Qiuying Liu

Vigilin interacts with CCCTC-binding factor (CTCF) and is involved in CTCF-dependent regulation of the imprinted genes Igf2 and H19.

CCCTC‐binding factor (CTCF), a highly conserved zinc finger protein, is a master organizer of genome spatial organization and has multiple functions in gene regulation. Mounting evidence indicates that CTCF regulates the imprinted genes Igf2 and H19 by organizing chromatin at the Igf2/H19 locus, although the mechanism by which CTCF carries out this function is not fully understood. By yeast two‐hybrid screening, we identified vigilin, a multi‐KH‐domain protein, as a new partner of CTCF. Subsequent coimmunoprecipitation and glutathione S‐transferase pulldown experiments confirmed that vigilin interacts with CTCF. Moreover, vigilin is present at several known CTCF target sites, such as the promoter regions of c‐myc and BRCA1, the locus control region of β‐globin, and several regions within the Igf2/H19 locus. In vivo depletion of vigilin did not affect CTCF binding; however, knockdown of CTCF reduced vigilin binding to the H19 imprinting control region. Furthermore, ectopic expression of vigilin significantly downregulated Igf2 and upregulated H19, whereas depletion of vigilin upregulated Igf2 and downregulated H19, in HepG2, CNE1 and HeLa cells. These results reveal the functional relevance of vigilin and CTCF, and show that the CTCF–vigilin complex contributes to regulation of Igf2/H19.

BORIS up-regulates OCT4 via histone methylation to promote cancer stem cell-like properties in human liver cancer cells

Accumulating evidence has revealed the importance of cancer stem cells (CSCs) in chemoresistance and recurrence. BORIS, a testes-specific CTCF paralog, has been shown to be associated with stemness traits of embryonic cancer cells and epithelial CSCs. We previously reported that BORIS is correlated with the expression of the CSC marker CD90 in hepatocellular carcinoma (HCC). These results encourage us to wonder whether BORIS exerts functions on CSC-like traits of human liver cancer cells. Here, we report that BORIS was enriched in HCC tissues. Exogenous overexpression of BORIS promoted CSC-like properties, including self-renewal, chemoresistance, migration and invasion in Huh7 and HCCLM3 cells. Conversely, BORIS knockdown suppressed CSC-like properties in SMMC-7721 and HepG2 cells and inhibited tumorigenicity in SMMC-7721 cells. Moreover, BORIS alteration did not affect the DNA methylation status of the minimal promoter and exon 1 region of OCT4. However, BORIS overexpression enhanced the amount of BORIS bound on the OCT4 promoter and increased H3K4me2, while reducing H3K27me3; BORIS depletion decreased BORIS and H3K4me2 on the OCT4 promoter, while increasing H3K27me3. These results revealed that BORIS is associated with the CSC-like traits of human liver cancer cells through the epigenetic regulation of OCT4.

CTCF-mediated reduction of vigilin binding affects the binding of HP1α to the satellite 2 locus

CCCTC‐binding factor (CTCF) has been implicated in numerous aspects of chromosome biology, and vigilin, a multi‐KH‐domain protein, participates in heterochromatin formation and chromosome segregation. We previously showed that CTCF interacts with vigilin. Here, we show that human vigilin, but not CTCF, colocalizes with HP1α on heterochromatic satellite 2 and β‐satellite repeats. CTCF up‐regulates the transcription of satellite 2, while vigilin down‐regulates it. Vigilin depletion or CTCF overexpression reduces the binding of HP1α on the satellite 2 locus. Furthermore, overexpression of CTCF resists the loading of vigilin onto the satellite 2 locus. Thus CTCF may regulate vigilin behavior and thus indirectly influence the binding of HP1α to the satellite 2 locus.

Hypomethylation of BORIS is a promising prognostic biomarker in hepatocellular carcinoma

The brother of the regulator of the imprinted site (BORIS), an 11 zinc finger (ZF) protein, is a paralogue of CCCTC-binding factor (CTCF), involves in a few crucial events of chromatin functions, complex transcription regulation during spermatogenesis. As a novel tumor oncogene, abnormal expression of BORIS is observed in human hepatocellular carcinoma, however, the underlying mechanisms remain largely unexplored. In this study, the methylation status of BORIS was tested by methylation specific polymerase chain reaction (MSP) in human HCC cell lines and 43 pairs of tissue specimens. Frequently demethylation of BORIS in HCC was significantly higher than that in the paired adjacent non-tumor tissues (P=0.019), and it was correlated with tumor size (P=0.025) and clinical TNM stage (P=0.035). Patients with hypomethylated BORIS had a shorter disease free survival than those without demethylated BORIS (P=0.006). Further, analyses using Cox regression have indicated that the BORIS demethylation status was an independent risk to the reduced overall survival rate of HCC patients (P=0.035). These findings provide clues to clarify whether the demethylation may lead to activation of the promoter for upregulation expression of BORIS. In conclusions, aberrant BORIS hypomethylation is a promising biomarker for the prognosis of HCC.

Disruption of human vigilin impairs chromosome condensation and segregation.

Appropriate packaging and condensation are critical for eukaryotic chromatins accommodation and separation during cell division. Human vigilin, a multi‐KH‐domain nucleic acid‐binding protein, is associated with alpha satellites of centromeres. DDP1, a vigilins homolog, is implicated with chromatin condensation and segregation. The expression of vigilin was previously reported to elevate in highly proliferating tissues and increased in a subset of hepatocellular carcinoma patients. Other studies showed that vigilin interacts with CTCF, contributes to regulation of imprinted genes Igf2/H19, and colocalizes with HP1α on heterochromatic satellite 2 and β‐satellite repeats. These studies indicate that human vigilin might be involved in chromatin remodeling and regular cell growth. To investigate the potential role of human vigilin in cell cycle, the correlations between vigilin and chromosomal condensation and segregation were studied. Depletion of human vigilin by RNA interference in HepG2 cells resulted in chromosome undercondensation and various chromosomal defects during mitotic phase, including chromosome misalignments, lagging chromosomes, and chromosome bridges. Aberrant polyploid nucleus in telophase was also observed. Unlike the abnormal staining pattern of chromosomes, the shape of spindle was normal. Furthermore, the chromatin showed a greater sensitivity to MNase digestion. Collectively, our findings show that human vigilin apparently participates in chromatin condensation and segregation.

Application of multiplex methylated-specific PCR with capillary electrophoresis to explore prognostic value of TSGs hypermethylation for hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a malignant tumor that severely threatens human health. To date, early detection for HCC patients is particularly significant due to their poor survival rates even after liver resection.

Vigilin interacts with CTCF and is involved in the maintenance of imprinting of IGF2 through a novel RNA–mediated mechanism

Accumulating evidence has revealed the imprinting of insulin-like growth factor-2 gene (IGF2) is maintained by binding of CCCTC binding factor (CTCF) to the unmethylated imprinting control region (ICR) between IGF2 and H19 genes. We have previously reported that high-density lipoprotein binding protein (HDLBP/vigilin), a multiKH-domain protein, interacts with CTCF and coexists with it at several CTCF-binding sites on the ICR to regulate general gene expression of IGF2. However, the impact of the interaction on imprinting of IGF2 remains unclear. Here, we demonstrate that cooperation of vigilin and CTCF protects IGF2 from losing of imprinting. Pull-down experiments show that KH1-7 domains of vigilin interact with zinc-finger domains of CTCF. We also display that some RNAs participate in the vigilin-CTCF interaction, one of which is H19 long noncoding RNA (lncRNA). Furthermore, we confirm that H19 lncRNA-knockdown alters the imprinting of IGF2. These data suggest that vigilin interacts with CTCF, mediated by H19 lncRNA, to keep the imprinting of IGF2.