The Molecular Evolution of Melanoma Distant Metastases.

The evolution of primary melanoma to lymph node and distant metastasis is incompletely understood. We examined the genomic diversity in melanoma progression in matched primary melanomas and lymph node and distant metastases from 17 patients. FISH analysis revealed cancer cell fractions with monotonic copy number alterations, including PHIP gain and PTEN loss, in the metastatic cascade. By contrast, the cancer cell fraction with copy number alterations for BPTF and MITF was reduced in lymph node metastases but increased in distant metastases. Separately, the cancer cell fraction with NCOA3 copy number alteration was comparable between primary tumors and lymph node metastases yet increased in distant metastases. These results suggest enrichment of the phosphoinositide 3-kinase and MITF pathways in the transition through the metastatic cascade. By contrast, next-generation sequencing analysis did not identify a consistent pattern of changes in variant allele frequency while revealing several intriguing findings, including decreased variant allele frequency in distant metastases and distinct drivers in lymph node versus distant metastases. These results provide evidence that distant melanoma metastasis does not always emanate from lymph node metastasis. These results enhance our understanding of clonal patterns of melanoma metastasis, with possible implications for targeted therapy and metastasis competency.

BPTF promotes the progression of distinct subtypes of breast cancer and is a therapeutic target.

Purpose: To assess the biomarker and functional role of the chromatin remodeling factor, bromodomain PHD finger transcription factor (BPTF), in breast cancer progression. Methods: BPTF copy number was assessed using fluorescence in situ hybridization. BPTF expression was regulated in breast cancer cells by shRNA/siRNA-mediated gene silencing and BPTF cDNA overexpression. The effects of regulating BPTF expression were examined on key oncogenic signaling pathways and on breast cancer cell proliferation, apoptosis, and cell cycle progression, as well as in xenograft models. The consequences of pharmacological bromodomain inhibition, alone or in combination with other targeted agents, on breast cancer progression were assessed in culture and in xenograft models. Results: BPTF copy number was gained in 34.1% and separately amplified in 8.2% of a breast cancer tissue cohort. Elevated BPTF copy number was significantly associated with increasing patient age and tumor grade and observed in both ER-positive and triple-negative breast cancer (TNBC) subtypes. BPTF copy number gain and amplification were also observed in The Cancer Genome Atlas (TCGA) breast cancer cohort. Stable shRNA-mediated silencing of BPTF significantly inhibited cell proliferation and induced apoptosis in TNBC and ER-positive human breast cancer cell lines. BPTF knockdown suppressed signaling through the phosphoinositide 3 kinase (PI3K) pathway, including reduced expression of phosphorylated AKT (Ser473), phosphorylated GSK-ß (Ser9), and CCND1. These findings were confirmed following transient BPTF knockdown by a distinct siRNA in TNBC and ER-positive breast cancer cells. Stable suppression of BPTF expression significantly inhibited the in vivo growth of TNBC cells. Conversely, BPTF cDNA overexpression in TNBC and ER-positive breast cancer cells enhanced breast cancer cell proliferation and reduced apoptosis. BPTF targeting with the bromodomain inhibitor bromosporine, alone or in combination with the PI3K pathway inhibitor gedatolisib, produced significant anti-tumor effects against TNBC cells in vitro and in vivo. Conclusion: These studies demonstrate BPTF activation in distinct breast cancer subtypes, identify pathways by which BPTF promotes breast cancer progression, and suggest BPTF as a rational target for breast cancer therapy.

Bromodomain inhibition overcomes treatment resistance in distinct molecular subtypes of melanoma.

Therapy of BRAF-mutant melanoma with selective inhibitors of BRAF (BRAFi) and MEK (MEKi) represents a major clinical advance but acquired resistance to therapy has emerged as a key obstacle. To date, no clinical approaches successfully resensitize to BRAF/MEK inhibition. Here, we develop a therapeutic strategy for melanoma using bromosporine, a bromodomain inhibitor. Bromosporine (bromo) monotherapy produced significant anti-tumor effects against established melanoma cell lines and patient-derived xenografts (PDXs). Combinatorial therapy involving bromosporine and cobimetinib (bromo/cobi) showed synergistic anti-tumor effects in multiple BRAFi-resistant PDX models. The bromo/cobi combination was superior in vivo to standard BRAFi/MEKi therapy in the treatment-naive BRAF-mutant setting and to MEKi alone in the setting of immunotherapy-resistant NRAS- and NF1-mutant melanoma. RNA sequencing of xenografts treated with bromo/cobi revealed profound down-regulation of genes critical to cell division and mitotic progression. Bromo/cobi treatment resulted in marked DNA damage and cell-cycle arrest, resulting in induction of apoptosis. These studies introduce bromodomain inhibition, alone or combined with agents targeting the mitogen activated protein kinase pathway, as a rational therapeutic approach for melanoma refractory to standard targeted or immunotherapeutic approaches.

The UVSSA protein is part of a genome integrity homeostasis network with links to transcription-coupled DNA repair and ATM signaling.

SignificanceTranscription-coupled repair (TCR) involves four core proteins: CSA, CSB, USP7, and UVSSA. CSA and CSB are mutated in the severe human neurocutaneous disease Cockayne syndrome. In contrast UVSSA is a mild photosensitive disease in which a mutated protein sequence prevents recruitment of USP7 protease to deubiquitinate and stabilize CSB. We deleted the UVSSA protein using CRISPR-Cas9 in an aneuploid cell line, HEK293, and determined the functional consequences. The knockout cell line was sensitive to transcription-blocking lesions but not sensitive to oxidative agents or PARP inhibitors, unlike CSB. Knockout of UVSSA also activated ATM, like CSB, in transcription-arrested cells. The phenotype of UVSSA, especially its rarity, suggests that many TCR-deficient patients and tumors fail to be recognized clinically.

Niraparib Suppresses Cholangiocarcinoma Tumor Growth by Inducing Oxidative and Replication Stress.

Cholangiocarcinoma (CCA) is the second most common hepatobiliary cancer, an aggressive malignancy with limited therapeutic options. PARP (poly (ADP-ribose) polymerase) 1 and 2 are important for deoxyribonucleotide acid (DNA) repair and maintenance of genomic stability. PARP inhibitors (PARPi) such as niraparib have been approved for different malignancies with genomic alteration in germline BRCA and DNA damage response (DDR) pathway genes. Genomic alterations were analyzed in DDR genes in CCA samples employing The Cancer Genome Atlas (TCGA) database. Mutations were observed in various DDR genes, and 35.8% cases had alterations in at least one of three genes (ARID1A, BAP1 and ATM), suggesting their susceptibility to PARPi. Niraparib treatment suppressed cancer cell viability and survival, and also caused G2/M cell cycle arrest in patient-derived xenograft cells lines (PDXC) and established CCA cells harboring DDR gene mutations. PARPi treatment also induced apoptosis and caspase3/7 activity in PDXC and CCA cell lines, and substantially reduced expression of BCL2, BCL-XL and MCL1 proteins. Niraparib caused a significant increase in oxidative stress, and induced activation of DNA damage markers, phosphorylation of CHK2 and replication fork stalling. Importantly, niraparib, in combination with gemcitabine, produced sustained and robust inhibition of tumor growth in vivo in a patient-derived xenograft (PDX) model more effectively than either treatment alone. Furthermore, tissue samples from mice treated with niraparib and gemcitabine display significantly lower expression levels of pHH3 and Ki-67, which are a mitotic and proliferative marker, respectively. Taken together, our results indicate niraparib as a novel therapeutic agent alone or in combination with gemcitabine for CCA.

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.

Dinaciclib, a cyclin-dependent kinase inhibitor, suppresses cholangiocarcinoma growth by targeting CDK2/5/9.

Cholangiocarcinoma (CCA) is a highly invasive cancer, diagnosed at an advanced stage, and refractory to surgical intervention and chemotherapy. Cyclin-dependent kinases (CDKs) regulate cell cycle progression and transcriptional processes, and are considered potential therapeutic targets for cancer. Dinaciclib is a small molecule multi-CDK inhibitor targeting CDK 2/5/9. In this study, the therapeutic efficacy of dinaciclib was assessed using patient-derived xenograft cells (PDXC) and CCA cell lines. Treatment with dinaciclib significantly suppressed cell proliferation, induced caspase 3/7 levels and apoptotic activity in PDXC and CCA cell lines. Dinaciclib suppressed expression of its molecular targets CDK2/5/9, and anti-apoptotic BCL-XL and BCL2 proteins. Despite the presence of cyclin D1 amplification in the PDXC line, palbociclib treatment had no effect on cell proliferation, cell cycle or apoptosis in the PDXC as well as other CCA cell lines. Importantly, dinaciclib, in combination with gemcitabine, produced a robust and sustained inhibition of tumor progression in vivo in a PDX mouse model, greater than either of the treatments alone. Expression levels of two proliferative markers, phospho-histone H3 and Ki-67, were substantially suppressed in samples treated with the combination regimen. Our results identify dinaciclib as a novel and potent therapeutic agent alone or in combination with gemcitabine for the treatment of CCA.

PHIP drives glioblastoma motility and invasion by regulating the focal adhesion complex.

The invasive behavior of glioblastoma is essential to its aggressive potential. Here, we show that pleckstrin homology domain interacting protein (PHIP), acting through effects on the force transduction layer of the focal adhesion complex, drives glioblastoma motility and invasion. Immunofluorescence analysis localized PHIP to the leading edge of glioblastoma cells, together with several focal adhesion proteins: vinculin (VCL), talin 1 (TLN1), integrin beta 1 (ITGB1), as well as phosphorylated forms of paxillin (pPXN) and focal adhesion kinase (pFAK). Confocal microscopy specifically localized PHIP to the force transduction layer, together with TLN1 and VCL. Immunoprecipitation revealed a physical interaction between PHIP and VCL. Targeted suppression of PHIP resulted in significant down-regulation of these focal adhesion proteins, along with zyxin (ZYX), and produced profoundly disorganized stress fibers. Live-cell imaging of glioblastoma cells overexpressing a ZYX-GFP construct demonstrated a role for PHIP in regulating focal adhesion dynamics. PHIP silencing significantly suppressed the migratory and invasive capacity of glioblastoma cells, partially restored following TLN1 or ZYX cDNA overexpression. PHIP knockdown produced substantial suppression of tumor growth upon intracranial implantation, as well as significantly reduced microvessel density and secreted VEGF levels. PHIP copy number was elevated in the classical glioblastoma subtype and correlated with elevated EGFR levels. These results demonstrate PHIP's role in regulating the actin cytoskeleton, focal adhesion dynamics, and tumor cell motility, and identify PHIP as a key driver of glioblastoma migration and invasion.

Novel tumor suppressor role of miRNA-876 in cholangiocarcinoma.

Cholangiocarcinoma (CCA) is a rare, highly invasive malignancy, and its incidence is increasing globally. MicroRNAs (miRNAs) mediate a wide array of cellular and biological processes and are dysregulated in various tumors. The functional and biological roles of miRNAs in CCA have not been fully elucidated. In this study, we show that miR-876 expression levels and copy number are significantly attenuated in the TCGA cohort of CCA tissue samples. TCGA expression data was consistent with the observed substantial decrease in miR-876 expression in patient samples and CCA cell lines. In-silico algorithm databases revealed BCL-XL as a potential target of miR-876. We observed miR-876 expression to be downregulated, whereas, BCL-XL upregulated in CCA cell lines. BCL-XL was identified as a direct functional target of miR-876 in CCA. miR-876-mediated reduction of BCL-XL regulated cell survival, induced apoptosis and caspase 3/7 expression in CCA. BCL-XL overexpression reversed the miR-876 mediated effect on CCA cell growth and apoptosis. Stable overexpression of miR-876 produced potent tumor suppressor activity and in vivo tumor cell growth reduction. Overexpression of miR-876 in a patient-derived xenograft (PDX) cell line significantly suppressed BCL-XL expression and spheroid formation with a concomitant induction of caspase 3/7 activity and apoptosis. This study demonstrates a novel tumor suppressor role for miR-876 in CCA, identifies BCL-XL as an actionable target, and suggests a potential therapeutic role for miR-876 in CCA.

PHIP as a therapeutic target for driver-negative subtypes of melanoma, breast, and lung cancer.

The identification and targeting of key molecular drivers of melanoma and breast and lung cancer have substantially improved their therapy. However, subtypes of each of these three common, lethal solid tumors lack identified molecular drivers, and are thus not amenable to targeted therapies. Here we show that pleckstrin homology domain-interacting protein (PHIP) promotes the progression of these "driver-negative" tumors. Suppression of PHIP expression significantly inhibited both tumor cell proliferation and invasion, coordinately suppressing phosphorylated AKT, cyclin D1, and talin1 expression in all three tumor types. Furthermore, PHIP's targetable bromodomain is functional, as it specifically binds the histone modification H4K91ac. Analysis of TCGA profiling efforts revealed PHIP overexpression in triple-negative and basal-like breast cancer, as well as in the bronchioid subtype of nonsmall cell lung cancer. These results identify a role for PHIP in the progression of melanoma and breast and lung cancer subtypes lacking identified targeted therapies. The use of selective, anti-PHIP bromodomain inhibitors may thus yield a broad-based, molecularly targeted therapy against currently nontargetable tumors.

Role of Elevated PHIP Copy Number as a Prognostic and Progression Marker for Cutaneous Melanoma.

Purpose: Previous studies have indicated an important role for pleckstrin homology domain-interacting protein (PHIP) as a marker and mediator of melanoma metastasis. Here we aimed to confirm the role of PHIP copy number in successive stages of melanoma progression.Experimental Design:PHIP copy number was examined using FISH in three independent cohorts by recording the percentage of cells harboring ≥3 copies of PHIP The impact of PHIP copy number on survival was assessed using Cox regression analysis. The enrichment of PHIP was assessed in various molecular melanoma subtypes. PHIP expression was analyzed in The Cancer Genome Atlas (TCGA) melanoma cohort.Results: Elevated PHIP copy number was significantly predictive of reduced distant metastasis-free survival (DMFS) and disease-specific survival (DSS), and increased prevalence of ulceration in primary melanoma (cohort No. 1). By multivariate analysis, PHIP FISH scores were independently predictive of DMFS and DSS. PHIP copy number was enriched in metastatic melanomas harboring mutant NRAS or expressing PTEN protein (cohort No. 2). PHIP copy number was significantly elevated in metastatic melanomas when compared with matched primary tumors from the same patient (cohort No. 3). Several of these associations were replicated using TCGA cohort analysis.Conclusions: These results underscore the important role of PHIP copy-number elevation in melanoma progression, and identify molecular subtypes of melanoma in which PHIP is enriched. Finally, as elevated PHIP copy number appears to be selected for during the progression of primary to metastatic melanoma, these results confirm PHIP as a promising therapeutic target for melanoma. Clin Cancer Res; 24(17); 4119-25. ©2018 AACR.

Why Cockayne syndrome patients do not get cancer despite their DNA repair deficiency.

Cockayne syndrome (CS) and xeroderma pigmentosum (XP) are human photosensitive diseases with mutations in the nucleotide excision repair (NER) pathway, which repairs DNA damage from UV exposure. CS is mutated in the transcription-coupled repair (TCR) branch of the NER pathway and exhibits developmental and neurological pathologies. The XP-C group of XP patients have mutations in the global genome repair (GGR) branch of the NER pathway and have a very high incidence of UV-induced skin cancer. Cultured cells from both diseases have similar sensitivity to UV-induced cytotoxicity, but CS patients have never been reported to develop cancer, although they often exhibit photosensitivity. Because cancers are associated with increased mutations, especially when initiated by DNA damage, we examined UV-induced mutagenesis in both XP-C and CS cells, using duplex sequencing for high-sensitivity mutation detection. Duplex sequencing detects rare mutagenic events, independent of selection and in multiple loci, enabling examination of all mutations rather than just those that confer major changes to a specific protein. We found telomerase-positive normal and CS-B cells had increased background mutation frequencies that decreased upon irradiation, purging the population of subclonal variants. Primary XP-C cells had increased UV-induced mutation frequencies compared with normal cells, consistent with their GGR deficiency. CS cells, in contrast, had normal levels of mutagenesis despite their TCR deficiency. The lack of elevated UV-induced mutagenesis in CS cells reveals that their TCR deficiency, although increasing cytotoxicity, is not mutagenic. Therefore the absence of cancer in CS patients results from the absence of UV-induced mutagenesis rather than from enhanced lethality.

BPTF transduces MITF-driven prosurvival signals in melanoma cells.

Microphthalmia-associated transcription factor (MITF) plays a critical and complex role in melanocyte transformation. Although several downstream targets of MITF action have been identified, the precise mechanisms by which MITF promotes melanocytic tumor progression are incompletely understood. Recent studies identified an oncogenic role for the bromodomain plant homeodomain finger transcription factor (BPTF) gene in melanoma progression, in part through activation of BCL2, a canonical target of MITF signaling. Analysis of the BPTF promoter identified a putative MITF-binding site, suggesting that MITF may regulate BPTF expression. Overexpression of MITF resulted in up-regulation of BPTF in a panel of melanoma and melanocyte cell lines. shRNA-mediated down-regulation of MITF in melanoma cells was accompanied by down-regulation of BPTF and BPTF-regulated genes (including BCL2) and resulted in reduced proliferative capacity of melanoma cells. The suppression of cell growth mediated by MITF silencing was rescued by overexpression of BPTF cDNA. Binding of MITF to the BPTF promoter was demonstrated using ChIP analysis. MITF overexpression resulted in direct transcriptional activation of BPTF, as evidenced by increased luciferase activity driven by the BPTF promoter. These results indicate that BPTF transduces key prosurvival signals driven by MITF, further supporting its important role in promoting melanoma cell survival and progression.

Tumor suppressor role of microRNA-1296 in triple-negative breast cancer.

UNLABELLED: Triple negative breast cancer (TNBC) is an aggressive subtype of breast cancer with a poor prognosis, which lacks effective targeted therapies. There is an urgent need to better understand the underlying molecular mechanisms of TNBC aggressiveness and identify novel, efficient targets for therapeutic intervention. METHODS: miRNA qRT-PCR was used to determine the expression of miR-1296 in cell lines. The miR-1296 overexpression effects in TNBC cell lines were investigated using assays of colony formation, cell cycle and apoptosis. Immunoblotting was performed to determine the expression of the miR-1296 target protein, and luciferase assays were performed to confirm the target of miR-1296 action. RESULTS: miR-1296 expression was significantly suppressed in TNBC cell lines and tissues samples. Overexpression of miR-1296 significantly suppressed cell proliferation of two TNBC cell lines when compared to control miRNA-expressing cells. A significant decrease in the S-phase of the cell cycle was observed following miR-1296 overexpression, accompanied by induction of apoptosis in TNBC cells. Cyclin D1 (CCND1) was identified as a target of miR-1296 action. miR-1296 overexpression significantly suppressed the luciferase activity of reporter plasmid containing the 3'UTR of CCND1 and protein expression levels of CCND1 in TNBC cells. The effects of miR-1296 overexpression on TNBC cell growth were reversed by CCND1 overexpression. miR-1296 expression sensitized TNBC cells to cisplatin treatment. CONCLUSION: Our results demonstrate a novel tumor suppressor role for miR-1296 in triple-negative breast cancer cell lines, identify CCND1 as its target of action, and demonstrate a potential role for miR-1296 in sensitizing breast cancer cells to cisplatin.

Cytomegalovirus Immediate-Early Proteins Promote Stemness Properties in Glioblastoma.

Glioblastoma (GBM) is the most common and aggressive human brain tumor. Human cytomegalovirus (HCMV) immediate-early (IE) proteins that are endogenously expressed in GBM cells are strong viral transactivators with oncogenic properties. Here, we show how HCMV IEs are preferentially expressed in glioma stem-like cells (GSC), where they colocalize with the other GBM stemness markers, CD133, Nestin, and Sox2. In patient-derived GSCs that are endogenously infected with HCMV, attenuating IE expression by an RNAi-based strategy was sufficient to inhibit tumorsphere formation, Sox2 expression, cell-cycle progression, and cell survival. Conversely, HCMV infection of HMCV-negative GSCs elicited robust self-renewal and proliferation of cells that could be partially reversed by IE attenuation. In HCMV-positive GSCs, IE attenuation induced a molecular program characterized by enhanced expression of mesenchymal markers and proinflammatory cytokines, resembling the therapeutically resistant GBM phenotype. Mechanistically, HCMV/IE regulation of Sox2 occurred via inhibition of miR-145, a negative regulator of Sox2 protein expression. In a spontaneous mouse model of glioma, ectopic expression of the IE1 gene (UL123) specifically increased Sox2 and Nestin levels in the IE1-positive tumors, upregulating stemness and proliferation markers in vivo. Similarly, human GSCs infected with the HCMV strain Towne but not the IE1-deficient strain CR208 showed enhanced growth as tumorspheres and intracranial tumor xenografts, compared with mock-infected human GSCs. Overall, our findings offer new mechanistic insights into how HCMV/IE control stemness properties in GBM cells.

The role of BPTF in melanoma progression and in response to BRAF-targeted therapy.

BACKGROUND: Bromodomain PHD finger transcription factor (BPTF) plays an important role in chromatin remodeling, but its functional role in tumor progression is incompletely understood. Here we explore the oncogenic effects of BPTF in melanoma. METHODS: The consequences of differential expression of BPTF were explored using shRNA-mediated knockdown in several melanoma cell lines. Immunoblotting was used to assess the expression of various proteins regulated by BPTF. The functional role of BPTF in melanoma progression was investigated using assays of colony formation, invasion, cell cycle, sensitivity to selective BRAF inhibitors, and in xenograft models of melanoma progression (n = 12 mice per group). The biomarker role of BPTF in melanoma progression was assessed using fluorescence in situ hybridization and immunohistochemical analyses. All statistical tests were two-sided. RESULTS: shRNA-mediated BPTF silencing suppressed the proliferative capacity (by 65.5%) and metastatic potential (by 66.4%) of melanoma cells. Elevated BPTF copy number (mean ≥ 3) was observed in 28 of 77 (36.4%) melanomas. BPTF overexpression predicted poor survival in a cohort of 311 melanoma patients (distant metastasis-free survival P = .03, and disease-specific survival P = .008), and promoted resistance to BRAF inhibitors in melanoma cell lines. Metastatic melanoma tumors progressing on BRAF inhibitors contained low BPTF-expressing, apoptotic tumor cell subclones, indicating the continued presence of drug-responsive subclones within tumors demonstrating overall resistance to anti-BRAF agents. CONCLUSIONS: These studies demonstrate multiple protumorigenic functions for BPTF and identify it as a novel target for anticancer therapy. They also suggest the combination of BPTF targeting with BRAF inhibitors as a novel therapeutic strategy for melanomas with mutant BRAF.

Antitumor activity of miR-1280 in melanoma by regulation of Src.

MicroRNAs (miRNAs) play a key role in cancer progression by coordinately repressing target genes involved in cell proliferation, migration, and invasion. miRNAs regulate gene expression by repressing translation or directing sequence-specific degradation of complementary mRNA. Here, we report that expression of miR-1280 is significantly suppressed in human melanoma specimens when compared with nevi, and in human melanoma cell lines when compared with cultured normal human melanocytes. The proto-oncogene Src was identified as a target of miR-1280 action. Levels of Src expression were significantly higher in melanoma samples and cell lines than in nevi and normal melanocytes. miR-1280 overexpression significantly suppressed the luciferase activity of reporter plasmids containing the full-length 3' untranslated region of Src. miR-1280-mediated suppression of Src led to substantial decreases in melanoma cell proliferation, cell cycle progression, invasion, as well as induced melanoma cell apoptosis. The effects of miR-1280 overexpression on melanoma cell proliferation and growth were reversed by Src overexpression. Intratumoral delivery of miR-1280 significantly suppressed melanoma cell growth in vivo. Our results demonstrate a novel role for miR-1280 as a tumor suppressor in melanoma, identify the Src signaling pathway as a target of miR-1280 action, and suggest a potential therapeutic role for miR-1280 in melanoma.

Mitochondrial reactive oxygen species are scavenged by Cockayne syndrome B protein in human fibroblasts without nuclear DNA damage.

Cockayne syndrome (CS) is a human DNA repair-deficient disease that involves transcription coupled repair (TCR), in which three gene products, Cockayne syndrome A (CSA), Cockayne syndrome B (CSB), and ultraviolet stimulated scaffold protein A (UVSSA) cooperate in relieving RNA polymerase II arrest at damaged sites to permit repair of the template strand. Mutation of any of these three genes results in cells with increased sensitivity to UV light and defective TCR. Mutations in CSA or CSB are associated with severe neurological disease but mutations in UVSSA are for the most part only associated with increased photosensitivity. This difference raises questions about the relevance of TCR to neurological disease in CS. We find that CSB-mutated cells, but not UVSSA-deficient cells, have increased levels of intramitochondrial reactive oxygen species (ROS), especially when mitochondrial complex I is inhibited by rotenone. Increased ROS would result in oxidative damage to mitochondrial proteins, lipids, and DNA. CSB appears to behave as an electron scavenger in the mitochondria whose absence leads to increased oxidative stress. Mitochondrial ROS, however, did not cause detectable nuclear DNA damage even when base excision repair was blocked by an inhibitor of polyADP ribose polymerase. Neurodegeneration in Cockayne syndrome may therefore be associated with ROS-induced damage in the mitochondria, independent of nuclear TCR. An implication of our present results is that mitochondrial dysfunction involving ROS has a major impact on CS-B pathology, whereas nuclear TCR may have a minimal role.