) is a PTEN (phosphatase and tensin homolog deleted on chromosome 10) binding protein that is significantly mutated in cutaneous melanoma and pancreatic ductal adenocarcinoma. Here, genetic and biochemical analyses were conducted to elucidate the nature and mechanistic basis of PREX2 mutation in melanoma development. By generating an inducible transgenic mouse model we showed an oncogenic role for a truncating PREX2 mutation (PREX2(E824)*) in vivo in the context of mutant NRAS. Using integrative cross-species gene expression analysis, we identified deregulated cell cycle and cytoskeleton organization as significantly perturbed biological pathways in PREX2 mutant tumors. Mechanistically, truncation of PREX2 activated its Rac1 guanine nucleotide exchange factor activity, abolished binding to PTEN and activated the PI3K (phosphatidyl inositol 3 kinase)/Akt signaling pathway. We further showed that PREX2 truncating mutations or PTEN deletion induces down-regulation of the tumor suppressor and cell cycle regulator CDKN1C (also known as p57(KIP2)). This down-regulation occurs, at least partially, through DNA hypomethylation of a differentially methylated region in chromosome 11 that is a known regulatory region for expression of the CDKN1C gene. Together, these findings identify PREX2 as a mediator of NRAS-mutant melanoma development that acts through the PI3K/PTEN/Akt pathway to regulate gene expression of a cell cycle regulator.

A caveolin-dependent and PI3K/AKT-independent role of PTEN in β-catenin transcriptional activity

Loss of the tumour suppressor PTEN is frequent in human melanoma, results in MAPK activation, suppresses senescence and mediates metastatic behaviour. How PTEN loss mediates these effects is unknown. Here we show that loss of PTEN in epithelial and melanocytic cell lines induces the nuclear localization and transcriptional activation of β-catenin independent of the PI3K-AKT-GSK3β axis. The absence of PTEN leads to caveolin-1 (CAV1)-dependent β-catenin transcriptional modulation in vitro, cooperates with NRAS(Q61K) to initiate melanomagenesis in vivo and induces efficient metastasis formation associated with E-cadherin internalization. The CAV1-β-catenin axis is mediated by a feedback loop in which β-catenin represses transcription of miR-199a-5p and miR-203, which suppress the levels of CAV1 mRNA in melanoma cells. These data reveal a mechanism by which loss of PTEN increases CAV1-mediated dissociation of β-catenin from membranous E-cadherin, which may promote senescence bypass and metastasis.

MiR-21: an environmental driver of malignant melanoma?

Since the mid-1950’s, melanoma incidence has been rising steadily in industrialized Caucasian populations, thereby pointing to the pivotal involvement of environmental factors in melanomagenesis. Recent evidence underlines the crucial role of microRNA (miR) signaling in cancer initiation and progression. Increased miR-21 expression has been observed during the transition from a benign melanocytic lesion to malignant melanoma, exhibiting highest expression of miR-21. Notably, common BRAF and NRAS mutations in cutaneous melanoma are associated with increased miR-21 expression. MiR-21 is an oncomiR that affects critical target genes of malignant melanoma, resulting in sustained proliferation (PTEN, PI3K, Sprouty, PDCD4, FOXO1, TIPE2, p53, cyclin D1), evasion from apoptosis (FOXO1, FBXO11, APAF1, TIMP3, TIPE2), genetic instability (MSH2, FBXO11, hTERT), increased oxidative stress (FOXO1), angiogenesis (PTEN, HIF1α, TIMP3), invasion and metastasis (APAF1, PTEN, PDCD4, TIMP3). The purpose of this review is to provide translational evidence for major environmental and individual factors that increase the risk of melanoma, such as UV irradiation, chemical noxes, air pollution, smoking, chronic inflammation, Western nutrition, obesity, sedentary lifestyle and higher age, which are associated with increased miR-21 signaling. Exosomal miR-21 induced by extrinsic and intrinsic stimuli may be superimposed on mutation-induced miR-21 pathways of melanoma cells. Thus, oncogenic miR-21 signaling may be the converging point of intrinsic and extrinsic stimuli driving melanomagenesis. Future strategies of melanoma treatment and prevention should thus aim at reducing the burden of miR-21 signal transduction.

KINATEST-ID: a pipeline to develop phosphorylation-dependent terbium sensitizing kinase assays

Nonreceptor protein tyrosine kinases (NRTKs) are essential for cellular homeostasis and thus are a major focus of current drug discovery efforts. Peptide substrates that can enhance lanthanide ion luminescence upon tyrosine phosphorylation enable rapid, sensitive screening of kinase activity, however design of suitable substrates that can distinguish between tyrosine kinase families is a huge challenge. Despite their different substrate preferences, many NRTKs are structurally similar even between families. Furthermore, the development of lanthanide-based kinase assays is hampered by incomplete understanding of how to integrate sequence selectivity with metal ion binding, necessitating laborious iterative substrate optimization. We used curated proteomic data from endogenous kinase substrates and known Tb(3+)-binding sequences to build a generalizable in silico pipeline with tools to generate, screen, align, and select potential phosphorylation-dependent Tb(3+)-sensitizing substrates that are most likely to be kinase specific. We demonstrated the approach by developing several substrates that are selective within kinase families and amenable to high-throughput screening (HTS) applications. Overall, this strategy represents a pipeline for developing efficient and specific assays for virtually any tyrosine kinase that use HTS-compatible lanthanide-based detection. The tools provided in the pipeline also have the potential to be adapted to identify peptides for other purposes, including other enzyme assays or protein-binding ligands.

CD271 is expressed in melanomas with more aggressive behaviour, with correlation of characteristic morphology by in vivo reflectance confocal microscopy

BACKGROUND

Melanoma is the most highly aggressive type of skin cancer. Its resistance to existing treatments and the rapid rise in incidence underscore the importance of acquiring a better understanding of melanomagenesis.

OBJECTIVES

To assess the impact of reflectance confocal microscopy (RCM) on the description of cell morphology, which may influence the growth pattern and changes with increasing tumour severity, correlating with biological aspects.

METHODS

A retrospective analysis of 30 primary melanomas in vivo, evaluated by RCM, to correlate cell morphology and cellular arrangement with a marker of melanoma progression (CD271) using immunohistochemical evaluations.

RESULTS

Typical cells organized in dermal nests with peculiar in vivo confocal morphology result in melanoma with high malignancy and positivity to CD271. This architecture might be due to the presence of a type of cells, intrinsically predisposed to invasion, as a result of dedifferentiation programming, revealed by expression of the neural crest marker CD271.

CONCLUSIONS

With the hypothesis that dedifferentiated cells would be strongly responsible for initiation of tumour development and progression, we propose that CD271 detection could be associated with RCM evaluation in order to detect more aggressive melanoma subtypes.

Transcription addiction: can we garner the Yin and Yang functions of E2F1 for cancer therapy?

Classically, as a transcription factor family, the E2Fs are known to regulate the expression of various genes whose products are involved in a multitude of biological functions, many of which are deregulated in diseases including cancers. E2F is deregulated and hyperactive in most human cancers with context dependent, dichotomous and contradictory roles in almost all cancers. Cancer cells have an insatiable demand for transcription to ensure that gene products are available to sustain various biological processes that support their rapid growth and survival. In this context, cutting-off hyperactivity of transcription factors that support transcription dependence could be a valuable therapeutic strategy. However, one of the greatest challenges of targeting a transcription factor is the global effects on non-cancerous cells given that they control cellular functions in general. Recently, there is growing realization regarding the possibility to target the oncogenic activation of transcription factors to modulate transcription addiction without affecting the normal activity required for cell functions. In this review, we used E2F1 as a prototype transcription factor to address transcription factor activity in cancer cell functions. We focused on melanoma considering that E2F1 executes critical functions in response to UV, an etiological factor of cutaneous melanoma and lies immediately downstream of the CDKN2A/pRb axis, which is frequently deregulated in melanoma. Further, activation of E2F1 in melanomas can also occur independent of loss of CDKN2A. Given its activated status and the ability to transcriptionally control a plethora of genes involved in regulating melanoma development and progression, we review the current literature on its differential role in controlling signaling pathways involved in melanoma as well as therapeutic resistance, and discuss the practical value of weaning melanoma cells from E2F1-mediated transcription dependence for melanoma management.

The antiproliferative response of indole-3-carbinol in human melanoma cells is triggered by an interaction with NEDD4-1 and disruption of wild-type PTEN degradation

Human melanoma cells displaying distinct PTEN genotypes were used to assess the cellular role of this important tumor-suppressor protein in the antiproliferative response induced by the chemopreventative agent indole-3-carbinol (I3C), a natural indolecarbinol compound derived from the breakdown of glucobrassicin produced in cruciferous vegetables such as broccoli and Brussels sprouts. I3C induced a G1-phase cell-cycle arrest and apoptosis by stabilization of PTEN in human melanoma cells that express wild-type PTEN, but not in cells with mutant or null PTEN genotypes. Importantly, normal human epidermal melanocytes were unaffected by I3C treatment. In wild-type PTEN-expressing melanoma xenografts, formed in athymic mice, I3C inhibited the in vivo tumor growth rate and increased PTEN protein levels in the residual tumors. Mechanistically, I3C disrupted the ubiquitination of PTEN by NEDD4-1 (NEDD4), which prevented the proteasome-mediated degradation of PTEN without altering its transcript levels. RNAi-mediated knockdown of PTEN prevented the I3C-induced apoptotic response, whereas knockdown of NEDD4-1 mimicked the I3C apoptotic response, stabilized PTEN protein levels, and downregulated phosphorylated AKT-1 levels. Co-knockdown of PTEN and NEDD4-1 revealed that I3C-regulated apoptotic signaling through NEDD4-1 requires the presence of the wild-type PTEN protein. Finally, in silico structural modeling, in combination with isothermal titration calorimetry analysis, demonstrated that I3C directly interacts with purified NEDD4-1 protein.

IMPLICATIONS

This study identifies NEDD4-1 as a new I3C target protein, and that the I3C disruption of NEDD4-1 ubiquitination activity triggers the stabilization of the wild-type PTEN tumor suppressor to induce an antiproliferative response in melanoma. Mol Cancer Res; 12(11); 1621-34. ©2014 AACR.

Targeting human apurinic/apyrimidinic endonuclease 1 (APE1) in phosphatase and tensin homolog (PTEN) deficient melanoma cells for personalized therapy

Phosphatase and tensin homolog (PTEN) loss is associated with genomic instability. APE1 is a key player in DNA base excision repair (BER) and an emerging drug target in cancer. We have developed small molecule inhibitors against APE1 repair nuclease activity. In the current study we explored a synthetic lethal relationship between PTEN and APE1 in melanoma. Clinicopathological significance of PTEN mRNA and APE1 mRNA expression was investigated in 191 human melanomas. Preclinically, PTEN-deficient BRAF-mutated (UACC62, HT144, and SKMel28), PTEN-proficient BRAF-wildtype (MeWo), and doxycycline-inducible PTEN-knockout BRAF-wildtype MeWo melanoma cells were DNA repair expression profiled and investigated for synthetic lethality using a panel of four prototypical APE1 inhibitors. In human tumours, low PTEN mRNA and high APE1 mRNA was significantly associated with reduced relapse free and overall survival. Pre-clinically, compared to PTEN-proficient cells, PTEN-deficient cells displayed impaired expression of genes involved in DNA double strand break (DSB) repair. Synthetic lethality in PTEN-deficient cells was evidenced by increased sensitivity, accumulation of DSBs and induction of apoptosis following treatment with APE1 inhibitors. We conclude that PTEN deficiency is not only a promising biomarker in melanoma, but can also be targeted by a synthetic lethality strategy using inhibitors of BER, such as those targeting APE1.

The role of the dysfunctional akt-related pathway in cancer: establishment and maintenance of a malignant cell phenotype, resistance to therapy, and future strategies for drug development

Akt serine/threonine kinases, or PKB, are key players in the regulation of a wide variety of cellular activities, such as growth, proliferation, protection from apoptotic injuries, control of DNA damage responses and genome stability, metabolism, migration, and angiogenesis. The Akt-related pathway responds to the stimulation mediated by growth factors, cytokines, hormones, and several nutrients. Akt is present in three isoforms: Akt1, Akt2, and Akt3, which may be alternatively named PKB α , PKB β , and PKB γ , respectively. The Akt isoforms are encoded on three diverse chromosomes and their biological functions are predominantly distinct. Deregulations in the Akt-related pathway were observed in many human maladies, including cancer, cardiopathies, neurological diseases, and type-2 diabetes. This review discusses the significance of the abnormal activities of the Akt axis in promoting and sustaining malignancies, along with the development of tumor cell populations that exhibit enhanced resistance to chemo- and/or radiotherapy. This occurrence may be responsible for the relapse of the disease, which is unfortunately very often related to fatal consequences in patients.

Matrine activates PTEN to induce growth inhibition and apoptosis in V600EBRAF harboring melanoma cells

Here, we report a natural chemical Matrine, which exhibits anti-melanoma potential with its PTEN activation mechanism. Matrine effectively inhibited proliferation of several carcinoma cell lines, including melanoma ^V600EBRAF harboring M21 cells. Flow cytometry analysis showed Matrine induced G₀/G₁ cell cycle arrest in M21 cells dose-dependently. Apoptosis in M21 cells induced by Matrine was identified by Terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) analysis and Annexin-V/FITC staining. Molecular mechanistic study suggested that Matrine upregulated both mRNA level and protein expression level of phosphatase and tensin homolog deleted on chromosome ten (PTEN), leading to inhibition of the PI3K/Akt pathway. Downregulation of phosphor-Akt^ser473 by Matrine activated p21 and Bax, which contributed to G₀/G₁ cell cycle and apoptosis. Besides, Matrine enhanced the PI3K/Akt inhibition effects to inhibit the cell proliferation with PI3K inhibitor, LY2940002. In summary, our findings suggest Matrine is a promising antitumor drug candidate with its possible PTEN activation mechanisms for treating cancer diseases, such as melanomas.