Faculty Bibliography

Malignant melanoma is the most lethal form of skin cancer with rising incidence. Once metastasis occurs, patients have a dismal prognosis, largely due to limited systemic treatment with chemotherapy and resistance to targeted therapies. Thus, effective therapies with long-term responses are currently lacking. Although much effort has focused on characterizing and targeting the genetic alterations in melanoma, the identification of epigenetic players remains poorly understood. Chromatin dynamics have recently been shown to exert a critical function in a number of cancers, including melanoma, and emerging evidence points towards a role of histone variants as key regulatory molecules in cancer. H2A.Z is a highly conserved H2A variant, harboring two different isoforms in vertebrates, H2A.Z.1 and H2A.Z.2. High levels of H2A.Z promote cell proliferation in breast, prostate and bladder cancers, however studies so far have focused primarily on H2A.Z.1 or did not clearly distinguish between the two isoforms. Here, we report a role for the unappreciated isoform H2A.Z.2 as a mediator of cell proliferation and drug sensitivity in malignant melanoma. To our knowledge, this is the first evidence to implicate a distinct role for this H2A.Z isoform in any tumor type. While both H2A.Z.1 and H2A.Z.2 are highly expressed in metastatic melanoma and correlate with decreased patient survival, only H2A.Z.2 deficiency results in impaired cellular proliferation, which occurs through a G1 to S arrest. Integrated gene expression and ChIP-seq analyses revealed that H2A.Z.2 positively regulates E2F target genes, which are highly expressed and acquire a distinct H2A.Z occupancy signature over the promoter and gene body in metastatic cells. We further identified the BET (bromodomain and extraterminal domain) family member BRD2 as an H2A.Z-interacting protein in melanoma cells, and our data suggest that H2A.Z.2 exerts its oncogenic function by maintaining the global levels of BRD2 and histone H4 acetylation. Furthermore, H2A.Z.2 depletion sensitizes melanoma cells to targeted therapies and chemotherapy. Collectively, our findings implicate H2A.Z.2 as a driver of melanoma pathogenesis. Owing to the fact that histone modification is a reversible process, H2A.Z.2 and BRD2 hold translational potential for novel therapeutic strategies

Transcription factors and chromatin-remodeling complexes are key determinants of embryonic stem cell (ESC) identity. Here, we demonstrate that BRD4, a member of the bromodomain and extraterminal domain (BET) family of epigenetic readers, regulates the self-renewal ability and pluripotency of ESCs. BRD4 inhibition resulted in induction of epithelial-to-mesenchymal transition (EMT) markers and commitment to the neuroectodermal lineage while reducing the ESC multidifferentiation capacity in teratoma assays. BRD4 maintains transcription of core stem cell genes such as OCT4 and PRDM14 by occupying their super-enhancers (SEs), large clusters of regulatory elements, and recruiting to them Mediator and CDK9, the catalytic subunit of the positive transcription elongation factor b (P-TEFb), to allow Pol-II-dependent productive elongation. Our study describes a mechanism of regulation of ESC identity that could be applied to improve the efficiency of ESC differentiation.

High-grade serous ovarian carcinoma (HGSOC) is a fatal disease, and its grave outcome is largely because of widespread metastasis at the time of diagnosis. Current chemotherapies reduce tumor burden, but they do not provide long-term benefits for patients with cancer. The aggressive tumor growth and metastatic behavior characteristic of these tumors demand novel treatment options such as anti-microRNA treatment, which is emerging as a potential modality for cancer therapy. MicroRNA-182 (miR182) overexpression contributes to aggressive ovarian cancer, largely by its negative regulation of multiple tumor suppressor genes involved in tumor growth, invasion, metastasis, and DNA instability. In this study, we examined the therapeutic potential of anti-miR182 utilizing the animal orthotopic model to mimic human ovarian cancer using ovarian cancer cells SKOV3 (intrabursal xenografts) and OVCAR3 (intraperitoneal injection). These models provide a valuable model system for the investigation of ovarian cancer therapy in vivo. Through a combination of imaging, histological, and molecular analyses, we found that anti-miR182 treatment can significantly reduce tumor burden (size), local invasion, and distant metastasis compared with its control in both models. The bases of anti-miR182 treatment are mainly through the restoration of miR182 target expression, including but not limited to BRCA1, FOXO3a, HMGA2, and MTSS1. Overall, our results strongly suggest that anti-miR182 can potentially be used as a therapeutic modality in treating HGSOC. Mol Cancer Ther; 13(7); 1729-39. (c)2014 AACR.

To better identify melanoma patients who are, at the time of primary melanoma diagnosis, at high risk of developing brain metastases, primary melanoma characteristics were examined as risk factors for brain metastasis development. In a study of two patient cohorts, clinicopathological characteristics prospectively collected at primary cutaneous melanoma diagnosis for patients with/without brain metastasis were assessed in univariate and multivariate analyses using data from two prospectively collected databases: the Melanoma Cooperative Group (MCG) (1972-1982) and the Interdisciplinary Melanoma Cooperative Group (IMCG) (2002-2009). Candidate risk factors were evaluated in association with time to brain metastasis using either the log-rank test or Cox proportional hazards regression analysis with/without considering competing risks. Out of 2341 total patients included in the study, 222 (9.5%) developed brain metastases (median follow-up: 98 months). The median time to brain metastases was 30.5 months and the median survival time after brain metastases was 4 months. Increased hazard ratios (HRs) for brain metastasis were found among thicker (logarithmic value in mm) (MCG: HR=1.97, P<0.0001; IMCG: HR=1.31, P=0.018), ulcerated (MCG: HR=1.93, P=0.01; IMCG: HR=3.14, P<0.0001), and advanced-stage (MCG: HR=2.08, P=0.008; IMCG: HR=2.56, P=0.0002) primary melanomas on the basis of multivariate Cox regression analysis assuming the presence of competing risks. Primary cutaneous melanoma thickness, ulceration, and stage were identified and validated as risk factors associated with time to melanoma brain metastasis.

Previous reports have demonstrated a role for hedgehog signaling in melanoma progression, prompting us to explore the therapeutic benefit of targeting this pathway in melanoma. We profiled a panel of human melanoma cell lines and control melanocytes for altered expression of hedgehog pathway members and determined the consequences of both genetic and pharmacological inhibition of the hedgehog pathway activator Smoothened (SMO) in melanoma, both in vitro and in vivo. We also examined the relationship between altered expression of hedgehog pathway mediators and survival in a well-characterized cohort of metastatic melanoma patients with prospectively collected follow up information. Studies revealed that over 40% of the melanoma cell lines examined harbored significantly elevated levels of the hedgehog pathway mediators SMO, GLI2, and PTCH1 compared to melanocytes (p < 0.05). SMO inhibition using siRNA and the small molecule inhibitor, NVP-LDE-225, suppressed melanoma growth in vitro, particularly in those cell lines with moderate SMO and GLI2 expression. NVP-LDE-225 also induced apoptosis in vitro and inhibited melanoma growth in a xenograft model. Gene expression data also revealed evidence of compensatory up-regulation of two other developmental pathways, Notch and WNT, in response to hedgehog pathway inhibition. Pharmacological and genetic SMO inhibition also downregulated genes involved in human embryonic stem cell pluripotency. Finally, increased SMO expression and decreased expression of the hedgehog pathway repressor GLI3 correlated with shorter post recurrence survival in metastatic melanoma patients. Our data demonstrate that hedgehog pathway inhibition might be a promising targeted therapy in appropriately selected metastatic melanoma patients.

Metastatic melanoma remains a mostly incurable disease. Although newly approved targeted therapies are efficacious in a subset of patients, resistance and relapse rapidly ensue. Alternative therapeutic strategies to manipulate epigenetic regulators and disrupt the transcriptional program that maintains tumor cell identity are emerging. Bromodomain and extraterminal domain (BET) proteins are epigenome readers known to exert key roles at the interface between chromatin remodeling and transcriptional regulation. Here, we report that BRD4, a BET family member, is significantly upregulated in primary and metastatic melanoma tissues compared with melanocytes and nevi. Treatment with BET inhibitors impaired melanoma cell proliferation in vitro and tumor growth and metastatic behavior in vivo, effects that were mostly recapitulated by individual silencing of BRD4. RNA sequencing of BET inhibitor-treated cells followed by Gene Ontology analysis showed a striking impact on transcriptional programs controlling cell growth, proliferation, cell-cycle regulation, and differentiation. In particular, we found that, rapidly after BET displacement, key cell-cycle genes (SKP2, ERK1, and c-MYC) were downregulated concomitantly with the accumulation of cyclin-dependent kinase (CDK) inhibitors (p21 and p27), followed by cell-cycle arrest. Importantly, BET inhibitor efficacy was not influenced by BRAF or NRAS mutational status, opening the possibility of using these small-molecule compounds to treat patients for whom no effective targeted therapy exists. Collectively, our study reveals a critical role for BRD4 in melanoma tumor maintenance and renders it a legitimate and novel target for epigenetic therapy directed against the core transcriptional program of melanoma. Cancer Res; 73(20); 6264-76. (c)2013 AACR.