Sumoylation of hypoxia inducible factor-1α and its significance in cancer

Circ-RAPGEF5 promotes intrahepatic cholangiocarcinoma progression by stabilizing SAE1 to facilitate SUMOylation

BACKGROUND

Intrahepatic cholangiocarcinoma (ICC) is an aggressive malignancy with a poor prognosis. The underlying functions and mechanisms of circular RNA and SUMOylation in the development of ICC remain poorly understood.

METHODS

Circular RNA hsa_circ_0001681 (termed Circ-RAPGEF5 hereafter) was identified by circular RNA sequencing from 19 pairs of ICC and adjacent tissue samples. The biological function of Circ-RAPGEF5 in tumor proliferation and metastasis was examined by a series of in vitro assays. A preclinical model was used to validate the therapeutic effect of targeting Circ-RAPGEF5. RNA pull-down and dual-luciferase reporter assays were used to access the RNA interactions. Western blot and Co-IP assays were used to detect SUMOylation levels.

RESULTS

Circ-RAPGEF5, which is generated from exons 2 to 6 of the host gene RAPGEF5, was upregulated in ICC. In vitro and in vivo assays showed that Circ-RAPGEF5 promoted ICC tumor proliferation and metastasis, and inhibited apoptosis. Additionally, high Circ-RAPGEF5 expression was significantly correlated with a poor prognosis. Further investigation showed that SAE1, a potential target of Circ-RAPGEF5, was also associated with poor oncological outcomes. RNA pull-down and dual-luciferase reporter assays showed an interaction of miR-3185 with Circ-RAPGEF5 and SAE1. Co-IP and western blot assays showed that Circ-RAPGEF5 is capable of regulating SUMOylation.

CONCLUSION

Circ-RAPGEF5 promotes ICC tumor progression and SUMOylation by acting as a sponge for miR-3185 to stabilize SAE1. Targeting Circ-RAPGEF5 or SAE1 might be a novel diagnostic and therapeutic strategy in ICC.

The emerging roles of SUMOylation in the tumor microenvironment and therapeutic implications

Tumor initiation, progression, and response to therapies depend to a great extent on interactions between malignant cells and the tumor microenvironment (TME), which denotes the cancerous/non-cancerous cells, cytokines, chemokines, and various other factors around tumors. Cancer cells as well as stroma cells can not only obtain adaption to the TME but also sculpt their microenvironment through a series of signaling pathways. The post-translational modification (PTM) of eukaryotic cells by small ubiquitin-related modifier (SUMO) proteins is now recognized as a key flexible pathway. Proteins involved in tumorigenesis guiding several biological processes including chromatin organization, DNA repair, transcription, protein trafficking, and signal conduction rely on SUMOylation. The purpose of this review is to explore the role that SUMOylation plays in the TME formation and reprogramming, emphasize the importance of targeting SUMOylation to intervene in the TME and discuss the potential of SUMOylation inhibitors (SUMOi) in ameliorating tumor prognosis.

SUMO E3 ligase CBX4 regulates hTERT-mediated transcription of CDH1 and promotes breast cancer cell migration and invasion

hTERT, the catalytic component of the human telomerase enzyme, is regulated by post-translational modifications, like phosphorylation and ubiquitination by multiple proteins which remarkably affects the overall activity of the enzyme. Here we report that hTERT gets SUMOylated by SUMO1 and polycomb protein CBX4 acts as the SUMO E3 ligase of hTERT. hTERT SUMOylation positively regulates its telomerase activity which can be inhibited by SENP3-mediated deSUMOylation. Interestingly, we have established a new role of hTERT SUMOylation in the repression of E-cadherin gene expression and consequent triggering on the epithelial-mesenchymal-transition (EMT) program in breast cancer cells. We also observed that catalytically active CBX4, leads to retention of hTERT/ZEB1 complex onto E-cadherin promoter leading to its repression through hTERT-SUMOylation. Further through wound healing and invasion assays in breast cancer cells, we showed the tumor promoting ability of hTERT was significantly compromised upon overexpression of SUMO-defective mutant of hTERT. Thus our findings establish a new post-translational modification of hTERT which on one hand is involved in telomerase activity maintenance and on the other hand plays a crucial role in the regulation of gene expression thereby promoting migration and invasion of breast cancer cells.

Combining combretastatin A4 phosphate with ginsenoside Rd synergistically inhibited hepatocellular carcinoma by reducing HIF-1α via PI3K/AKT/mTOR signalling pathway

OBJECTIVES

Combretastatin A4 phosphate (CA4P), a vascular disrupting agent (VDA), can cause rapid tumour vessel occlusion. Subsequently, extensive necrosis is discovered in the tumour center, which induces widespread hypoxia and the rise of the α subunit of hypoxia-inducible factor-1 (HIF-1α). The aim of this study was to evaluate the inhibition of hepatocellular carcinoma growth by combining CA4P with HIF-1 α inhibitor and investigate the mechanism of this combination.

METHODS

Ginsenoside Rd (Rd) was used in combination with CA4P to estimate the inhibition effect in HepG2 cells and HepG2 xenograft mouse model. The efficacy of anti-tumour was evaluated by tumour growth curve. The protein expression of HIF-1α and PI3K/AKT/mTOR signalling pathway were analysed by western blot.

KEY FINDINGS

Combination of CA4P and Rd inhibited HepG2 cell proliferation and induced apoptosis in vivo and in vitro. It also increased the necrotic area of the tumour and delayed the tumour growth. Moreover, Rd down-regulated HIF-1α protein expression by inhibiting PI3K/AKT/mTOR signalling pathway.

CONCLUSIONS

Combination of CA4P and Rd had synergistic anti-tumour effects. The mechanism may be related to the inhibition of HIF-1α by PI3K/AKT/mTOR signalling pathway. This strategy provides a new thought for the combinative therapy of VDAs.

Lycium barbarum Polysaccharide Inhibited Hypoxia-Inducible Factor 1 in COPD Patients

Background

Chronic obstructive pulmonary disease (COPD) is a chronic airway inflammatory disease characterized by irreversible airflow obstruction. Pathogenic mechanisms underlying COPD remain largely unknown.

Objective

The current study was designed to explore serum concentration of hypoxia-inducible factor 1α (HIF-1α) in stable COPD patients and the potential effect of Lycium barbarum polysaccharides (LBP) on HIF-1α protein expression.

Methods

Serum HIF-1α was quantified by ELISA in 102 stable COPD patients before and after 2-week orally taken LBP (100 mL/time, twice daily, 5–15 mg/mL). Correlation of serum LBP and lung function (FEV1%) or blood gas (PO₂ and PCO₂) was also analyzed. As a control, 105 healthy subjects were also enrolled into this study.

Results

Serum concentration of HIF-1α was significantly higher in the stable COPD patients (37.34 ± 7.20 pg/mL) than that in the healthy subjects (29.55 ± 9.66 pg/mL, P<0.001). Oral administration of LBP (5 mg/mL, 100 mL, twice daily for 2 weeks) not only relieved COPD symptoms but also significantly reduced serum HIF-1α concentration (36.94 ± 9.23 vs 30.49 ± 6.42 pg/mL, P<0.05). In addition, level of serum HIF-1α concentration was significantly correlated with PCO₂ (r = 0.283, P<0.001), but negatively and significantly correlated with PO₂ (r = −0.490, P=0.005) or FEV1%(r = −0.420, P=0.018).

Conclusion

These findings suggested that activation of HIF-1 signaling pathway may be involved in the pathophysiology of COPD and that stabilization of serum HIF-1α concentration by LBP might benefit the stable COPD patients.

Effects of microRNA regulation on antiangiogenic therapy resistance in non-small cell lung cancer

Antiangiogenic drugs have become a standard therapeutic regimen for advanced non-small cell lung cancer (NSCLC); however, many issues remain to be solved. Identifying specific markers to predict patient response to antiangiogenic drugs to ensure therapeutic efficacy would increase their clinical benefit. MicroRNAs (miRNAs) are involved in the process of resistance to antiangiogenic therapy, as they regulate various key signaling pathways. Therefore, miRNAs may be used as targets for reversing tumor resistance to antiangiogenic therapy. This article reviews the molecular mechanisms of antiangiogenic therapy resistance and the specific mechanisms of miRNA regulation of resistance. Signal transducer and activator of transcription 3 (STAT3) is one of multiple target genes of miRNAs, and is closely related to antiangiogenic research. Thus, it is described separately in this review article.

Basic Biology of Hypoxic Responses Mediated by the Transcription Factor HIFs and its Implication for Medicine

Oxygen (O₂) is essential for human life. Molecular oxygen is vital for the production of adenosine triphosphate (ATP) in human cells. O₂ deficiency leads to a reduction in the energy levels that are required to maintain biological functions. O₂ acts as the final acceptor of electrons during oxidative phosphorylation, a series of ATP synthesis reactions that occur in conjunction with the electron transport system in mitochondria. Persistent O₂ deficiency may cause death due to malfunctioning biological processes. The above account summarizes the classic view of oxygen. However, this classic view has been reviewed over the last two decades. Although O₂ is essential for life, higher organisms such as mammals are unable to biosynthesize molecular O₂ in the body. Because the multiple organs of higher organisms are constantly exposed to the risk of “O₂ deficiency,” living organisms have evolved elaborate strategies to respond to hypoxia. In this review, I will describe the system that governs oxygen homeostasis in the living body from the point-of-view of the transcription factor hypoxia-inducible factor (HIF).

The Protein Phosphatase PPM1G Destabilizes HIF-1α Expression

Hypoxia-inducible factors (HIFs) are key regulators of hypoxic responses, and their stability and transcriptional activity are controlled by several kinases. However, the regulation of HIF by protein phosphatases has not been thoroughly investigated. Here, we found that overexpression of Mg²⁺/Mn²⁺-dependent protein phosphatase 1 gamma (PPM1G), one of Ser/Thr protein phosphatases, downregulated protein expression of ectopic HIF-1α under normoxic or acute hypoxic conditions. In addition, the deficiency of PPM1G upregulated protein expression of endogenous HIF-1α under normoxic or acute oxidative stress conditions. PPM1G decreased expression of HIF-1α via the proteasomal pathway. PPM1G-mediated HIF-1α degradation was dependent on prolyl hydroxylase (PHD), but independent of von Hippel-Lindau (VHL). These data suggest that PPM1G is critical for the control of HIF-1α-dependent responses.

Fibrogenic/Angiogenic Linker for Non-Invasive Assessment of Hepatic Fibrosis Staging in Chronic Hepatitis C Among Egyptian Patients

Background and rationale for the study. Liver biopsy is the golden standard for staging liver fibrosis, but it may be accompanied by complications. Because of this complication, the aim of this study is to evaluate a simple noninvasive score to assess hepatic fibrosis in chronic hepatitis C genotype 4 patients which is very may have an important in diagnosis and therapeutic decision. This score [HA vascular (HAV) score] is a combination of direct markers [hyaluronic acid (HA) and vascular endothelial growth factor (VEGF)] and indirect markers [aspartate aminotransferase (AST)/alanine aminotransferase (ALT) ratio (AAR)].

RESULTS

Samples were collected from 220 patients (F0-F4): an estimated group (n = 120) and a validated group (n = 100). HA and VEGF levels, HCV RNA, liver function tests, platelet counts were assayed, Fibroscan was done and liver biopsy was taken and the stage of liver fibrosis and the grade of inflammatory activity was calculated according to Metavir score system. HA vascular (HAV) score = -35.1 + 0.14 (HA) (ng/L) + 0.03 (VEGF) (pg/mL) + (-6.7) [AAR (AST/ALT ratio)]. The HAV score produced areas under curve of 0.979 and 0.994 for significant (F2-F4) and advanced fibrosis (F3-F4) (cut off = 0.583 and 6.3, respectively). Surprisingly, the validation study of this score gave very good values of AUCs i.e. 0.990, 0.996 and 0.995 for significant, advanced and liver cirrhosis.

CONCLUSIONS

Our developed score can not only help to assess liver fibrosis staging effectively but also avoid the invasiveness and the limitations of liver biopsy in Egyptian hepatitis C virus patients.

Association between Sumoylation-Related Gene rs77447679 Polymorphism and Risk of Gastric Cancer (GC) in a Chinese Population

Purpose: Sumoylation plays a critical role in gene regulation and tumorigenesis, and is hypothesized to correlate with the development of various cancers. So far, there has been no reported association between sumoylation-related genes and the risk of gastric cancer (GC).

Methods: A total of 17 tagging single-nucleotide polymorphisms (tag-SNPs) in 5 sumoylation-related genes were selected and genotyped by SNaPshot in a case-control study, including 1021 GC patients and 1304 controls. Odds ratio (OR) and 95% confidential interval (CI) were computed to evaluate the genetic association of the onset of GC.

Results: We demonstrated that CBX4 rs77447679 polymorphism was significantly associated with GC risk (P= 0.017; adjusted OR: 1.71; 95% CI: 1.10-2.66). The patients with CC genotype had a lower risk of GC (CC vs. CA+AA, P= 0.017; adjusted OR: 1.24; 95% CI: 1.04-1.49).

Conclusion: This study revealed that CBX4 rs77447679 polymorphism was positively associated with GC, and individuals with CC genotype had less risk of GC. The risky effects and functional effect of this polymorphism in GC require further investigation.

Roles of SHARP1 in thyroid cancer

SHARP1 is a basic helix‑loop‑helix transcription factor involved in various cellular processes, including proliferation and differentiation. The present study assessed the role of SHARP1 in the progression and invasion of thyroid cancer. PCR and western blot analysis demonstrated that in thyroid cancer tissues, SHARP1 was significantly downregulated at the mRNA and protein level compared with that in normal tissues. Furthermore, SHARP1 was downregulated in the TT and TPC‑1 thyroid cancer cell lines compared with a normal thyroid cell line, while it was upregulated in other thyroid cancer cell lines. Overexpression of SHARP1 in TT and TPC‑1 cells significantly inhibited the cell viability, migration and invasion in vitro. Furthermore, the protein and mRNA levels of HIF‑1α were found to be decreased in TT and TPC‑1 cells following forced overexpression of SHARP1. In addition, silencing of HIF‑1α reduced the viability, migration and invasion of TT and TPC-1 cells. In conclusion, the present study indicated that SHARP1 acts as a tumor suppressor in thyroid cancer and that its downregulation may contribute to the proliferation, migration and invasion of thyroid cancer cells through mechanisms possibly involving HIF‑1α, suggesting that SHARP1 may be an important therapeutic target for the treatment of thyroid cancer.

Prognostic significance of Cbx4 expression and its beneficial effect for transarterial chemoembolization in hepatocellular carcinoma

Our recent investigations showed that polycomb chromobox 4 (Cbx4) promotes angiogenesis and metastasis of hepatocellular carcinoma (HCC) through its sumoylating action on hypoxia-inducible factor-1α protein. Here, we attempt to identify the prognostic significances of Cbx4 by a retrospective analyses in 727 cases of HCC patients with and without postoperative transarterial chemoembolization (TACE) or transarterial embolization (TAE). Binary logistic regression tests indicated that Cbx4 is correlated with histological grading, tumor-node-metastasis stage, microvessel density, distant metastasis and hematogenous metastasis of HCC. By univariate and multivariate analyses, we show that Cbx4 is an independent prognostic factor of HCC, and both TAE and TACE treatments have no effects on the overall survival in HCC patients with low Cbx4 expression. More intriguingly, TACE prolongs, while TAE shortens, the overall survival of HCC patients with high Cbx4 expression, indicating that Cbx4 is a good biomarker on decision-making to perform postoperative TACE in HCC patients. Moreover, Cbx4 overexpression enhances while Cbx4 silencing antagonizes doxorubicin-induced cell death of HCC cell lines. In conclusion, Cbx4 is an independent prognostic factor for HCC patients, and the patients with high Cbx4 expression should receive postoperative TACE treatment to improve their survival.

PubAngioGen: a database and knowledge for angiogenesis and related diseases

Angiogenesis is the process of generating new blood vessels based on existing ones, which is involved in many diseases including cancers, cardiovascular diseases and diabetes mellitus. Recently, great efforts have been made to explore the mechanisms of angiogenesis in various diseases and many angiogenic factors have been discovered as therapeutic targets in anti- or pro-angiogenic drug development. However, the resulted information is sparsely distributed and no systematical summarization has been made. In order to integrate these related results and facilitate the researches for the community, we conducted manual text-mining from published literature and built a database named as PubAngioGen (http://www.megabionet.org/aspd/). Our online application displays a comprehensive network for exploring the connection between angiogenesis and diseases at multilevels including protein–protein interaction, drug-target, disease-gene and signaling pathways among various cells and animal models recorded through text-mining. To enlarge the scope of the PubAngioGen application, our database also links to other common resources including STRING, DrugBank and OMIM databases, which will facilitate understanding the underlying molecular mechanisms of angiogenesis and drug development in clinical therapy.