Xiangfan Liu

CREB up-regulates long non-coding RNA, HULC expression through interaction with microRNA-372 in liver cancer

Long non-coding RNA (lncRNA), highly up-regulated in liver cancer (HULC) plays an important role in tumorigenesis. Depletion of HULC resulted in a significant deregulation of several genes involved in liver cancer. Although up-regulation of HULC expression in hepatocellular carcinoma has been reported, the molecular mechanisms remain unknown. In this study, we used in vivo and in vitro approaches to characterize cancer-dependent alterations in the chromatin organization and find a CREB binding site (encompassing from −67 to −53 nt) in the core promoter. Besides, we also provided evidence that PKA pathway may involved in up-regulation of HULC. Furthermore, we demonstrated HULC may act as an endogenous ‘sponge’, which down-regulates a series of microRNAs (miRNAs) activities, including miR-372. Inhibition of miR-372 leads to reducing translational repression of its target gene, PRKACB, which in turn induces phosphorylation of CREB. Over-expression of miR-372 decreases the association of CREB with the proximal promoter, followed by the dissociation of P300, resulting in a change of the histone ‘code’, such as in deacetylation and methylation. The study elucidates that fine tuning of HULC expression is part of an auto-regulatory loop in which it’s inhibitory to expression and activity of miR-372 allows lncRNA up-regulated expression in liver cancer.

NF-kappaB P50/P65 hetero-dimer mediates differential regulation of CD166/ALCAM expression via interaction with micoRNA-9 after serum deprivation, providing evidence for a novel negative auto-regulatory loop

CD166/ALCAM plays an important role in tumor aggression and progression as well as protecting cancer cells against apoptosis and autophagy. However, the mechanism by which pro-cell death signals control CD166 expression remains unclear. Here we show that following serum deprivation (SD), upregulation of CD166 protein is shorter than that of CD166 mRNA. Molecular analysis revealed both CD166 and miR-9-1 as two novel NF-κB target genes in hepatoma cells. In vivo activation and translocation of the NF-κB P50/P65 hetero-dimer into the nucleus following the phosphorylation and accompanied degradation of its inhibitor, IκBα, contributes to efficient transcription of both genes following SD. We show that following serum starvation, delayed up-regulation of miR-9 represses translation of CD166 protein through its target sites in the 3′-UTR of CD166 mRNA. We also propose that miR-9 promotes cell migration largely due to inhibition of CD166. Collectively, the study elucidates a novel negative auto-regulatory loop in which NF-κB mediates differential regulation of CD166 after SD.

Rab5a overexpression promoting ovarian cancer cell proliferation may be associated with APPL1‐related epidermal growth factor signaling pathway

Rab5a is a regulatory guanosine triphosphatase that is associated with the transport and fusion of endocytic vesicles, and participates in regulation of intracellular signaling pathways embraced by cells to adapt to the specific environment. Rab5a is also correlated with lung, stomach, and hepatocellular carcinomas. Here, we detected Rab5a in paraffin‐embedded samples of 20 ovarian cysts, 20 benign cystadenomas, and 39 ovarian cancers by immunohistochemistry, and observed that Rab5a expression was significantly higher in ovarian cancer (P = 0.0001). By setting up stable HO‐8910 cell lines expressing Rab5a or dominant negative Rab5a (Rab5a:S34N), we found that Rab5a overexpression enhanced the cell growth by promoting G1 into S phase. In contrast, Rab5a:S34N inhibited this process. Additionally, APPL1 (adaptor protein containing PH domain, PTB domain, and Leucine zipper motif), a downstream effector of Rab5a, was also involved in promoting HO‐8910 cell cycle progress. But this function was blocked by Rab5a:S34N. Laser scanning confocal microscopy represented the colocalization of APPL1 and Rab5a in the plasmolemma, which changed with the time of epidermal growth factor (EGF) stimulation. We also found APPL1 could transfer from the membranes into the nucleus where it interacted with NuRD/MeCP1 (the nucleosome remodeling and histone deacetylase multiprotein complex). NuRD is reported to be involved in the deacetylation of histone H3 and H4 to regulate nuclear transcription. So Rab5a promoted proliferation of ovarian cancer cells, which may be associated with the APPL1‐related epidermal growth factor signaling pathway. (Cancer Sci 2010)

The essential role of YAP O-GlcNAcylation in high-glucose-stimulated liver tumorigenesis

O-GlcNAcylation has been implicated in the tumorigenesis of various tissue origins, but its function in liver tumorigenesis is not clear. Here, we demonstrate that O-GlcNAcylation can enhance the expression, stability and function of Yes-associated protein (YAP), the downstream transcriptional regulator of the Hippo pathway and a potent oncogenic factor in liver cancer. O-GlcNAcylation induces transformative phenotypes of liver cancer cells in a YAP-dependent manner. An O-GlcNAc site of YAP was identified at Thr241, and mutating this site decreased the O-GlcNAcylation, stability, and pro-tumorigenic capacities of YAP, while increasing YAP phosphorylation. Importantly, we found via in vitro cell-based and in vivo mouse model experiments that O-GlcNAcylation of YAP was required for high-glucose-induced liver tumorigenesis. Interestingly, a positive feedback between YAP and global cellular O-GlcNAcylation is also uncovered. We conclude that YAP O-GlcNAcylation is a potential therapeutic intervention point for treating liver cancer associated with high blood glucose levels and possibly diabetes.

miR-598 inhibits metastasis in colorectal cancer by suppressing JAG1/Notch2 pathway stimulating EMT

ABSTRACT MicroRNAs (miRNAs) are a class of endogenous, evolutionarily conserved small non‐coding RNA molecules that mediate the posttranscriptional process of target gene, leading to translational repression or degradation of target mRNAs. A series of studies have indicated that miRNAs play an important role in tumor initiation, development and progression. In this study, we found that down regulation of miR‐598 was a frequent event in CRC tissues compared to the paracarcinoma tissues. And the study demonstrated that miR‐598 was implicated in CRC metastasis. Transwell migration assay revealed that elevated miR‐598 expression reduces CRC cell migration. Moreover, our study showed that suppression of miR‐598 expression induces CRC cell epithelialmesenchymal transition(EMT) and overexpression of miR‐598 inhibits CRC cell EMT. In addition, bioinformatics target prediction identified JAG1 as a putative target of miR‐598. Knockdown of miR‐598 was shown to upregulate JAG1 expression. Furthermore, overexpression of miR‐598 suppressed the expression of JAG1. Consistent results were also obtained when the regulation of JAG1 expression by miR‐598 was further specified in CRC tissues. Moreover, overexpression of JAG1 induces epithelialmesenchymal transition(EMT) and promotes the metastasis of CRC cells. Decreased Notch2 expression suppresses CRC cells metastasis and EMT. Together, these results indicate that miR‐598 is a novel regulator of colorectal cancer metastasis. Our data suggest miR‐598 is implicated in regulating Epithelial‐mesenchymal transitions by directly suppressing its downstream target gene JAG1 to inactivate Notch signaling pathway. HIGHLIGHTSmiR‐598 expression in CRC tissues was significantly lower than corresponding adjacent noncancerous tissues.miR‐598 suppresses CRC cells metastasis and EMT.JAG1 is direct target of miR‐598.miR‐598 inhibits metastasis in colorectal cancer by suppressing JAG1/Notch2 pathway stimulating EMT.

High Glucose Stimulates Tumorigenesis in Hepatocellular Carcinoma Cells Through AGER-Dependent O-GlcNAcylation of c-Jun

Epidemiologic studies suggest that hepatocellular carcinoma (HCC) has a strong relationship with diabetes. However, the underlying molecular mechanisms still remain unclear. Here, we demonstrated that high glucose (HG), one of the main characteristics of diabetes, was capable of accelerating tumorigenesis in HCC cells. Advanced glycosylation end product–specific receptor (AGER) was identified as a stimulator during this process. Mechanistically, AGER activated a hexosamine biosynthetic pathway, leading to enhanced O-GlcNAcylation of target proteins. Notably, AGER was capable of increasing activity and stability of proto-oncoprotein c-Jun via O-GlcNAcylation of this protein at Ser73. Interestingly, c-Jun can conversely enhance AGER transcription. Thereby, a positive autoregulatory feedback loop that stimulates diabetic HCC was established. Finally, we found that AG490, an inhibitor of Janus kinase, has the ability to impair AGER expression and its functions in HCC cells. In conclusion, AGER and its functions to stimulate O-GlcNAcylation are important during liver tumorigenesis, when high blood glucose levels are inadequately controlled.

SIRT1 increases YAP- and MKK3-dependent p38 phosphorylation in mouse liver and human hepatocellular carcinoma.

Both oncoprotein and tumor-suppressor activity have been reported for SIRTUIN1 (SIRT1) and p38 in many types of cancer. The effect of SIRT1 on p38 phosphorylation (p-p38) remains controversial and may be organ- and cell-specific. We found that SIRT1 is essential for maintaining liver size and weight in mice. SIRT1 levels were elevated in human HCC compared to adjacent normal liver tissue, and its expression correlated positively with p-p38 levels. Additionally, SIRT1-activated p38 increased liver cancer malignancy. SIRT1 increased phosphorylation and nuclear accumulation of p38, possibly by increasing MKK3 expression. SIRT1 also induced YAP expression, which in turn increased MKK3 transcription. Positive correlations between SIRT1, YAP, MKK3, and p-p38 levels indicate that blocking their activity may prove helpful in treating HCC.

Somatic mutational analysis of FAK in breast cancer: a novel gain-of-function mutation due to deletion of exon 33.

Focal adhesion kinase (FAK) regulates cell adhesion, migration, proliferation, and survival. We identified a novel splicing mutant, FAK-Del33 (exon 33 deletion, KF437463), in both breast and thyroid cancers through colony sequencing. Considering the low proportion of mutant transcripts in samples, this mutation was detected by TaqMan-MGB probes based qPCR. In total, three in 21 paired breast tissues were identified with the FAK-Del33 mutation, and no mutations were found in the corresponding normal tissues. When introduced into a breast cell line through lentivirus infection, FAK-Del33 regulated cell motility and migration based on a wound healing assay. We demonstrated that the expression of Tyr397 (main auto-phosphorylation of FAK) was strongly increased in FAK-Del33 overexpressed breast tumor cells compared to wild-type following FAK/Src RTK signaling activation. These results suggest a novel and unique role of the FAK-Del33 mutation in FAK/Src signaling in breast cancer with significant implications for metastatic potential.

TFCP2 Is Required for YAP-Dependent Transcription to Stimulate Liver Malignancy

Although YAP-dependent transcription is closely associated with liver tumorigenesis, the mechanism by which YAP maintains its function is poorly understood. Here, we show that TFCP2 is required for YAP-dependent transcription and liver malignancy. Mechanistically, YAP function is stimulated by TFCP2 via a WW-PSY interaction. TFCP2 also maintains YAP stability by inhibiting βTrCP. Notably, genomic co-occupancy of YAP and TFCP2 is revealed. TFCP2 acts as a transcription co-factor that stimulates YAP transcription by facilitating YAP binding with YAP binding motif (YBF)-containing transcription factors. Interestingly, TFCP2 also stimulated the YAP-TEAD interaction and TEAD target gene expression. Finally, several genes co-regulated by YAP and TFCP2 that contribute to YAP-dependent tumorigenesis are identified and verified. Thus, we establish a model showing that TFCP2 acts as a YAP co-factor to maintain YAP-dependent transcription in liver cancer cells, suggesting that simultaneous targeting of both YAP and TFCP2 may be an effective therapeutic approach.

New Insights into FAK Phosphorylation Based on a FAT Domain-Defective Mutation

Mounting evidence suggests that the FAK N-terminal (FERM) domain controls FAK phosphorylation and function; however, little is known regarding the role of the C terminal (FAT) domain in FAK regulation. We identified a patient-derived FAK mutant, in which a 27-amino acid segment was deleted from the C-terminal FAT domain (named FAK-Del33). When FAK-Del33 was overexpressed in specific tumor cell lines, Y397 phosphorylation increased compared with that observed in cells expressing FAK-WT. Here, we attempt to unveil the mechanism of this increased phosphorylation. Using cell biology experiments, we show that FAK-Del33 is incapable of co-localizing with paxillin, and has constitutively high Y397 phosphorylation. With a kinase-dead mutation, it showed phosphorylation of FAK-Del33 has enhanced through auto-phosphorylation. It was also demonstrated that phosphorylation of FAK-Del33 is not Src dependent or enhanced intermolecular interactions, and that the hyperphosphorylation can be lowered using increasing amounts of transfected FERM domain. This result suggests that Del33 mutation disrupting of FATs structural integrity and paxillin binding capacity leads to incapable of targeting Focal adhesions, but has gained the capacity for auto-phosphorylation in cis.