Merkel cell carcinoma (MCC) is an aggressive neuroendocrine tumor of the skin currently with no cure. In this study, we have first demonstrated that c-Myc overexpression is common in MCC. By targeting c-Myc, bromodomain inhibitors have demonstrated antitumor efficacy in several preclinical human cancer models. Thus we interrogated the role of c-Myc inhibition in MCC with c-Myc amplification by employing the BET inhibitor JQ1. We have uncovered that c-Myc can be regulated by JQ1 in MCC cells with pathological c-Myc activation. Moreover, JQ1 potently abrogates c-Myc expression in MCC cells and causes marked G1 cell cycle arrest. Mechanistically, JQ1 induced cell cycle arrest coincides with downrgulation of cyclin D1 and upregulation of p21, p27 and p57, whereas JQ1 exerts no effect on apoptosis in MCC cells. Further knockdown of p21, p27 or p57 by shRNA partially protects cells from JQ1 induced cell cycle arrest. Additionally, c-Myc knockdown by shRNA generates significant cell cycle arrest, suggesting that c-Myc overexpression plays a role in MCC pathogenesis. Most importantly, JQ1 significantly attenuates tumor growth in xenograft MCC mouse models. Our results provide initial evidence indicating the potential clinical utility of BET protein inhibitors in the treatment of MCC with pathologic activation of c-Myc.

It is increasingly evident that long noncoding RNAs (lncRNA) have causative roles in carcinogenesis. In this study, we report findings implicating a novel lncRNA in gastric cancer, termed GAPLINC (gastric adenocarcinoma predictive long intergenic noncoding RNA), based on the use of global microarray and in situ hybridization (ISH) analyses to identify aberrantly expressed lncRNA in human gastric cancer specimens. GAPLINC is a 924-bp-long lncRNA that is highly expressed in gastric cancer tissues. GAPLINC suppression and with gene expression profiling in gastric cancer cells revealed alterations in cell migration pathways, with CD44 expression the most highly correlated. Manipulating GAPLINC expression altered CD44 mRNA abundance and the effects of GAPLINC on cell migration and proliferation were neutralized by suppressing CD44 expression. Mechanistic investigations revealed that GAPLINC regulates CD44 as a molecular decoy for miR211-3p, a microRNA that targets both CD44 and GAPLINC. Tissue ISH analysis suggested that GAPLINC overexpression defines a subgroup of patients with gastric cancer with very poor survival. Taken together, our results identify a noncoding regulatory pathway for the CD44 oncogene, shedding new light on the basis for gastric cancer cell invasiveness. Cancer Res; 74(23); 1–13. ©2014 AACR.

It is increasingly evident that long non-coding RNAs (lncRNA) have causative roles in carcinogenesis. In this study, we report findings implicating a novel lncRNA in gastric cancer (GC), termed GAPLINC, based on the use of global microarray and in situ hybridization (ISH) analyses to identify aberrantly expressed lncRNA in human GC specimens. GAPLINC is a 924-bp long lncRNA that is highly expressed in GC tissues. GAPLINC suppression and with gene expression profiling in GC cells revealed alterations in cell migration pathways, with CD44 expression the most highly correlated. Manipulating GAPLINC expression altered CD44 mRNA abundance and the effects of GAPLINC on cell migration and proliferation were neutralized by suppressing CD44 expression. Mechanistic investigations revealed that GAPLINC regulates CD44 as a molecular decoy for miR211-3p, a microRNA that targets both CD44 and GAPLINC. Tissue ISH analysis suggested that GAPLINC overexpression defines a subgroup of GC patients with very poor survival. Taken together, our results identify a non-coding regulatory pathway for the CD44 oncogene, shedding new light on the basis for GC cell invasiveness.

Glioblastoma multiforme (GBM) is the most common and severe form of brain cancer. The median survival time of patients is approximately 12 months due to poor responses to surgery and chemoradiation. To understand the mechanisms involved in radioresistance, we conducted a genetic screen using an shRNA library to identify genes in which inhibition would sensitize cells to radiation. The results were cross-referenced with the Oncomine and Rembrandt databases to focus on genes that are highly expressed in GBM tumors and associated with poor patient outcomes. Spermidine/spermine-N1-acetyltransferase 1 (SAT1), an enzyme involved in polyamine catabolism, was identified as a gene that promotes resistance to ionizing radiation (IR), is overexpressed in brain tumors, and correlates with poor outcomes. Knockdown of SAT1 using shRNA and siRNA approaches in multiple cell and neurosphere lines resulted in sensitization of GBM cells to radiation in colony formation assays and tumors, and decreased tumorigenesis in vivo. Radiosensitization occurred specifically in G2–M and S phases, suggesting a role for SAT1 in homologous recombination (HR) that was confirmed in a DR-GFP reporter system. Mechanistically, we found that SAT1 promotes acetylation of histone H3, suggesting a new role of SAT1 in chromatin remodeling and regulation of gene expression. In particular, SAT1 depletion led to a dramatic reduction in BRCA1 expression, explaining decreased HR capacity. Our findings suggest that the biologic significance of elevated SAT1 expression in GBM lies in its contribution to cell radioresistance and that SAT1 may potentially be a therapeutic target to sensitize GBM to cancer therapies. Cancer Res; 74(23); 1–10. ©2014 AACR.

Glioblastoma multiforme (GBM) is the most common and severe form of brain cancer. The median survival time of patients is approximately 12 months due to poor responses to surgery and chemoradiation. In order to understand the mechanisms involved in radioresistance, we conducted a genetic screen using an shRNA library to identify genes whose inhibition would sensitize cells to radiation. The results were cross-referenced with the Oncomine and Rembrandt databases to focus on genes that are highly expressed in GBM tumors and associated with poor patient outcomes. Spermidine/spermine-N1-acetyltransferase 1 (SAT1), an enzyme involved in polyamine catabolism, was identified as a gene that promotes resistance to ionizing radiation (IR), is overexpressed in brain tumors, and correlates with poor outcomes. Knockdown of SAT1 using shRNA and siRNA approaches in multiple cell and neurosphere lines resulted in sensitization of GBM cells to radiation in colony formation assays and tumors, and decreased tumorigenesis in vivo. Radiosensitization occurred specifically in G2/M and S phases, suggesting a role for SAT1 in homologous recombination (HR) that was confirmed in a DR-GFP reporter system. Mechanistically, we found that SAT1 promotes acetylation of histone H3, suggesting a new role of SAT1 in chromatin remodeling and regulation of gene expression. In particular, SAT1 depletion led to a dramatic reduction in BRCA1 expression, explaining decreased HR capacity. Our findings suggest that the biological significance of elevated SAT1 expression in GBM lies in its contribution to cell radioresistance and that SAT1 may potentially be a therapeutic target to sensitize GBM to cancer therapies.