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RBBP6 is a multidomain protein, with four splice variants translated into four functional isoforms. RBBP6 isoform 1 has been reported to interact with TP53 and pRb as well as with proteins that regulate transcriptional response to tumorigenesis such as HDM2, ZBTB38, YBX1 and NEK6. Experimental validation of isoforms 2 and 4 is yet to be conducted. The third isoform, consisting of only the DWNN domain and a short unordered c terminus, has been shown to be down-regulated in several human cancers and demonstrated as a regulator of G2/M cell cycle arrest. A number of studies have supported the role of DWNN in cell cycle regulation, however, its mechanism in these processes remains obscure. Posttranslational modification of DWNN could be critical for its function and this study was formulated to understand how the DWNN regulates the cell cycle. Our study identified 12 cell cycle-related proteins interacting with DWNN using various bioinformatics tools. We also identified 10 ubiquitin ligases that interact with DWNN. The most relevant interacting partner, the cell cycle regulator Nek6, has been reported to interact with DWNN during the cell cycle. It was therefore critical to interrogate the interaction between Nek6 and DWNN by homology modelling and docking. The DWNN mutants had a reduced affinity for NEK6 with at least one of the mutants having changes that affect at least one phosphorylation site. It is likely that NEK6 promotes cell proliferation by phosphorylating DWNN. This work suggests that DWNN co-regulates RNA splicing, ubiquitination, and cell cycle control. DWNN may therefore, be targeted for novel anticancer therapies through cell cycle regulation.

Alterations in distal regulatory elements that control gene expression underlie many diseases, including cancer. Epigenomic analyses of normal and diseased cells have produced correlative predictions for connections between dysregulated enhancers and target genes involved in pathogenesis. However, with few exceptions, these predicted cis-regulatory circuits remain untested. Here, we dissect cis-regulatory circuits that lead to overexpression of NEK6, a mitosis-associated kinase, in human B cell lymphoma. We find that only a minor subset of predicted enhancers is required for NEK6 expression. Indeed, an annotated super-enhancer is dispensable for NEK6 overexpression and for maintaining the architecture of a B cell-specific regulatory hub. A CTCF cluster serves as a chromatin and architectural boundary to block communication of the NEK6 regulatory hub with neighboring genes. Our findings emphasize that validation of predicted cis-regulatory circuits and super-enhancers is needed to prioritize transcriptional control elements as therapeutic targets.

MicroRNA (miRNA) are a class of highly conserved, small noncoding RNA that emerge as key posttranscriptional regulators in various neoplastic transformations. Our previous study profiling the miRNA transcriptome in Marek's disease virus (MDV)-induced lymphoma revealed many novel and differentially expressed miRNA, including gga-miR-26a, which was downregulated in MDV-infected spleens of chickens. In this study, differential expression of gga-miR-26a between MDV-infected and noninfected spleens at 4, 7, 14, 21, and 28 d postinfection was analyzed by real-time PCR. The results showed gga-miR-26a were downregulated in MDV-infected spleens at cytolytic infection, latency, and tumor transformation phases. Subsequent cell proliferation assay revealed cell viability was lower in gga-miR-26a mimic transfection group than that in negative controls. Target genes of gga-miR-26a were identified by luciferase reporter gene assay. The results showed significant interaction between gga-miR-26a and Never In Mitosis Gene A (NIMA)-related kinase 6 (NEK6) gene. Subsequent gain of function experiment and Western blot assay showed that mRNA and protein levels of NEK6 were downregulated after gga-miR-26 mimic was transfected into MDV-transformed lymphoid cell line (MSB-1), indicating that NEK6 was modulated by gga-miR-26a. The expression of NEK6 showed a higher trend in MDV-infected samples including tumorous spleen and MD lymphoma from liver than that in noninfected controls. The results suggested that gga-miR-26a inhibited MSB-1 cell proliferation. Gga-miR-26a and its direct target, NEK6, might play important roles in MDV infection.