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Profiling chromatin accessible regions in Merkel cell carcinoma cells

ABSTRACT: Merkel cell carcinoma (MCC) is an aggressive neuroendocrine cancer of the skin, caused by either excessive UV damage or integration of the Merkel cell polyomavirus (MCV) genome. Here, we report that virally encoded MCV small T antigen (ST) establishes dependence on the LSD1 transcriptional repressor. Inhibition of LSD1 reduces growth of MCV-positive MCC and suppresses ST’s transformation capacity in vitro and in vivo. To define the mechanism of LSD1 inhibition in MCC, we performed a CRISPR loss-of-function library screen. We found that deletion of components of the non-canonical (ncBAF) chromatin remodeler complex confers resistance to LSD1 inhibitors and that LSD1 and ncBAF antagonistically regulate an overlapping set of genes involved in neuron differentiation. Our work provides mechanistic insight into the dependence of MCC on LSD1 and the role of ncBAF as a tumor suppressor in cancer.

ORGANISM(S): Homo sapiens

PROVIDER: GSE140505 | GEO | 2020/02/16

REPOSITORIES: GEO

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Project description:Merkel cell carcinoma (MCC) is an aggressive cutaneous neuroendocrine tumor with high mortality rates. Merkel cell polyomavirus (MCPyV), identified in the majority of MCC, may drive tumorigenesis via viral T antigens. However, mechanisms underlying pathogenesis in MCPyV-negative MCC remain poorly understood. To nominate genes contributing to pathogenesis of MCPyV-negative MCC, we performed DNA microarray analysis on 30 MCCs. MCPyV status of MCCs was determined by PCR for viral DNA and RNA. 1593 probe-sets were differentially expressed between MCPyV-negative and -positive MCC, with significant differential expression defined as at least 2-fold change in either direction and p-value of ≤ 0.05. MCPyV-negative tumors showed decreased RB1 expression, whereas MCPyV-positive tumors were enriched for immune response genes. Validation studies included immunohistochemistry demonstration of decreased RB protein expression in MCPyV-negative tumors and increased peritumoral CD8+ T lymphocytes surrounding MCPyV-positive tumors. In conclusion, our data suggest that loss of RB1 expression may play an important role in tumorigenesis of MCPyV-negative MCC. Functional and clinical validation studies are needed to determine whether this tumor suppressor pathway represents an avenue for targeted therapy. We used microarrays to characterize global gene expression patterns related to Merkel cell polyomavirus status in Merkel cell carcinoma. Furthermore, we compared Merkel cell carcinoma to less aggressive primary cutaneous carcinomas. We utilized flash-frozen tumor tissue from primary Merkel cell carcinomas, metastatic Merkel cell carcinomas, primary cutaneous squamous cell carcinomas, and basal cell carcinomas. Merkel cell carcinoma cell lines, which represent a pure population of tumor cells, were also included. Merkel cell polyomavirus status was determined at the DNA and RNA level using multiple primers for viral T-antigen and capsid protein sequences. This Series represents two analyses - one with new Samples normalized together, and another with some of the new Samples re-normalized with Samples previously submitted under Series GSE13355. The latter group contain 'renormalized' in the titles.

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Profiling chromatin accessible regions in Merkel cell carcinoma cells

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