GSK3β inhibition blocks melanoma cell/host interactions by downregulating N-cadherin expression and decreasing FAK phosphorylation

Canonical Wnt and TGF-β/BMP signaling enhance melanocyte regeneration but suppress invasiveness, migration, and proliferation of melanoma cells

Melanoma is the deadliest form of skin cancer and develops from the melanocytes that are responsible for the pigmentation of the skin. The skin is also a highly regenerative organ, harboring a pool of undifferentiated melanocyte stem cells that proliferate and differentiate into mature melanocytes during regenerative processes in the adult. Melanoma and melanocyte regeneration share remarkable cellular features, including activation of cell proliferation and migration. Yet, melanoma considerably differs from the regenerating melanocytes with respect to abnormal proliferation, invasive growth, and metastasis. Thus, it is likely that at the cellular level, melanoma resembles early stages of melanocyte regeneration with increased proliferation but separates from the later melanocyte regeneration stages due to reduced proliferation and enhanced differentiation. Here, by exploiting the zebrafish melanocytes that can efficiently regenerate and be induced to undergo malignant melanoma, we unravel the transcriptome profiles of the regenerating melanocytes during early and late regeneration and the melanocytic nevi and malignant melanoma. Our global comparison of the gene expression profiles of melanocyte regeneration and nevi/melanoma uncovers the opposite regulation of a substantial number of genes related to Wnt signaling and transforming growth factor beta (TGF-β)/(bone morphogenetic protein) BMP signaling pathways between regeneration and cancer. Functional activation of canonical Wnt or TGF-β/BMP pathways during melanocyte regeneration promoted melanocyte regeneration but potently suppressed the invasiveness, migration, and proliferation of human melanoma cells in vitro and in vivo. Therefore, the opposite regulation of signaling mechanisms between melanocyte regeneration and melanoma can be exploited to stop tumor growth and develop new anti-cancer therapies.

YAP1 controls the N-cadherin-mediated tumor-stroma interaction in melanoma progression

Epithelial-to-mesenchymal transition (EMT) is crucial for melanoma cells to escape keratinocyte control, invade underlying dermal tissues, and metastasize to distant organs. The hallmark of EMT is the switch from epithelial cadherin (E-cadherin) to neural cadherin (N-cadherin), allowing melanoma cells to form a homotypic N-cadherin-mediated adhesion with stromal fibroblasts. However, how "cadherin switching" is initiated, maintained, and regulated in melanoma remains unknown. Here, we show that upon Yes-associated protein 1 (YAP1) ablation in cancer-associated fibroblasts (CAFs), the progression of a BRAF-mutant mouse melanoma was significantly suppressed in vivo, and overexpressing YAP1 in CAFs accelerated melanoma growth. CAFs require the YAP1 function to proliferate, migrate, remodel the cytoskeletal machinery and matrix, and promote cancer cell invasion. By RNA-Seq, N-cadherin was identified as a major downstream effector of YAP1 signaling in CAFs. YAP1 silencing led to N-cadherin downregulation in CAFs, which subsequently induced the downregulation of N-cadherin in neighboring melanoma cells. N-cadherin downregulation inhibited the PI3K-AKT signaling pathway in melanoma cells and suppressed melanoma growth in vivo, supporting the role of N-cadherin as an adhesive and signaling molecule in melanoma cells. This finding suggests that YAP1 depletion in CAFs induces the downregulation of p-AKT signaling in melanoma cells through the N-cadherin-mediated interaction between melanoma cells and CAFs. Importantly, our data underscore that CAFs can regulate N-cadherin-mediated interactions with melanoma cells. Thus, disentangling cadherin-mediated cell-cell interactions can potentially disrupt tumor-stroma interactions and reverse the tumor cell invasive phenotype.

Phytochemical Analysis, In Vitro Biological Activities, and Computer-Aided Analysis of Potentilla nepalensis Hook Compounds as Potential Melanoma Inhibitors Based on Molecular Docking, MD Simulations, and ADMET

Potentilla nepalensis Hook is a perennial Himalayan medicinal herb of the Rosaceae family. The present study aimed to evaluate biological activities such as the antioxidant, antibacterial, and anticancer activities of roots and shoots of P. nepalensis and its synergistic antibacterial activity with antibacterial drugs. Folin-Ciocalteau and aluminium chloride methods were used for the calculation of total phenolic (TPC) and flavonoid content (TFC). A DPPH radical scavenging assay and broth dilution method were used for the determination of the antioxidant and antibacterial activity of the root and shoot extracts of P. nepalensis. Cytotoxic activity was determined using a colorimetric MTT assay. Further, phytochemical characterization of the root and shoot extracts was performed using the Gas chromatography-mass spectrophotometry (GC-MS) method. The TPC and TFC were found to be higher in the methanolic root extract of P. nepalensis. The methanolic shoot extract of P. nepalensis showed good antioxidant activity, while then-hexane root extract of P. nepalensis showed strong cytotoxic activity against tested SK-MEL-28 cells. Subsequently, in silico molecular docking studies of the identified bioactive compounds predicted potential anticancer properties. This study can lead to the production of new herbal medicines for various diseases employing P. nepalensis, leading to the creation of new medications.

Programmed cell death-1 blockade therapy in melanoma: Resistance mechanisms and combination strategies

Melanoma is a highly aggressive tumor derived from melanocytes. In recent years, the incidence and mortality of melanoma have gradually increased, seriously threatening human health. Classic treatments like surgery, chemotherapy, and radiotherapy show very limited efficacy. Due to the high immunogenicity of melanoma cells, immune checkpoint inhibitors have received considerable attention as melanoma treatments. One such therapy is blockade of programmed cell death-1 (PD-1), which is one of the most important negative immune regulators and is mainly expressed on activated T cells. Disruption of the interactions between PD-1 and its ligands, programmed death-ligand 1 (PD-L1) or programmed death-ligand 2 (PD-L2) rejuvenates exhausted T cells and enhances antitumor immunity. Although PD-1 blockade therapy is widely used in melanoma, a substantial proportion of patients still show no response or short durations of remission. Recent researches have focused on revealing the underlying mechanisms for resistance to this treatment and improving its efficacy through combination therapy. Here, we will introduce the resistance mechanisms associated with PD-1 blockade therapy in melanoma and review the combination therapies available.

NUMB as a Therapeutic Target for Melanoma

The upregulation of the adaptor protein NUMB triggers melanocytic differentiation from multipotent skin stem cells, which share many properties with aggressive melanoma cells. Although NUMB acts as a tumor suppressor in various human cancer types, little is known about its role in melanoma. In this study, we investigated the role of NUMB in melanoma progression and its regulatory mechanism. Analysis of The Cancer Genome Atlas melanoma datasets revealed that high NUMB expression in melanoma tissues correlates with improved patient survival. Moreover, NUMB expression is downregulated in metastatic melanoma cells. NUMB knockdown significantly increased the invasion potential of melanoma cells in a three-dimensional collagen matrix in vitro and in the lungs of a mouse model in vivo; it also significantly upregulated the expression of the NOTCH target gene CCNE. Previous studies suggested that Wnt signaling increases NUMB expression. By mimicking Wnt stimulation through glycogen synthase kinase-3 inhibition, we increased NUMB expression in melanoma cells. Furthermore, a glycogen synthase kinase-3 inhibitor reduced the invasion of melanoma cells in a NUMB-dependent manner. Together, our results suggest that NUMB suppresses invasion and metastasis in melanoma, potentially through its regulation of the NOTCH‒CCNE axis and that the inhibitors that upregulate NUMB can exert therapeutic effects in melanoma.

Cocktail of Astragalus Membranaceus and Radix Trichosanthis Suppresses Melanoma Tumor Growth and Cell Migration Through Regulation of Akt-Related Signaling Pathway

Background: Malignant melanoma has high morbidity and mortality and limited treatment options. Traditional Chinese medicine has great potential in the clinical therapy of cancer, and the theory of compatibility is one core content of Chinese medical theory. Astragalus Membranaceus and Radix Trichosanthis are clinically effective for the treatment of various cancers.

Methods: We verified the effects of AMD, RTD, and their “cocktail” on melanoma model in vitro and in vivo and the mechanism of its effect on the Akt-related signaling pathway by network pharmacology, MTT, flow cytometry, LDH, SOD, MDA assay, and Western blot.

Results: The network pharmacology analysis indicated that the PI3K-Akt pathway plays a crucial role in the treatment of malignant melanoma with these two herbs. In addition, AMD, RTD, and their “cocktail” could inhibit the proliferation of A375 cells by reducing the survival rate in a concentration-dependent manner and by regulating the cell cycle, and the compatibility of two herbs also could inhibit melanoma growth. They could, respectively, induce apoptosis and inhibit migration by affecting the expression of Bcl-2, Bax, p53, snail, E-cadherin, and N-cadherin. Furthermore, LDH activity was decreased, while SOD increased and MDA reduced. The factors of the Akt-related signaling pathway, Akt and p-Akt, were decreased.

Conclusion: This study showed that AMD, RTD, and their “cocktail” could regulate cell proliferation, apoptosis, and metastasis in A375 cells through the suppression of the Akt-related signaling pathway, and the “cocktail” groups had detoxification and additive effects. The best compatibility of the two herbs also can inhibit tumor growth and metastasis in vivo.

GSK3 as a Regulator of Cytoskeleton Architecture: Consequences for Health and Disease

Glycogen synthase kinase 3 (GSK3) was initially isolated as a critical protein in energy metabolism. However, subsequent studies indicate that GSK-3 is a multi-tasking kinase that links numerous signaling pathways in a cell and plays a vital role in the regulation of many aspects of cellular physiology. As a regulator of actin and tubulin cytoskeleton, GSK3 influences processes of cell polarization, interaction with the extracellular matrix, and directional migration of cells and their organelles during the growth and development of an animal organism. In this review, the roles of GSK3–cytoskeleton interactions in brain development and pathology, migration of healthy and cancer cells, and in cellular trafficking of mitochondria will be discussed.

Potential Health Benefits Associated with Lunasin Concentration in Dietary Supplements and Lunasin-Enriched Soy Extract

Lunasin has demonstrated antioxidative, anti-inflammatory, and chemopreventive properties. The objectives were to evaluate the concentration of lunasin in different lunasin-based commercial dietary supplements, to produce a lunasin-enriched soy extract (LESE) using a two-step pilot-plant-based ultrafiltration process, and to evaluate their biological potential in vitro. LESE was produced using 30 and 1 kDa membranes in a custom-made ultrafiltration skid. Lunasin was quantified in eight products and LESE. Lunasin concentrations of the lunasin-based products ranged from 9.2 ± 0.6 to 25.7 ± 1.1 mg lunasin/g protein. The LESE extract contained 58.2 mg lunasin/g protein, up to 6.3-fold higher lunasin enrichment than lunasin-based dietary supplements. Antioxidant capacity ranged from 121.5 mmol Trolox equivalents (TE)/g in Now® Kids to 354.4 mmol TE/g in LESE. Histone acetyltransferase (HAT) inhibition ranged from 5.3% on Soy Sentials® to 38.3% on synthetic lunasin. ORAC and lunasin concentrations were positively correlated, and HAT and lunasin concentrations were negatively correlated (p < 0.05). Melanoma B16-F10 and A375 cells treated with lunasin showed dose-dependent inhibitory potential (IC50 equivalent to 330 and 370 μM lunasin, respectively). Lunasin showed protein kinase B expression (57 ± 14%) compared to the control (100%) in B16-F10. Lunasin concentration found in commercial products and lunasin-enriched soy extract could exert benefits to consumers.

Glycogen synthase kinase 3β promotes osteosarcoma invasion and migration via regulating PTEN and phosphorylation of focal adhesion kinase

Aim: Typical features of human osteosarcoma are highly invasive and migratory capacities. Our study aimed to investigate the roles of glycogen synthase kinase 3β (GSK3β) in human osteosarcoma metastasis.

Methods: GSK3β expressions in clinical osteosarcoma tissues with or without metastasis were examined by immunohistochemical staining. The expressions of GSK3β, p-GSK3β^Ser9, and p-GSK3β^Tyr216 in human osteoblast cells (hFOB1.19) and human osteosarcoma cells (MG63, SaOS-2, and U2-OS) were detected by Western blotting. The GSK3β activity was measured by non-radio isotopic in vitro kinase assay. Migration and invasion abilities of MG-63 cells treated with small-molecular GSK3β inhibitors were respectively examined by monolayer-based wound-healing assay and transwell assay. The mRNA expressions of GSK3β, matrix metalloproteinase-2 (MMP-2), MMP-9, phosphatase with tensin homology (PTEN), and focal adhesion kinase (FAK) were detected after siRNA transfection for 72 h. Meanwhile, protein expressions of GSK3β, FAK, p-FAK^Y397, PTEN, MMP-2, and MMP-9 were measured by Western blotting.

Results: Clinical osteosarcoma tissues with metastasis showed higher GSK3β expressions. MG63 and U2-OS cells that were easy to occur metastasis showed significantly higher expressions and activities of GSK3β than SaOS-2 cells. Inhibition of GSK3β with small-molecular GSK3β inhibitors in MG63 cells significantly attenuated cell migration and invasion. These effects were associated with reduced expressions of MMP-2 and MMP-9. Moreover, increased PTEN and decreased p-FAK^Y397 expressions were observed following GSK3β knockdown by siRNA transfection. Conclusion: GSK3β might promote osteosarcoma invasion and migration via pathways associated with PTEN and phosphorylation of FAK.

The Landscape of Glycogen Synthase Kinase-3 Beta Genomic Alterations in Cancer

Glycogen synthase kinase-3β (GSK-3β), a serine/threonine kinase, has been implicated in the pathogenesis of many cancers, with involvement in cell-cycle regulation, apoptosis, and immune response. Small-molecule GSK-3β inhibitors are currently undergoing clinical investigation. Tumor sequencing has revealed genomic alterations in GSK-3β, yet an assessment of the genomic landscape in malignancies is lacking. This study assessed >100,000 tumors from two databases to analyze GSK-3β alterations. GSK-3β expression and immune cell infiltrate data were analyzed across cancer types, and programmed death-ligand 1 (PD-L1) expression was compared between GSK-3β-mutated and wild-type tumors. GSK-3β was mutated at a rate of 1%. The majority of mutated residues were in the kinase domain, with frequent mutations occurring in a GSK-3β substrate binding pocket. Uterine endometrioid carcinoma was the most commonly mutated (4%) tumor, and copy-number variations were most commonly observed in squamous histologies. Significant differences across cancer types for GSK-3β-mutated tumors were observed for B cells (P = 0.018), monocytes (P = 0.002), dendritic cells (P = 0.005), neutrophils (P = 0.0003), and endothelial cells (P = 0.014). GSK-3β mRNA expression was highest in melanoma. The frequency of PD-L1 expression was higher among GSK-3β-mutated tumors compared with wild type in colorectal cancer (P = 0.03), endometrial cancer (P = 0.05), melanoma (P = 0.02), ovarian carcinoma (P = 0.0001), and uterine sarcoma (P = 0.002). Overall, GSK-3β molecular alterations were detected in approximately 1% of solid tumors, tumors with GSK-3β mutations displayed a microenvironment with increased infiltration of B cells, and GSK-3β mutations were associated with increased PD-L1 expression in selected histologies. These results advance the understanding of GSK-3β complex signaling network interfacing with key pathways involved in carcinogenesis and immune response.

GSK-3β-Targeting Fisetin Promotes Melanogenesis in B16F10 Melanoma Cells and Zebrafish Larvae through β-Catenin Activation

Fisetin is found in many fruits and plants such as grapes and onions, and exerts anti-inflammatory, anti-proliferative, and anticancer activity. However, whether fisetin regulates melanogenesis has been rarely studied. Therefore, we evaluated the effects of fisetin on melanogenesis in B16F10 melanoma cell and zebrafish larvae. The current study revealed that fisetin slightly suppressed in vitro mushroom tyrosinase activity; however, molecular docking data showed that fisetin did not directly bind to mushroom tyrosinase. Unexpectedly, fisetin significantly increased intracellular and extracellular melanin production in B16F10 melanoma cells regardless of the presence or absence of α-melanocyte stimulating hormone (α-MSH). We also found that the expression of melanogenesis-related genes such as tyrosinase and microphthalmia-associated transcription factor (MITF), were highly increased 48 h after fisetin treatment. Pigmentation of zebrafish larvae by fisetin treatment also increased at the concentrations up to 200 µM and then slightly decreased at 400 µM, with no alteration in the heart rates. Molecular docking data also revealed that fisetin binds to glycogen synthase kinase-3β (GSK-3β). Therefore, we evaluated whether fisetin negatively regulated GSK-3β, which subsequently activates β-catenin, resulting in melanogenesis. As expected, fisetin increased the expression of β-catenin, which was subsequently translocated into the nucleus. In the functional assay, FH535, a Wnt/β-catenin inhibitor, significantly inhibited fisetin-mediated melanogenesis in zebrafish larvae. Our data suggested that fisetin inhibits GSK-3β, which activates β-catenin, resulting in melanogenesis through the revitalization of MITF and tyrosinase.

PTPN11 Plays Oncogenic Roles and Is a Therapeutic Target for BRAF Wild-Type Melanomas

Melanoma is one of the most highly mutated cancer types. To identify functional drivers of melanoma, we searched for cross-species conserved mutations utilizing a mouse melanoma model driven by loss of PTEN and CDKN2A, and identified mutations in Kras, Erbb3, and Ptpn11. PTPN11 encodes the SHP2 protein tyrosine phosphatase that activates the RAS/RAF/MAPK pathway. Although PTPN11 is an oncogene in leukemia, lung, and breast cancers, its roles in melanoma are not clear. In this study, we found that PTPN11 is frequently activated in human melanoma specimens and cell lines and is required for full RAS/RAF/MAPK signaling activation in BRAF wild-type (either NRAS mutant or wild-type) melanoma cells. PTPN11 played oncogenic roles in melanoma by driving anchorage-independent colony formation and tumor growth. In Pten- and Cdkn2a-null mice, tet-inducible and melanocyte-specific PTPN11^E76K expression significantly enhanced melanoma tumorigenesis. Melanoma cells derived from this mouse model showed doxycycline-dependent tumor growth in nude mice. Silencing PTPN11^E76K expression by doxycycline withdrawal caused regression of established tumors by induction of apoptosis and senescence, and suppression of proliferation. Moreover, the PTPN11 inhibitor (SHP099) also caused regression of NRAS^Q61K -mutant melanoma. Using a quantitative tyrosine phosphoproteomics approach, we identified GSK3α/β as one of the key substrates that were differentially tyrosine-phosphorylated in these experiments modulating PTPN11. This study demonstrates that PTPN11 plays oncogenic roles in melanoma and regulates RAS and GSK3β signaling pathways. IMPLICATIONS: This study identifies PTPN11 as an oncogenic driver and a novel and actionable therapeutic target for BRAF wild-type melanoma.

Glucopyranosylbianthrones from the Algerian Asphodelus tenuifolius: Structural Insights and Biological Evaluation on Melanoma Cancer Cells

Two new glucopyranosylbianthrones (1 and 2) were isolated from the aerial part of the plant Asphodelus tenuifolius, collected in Southwest Algeria. The 2D structures of 1 and 2 were defined by NMR analysis, HRESIMS data, and comparison with literature data. The comparison of experimental and calculated electronic circular dichroism and NMR data led to characterization of the ( M) and ( P) atropisomeric forms of the glucopyranosylbianthrones, asphodelins (1) and (2), respectively. The in vitro activities of these two metabolites were evaluated in human melanoma A375 cells, and both the compounds inhibited cell proliferation in a concentration-dependent manner, with IC₅₀ values of 20.6 ± 0.8 and 23.2 ± 1.1 μM, respectively. Considering their biological profile, an inverse virtual screening approach was employed to identify and suggest putative anticancer interacting targets.

Interleukin-32α induces migration of human melanoma cells through downregulation of E-cadherin

Interleukin (IL)-32α, the shortest isoform of proinflammatory cytokine IL-32, is associated with various inflammatory diseases and cancers. However, its involvement in human melanoma is not understood. To determine the effect of IL-32α in melanoma, IL-32α levels were examined in human melanoma cell lines that exhibit different migratory abilities. IL-32α levels were higher in human melanoma cell lines with more migratory ability. An IL-32α-overexpressing G361 human melanoma cell line was generated to investigate the effect of IL-32α on melanoma migration. IL-32α-overexpressing G361 cells (G361-IL-32α) exhibit an increased migratory ability compared to vector control cells (G361-vector). To identify factors involved in IL-32α-induced migration, we compared expression of E-cadherin in G361-vector and G361-IL-32α cells. We observed decreased levels of E-cadherin in G361-IL-32α cells, resulting in F-actin polymerization. To further investigate signaling pathways related to IL-32α-induced migration, we treated G361-vector and G361-IL-32α cells with PD98059, a selective MEK inhibitor. Inhibition of Erk1/2 by PD98059 restored E-cadherin expression and decreased IL-32α-induced migration. In addition, cell invasiveness of G361-IL-32α cells was tested using an in vivo lung metastasis model. As results, lung metastasis was significantly increased by IL-32α overexpression. Taken together, these data indicate that IL-32α induced human melanoma migration via Erk1/2 activation, which repressed E-cadherin expression. Our findings suggest that IL-32α is a novel regulator of migration in melanoma.

Roles of GSK-3 and microRNAs on epithelial mesenchymal transition and cancer stem cells

Various signaling pathways exert critical roles in the epithelial to mesenchymal transition (EMT) and cancer stem cells (CSCs). The Wnt/beta-catenin, PI3K/PTEN/Akt/mTORC, Ras/Raf/MEK/ERK, hedgehog (Hh), Notch and TP53 pathways elicit essential regulatory influences on cancer initiation, EMT and progression. A common kinase involved in all these pathways is moon-lighting kinase glycogen synthase kinase-3 (GSK-3). These pathways are also regulated by micro-RNAs (miRs). TP53 and components of these pathways can regulate the expression of miRs. Targeting members of these pathways may improve cancer therapy in those malignancies that display their abnormal regulation. This review will discuss the interactions of the multi-functional GSK-3 enzyme in the Wnt/beta-catenin, PI3K/PTEN/Akt/mTORC, Ras/Raf/MEK/ERK, Hh, Notch and TP53 pathways. The regulation of these pathways by miRs and their effects on CSC generation, EMT, invasion and metastasis will be discussed.

SphK1 modulates cell migration and EMT-related marker expression by regulating the expression of p-FAK in colorectal cancer cells

Sphingosine kinase 1 (SphK1) plays an important role in colorectal carcinoma metastasis. However, whether SphK1 modulates epithelial-mesenchymal transition (EMT)-related marker expression and the underlying mechanisms remain unclear. In this study, in order to clarify this issue, we used various colorectal cancer (CRC) cell lines, Caco2, HT29, RKO and HCT116. Each of the cell lines was divided into 3 groups as follows: the control group, SKI-Ⅱ (SphK1 inhibitor) group and PF-562271 [focal adhesion kinase (FAK) inhibitor] group. The migratory ability of the cells was examined by Transwell chamber assay. The mRNA and protein expression levels of SphK1, FAK (p-FAK), Slug, vimentin, N-cadherin and E-cadherin were detected by PCR and western blot analysis, respectively. The results revealed that the suppression of SphK1 reduced the cell migratory ability, and decreased the expression of Slug, vimentin and N-cadherin; however, the expression of E-cadherin was increased. Moreover, the inhibition of SphK1 reduced the expression of p-FAK. The inhibition of FAK (p-FAK) also decreased the cell migratory ability, and decreased the expression of Slug, vimentin and N-cadherin, whereas the expression of E-cadherin was increased. Thus, our data suggest that SphK1 modulates the expression of EMT-related markers and cell migration by regulating the expression of p-FAK in CRC cells. Thus, SphK1 may play a functional role in mediating the EMT process in CRC.

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.

Targeting protein kinase-b3 (akt3) signaling in melanoma

INTRODUCTION

Deregulated Akt activity leading to apoptosis inhibition, enhanced proliferation and drug resistance has been shown to be responsible for 35-70% of advanced metastatic melanomas. Of the three isoforms, the majority of melanomas have elevated Akt3 expression and activity. Hence, potent inhibitors targeting Akt are urgently required, which is possible only if (a) the factors responsible for the failure of Akt inhibitors in clinical trials is known; and (b) the information pertaining to synergistically acting targeted therapeutics is available. Areas covered: This review provides a brief introduction of the PI3K-Akt signaling pathway and its role in melanoma development. In addition, the functional role of key Akt pathway members such as PRAS40, GSK3 kinases, WEE1 kinase in melanoma development are discussed together with strategies to modulate these targets. Efficacy and safety of Akt inhibitors is also discussed. Finally, the mechanism(s) through which Akt leads to drug resistance is discussed in this expert opinion review. Expert opinion: Even though Akt play key roles in melanoma tumor progression, cell survival and drug resistance, many gaps still exist that require further understanding of Akt functions, especially in the (a) metastatic spread; (b) circulating melanoma cells survival; and

Analysis of epithelial-mesenchymal transition markers in psoriatic epidermal keratinocytes

Psoriasis is similar to endpoints of epithelial–mesenchymal transition (EMT), a process of epithelial cells transformed into fibroblast-like cells. The molecular epithelial and mesenchymal markers were analysed in psoriatic keratinocytes. No obvious alteration of epithelial markers E-cadherin (E-cad), keratin 10 (K10), K14 and K16 was detected in psoriatic keratinocytes. However, significantly increased expression of Vim, FN, plasminogen activator inhibitor 1 (PAI-1) and Slug was seen. IL-17A and IL-13 at 50 ng ml⁻¹ strongly decreased expression of K10, Vim and FN. TGF-β1 at 50 ng ml⁻¹ promoted the production of N-cad, Vim, FN and PAI-1. Slug was decreased by dexamethasone (Dex), but E-cad was upregulated by Dex. Silencing of ERK partially increased E-cad and K16, but remarkably inhibited K14, FN, Vim, β-catenin, Slug and α5 integrin. Moreover, inhibition of Rho and GSK3 by their inhibitors Y27632 and SB216763, respectively, strongly raised E-cad, β-catenin and Slug. Dex decreased Y27632-mediated increase of β-catenin. Dex at 2.0 µM inhibited SB216763-regulated E-cad, β-catenin and slug. In conclusion, EMT in psoriatic keratinocytes may be defined as an intermediate phenotype of type 2 EMT. ERK, Rho and GSK3 play active roles in the process of EMT in psoriatic keratinocytes.

SASH1 inhibits cervical cancer cell proliferation and invasion by suppressing the FAK pathway

SAM and SH3 domain containing 1 (SASH1), a member of the SLY-family of signal adapter proteins, is a candidate tumor suppressor in several types of cancer. However, the role of SASH1 in cervical cancer remains to be elucidated. Therefore, in the present study, the role of SASH1 in cervical cancer and the underlying mechanism was investigated. Cell proliferation was detected by the MTT assay. Cell invasion was measured by Transwell assay. The mRNA expression levels of SASH1, matrix metalloproteinase (MMP)‑2 and MMP‑9 were determined by reverse transcription quantitative polymerase chain reaction. The protein expression levels of SASH1, MMP‑2, MMP‑9 and focal adhesion kinase (FAK) were determined by western blot analysis. The results demonstrated that SASH1 was downregulated in cervical cancer tissues and cell lines. Subsequently, a vector that overexpresses SASH1 was constructed. Overexpression of SASH1 was found to significantly inhibit cervical cancer cell proliferation and invasion, and also significantly reduce the expression of MMP‑2 and MMP‑9 in cancer cells. In addition, SASH1 modulated the FAK signaling pathway. Overexpression of SASH1 suppressed the expression of FAK in cancer cells. Taken together, the results suggested that SASH1 inhibits cervical cancer cell proliferation and invasion by suppressing the FAK pathway.

Ligand-independent EPHA2 signaling drives the adoption of a targeted therapy-mediated metastatic melanoma phenotype

Many patients with BRAF inhibitor resistance can develop disease at new sites, suggesting that drug-induced selection pressure drives metastasis. Here, we used mass spectrometry-based phosphoproteomic screening to uncover ligand-independent EPHA2 signaling as an adaptation to BRAF inhibitor therapy that led to the adoption of a metastatic phenotype. The EPHA2-mediated invasion was AKT-dependent and readily reversible upon removal of the drug as well as through PI3K and AKT inhibition. In xenograft models, BRAF inhibition led to the development of EPHA2-positive metastases. A retrospective analysis of patients with melanoma on BRAF inhibitor therapy showed that 68% of those failing therapy develop metastases at new disease sites, compared with 35% of patients on dacarbazine. Further IHC staining of melanoma specimens taken from patients on BRAF inhibitor therapy as well as metastatic samples taken from patients failing therapy showed increased EPHA2 staining. We suggest that inhibition of ligand-independent EPHA2 signaling may limit metastases associated with BRAF inhibitor therapy.

SIGNIFICANCE

This study provides evidence that BRAF inhibition promotes the adoption of a reversible, therapy-driven metastatic phenotype in melanoma. The cotargeting of ligand-independent EPHA2 signaling and BRAF may be one strategy to prevent the development of therapy-mediated disease at new sites.

Phosphoproteomic analysis of basal and therapy-induced adaptive signaling networks in BRAF and NRAS mutant melanoma

Basal and kinase inhibitor driven adaptive signaling has been examined in a panel of melanoma cell lines using phosphoproteomics in conjunction with pathway analysis. A considerable divergence in the spectrum of tyrosine-phosphorylated peptides was noted at the cell line level. The unification of genotype-specific cell line data revealed the enrichment for the tyrosine-phosphorylated cytoskeletal proteins to be associated with the presence of a BRAF mutation and oncogenic NRAS to be associated with increased receptor tyrosine kinase phosphorylation. A number of proteins including cell cycle regulators (cyclin dependent kinase 1, cyclin dependent kinase 2, and cyclin dependent kinase 3), MAPK pathway components (Extracellular signal regulated kinase 1 and Extracellular signal regulated kinase 2), interferon regulators (tyrosine kinase-2), GTPase regulators (Ras-Rasb interactor 1), and controllers of protein tyrosine phosphorylation (dual specificity tyrosine (Y) phosphorylation regulated kinase 1A and protein tyrosine phosphatase receptor type A) were common to all genotypes. Treatment of a BRAF-mutant/phosphatase and tensin homologue (PTEN) null melanoma cell line with vemurafenib led to decreased phosphorylation of ERK, phospholipase C1, and β-catenin with increases in receptor tyrosine kinase phosphorylation, signal transduction and activator of signaling 3, and glycogen synthase kinase 3α noted. In NRAS-mutant melanoma, MEK inhibition led to increased phosphorylation of epidermal growth factor receptor signaling pathway components, Src family kinases, and protein kinase Cδ with decreased phosphorylation seen in STAT3 and ERK1/2. Together these data present the first systems level view of adaptive and basal phosphotyrosine signaling in BRAF- and NRAS-mutant melanoma.

Focal adhesion kinase-mediated activation of glycogen synthase kinase 3β regulates IL-33 receptor internalization and IL-33 signaling

IL-33, a relatively new member of the IL-1 cytokine family, plays a crucial role in allergic inflammation and acute lung injury. Long form ST2 (ST2L), the receptor for IL-33, is expressed on immune effector cells and lung epithelia and plays a critical role in triggering inflammation. We have previously shown that ST2L stability is regulated by the ubiquitin-proteasome system; however, its upstream internalization has not been studied. In this study, we demonstrate that glycogen synthase kinase 3β (GSK3β) regulates ST2L internalization and IL-33 signaling. IL-33 treatment induced ST2L internalization, and an effect was attenuated by inhibition or downregulation of GSK3β. GSK3β was found to interact with ST2L on serine residue 446 in response to IL-33 treatment. GSK3β binding site mutant (ST2L(S446A)) and phosphorylation site mutant (ST2L(S442A)) are resistant to IL-33-induced ST2L internalization. We also found that IL-33 activated focal adhesion kinase (FAK). Inhibition of FAK impaired IL-33-induced GSK3β activation and ST2L internalization. Furthermore, inhibition of ST2L internalization enhanced IL-33-induced cytokine release in lung epithelial cells. These results suggest that modulation of the ST2L internalization by FAK/GSK3β might serve as a unique strategy to lessen pulmonary inflammation.

Expression of stress ligands of the immunoreceptor NKG2D in melanoma: regulation and clinical significance

Tumor cells, in particular melanoma cells, can be detected as abnormal self by cytotoxic lymphocytes of the innate and adaptive immune system. Of major importance in this process is the activating lymphocyte receptor NKG2D that in humans binds to MIC and ULBP surface molecules on tumor cells. Expression of NKG2D ligands (NKG2DL) is an early event in malignant transformation, induced by stress-associated and oncogene-driven pathways. Thus NKG2DL expression is considered as an innate barrier against tumor development. However, tumor cells can overcome this barrier by shedding of NKG2DL. Ligand shedding leads to elevated levels of soluble ligands in sera of tumor patients that in case of melanoma are of strong prognostic relevance. Here we review important aspects of NKG2DL expression and regulation in tumor cells with a focus on melanoma, and discuss their clinical relevance and potential in immunotherapy.

The emerging role of insulin and insulin-like growth factor signaling in cancer stem cells

Cancer cells frequently exploit the IGF signaling, a fundamental pathway mediating development, cell growth, and survival. As a consequence, several components of the IGF signaling are deregulated in cancer and sustain cancer progression. However, specific targeting of IGF-IR in humans has resulted efficacious only in small subsets of cancers, making researches wondering whether IGF system targeting is still worth pursuing in the clinical setting. Although no definite answer is yet available, it has become increasingly clear that other components of the IGF signaling pathway, such as IR-A, may substitute for the lack of IGF-IR, and induce cancer resistance and/or clonal selection. Moreover, accumulating evidence now indicates that IGF signaling is a central player in the induction/maintenance of epithelial mesenchymal transition (EMT) and cell stemness, two strictly related programs, which play a key role in metastatic spread and resistance to cancer treatments. Here we review the evidences indicating that IGF signaling enhances the expression of transcription factors implicated in the EMT program and has extensive cross-talk with specific pathways involved in cell pluripotency and stemness maintenance. In turn, EMT and cell stemness activate positive feed-back mechanisms causing up-regulation of various IGF signaling components. These findings may have novel translational implications.

Molecular networks in melanoma invasion and metastasis

Metastatic melanoma accounts for approximately 80% of skin cancer-related deaths. Up to now there has been no effective treatment for stage IV melanoma patients due to the complexity and dissemination potential of this disease. Melanomas are heterogeneous tumors in which conventional therapies fail to improve overall survival. Targeted therapies are being developed, but the final outcome can be hampered by the incomplete knowledge of the process of melanoma progression. Even if the intracellular pathways are similar, the interaction of the cells with the surrounding environment should be taken into consideration. This article seeks to highlight some of the advances in the understanding of the molecular mechanisms underlying melanoma dissemination.

Identification of glycogen synthase kinase 3α as a therapeutic target in melanoma

Deregulated expression or activity of kinases can lead to melanomas, but often the particular kinase isoform causing the effect is not well established, making identification and validation of different isoforms regulating disease development especially important. To accomplish this objective, an siRNA screen was undertaken that which identified glycogen synthase kinase 3α (GSK3α) as an important melanoma growth regulator. Melanocytes and melanoma cell lines representing various stages of melanoma tumor progression expressed both GSK3α and GSK3β, but analysis of tumors in patients with melanoma showed elevated expression of GSK3α in 72% of samples, which was not observed for GSK3β. Furthermore, 80% of tumors in patients with melanoma expressed elevated levels of catalytically active phosphorylated GSK3α (pGSK3αY279), but not phosphorylated GSK3β (pGSK3βY216). siRNA-mediated reduction in GSK3α protein levels reduced melanoma cell survival and proliferation, sensitized cells to apoptosis-inducing agents and decreased xenografted tumor development by up to 56%. Mechanistically, inhibiting GSK3α expression using siRNA or the pharmacological agent AR-A014418 arrested melanoma cells in the G0/G1 phase of the cell cycle and induced apoptotic death to retard tumorigenesis. Therefore, GSK3α is a key therapeutic target in melanoma.

GSK3β controls epithelial-mesenchymal transition and tumor metastasis by CHIP-mediated degradation of Slug

Glycogen synthase kinase 3 beta (GSK3β) is highly inactivated in epithelial cancers and is known to inhibit tumor migration and invasion. The zinc-finger-containing transcriptional repressor, Slug, represses E-cadherin transcription and enhances epithelial-mesenchymal transition (EMT). In this study, we find that the GSK3β-pSer9 level is associated with the expression of Slug in non-small cell lung cancer. GSK3β-mediated phosphorylation of Slug facilitates Slug protein turnover. Proteomic analysis reveals that the carboxyl terminus of Hsc70-interacting protein (CHIP) interacts with wild-type Slug (wtSlug). Knockdown of CHIP stabilizes the wtSlug protein and reduces Slug ubiquitylation and degradation. In contrast, nonphosphorylatable Slug-4SA is not degraded by CHIP. The accumulation of nondegradable Slug may further lead to the repression of E-cadherin expression and promote cancer cell migration, invasion and metastasis. Our findings provide evidence of a de novo GSK3β-CHIP-Slug pathway that may be involved in the progression of metastasis in lung cancer.

Activation of Wnt/β-catenin signaling increases apoptosis in melanoma cells treated with trail

While the TRAIL pathway represents a promising therapeutic target in melanoma, resistance to TRAIL-mediated apoptosis remains a barrier to its successful adoption. Since the Wnt/β-catenin pathway has been implicated in facilitating melanoma cell apoptosis, we investigated the effect of Wnt/β-catenin signaling on regulating the responses of melanoma cells to TRAIL. Co-treatment of melanoma cell lines with WNT3A-conditioned media and recombinant TRAIL significantly enhanced apoptosis compared to treatment with TRAIL alone. This apoptosis correlates with increased abundance of the pro-apoptotic proteins BCL2L11 and BBC3, and with decreased abundance of the anti-apoptotic regulator Mcl1. We then confirmed the involvement of the Wnt/β-catenin signaling pathway by demonstrating that siRNA-mediated knockdown of an intracellular β-catenin antagonist, AXIN1, or treating cells with an inhibitor of GSK-3 also enhanced melanoma cell sensitivity to TRAIL. These studies describe a novel regulation of TRAIL sensitivity in melanoma by Wnt/β-catenin signaling, and suggest that strategies to enhance Wnt/β-catenin signaling in combination with TRAIL agonists warrant further investigation.