Novel Therapeutic Target For Melanoma Research Articles

HDAC8 Deacetylates HIF-1α and Enhances Its Protein Stability to Promote Tumor Growth and Migration in Melanoma

Melanoma is the most lethal type of skin cancer, and it causes more than 55,000 deaths annually. Although regional melanoma can be surgically removed, once melanoma metastasizes to other regions of the body, the survival rate drops dramatically. The current treatment options are chemotherapy, immunotherapy, and targeted therapy. However, the low response rate and the development of resistance necessitate the search for a novel therapeutic target in melanoma. Hypoxia-inducible factor-1 α (HIF-1α) is overexpressed in melanoma and plays a crucial role in driving malignant transformation in cancer cells. Here, we identified that histone deacetylase 8 (HDAC8) enhances the protein stability of HIF-1α. HDAC8 directly binds to and deacetylates HIF-1α, thereby promoting its protein stability. This, in turn, upregulates the transcriptional activity of HIF-1α and promotes the expressions of its target genes, such as hexokinase 2 (HK2) and glucose transporter 1 (GLUT1). The inhibition of HDAC8 suppresses the proliferation and metastasis of melanoma cells. Furthermore, HDAC8 is correlated with HIF1A expression and poor prognosis in samples from patients with melanoma. These findings uncover a novel epigenetic mechanism that maintains HIF-1α stability and implicates the potential of HDAC8 inhibitors for melanoma therapy.

Hypoxia Modulates Melanoma Cells Proliferation and Apoptosis via miRNA-210/ISCU/ROS Signaling.

In this study, luciferase reporter assay was used to establish the relationship between miR-210 and ISCU. This research was performed on both cell lines (A2058, G361, and 293T) and tissue samples. We found that miR-210 was upregulated in hypoxia and was elevated in melanoma in comparison with adjacent normal tissues. Expression of ISCU protein was decreased in melanoma tissues, and ISCU gene is a direct target of miR-210. ISCU knockdown with miR-210 enhanced ROS production. The results of our study showed that miR-210/ISCU/ROS axis can serve as a novel therapeutic target in melanoma.

LB994 A novel MIF inhibitor for treatment of melanoma

Macrophage migration inhibiting factor (MIF) is expressed by both immune and tumor cells and MIF overexpression is increasingly recognized as implicated in worse outcomes in melanoma patients and thus is a novel therapeutic target for melanoma. This is particularly important as although checkpoint inhibitor blockade has positively impacted advanced melanoma outcomes, there are few treatment options for non-responders (primary resistance) or those who have resistance after initial response (secondary resistance).

STAT3-induced ZBED3-AS1 promotes the malignant phenotypes of melanoma cells by activating PI3K/AKT signaling pathway

ABSTRACT Melanoma is considered as the most frequent primary malignancy occurring in skin. Accumulating studies have suggested that long non-coding RNAs (lncRNAs) play critical parts in multiple cancers. In this study, we explored the molecular mechanism of ZBED3 antisense RNA 1 (ZBED3-AS1) in melanoma. We observed that ZBED3-AS1 expression was remarkably up-regulated in melanoma tissues, and high ZBED3-AS1 level was linked to unsatisfactory survival of melanoma patients. Then, we discovered that ZBED3-AS1 was overexpressed in melanoma cells compared with human epidermal melanocytes. In addition, loss-of-function assays verified that ZBED3-AS1 knockdown restrained cell proliferation, migration, epithelial–mesenchymal transition (EMT), and stemness in melanoma. In addition, signal transducer and activator of transcription 3 (STAT3), which also showed tumour-facilitating functions in melanoma, was confirmed as a transcriptional activator of ZBED3-AS1. Moreover, ZBED3-AS1 enhanced the expression of AT-rich interaction domain 4B (ARID4B) through sequestering miR-381-3p. Importantly, we further confirmed that ZBED3-AS1 promoted the malignant progression of melanoma by regulating miR-381-3p/ARID4B axis to activate the phosphatidylinositol 3-kinase/AKT serine/threonine kinase (PI3K/AKT) signalling pathway. In a word, our research might provide a novel therapeutic target for melanoma.

USP8 is a Novel Therapeutic Target in Melanoma Through Regulating Receptor Tyrosine Kinase Levels.

IntroductionThe hyperactivation of receptor tyrosine kinase (RTK)-mediated pathways plays an important role in melanoma progression and resistance to therapy. The ubiquitin-specific protease 8 (USP8) is a deubiquitinating enzyme and its inhibition induces degradation of RTKs. This work explored the expression and role of USP8 in melanoma.MethodsELISA and qPCR were performed to assess USP8 expression in melanoma tissues and cells, as well as their normal counterparts. Cellular proliferation, migration and apoptosis assays were performed to determine USP8 functions in three melanoma cell lines. Western blot was performed to analyze RTK signaling in melanoma cells after USP8 inhibition.ResultsmRNA and protein level of USP8 were higher in melanoma cells than normal melanocytes. Higher USP8 expression was also found in tumors in the majority of melanoma patients. USP8 expression was not associated with clinicopathological features, such as age, disease stage, histology, ulceration and BRAF status. Functional analysis demonstrated that USP8 overexpression promoted melanoma cell activities and alleviated the inhibitory effects of therapeutic drugs. In contrast, USP8 knockdown suppressed melanoma cell growth, survival and migration, and augmented the inhibitory effects of therapeutic drugs. Mechanism studies revealed that USP8 inhibition remarkably reduced the expression level of multiple oncogenic RTKs, including c-Met, Kit, EGFR and GPCR. Consistently, RTK-mediated downstream pathways were disrupted in USP8-depleted cells, leading to the increased level of pro-apoptotic proteins and decreased level of anti-apoptotic proteins.ConclusionInhibition of USP8 activity is a novel sensitizing strategy to overcome therapy resistance in melanoma.

Nuclear Receptor Coactivator NCOA3 Regulates UV Radiation-Induced DNA Damage and Melanoma Susceptibility.

Melanoma occurs as a consequence of inherited susceptibility to the disease and exposure to UV radiation (UVR) and is characterized by uncontrolled cellular proliferation and a high mutational load. The precise mechanisms by which UVR contributes to the development of melanoma remain poorly understood. Here we show that activation of nuclear receptor coactivator 3 (NCOA3) promotes melanomagenesis through regulation of UVR sensitivity, cell-cycle progression, and circumvention of the DNA damage response (DDR). Downregulation of NCOA3 expression, either by genetic silencing or small-molecule inhibition, significantly suppressed melanoma proliferation in melanoma cell lines and patient-derived xenografts. NCOA3 silencing suppressed expression of xeroderma pigmentosum C and increased melanoma cell sensitivity to UVR. Suppression of NCOA3 expression led to activation of DDR effectors and reduced expression of cyclin B1, resulting in G2-M arrest and mitotic catastrophe. A SNP in NCOA3 (T960T) reduced NCOA3 protein expression and was associated with decreased melanoma risk, given a significantly lower prevalence in a familial melanoma cohort than in a control cohort without cancer. Overexpression of wild-type NCOA3 promoted melanocyte survival following UVR and was accompanied by increased levels of UVR-induced DNA damage, both of which were attenuated by overexpression of NCOA3 (T960T). These results describe NCOA3-regulated pathways by which melanoma can develop, with germline NCOA3 polymorphisms enabling enhanced melanocyte survival in the setting of UVR exposure, despite an increased mutational burden. They also identify NCOA3 as a novel therapeutic target for melanoma. SIGNIFICANCE: This study explores NCOA3 as a regulator of the DDR and a therapeutic target in melanoma, where activation of NCOA3 contributes to melanoma development following exposure to ultraviolet light.

NECTIN4: A Novel Therapeutic Target for Melanoma.

Malignant melanoma is the most common lethal skin cancer and causes death in a short time when metastasized. Although BRAF inhibitors (BRAFi) have greatly improved the prognosis of BRAF-mutated melanoma, drug resistance is a major concern even when they are combined with MEK inhibitors. Alternative treatments for BRAFi-resistant melanoma are highly anticipated. Nectin cell adhesion molecule 4 (NECTIN4) is highly expressed and associated with progression in tumors. We aimed to investigate the role of NECTIN4 in melanoma and its potency as a therapeutic target using 126 melanoma samples and BRAFi-resistant cells. Immunohistochemically, most of the clinical samples expressed NECTIN4, at least in part. NECTIN4 was highly expressed in BRAF-mutated melanoma and its high expression was associated with disease-free survival. In BRAFi-resistant melanoma cells, NECTIN4 and the PI3K/Akt pathway were upregulated, along with the acquisition of BRAFi resistance. Monomethyl auristatin E, a cytotoxic part of NECTIN4-targeted antibody–drug conjugate, was effective for BRAF-mutated or BRAFi-resistant melanoma cells. NECTIN4 inhibition increased the sensitivity of BRAFi-resistant cells to BRAFi and induced apoptosis. In conclusion, we revealed the expression and roles of NECTIN4 in melanoma. Targeted therapies against NECTIN4 can be a novel treatment strategy for melanoma, even after the acquisition of BRAFi resistance.

Heat Shock Proteins Regulating Toll-like Receptors and the Immune System could be a Novel Therapeutic Target for Melanoma

Heat Shock Proteins Regulating Toll-like Receptors and the Immune System could be a Novel Therapeutic Target for Melanoma

Heat Shock Proteins Regulating Toll-like Receptors and the Immune System could be a Novel Therapeutic Target for Melanoma

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Long non-coding RNA SNHG6 promotes tumorigenesis in melanoma cells via the microRNA-101-3p/RAP2B axis.

Numerous studies have reported that the long non-coding RNA (lncRNA) small nucleolar RNA host gene 6 (SNHG6; ENSG00000245910) participates in the development of malignant tumors. However, the underlying mechanism of SNHG6 in the development of melanoma remains unknown. Thus, the present study aimed to investigate the biological role of SNHG6 in the progression of melanoma. SNHG6 expression in melanoma tissues and cells was assessed using a bioinformatics approach and reverse transcription-quantitative PCR analysis. Cell viability was determined using the Cell Counting Kit-8 and colony formation assays. The correlation between microRNA (miR)-101-3p, SNHG6 and RAP2B expression levels was assessed using Pearson's correlation analysis. Bioinformatic analysis and luciferase reporter assay were utilized to confirm the interaction between miR-101-3p and SNHG6 or RAP2B. The Transwell assay was conducted to examine the migratory and invasive activities of melanoma cells. In the present study, SNHG6 expression was upregulated in melanoma tissues and cell lines, and SNHG6 silencing suppressed melanoma cell viability, migration and invasion. SNHG6 was directly bound to miR-101-3p, which interacted with RAP2B. In addition, miR-101-3p expression was negatively correlated with SNHG6 or RAP2B expression. miR-101-3p silencing partially abrogated the suppressive effect of SNHG6-knockdown on RAP2B expression. Moreover, the data demonstrated that RAP2B overexpression reversed the inhibitory effects on melanoma cell proliferation, migration and invasion induced by SNHG6 silencing. In conclusion, the present study identified that SNHG6 accelerated melanoma progression via regulating the miR-101-3p/RAP2B axis. Thus, the SNHG6/miR-101-3p/RAP2B signaling pathway may be a novel therapeutic target for melanoma.

Heat Shock Proteins Regulating Toll-like Receptors and the Immune System could be a Novel Therapeutic Target for Melanoma.

Melanoma is a serious type of skin cancer, which develops in melanocyte cells. Although it is less common than some other skin cancers, it can be far more dangerous if not treated at an early stage because of its ability to spread rapidly to other organs. Heat shock proteins (HSP) are intracellular molecular chaperones of naive proteins, which are induced in response to stressful conditions. HSP is released into the extracellular milieu and binds to Toll-like receptors (TLRs) to regulate immune responses, such as cytokine and chemokine release. HSPs can release and bind to tumor-specific antigens, with cross-presentation of major histocompatibility complex (MHC) class I antigens. TLRs are innate immune system receptors, involved in the melanoma growth pathway through HSP activation. Melanocytes express TLR4 and TLR9 to modulate immune responses. Many TLR ligands are considered as proper adjuvant candidates, as they can activate dendritic cells. Targeting some TLRs, such as TLR7 and TLR9, is an available option for treating melanoma. In this review, we aimed to determine the relationship between TLRs and HSP groups in melanoma.

Complex Formation with Monomeric α-Tubulin and Importin 13 Fosters c-Jun Protein Stability and Is Required for c-Jun's Nuclear Translocation and Activity.

Microtubules are highly dynamic structures, which consist of α- and β-tubulin heterodimers. They are essential for a number of cellular processes, including intracellular trafficking and mitosis. Tubulin-binding chemotherapeutics are used to treat different types of tumors, including malignant melanoma. The transcription factor c-Jun is a central driver of melanoma development and progression. Here, we identify the microtubule network as a main regulator of c-Jun activity. Monomeric α-tubulin fosters c-Jun protein stability by protein–protein interaction. In addition, this complex formation is necessary for c-Jun’s nuclear localization sequence binding to importin 13, and consequent nuclear import and activity of c-Jun. A reduction in monomeric α-tubulin levels by treatment with the chemotherapeutic paclitaxel resulted in a decline in the nuclear accumulation of c-Jun in melanoma cells in an experimental murine model and in patients’ tissues. These findings add important knowledge to the mechanism of the action of microtubule-targeting drugs and indicate the newly discovered regulation of c-Jun by the microtubule cytoskeleton as a novel therapeutic target for melanoma and potentially also other types of cancer.

NFAT5 promotes in vivo development of murine melanoma metastasis

Malignant melanoma is one of the most fatal and aggressive skin cancers, originating from pigment-containing melanocytes. Despite progress in clinical research, treatment options for malignant melanoma have been limited. The nuclear factor of activated T-cell 5 (NFAT5), originally identified as tonicity regulated transcription factor Ton/EBP, is now known as a carcinogenic gene in several types of cancer pathology. In this study, we knocked down NFAT5 to investigate its role in melanoma cancer. shRNA-mediated knockdown of NFAT5 led to a significant decrease in cell proliferation in vitro. Additionally, depletion of NFAT5 inhibited the cell migratory ability of B16BL6 melanoma cells and led to more accumulation at the G2/M phase of the cell cycle. Furthermore, NFAT5 was essential for the development of melanoma cancer pathophysiology in an in vivo mouse model. NFAT5 knockdown-induced tumor growth was slow and tumor volume was significantly reduced compared to mock controls. Moreover, NFAT5 knockdown was associated with a low number of metastatic nodules on the lung and liver. To our knowledge, our data demonstrate for the first time a role of NFAT5 in the development of melanoma. We provide evidence for NFAT5 as a marker of cell migration and metastasis, indicating that NFAT5 represents a novel therapeutic target in melanoma.

Long Noncoding RNA PVT1 Promotes Melanoma Progression via Endogenous Sponging miR-26b.

Melanoma is an extremely aggressive malignant skin tumor with a high mortality. Various long noncoding RNAs (lncRNAs) have been reported to be associated with the oncogenesis of melanoma. The purposes of this study were to investigate the potential role of lncRNA PVT1 in melanoma progression and to explore its possible mechanisms. A total of 35 patients who were diagnosed with malignant melanoma were enrolled in this study. Expression of PVT1 was significantly upregulated in melanoma tissue and was associated with a poor prognosis. Loss-of-function experiments showed that PVT1 knockdown markedly suppressed the proliferation activity, induced cell cycle arrest at the G0/G1 phase, and enhanced the apoptosis of melanoma cell lines. Bioinformatics analysis and dual-luciferase reporter assay revealed that PVT1 directly bound to miR-26b, which had been verified to be a tumor suppressor in melanoma. Moreover, further functional rescue experiments revealed that PVT1 knockdown could observably reverse the tumor-promoting role of the miR-26b inhibitor. Overall, our study demonstrates the oncogenic role of PVT1 as a miR-26b sponge, possibly providing a novel therapeutic target for melanoma.

Targeting insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) in metastatic melanoma to increase efficacy of BRAFV600E inhibitors.

Melanoma is one of the deadliest forms of skin cancer. Although BRAF inhibitors significantly enhance survival of metastatic melanoma patients, most patients relapse after less than a year of treatment. We previously reported that mRNA binding protein Insulin-like growth factor 2 mRNA-binding protein 1 (IGF2BP1) is overexpressed in metastatic melanoma and that expression of IGF2BP1 confers resistance to chemotherapeutic agents. Here we demonstrate that IGF2BP1 plays an important role in the sensitivity of melanoma to targeted therapy. Inhibition of IGF2BP1 enhances the effects of BRAF-inhibitor and BRAF-MEK inhibitors in BRAFV600E melanoma. Also, knockdown of IGF2BP1 alone is sufficient to reduce tumorigenic characteristics in vemurafenib-resistant melanoma. These findings suggest that IGF2BP1 can be a novel therapeutic target for melanoma.

Wild-type KRAS is a novel therapeutic target for melanoma contributing to primary and acquired resistance to BRAF inhibition.

Malignant melanoma reveals rapidly increasing incidence and mortality rates worldwide. By now, BRAF inhibition is the standard therapy for advanced melanoma in patients carrying BRAF mutations. However, only approximately 50% of melanoma patients harbor therapeutically attackable BRAF mutations, and overall survival after treatment with BRAF inhibitors is modest. KRAS (Kirsten Rat sarcoma) proteins are acting upstream of BRAF and have a major role in human cancer. Recent approaches awaken the hope to use KRAS inhibition (KRASi) as a clinical tool. In this study, we identified wild-type KRAS as a novel therapeutic target in melanoma. KRASi functions synergistically with BRAF inhibition to reduce melanoma proliferation and to induce apoptosis independently of BRAF mutational status. Moreover, acquired resistance to BRAF inhibitors in melanoma is dependent on dynamic regulation of KRAS expression with subsequent AKT and extracellular-signal regulated kinase activation and can be overcome by KRASi. This suggests KRASi as novel approach in melanoma-alone or in combination with other therapeutic regimes.

Human melanoma cells resistant to MAPK inhibitors can be effectively targeted by inhibition of the p90 ribosomal S6 kinase.

The clinical availability of small molecule inhibitors specifically targeting mutated BRAF marked a significant breakthrough in melanoma therapy. Despite a dramatic anti-tumour activity and improved patient survival, rapidly emerging resistance, however, greatly limits the clinical benefit. The majority of the already described resistance mechanisms involve a reactivation of the MAPK signalling pathway. The p90 ribosomal S6 kinase (RSK), a downstream effector of the MAPK signalling cascade, has been reported to enhance survival of melanoma cells in response to chemotherapy. Here, we can show that RSK activity is significantly increased in human melanoma cells with acquired resistance to the BRAFV600E/K inhibitor vemurafenib. Interestingly, inhibition of RSK signalling markedly impairs the viability of vemurafenib resistant melanoma cells and is effective both in two-dimensional and in three-dimensional culture systems, especially in a chronic, long-term application. The effect of RSK inhibition can be partly replicated by downregulation of the well-known RSK target, Y-box binding protein 1 (YB-1). Intriguingly, RSK inhibition also retains its efficacy in melanoma cells with combined resistance to vemurafenib and the MEK inhibitor trametinib. These data suggest that active RSK signalling might be an attractive novel therapeutic target in melanoma with acquired resistance to MAPK pathway inhibitors.

293 - Human Melanoma Cell Need SIRT5 to Survive

Melanoma is among the most aggressive skin cancers. Many cancer types, including melanoma, show marked alterations in cellular metabolism, melanoma cells show robust aerobic glycolysis and glutamine-driven anaplerosis, phenotypes modulated BRAF and PGC1α. Sirtuins interact with cancer in complex, cell- and tissue-specific ways, often via regulation of tumor cell metabolism. SIRT5 is a mitochondrial sirtuin of NAD+-dependent deacylases family and possesses activity towards non-canonical post-translational modifications. Among mitochondrial sirtuins, SIRT3 and SIRT4 act as a tumor suppressor, however SIRT5 functions in cancer are unknown. To elucidate the function of Sirt5 in human melanoma, 5×103 SIRT5 knockdown (KD) melanoma cells were seeded in triplicate in 6-well plates and cell numbers were counted every day over a 5-day period. 6 weeks old female NOD/SCID mice had SQ injection with 2.5x106 melanoma cells and tumor volume and weight were monitored for 2 weeks. SIRT5 protein was detected via IHC using anti-SIRT5 antibody. 24 hours labeled melanoma cells with 13C- glucose or glutamine were analyzed by GC-MS for monitoring metablites. Oxygen consumption was performed using a Seahorse XFe96 Extracellular Flux Analyze. We have found that SIRT5 plays a key role in the survival of melanoma cells of diverse genetic etiology. In 7/7 melanoma cell lines tested, SIRT5 depletion resulted in rapid loss of proliferative potential and apoptosis, and greatly reduced colony formation. SIRT5 KD also dramatically attenuated the ability of melanoma cells to form tumors in nude mice. In vitro, impaired survival of SIRT5-depleted melanoma cells was recovered by SIRT5 rescue, overexpression of the Pyruvate Dehydrogenase Complex Kinase (PDK1), or supplementation with non-essential amino acids and dimethyl alpha ketoglutarate supplementation. Glutamine dependent respiration and metabolic flux was decreased with SIRT5 depletion. We conclude that SIRT5 promotes melanoma cell survival by controlling glucose and glutamine metabolism, via PDC and glutamine metabolism. SIRT5 deficiency is well tolerated in normal cell types and in mice. Therefore, SIRT5 may represent a novel therapeutic target in melanoma.

Abstract PR02: Specific inhibition of hTERT expression in melanoma by targeting common promoter mutations which cause quadruplex DNA instability

Abstract Background: Telomerase reverse transcriptase (hTERT) is a catalytic subunit of the enzyme telomerase. It has recently been shown that the hTERT promoter is commonly mutated (>75% of cases) in malignant melanoma. These mutations occur at four sites in a G-rich region of the promoter which has previously been shown to form quadruplex DNA and to downregulate hTERT expression. We have tested the hypothesis that mutations in the quadruplex-forming region of the hTERT promoter destabilize quadruplex-formation resulting in increased hTERT expression and cellular proliferation, thus providing a novel therapeutic target for melanoma. Materials and Methods: Quadruplex formation by the mutated and wild type hTERT promoter oligonucleotides was determined by circular dichroism. Analytical ultracentrifugation was used for sedimentation equilibrium analysis. Thermal denaturation was used to characterize the relative stability of the mutated and wild type oligonucleotides. The growth inhibitory effect of mutated and wild type oligonucleotides were determined in four cell lines which contained mutated or wild type hTERT promoter sequences. Cell proliferation was characterized by MTT and cell counting. Results: In order to characterize the effects of the hTERT mutations, the biophysical properties of structures formed by wild-type and mutant TERT sequences were explored by several methods. Circular dichroism and thermal denaturation studies showed that all sequences formed quadruplex structures but that those formed by the mutated sequences were markedly less stable than the wild-type. Analytical ultracentrifugation showed that all sequences formed one major unimolecular folded form but that mutant sequences had a greater tendency to form misfolded aggregated species than the wild-type. Addition of the quadruplex binder TmPyP4 to the mutant sequences lessened that amount of such aggregates and resulted in sedimentation profiles that closely resembled the wild-type sequences. Treatment of cells with mutated hTERT promoter sequence with oligonucleotides encoding the mutated or wild type sequence resulted in significant growth inhibition that was time and concentration dependent. DNA crosslinking studies indicate that the G-rich oligonucleotide is binding to the C-rich strand by Watson-Crick base pairing suggesting that it inhibits transcription initiation by strand invasion. A similar growth inhibitory effect was seen in cells exposed to quadruplex stabilizing agents. Conclusions: The common mutations in the hTERT promoter destabilize quadruplex formation and likely prevent quadruplex-mediated transcriptional silencing. This instability can be overcome by quadruplex-binding drugs and/or oligonucleotides encoding this sequence. The growth of cell lines containing the hTERT promoter mutations is inhibited by oligonucleotides encoding the wild type and mutated sequences. These oligonucleotides stabilize the mutated genomic quadruplex structure, resulting in transcriptional silencing. This approach has obvious clinical potential. This abstract is also being presented as Poster A07. Citation Format: Donald M. Miller, Alexandra Sokolova, Francine Rezzoug, Shelia Thomas, Jonathan Chaires, Jonathan Chaires, William Dean, John Trent. Specific inhibition of hTERT expression in melanoma by targeting common promoter mutations which cause quadruplex DNA instability. [abstract]. In: Proceedings of the AACR Special Conference on Advances in Melanoma: From Biology to Therapy; Sep 20-23, 2014; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(14 Suppl):Abstract nr PR02.

IL2 Inducible T-cell Kinase, a Novel Therapeutic Target in Melanoma.

IL2 inducible T-cell kinase (ITK) promoter CpG sites are hypomethylated in melanomas compared with nevi. The expression of ITK in melanomas, however, has not been established and requires elucidation. An ITK-specific monoclonal antibody was used to probe sections from deidentified, formalin-fixed paraffin-embedded tumor blocks or cell line arrays and ITK was visualized by IHC. Levels of ITK protein differed among melanoma cell lines and representative lines were transduced with four different lentiviral constructs that each contained an shRNA designed to knockdown ITK mRNA levels. The effects of the selective ITK inhibitor BI 10N on cell lines and mouse models were also determined. ITK protein expression increased with nevus to metastatic melanoma progression. In melanoma cell lines, genetic or pharmacologic inhibition of ITK decreased proliferation and migration and increased the percentage of cells in the G0-G1 phase. Treatment of melanoma-bearing mice with BI 10N reduced growth of ITK-expressing xenografts or established autochthonous (Tyr-Cre/Pten(null)/Braf(V600E)) melanomas. We conclude that ITK, formerly considered an immune cell-specific protein, is aberrantly expressed in melanoma and promotes tumor development and progression. Our finding that ITK is aberrantly expressed in most metastatic melanomas suggests that inhibitors of ITK may be efficacious for melanoma treatment. The efficacy of a small-molecule ITK inhibitor in the Tyr-Cre/Pten(null)/Braf(V600E) mouse melanoma model supports this possibility.