Meng Zhuo

Background: The bromodomain and extra-terminal domain (BET) family of proteins, especially BRD4 play an important role in epigenetic regulation, and are essential for cell survival and also are promising anticancer targets. This study aims to analyze the effect of BRD4 on the cell growth and progression of pancreatic cancer and novel mechanisms involved.Methods: Expression of BRD4 in pancreatic cancer and paired adjacent noncancerous tissues from 76 patients was analyzed by western blotting, immunohistochemistry, and real time PCR. Its correlation with the clinicopathological characteristics and prognosis of pancreatic cancer patients was analyzed. The effects of BRD4 on the cell proliferation were detected by colony formation assay and sulforhodamine B assay. Migration and invasion were determined by Transwell assays, and the effect of BRD4 on subcutaneous tumor formation was verified in nude mice. Cell cycle analysis was detected by flow cytometry. The potential downstream targets of BRD4 and related molecular mechanisms were clarified by RNA sequencing, chromatin immunoprecipitation and dual luciferase reporter assay.Results: BRD4 was overexpressed in pancreatic cancer. Biological results showed that BRD4 functioned as tumor promoter, facilitated cell proliferation, migration and invasion in vitro and in vivo. Further, caveolin-2 was selected as the downstream gene of BRD4 by RNA sequencing. Caveolin-2 overexpression can partially reverse the decreased cell growth ability caused by BRD4 knockdown, but did not affect cell migration and invasion. Chromatin immunoprecipitation assay and dual luciferase reporter assay revealed BRD4 could bind to the promoter region of caveolin-2 and upregulate caveolin-2 expression. Clinical data further indicated a positive correlation between BRD4 and caveolin-2 expression. BRD4 (high)/caveolin-2 (high) correlated with shorter overall survival of patients with pancreatic cancer. Multivariate analysis revealed that both BRD4 and caveolin-2 were independent factors.Conclusions: Our findings reveal the oncogenic effects of BRD4 in pancreatic cancer and elucidate a possible mechanism by which BRD4 and caveolin-2 act to enhance cell growth. Targeting the BRD4-caveolin-2 interaction by development of BET inhibitors will be a therapeutic strategy for pancreatic cancer.

It was demonstrated that long non-coding RNAs occupied an important position in tumor pathogenesis and progression. We have previously found that the metastasis-associated lung adenocarcinoma transcript 1 (MALAT-1) promotes cell proliferation and metastases in pancreatic ductal adenocarcinoma (PDAC). The present study was aimed to discuss the underlying mechanisms. Bioinformatics method was used to identify the miRNA target of MALAT-1. Expressions of relative genes were assessed by quantitative real-time PCR and western blotting, respectively. Sulforhodamine B assay and Transwell assay were employed to detect cell proliferation, migration and invasion, respectively. Moreover, RNA immunoprecipitation was performed to determine whether RNA-induced silencing complex contained MALAT-1 and its potential binding miRNA. Luciferase assays was used to confirm potential binding site. Bioinformatics search predicted that miR-200c-3p was a direct target of MALAT-1. Further, we found a reciprocal suppression between MALAT-1 and miR-200c-3p expression. In terms of mechanisms, high MALAT-1 and low miR-200c-3p may form a novel feedback loop. On the one hand, MALAT-1 functioned as a competing endogenous RNA to suppress miR-200c-3p expression, leading to upregulation of ZEB1 expression. On the other hand, miR-200c-3p inhibited the level of MALAT-1 expression was in a way similar to miRNA-mediated downregulation of target genes. Clinical data further indicated that MALAT-1 and ZEB1 expression was negatively correlated with miR-200c-3p transcript level of PDAC tissues. There was a positive correlation between MALAT-1 and ZEB1 level. MALAT-1 (high)/miR-200c-3p (low) correlated with shorter overall survival of PDAC patients. Multivariate analysis revealed that both MALAT-1 and miR-200c-3p levels were independent prognostic factors. Our findings firstly revealed a novel feedback loop between high MALAT-1 and low miR-200c-3p. Targeting the feedback loop between high MALAT-1 and low miR-200c-3p will be a therapeutic strategy for PDAC.

Multiple primary cancers (MPC) have been identified as two or more cancers without any subordinate relationship that occur either simultaneously or metachronously in the same or different organs of an individual. Lynch syndrome is an autosomal dominant genetic disorder that increases the risk of many types of cancers. Lynch syndrome patients who suffer more than two cancers can also be considered as MPC; patients of this kind provide unique resources to learn how genetic mutation causes MPC in different tissues. We performed a whole genome sequencing on blood cells and two tumor samples of a Lynch syndrome patient who was diagnosed with five primary cancers. The mutational landscape of the tumors, including somatic point mutations and copy number alternations, was characterized. We also compared Lynch syndrome with sporadic cancers and proposed a model to illustrate the mutational process by which Lynch syndrome progresses to MPC. We revealed a novel pathologic mutation on the MSH2 gene (G504 splicing) that associates with Lynch syndrome. Systematical comparison of the mutation landscape revealed that multiple cancers in the proband were evolutionarily independent. Integrative analysis showed that truncating mutations of DNA mismatch repair (MMR) genes were significantly enriched in the patient. A mutation progress model that included germline mutations of MMR genes, double hits of MMR system, mutations in tissue-specific driver genes, and rapid accumulation of additional passenger mutations was proposed to illustrate how MPC occurs in Lynch syndrome patients. Our findings demonstrate that both germline and somatic alterations are driving forces of carcinogenesis, which may resolve the carcinogenic theory of Lynch syndrome.