Transcriptional modulator ZBED6 affects cell cycle and growth of human colorectal cancer cells.

The transcription factor ZBED6 (zinc finger, BED-type containing 6) is a repressor of IGF2 whose action impacts development, cell proliferation, and growth in placental mammals. In human colorectal cancers, IGF2 overexpression is mutually exclusive with somatic mutations in PI3K signaling components, providing genetic evidence for a role in the PI3K pathway. To understand the role of ZBED6 in tumorigenesis, we engineered and validated somatic cell ZBED6 knock-outs in the human colorectal cancer cell lines RKO and HCT116. Ablation of ZBED6 affected the cell cycle and led to increased growth rate in RKO cells but reduced growth in HCT116 cells. This striking difference was reflected in the transcriptome analyses, which revealed enrichment of cell-cycle-related processes among differentially expressed genes in both cell lines, but the direction of change often differed between the cell lines. ChIP sequencing analyses displayed enrichment of ZBED6 binding at genes up-regulated in ZBED6-knockout clones, consistent with the view that ZBED6 modulates gene expression primarily by repressing transcription. Ten differentially expressed genes were identified as putative direct gene targets, and their down-regulation by ZBED6 was validated experimentally. Eight of these genes were linked to the Wnt, Hippo, TGF-ß, EGF receptor, or PI3K pathways, all involved in colorectal cancer development. The results of this study show that the effect of ZBED6 on tumor development depends on the genetic background and the transcriptional state of its target genes.

SHISA3, an antagonist of the Wnt/ß-catenin signaling, is epigenetically silenced and its ectopic expression suppresses growth in breast cancer.

Breast cancer (BC) is the foremost cause of cancer related deaths in women globally. Currently there is a scarcity of reliable biomarkers for its early stage diagnosis and theranostics monitoring. Altered DNA methylation patterns leading to the silencing of tumor suppressor genes are considered as an important mechanism underlying tumor development and progression in various cancer types, including BC. Very recently, epigenetic silencing of SHISA3, an antagonist of ß-catenin, has been reported in various types of tumor. However, the role of SHISA3 in BC has not been investigated yet. Therefore, we aimed at evaluating the contribution of SHISA3 in BC causation by analyzing its expression and methylation levels in BC cell lines (MDA-MB231, MCF-7 and BT-474) and in 103 paired BC tissue samples. The SHISA3 expression and methylation status was determined by qPCR and methylation specific PCR (MSP) respectively. The role of SHISA3 in BC tumorigenesis was evaluated by proliferation and migration assays after ectopic expression of SHISA3. The association between SHISA3 hypermethylation and clinicopathological parameters of BC patients was also studied. The downregulation of SHISA3 expression was found in three BC cell lines used and in all BC tissue samples. However, SHISA3 promoter region was hypermethylated in 61% (63/103) tumorous tissues in comparison to the 18% of their matched normal tissues. The 5-aza-2'-deoxycytidine treatment restored SHISA3 expression by reversing promoter hypermethylation in both MDA-MB231 and MCF-7 cells. Furthermore, ectopic expression of SHISA3 significantly reduced the proliferation and migration ability of these cells. Taken together, our findings for the first time reveal epigenetic silencing and tumor suppressing role of SHISA3 in BC. Henceforth, this study has identified SHISA3 as potentially powerful target for the development of new therapies against BC, as well as novel diagnostic and therapy response monitoring approaches.

Transposon Mutagenesis Reveals Fludarabine Resistance Mechanisms in Chronic Lymphocytic Leukemia.

PURPOSE: To identify resistance mechanisms for the chemotherapeutic drug fludarabine in chronic lymphocytic leukemia (CLL), as innate and acquired resistance to fludarabine-based chemotherapy represents a major challenge for long-term disease control. EXPERIMENTAL DESIGN: We used piggyBac transposon-mediated mutagenesis, combined with next-generation sequencing, to identify genes that confer resistance to fludarabine in a human CLL cell line. RESULTS: In total, this screen identified 782 genes with transposon integrations in fludarabine-resistant pools of cells. One of the identified genes is a known resistance mediator DCK (deoxycytidine kinase), which encodes an enzyme that is essential for the phosphorylation of the prodrug to the active metabolite. BMP2K, a gene not previously linked to CLL, was also identified as a modulator of response to fludarabine. In addition, 10 of 782 transposon-targeted genes had previously been implicated in treatment resistance based on somatic mutations seen in patients refractory to fludarabine-based therapy. Functional characterization of these genes supported a significant role for ARID5B and BRAF in fludarabine sensitivity. Finally, pathway analysis of transposon-targeted genes and RNA-seq profiling of fludarabine-resistant cells suggested deregulated MAPK signaling as involved in mediating drug resistance in CLL. CONCLUSIONS: To our knowledge, this is the first forward genetic screen for chemotherapy resistance in CLL. The screen pinpointed novel genes and pathways involved in fludarabine resistance along with previously known resistance mechanisms. Transposon screens can therefore aid interpretation of cancer genome sequencing data in the identification of genes modifying sensitivity to chemotherapy. Clin Cancer Res; 22(24); 6217-27. ©2016 AACR.