Hepatitis B virus X protein confers resistance of hepatoma cells to anoikis by up-regulating and activating p21-activated kinase 1

The role of p21-activated kinases in hepatocellular carcinoma metastasis

The p21-activated kinases (PAKs) are downstream effectors of the Rho family small GTPases as well as a wide variety of mitogenic factors and have been implicated in cancer formation, development and metastasis. PAKs phosphorylate a wide spectrum of substrates to mediate extracellular signals and regulate cytoskeletal remodeling, cell motility and survival. In this review, we aim to summarize the findings regarding the oncogenic role and the underlying mechanisms of PAKs signaling in various cancers, and in particular highlight the prime importance of PAKs in hepatocellular carcinoma (HCC) progression and metastasis. Recent studies exploring the potential therapeutic application of PAK inhibitors will also be discussed.

Tracing PAKs from GI inflammation to cancer

P-21 activated kinases (PAKs) are effectors of Rac1/Cdc42 which coordinate signals from the cell membrane to the nucleus. Activation of PAKs drive important signalling pathways including mitogen activated protein kinase, phospoinositide 3-kinase (PI3K/AKT), NF-κB and Wnt/β-catenin. Intestinal PAK1 expression increases with inflammation and malignant transformation, although the biological relevance of PAKs in the development and progression of GI disease is only incompletely understood. This review highlights the importance of altered PAK activation within GI inflammation, emphasises its effect on oncogenic signalling and discusses PAKs as therapeutic targets of chemoprevention.

Hepatitis B virus-induced hepatocellular carcinoma

Many factors are considered to contribute to hepatitis B virus (HBV) associated hepatocellular carcinoma (HCC), including products of HBV, HBV integration and mutation, and host susceptibility. HBV X protein (HBx) can interfere with several signal pathways that associated with cell proliferation and apoptosis, and the impact of HBx C-terminal truncation in the development of HCC has been implicated. Recent studies by advanced sequencing technologies have revealed recurrent HBV DNA integration sites in hepatoma cells and susceptible genes/SNPs play an important role in the pathogenesis of liver cancer. Epigenetic changes, immune and inflammatory factors are also important contributing factors for liver cancer. This mini-review provides an overview on the recent development of HBV induced HCC.

HBV induced HCC: major risk factors from genetic to molecular level

Hepatocellular carcinoma (HCC) is a deadly and emerging disease leading to death in Asian countries. High hepatitis B virus (HBV) load and chronic hepatitis B (CHB) infection increase the risk of developing HCC. HBV is a DNA virus that can integrate DNA into host genome thereby increase the yield of transactivator protein HBxAg that may deregulate many pathways involving in metabolism of cells. Several monogenic and polygenic risk factors are also involved in HCC development. This review summarizes the mechanism involved in HCC development and discusses some promising therapies to make HCC curative.

Unraveling the complexity of hepatitis B virus: from molecular understanding to therapeutic strategy in 50 years

Hepatitis B virus (HBV) is a well-known hepadnavirus with a double-stranded circular DNA genome. Although HBV was first described approximately 50 years ago, the precise mechanisms of HBV infection and effective therapeutic strategies remain unclear. Here, we focus on summarizing the complicated mechanisms of HBV replication and infection, as well as genomic factors and epigenetic regulation. Additionally, we discuss in vivo models of HBV, as well as diagnosis, prevention and therapeutic drugs for HBV. Together, the data in this 50-year review may provide new clues to elucidate molecular mechanisms of HBV pathogenesis and shed new light on the future HBV therapies.

N-acetylglucosaminyltransferase V confers hepatoma cells with resistance to anoikis through EGFR/PAK1 activation

Elevated expression and activity of N-acetylglucosaminyltransferase V (Mgat5) in hepatocellular carcinoma (HCC) is a common early event involved in tumor invasion during hepatocarcinogenesis. A better understanding of the functional role and the molecular mechanism for Mgat5-targeted protein and downstream signaling pathway behind hepatoma invasion and metastasis is urgently needed. Here, we show that Mgat5 overexpression promoted anchorage-independent growth and inhibited anoikis in hepatoma cells. This effect was reversed by glycosyltransferase inactive mutant Mgat5 L188R transfection, α-mannosidase II inhibitor swainsonine treatment and N-acetyl glucosamine (GlcNAc) phosphotransferase (GPT) inhibitor tunicamycin administration. Mgat5 overexpression increased p21-activated kinase 1 (PAK1) expression and shRNA-mediated PAK1 knockdown and kinase inactivation with kinase dead mutant PAK1 K299R coexpression or allosteric inhibitor P21-activated kinase inhibitor III (IPA3) treatment reversed anoikis resistance in Mgat5-overexpressed hepatoma cells. Furthermore, Mgat5 overexpression upregulated β-1-6-GlcNAc branched N-glycosylation and following phosphorylation of epidermal growth factor receptor (EGFR) in hepatoma cells. EGFR tyrosine kinase inhibitors AG1478 and Iressa treatment declined anchorage-independent growth and anoikis resistance, which could be rescued by constitutive active mutant PAK1 T423E coexpression in Mgat5-overexpressed hepatoma cells. Conversely, knockdown of Mgat5 reduced EGFR/PAK1-dependent anoikis resistance, which could be reversed by PAK1 T423E. These results identified Mgat5-mediated β-1-6-GlcNAc branched N-glycosylation and following activation of EGFR as a potential novel upstream molecular event for PAK1-induced anoikis resistance in hepatoma cells, implicating that molecular targeted therapeutics against Mgat5/EGFR/PAK1 might open a new avenue for personalized medicine in advanced-stage HCC patients.

Sunitinib induces cellular senescence via p53/Dec1 activation in renal cell carcinoma cells

Although multitargeted tyrosine kinase inhibitor sunitinib has been used as first-line therapeutic agent against metastatic renal cell carcinoma (mRCC), the molecular mechanism and functional role per se for its therapeutic performance remains obscure. Our present study revealed that sunitinib-treated RCC cells exhibit senescence characteristics including increased SA-β-gal activity, DcR2 and Dec1 expression, and senescence-associated secretary phenotype (SASP) such as proinflammatory cytokines interleukin (IL)-1α, IL-6 and IL-8 secretion. Moreover, sunitinib administration also led to cell growth inhibition, G1-S cell cycle arrest and DNA damage response in RCC cells, suggesting therapeutic significance of sunitinib-induced RCC cellular senescence. Mechanistic investigations indicated that therapy-induced senescence (TIS) following sunitinib treatment mainly attributed to p53/Dec1 signaling activation mediated by Raf-1/NF-κB inhibition in vitro. Importantly, in vivo study showed tumor growth inhibition and prolonged overall survival were associated with increased p53 and Dec1 expression, decreased Raf-1 and Ki67 staining, and upregulated SA-β-gal activity after sunitinib treatment. Immunohistochemistry analysis of tumor tissues from RCC patients receiving sunitinib neoadjuvant therapy confirmed the similar treating phenotype. Taken together, our findings suggested that sunitinib treatment performance could be attributable to TIS, depending on p53/Dec1 activation via inhibited Raf-1/nuclear factor (NF)-κB activity. These data indicated potential insights into therapeutic improvement with reinforcing TIS-related performance or overcoming SASP-induced resistance.

Group I p21-activated kinases facilitate Tax-mediated transcriptional activation of the human T-cell leukemia virus type 1 long terminal repeats

Background

Human T-cell leukemia virus type 1 (HTLV-1) is the causative agent of adult T-cell leukemia and tropical spastic paraparesis. HTLV-1 encodes transactivator protein Tax that interacts with various cellular factors to modulate transcription and other biological functions. Additional cellular mediators of Tax-mediated transcriptional activation of HTLV-1 long terminal repeats (LTR) remain to be identified and characterized.

Results

In this study, we investigated the regulatory role of group I p21-activated kinases (Paks) in Tax-induced LTR activation. Both wild-type and kinase-dead mutants of Pak3 were capable of potentiating the activity of Tax to activate LTR transcription. The effect of Paks on the LTR was attributed to the N-terminal regulatory domain and required the action of CREB, CREB-regulating transcriptional coactivators (CRTCs) and p300/CREB-binding protein. Paks physically associated with Tax and CRTCs. Paks were recruited to the LTR in the presence of Tax. siRNAs against either Pak1 or Pak3 prevented the interaction of Tax with CRTC1 and the recruitment of Tax to the LTR. These siRNAs also inhibited LTR-dependent transcription in HTLV-1-transformed MT4 cells and in cells transfected with an infectious clone of HTLV-1.

Conclusion

Group I Paks augment Tax-mediated transcriptional activation of HTLV-1 LTR in a kinase-independent manner.

DNA-dependent activator of interferon-regulatory factors (DAI) promotes lupus nephritis by activating the calcium pathway

BACKGROUND

Macrophage M2b polarization conferred by self-DNA immunization initiates and propagates lupus nephritis.

RESULTS

Knockdown of DNA-dependent activator of interferon-regulatory factors (DAI) ameliorates SLE syndrome via blunting macrophage M2b polarization.

CONCLUSION

DAI functions as a DNA sensor in self-DNA-induced macrophage M2b polarization and lupus nephritis.

SIGNIFICANCE

We disclose the mechanism by which self-DNA induces macrophage M2b polarization and lupus nephritis DNA-dependent activator of interferon-regulatory factors (DAI) functions as a cytoplasmic DNA sensor that activates the innate immune system. We previously found that activated lymphocyte-derived self-apoptotic DNA (ALD-DNA) immunization led to pathological macrophage activation and M2b polarization, which could initiate and propagate murine lupus nephritis. However, the specific DNA sensor(s) as well as underlying molecular mechanisms involved in ALD-DNA-induced macrophage M2b polarization in systemic lupus erythematosus (SLE) disease remains unknown. In this study, we reported that DAI expression was significantly increased in SLE patients as well as in lupus mice. Gain- and loss-of-function studies revealed that DAI was involved in ALD-DNA-induced macrophage activation and M2b polarization. Moreover, ALD-DNA notably induced dimerization/oligomerization of DAI and consequently activation of nuclear factor κB (NF-κB) and interferon regulatory factor 3 (IRF3) signaling pathways via calcium signaling, resulting in macrophage activation and M2b polarization. More importantly, blockade of DAI in vivo or selective knockdown of DAI in macrophages could ameliorate SLE syndrome via blunting macrophage M2b polarization and inhibiting inflammatory response in lupus mice. Our results suggest that DAI could function as a DNA sensor and a regulator in ALD-DNA-induced macrophage M2b polarization and lupus nephritis, providing the possible molecular mechanisms involved in ALD-DNA-induced macrophage M2b polarization in SLE disease and making DAI as a potential therapeutic target for the treatment of SLE.

Klotho suppresses tumor progression via inhibiting PI3K/Akt/GSK3β/Snail signaling in renal cell carcinoma

Klotho is an anti-aging protein predominantly expressed in renal tubular epithelial cells. Although Klotho was recently identified as a tumor suppressor gene in a variety of cancers, the potential role and molecular events for Klotho in renal cell carcinoma (RCC) remain obscure. In the present study, immunohistochemical staining in tissue microarrays containing 125 RCC samples showed that intratumoral Klotho levels were negatively correlated with tumor size, TNM stage and nuclear grade. The overall survival rate of RCC patients with high Klotho expression was significantly higher than that of patients with low Klotho expression. Functional analysis after gain and loss of Klotho expression revealed that Klotho blunted epithelial-mesenchymal transition and cellular migration and invasion in RCC. Also, no alteration of α-2,6-sialidase activity was found after Klotho overexpression in RCC. The molecular signals for this phenomenon involved the Klotho-mediated inhibition of PI3K/Akt/GSK3β/Snail pathway. Importantly, compared to localized RCC tissues, advanced RCC tissues exhibited low Klotho expression accompanied with high pAkt and Snail expression. These results indicate Klotho acts as a tumor suppressor by inhibiting PI3K/Akt/GSK3β/Snail signaling, thus suppressing epithelial-mesenchymal transition and tumor migration and invasion during RCC progression. As a result, Klotho might be used as a potential therapy for advanced RCC.

Sorafenib suppresses growth and survival of hepatoma cells by accelerating degradation of enhancer of zeste homolog 2

Enhancer of zeste homolog 2 (EZH2) is a mammalian histone methyltransferase that contributes to the epigenetic silencing of target genes that regulate cancer cell growth and survival. It is overexpressed in hepatocellular carcinoma (HCC) with a clinical significance that remains obscure. Sorafenib, a multikinase inhibitor, has been used as a first-line therapeutic drug and shown clinical efficiency for advanced-stage HCC patients. In the present study, we found that sorafenib lowered the protein level of EZH2 through accelerating proteasome-mediated EZH2 degradation in hepatoma cells. Overexpression of EZH2 reversed sorafenib-induced cell growth arrest, cell cycle arrest, and cell apoptosis dependent on histone methyltransferase activity in hepatoma cells. More importantly, shRNA-mediated EZH2 knockdown or EZH2 inhibition with 3-deazaneplanocin A treatment promoted sorafenib-induced hepatoma cell growth arrest and apoptosis. Sorafenib altered the hepatoma epigenome by reducing EZH2 and H3K27 trimethylation. These results revealed a novel therapeutic mechanism underlying sorafenib treatment in suppressing hepatoma growth and survival by accelerating EZH2 degradation. Genetic deletion or pharmacological ablation of EZH2 made hepatoma cells more sensitive to sorafenib, which helps provide a strong framework for exploring innovative combined therapies for advanced-stage HCC patients.

Klotho endows hepatoma cells with resistance to anoikis via VEGFR2/PAK1 activation in hepatocellular carcinoma

Klotho was originally characterized as an aging suppressor gene that predisposed Klotho-deficient mice to premature aging-like syndrome. Although Klotho was recently reported to exhibit tumor suppressive properties during various malignant transformations, the functional role and molecular mechanism of Klotho in hepatocarcinogenesis remains poorly understood. In our present study, immunohistochemical Klotho staining levels in a clinical follow-up of 52 hepatoma patients were significantly associated with liver cirrhosis, tumor multiplicity and venous invasion. The overall survival rate of hepatoma patients with high Klotho expression was significantly lower than those patients with low Klotho expression. Moreover, Klotho overexpression increased cellular migration, anchorage-independent growth, and anoikis resistance in hepatoma cells. Klotho overexpression elevated p21-activated kinase 1 (PAK1) expression and shRNA-mediated PAK1 knockdown and kinase activity inhibition with kinase dead mutant PAK1 K299R coexpression or allosteric inhibitor IPA3 treatment reversed anoikis resistance in Klotho-overexpressed hepatoma cells. More importantly, the pivotal significance of upregulated VEGFR2 protein levels mediated by Klotho expression was confirmed by VEGFR2 inhibitor Axitinib and blocking antibody treatment in hepatoma cells. Axitinib treatment sensitized anoikis was reversed by constitutive active mutant PAK1 T423E coexpression in Klotho-overexpressed hepatoma cells. Conversely, knockdown of Klotho reduced VEGFR2/PAK1 dependent anoikis resistance, which could be reversed by PAK1 T423E. These results revealed a novel oncogenic function of Klotho in promoting anoikis resistance via activating VEGFR2/PAK1 signaling, thus facilitating tumor migration and invasion during hepatoma progression, which could provide a putative molecular mechanism for tumor metastasis.

Prognostic importance and therapeutic implications of PAK1, a drugable protein kinase, in gastroesophageal junction adenocarcinoma

Gastroesophageal junction (GEJ) adenocarcinoma is a lethal cancer with rising incidence, yet the molecular biomarkers that have strong prognostic impact and also hold great therapeutic promise remain elusive. We used a data mining approach and identified the p21 protein-activated kinase 1 (PAK1), an oncogene and drugable protein kinase, to be among the most promising targets for GEJ adenocarcinoma. Immunoblot analysis and data mining demonstrated that PAK1 protein and mRNA were upregulated in cancer tissues compared to the noncancerous tissues. Immunohistochemistry revealed PAK1 overexpression in 72.6% of primary GEJ adenocarcinomas (n = 113). A step-wise increase in PAK1 levels was noted from paired normal epithelium, to atypical hyperplasia and adenocarcinoma. PAK1 overexpression in tumor was associated with lymph node (LN) metastasis (P<0.001), advanced tumor stage (P<0.001), large tumor size (P = 0.006), residual surgical margin (P = 0.033), and unfavorable overall survival (P<0.001). Multivariate analysis showed PAK1 overexpression is an independent high-risk prognostic predictor (P<0.001). Collectively, PAK1 is overexpressed during tumorigenic progression and its upregulation correlates with malignant properties mainly relevant to invasion and metastasis. PAK1 expression could serve as a prognostic predictor that holds therapeutic promise for GEJ adenocarcinoma.

p21-activated kinases and gastrointestinal cancer

p21-activated kinases (PAKs) were initially identified as effector proteins downstream from GTPases of the Rho family. To date, six members of the PAK family have been discovered in mammalian cells. PAKs play important roles in growth factor signalling, cytoskeletal remodelling, gene transcription, cell proliferation and oncogenic transformation. A large body of research has demonstrated that PAKs are up-regulated in several human cancers, and that their overexpression is linked to tumour progression and resistance to therapy. Structural and biochemical studies have revealed the mechanisms involved in PAK signalling, and opened the way to the development of PAK-targeted therapies for cancer treatment. Here we summarise recent findings from biological and clinical research on the role of PAKs in gastrointestinal cancer, and discuss the current status of PAK-targeted anticancer therapies.

Hepatitis B virus X protein promotes hepatoma cell invasion and metastasis by stabilizing Snail protein

A high incidence of tumor recurrence and metastasis has been reported in hepatocellular carcinoma (HCC) patients with chronic hepatitis B virus (HBV) infection. Although the pathological relevance and significance of hepatitis B virus X protein (HBx) in HBV-associated hepatocarcinogenesis attracted much attention in recent years, the role and molecular mechanism for HBx in hepatoma invasion and metastasis remains poorly understood. In the present study, we found that HBx expression could induce epithelial-mesenchymal transition in hepatoma and hepatic cells. This effect was shown due to stabilized Snail protein through activating the phosphatidylinositol 3-kinase/protein kinase B/glycogen synthase kinase-3β (PI3K/AKT/GSK-3β) signal pathway by HBx expression. Functional studies revealed that HBx expression could enhance hepatoma cell migration and invasion in vitro. Moreover, stable HBx expression could also facilitate intrahepatic and distant lung metastasis of HCC in a nude mice tumor metastasis model in vivo. The correlation between increased PI3K/AKT/GSK-3β signaling with elevated Snail protein level was also observed in HCC tumor tissues with intrahepatic metastasis or chronic HBV infection. These results revealed a novel function of HBx in promoting epithelial-mesenchymal transition through Snail protein stabilization by activating PI3K/AKT/GSK-3β signaling, thus facilitating tumor invasion and metastasis during HCC progression. This could provide a putative molecular mechanism for tumor recurrence and metastasis in HBV-associated HCC patients.