Hypoxia inducible factor HIF-1 promotes myeloid-derived suppressor cells accumulation through ENTPD2/CD39L1 in hepatocellular carcinoma

Myeloid-derived suppressor cells (MDSCs) possess immunosuppressive activities, which allow cancers to escape immune surveillance and become non-responsive to immune checkpoints blockade.

Here we report hypoxia as a cause of MDSC accumulation. Using hepatocellular carcinoma (HCC) as a cancer model, we show that hypoxia, through stabilization of hypoxia-inducible factor-1 (HIF-1), induces ectoenzyme, ectonucleoside triphosphate diphosphohydrolase 2 (ENTPD2/CD39L1), in cancer cells, causing its overexpression in HCC clinical specimens.

Overexpression of ENTPD2 is found as a poor prognostic indicator for HCC. Mechanistically, we demonstrate that ENTPD2 converts extracellular ATP to 5′-AMP, which prevents the differentiation of MDSCs and therefore promotes the maintenance of MDSCs. We further find that ENTPD2 inhibition is able to mitigate cancer growth and enhance the efficiency and efficacy of immune checkpoint inhibitors. Our data suggest that ENTPD2 may be a good prognostic marker and therapeutic target for cancer patients, especially those receiving immune therapy.
Transketolase counteracts oxidative stress to drive cancer development

Cancer cells experience an increase in oxidative stress. The pentose phosphate pathway (PPP) is a major biochemical pathway that generates antioxidant NADPH. Here, we show that transketolase (TKT), an enzyme in the PPP, is required for cancer growth because of its ability to affect the production of NAPDH to counteract oxidative stress.

We show that TKT expression is tightly regulated by the Nuclear Factor, Erythroid 2-Like 2 (NRF2)/Kelch-Like ECH-Associated Protein 1 (KEAP1)/BTB and CNC Homolog 1 (BACH1) oxidative stress sensor pathway in cancers. Disturbing the redox homeostasis of cancer cells by genetic knockdown or pharmacologic inhibition of TKT sensitizes cancer cells to existing targeted therapy (Sorafenib).

Our study strengthens the notion that antioxidants are beneficial to cancer growth and highlights the therapeutic benefits of targeting pathways that generate antioxidants.
Up‐regulation of histone methyltransferase SETDB1 by multiple mechanisms in hepatocellular carcinoma promotes cancer metastasis

Epigenetic deregulation plays an important role in liver carcinogenesis. Using transcriptome sequencing, we examined the expression of 591 epigenetic regulators in hepatitis B-associated human hepatocellular carcinoma (HCC).

We found that aberrant expression of epigenetic regulators was a common event in HCC. We further identified SETDB1 (SET domain, bifurcated 1), an H3K9-specific histone methyltransferase, as the most significantly up-regulated epigenetic regulator in human HCCs. Up-regulation of SETDB1 was significantly associated with HCC disease progression, cancer aggressiveness, and poorer prognosis of HCC patients.

Functionally, we showed that knockdown of SETDB1 reduced HCC cell proliferation in vitro and suppressed orthotopic tumorigenicity in vivo. Inactivation of SETDB1 also impeded HCC cell migration and abolished lung metastasis in nude mice. Interestingly, SETDB1 protein was consistently up-regulated in all metastatic foci found in different organs, suggesting that SETDB1 was essential for HCC metastatic progression.

Mechanistically, we showed that the frequent up-regulation of SETDB1 in human HCC was attributed to the recurrent SETDB1 gene copy gain at chromosome 1q21. In addition, hyperactivation of specificity protein 1 transcription factor in HCC enhanced SETDB1 expression at the transcriptional level. Furthermore, we identified miR-29 as a negative regulator of SETDB1. Down-regulation of miR-29 expression in human HCC contributed to SETDB1 up-regulation by relieving its post-transcriptional regulation.

CONCLUSION: SETDB1 is an oncogene that is frequently up-regulated in human HCCs; the multiplicity of SETDB1 activating mechanisms at the chromosomal, transcriptional, and posttranscriptional levels together facilitates SETDB1 up-regulation in human HCC.

Development of Hong Kong Liver Cancer Staging System With Treatment Stratification for Patients With Hepatocellular Carcinoma

Background & Aims: We aimed to develop a prognostic classification scheme with treatment guidance for Asian patients with hepatocellular carcinoma (HCC).

Methods: We collected data from 3856 patients with HCC predominantly related to hepatitis B treated at Queen Mary Hospital in Hong Kong from January 1995 through December 2008. Data on patient performance status, Child–Pugh grade, tumor status (size, number of nodules, and presence of intrahepatic vascular invasion), and presence of extrahepatic vascular invasion or metastasis were included, and randomly separated into training and test sets for analysis. Cox regression and classification and regression tree analyses were used to account for the relative effects of factors in predicting overall survival times and to classify disparate treatment decision rules, respectively; the staging system and treatment recommendation then were constructed by integration of clinical judgments. The Hong Kong Liver Cancer (HKLC) classification was compared with the Barcelona Clinic Liver Cancer (BCLC) classification in terms of discriminatory ability and effectiveness of treatment recommendation.

Results: The HKLC system had significantly better ability than the BCLC system to distinguish between patients with specific overall survival times (area under the receiver operating characteristic curve values, approximately 0.84 vs 0.80; concordance index, 0.74 vs 0.70). More importantly, HKLC identified subsets of BCLC intermediate- and advanced-stage patients for more aggressive treatments than what were recommended by the BCLC system, which improved survival outcomes. Of BCLC-B patients classified as HKLC-II in our system, the survival benefit of radical therapies, compared with transarterial chemoembolization, was substantial (5-year survival probability, 52.1% vs 18.7%; P < .0001). In BCLC-C patients classified as HKLC-II, the survival benefit of radical therapies compared with systemic therapy was even more pronounced (5-year survival probability, 48.6% vs 0.0%; P < .0001).

Conclusions: We collected data from patients with HCC in Hong Kong to create a system to identify patients who are suitable for more aggressive treatment than the currently used BCLC system. The HKLC system should be validated in non-Asian patient populations and in patients with different etiologies of HCC.

Recoding RNA editing of antizyme inhibitor 1 predisposes to hepatocellular carcinoma

Better understanding of human hepatocellular carcinoma (HCC) pathogenesis at the molecular level will facilitate the discovery of tumor initiating events. Herein, transcriptome sequencing revealed that adenosine (A)-to-inosine (I) RNA editing of antizyme inhibitor 1 (AZIN1) displays a high modification rate in HCC specimens. A-to-I editing of AZIN1 transcripts is specifically regulated by adenosine deaminase acting on RNA-1 (ADAR1).

The serine (S) → glycine (G) substitution at residue 367, located in β-strand 15 (β15), predicted a conformational change, induced a cytoplasmic-to-nuclear translocation, and conferred “gain-of-function” phenotypes manifested by augmented tumor initiating potential and more aggressive behavior.

Compared with wild-type AZIN1 protein, the edited form possesses stronger affinity to antizyme, and the resultant higher protein stability promotes cell proliferation via the neutralization of antizyme-mediated degradation of ornithine decarboxylase (ODC) and cyclin D1 (CCND1). Collectively, A-to-I RNA editing of AZIN1 may be a potential driver in the pathogenesis of human cancers, particularly HCC.

PKA-induced dimerization of the RhoGAP DLC1 promotes its inhibition of tumorigenesis and metastasis

Deleted in Liver Cancer 1 (DLC1) is a tumour suppressor that encodes a RhoGTPase-activating protein (RhoGAP) and is frequently inactivated in many human cancers.

The RhoGAP activity of DLC1 against Rho signalling is well documented and is strongly associated with the tumour suppressor functions of DLC1. However, the mechanism by which the RhoGAP activity of DLC1 is regulated remains obscure. Here, we report that phosphorylation of DLC1 at Ser549 by cyclic AMP-dependent protein kinase A contributes to enhanced RhoGAP activity and promotes the activation of DLC1, which suppresses hepatoma cell growth, motility and metastasis in both in vitro and in vivo models. Intriguingly, we found that Ser549 phosphorylation induces the dimerization of DLC1 and that inducible dimerization of DLC1 can rescue the tumour suppressive and RhoGAP activities of DLC1 containing a Ser549 deletion.

Our study establishes a novel regulatory mechanism for DLC1 RhoGAP activity via dimerization induced by protein kinase A signalling.

CD24+ Liver Tumor-Initiating Cells Drive Self-Renewal and Tumor Initiation through STAT3-Mediated NANOG Regulation

Tumor-initiating cells (T-ICs) are a subpopulation of chemoresistant tumor cells that have been shown to cause tumor recurrence upon chemotherapy. Identification of T-ICs and their related pathways are therefore priorities for the development of new therapeutic paradigms.

We established chemoresistant hepatocellular carcinoma (HCC) xenograft tumors in immunocompromised mice in which an enriched T-IC population was capable of tumor initiation and self-renewal. With this model, we found CD24 to be upregulated in residual chemoresistant tumors when compared with bulk tumor upon cisplatin treatment. CD24+ HCC cells were found to be critical for the maintenance, self-renewal, differentiation, and metastasis of tumors and to significantly impact patients' clinical outcome.

With a lentiviral-based knockdown approach, CD24 was found to be a functional liver T-IC marker that drives T-IC genesis through STAT3-mediated NANOG regulation. Our findings point to a CD24 cascade in liver T-ICs that may provide an attractive therapeutic target for HCC patients.

miR-130b Promotes CD133+ Liver Tumor-Initiating Cell Growth and Self-Renewal via Tumor Protein 53-Induced Nuclear Protein 1

A novel paradigm in tumor biology suggests that cancer growth is driven by stem-like cells within a tumor, called tumor-initiating cells (TICs) or cancer stem cells (CSCs). Here we describe the identification and characterization of such cells from hepatocellular carcinoma (HCC) using the marker CD133.

CD133 accounts for approximately 1.3%–13.6% of the cells in the bulk tumor of human primary HCC samples. When compared with their CD133− counterparts, CD133+ cells not only possess the preferential ability to form undifferentiated tumor spheroids in vitro but also express an enhanced level of stem cell-associated genes, have a greater ability to form tumors when implanted orthotopically in immunodeficient mice, and can be serially passaged into secondary animal recipients. Xenografts resemble the original human tumor and maintain a similar percentage of tumorigenic CD133+ cells.

Quantitative PCR analysis of 41 separate HCC tissue specimens with follow-up data found that CD133+ tumor cells were frequently detected at low quantities in HCC, and their presence was also associated with worse overall survival and higher recurrence rates. Subsequent differential microRNA expression profiling of CD133+ and CD133− cells from human HCC clinical specimens and cell lines identified an overexpression of miR-130b in CD133+ TICs.

Functional studies on miR-130b lentiviral-transduced CD133− cells demonstrated superior resistance to chemotherapeutic agents, enhanced tumorigenicity in vivo, and a greater potential for self renewal. Conversely, antagonizing miR-130b in CD133+ TICs yielded an opposing effect. The increased miR-130b paralleled the reduced TP53INP1, a known miR-130b target. Silencing TP53INP1 in CD133− cells enhanced both self renewal and tumorigenicity in vivo. Collectively, miR-130b regulates CD133+ liver TICs, in part, via silencing TP53INP1.