Junchao Cai

MicroRNA-374a activates Wnt/β-catenin signaling to promote breast cancer metastasis

Tumor metastasis involves a series of biological steps during which the tumor cells acquire the ability to invade surrounding tissues and survive outside the original tumor site. During the early stages, the cancer cells undergo an epithelial-mesenchymal transition (EMT). Wnt/β-catenin signaling is known to drive EMT and metastasis. Here we report that Wnt/β-catenin signaling is hyperactivated in metastatic breast cancer cells that express microRNA 374a (miR-374a). In breast cancer cell lines, ectopic overexpression of miR-374a promoted EMT and metastasis both in vitro and in vivo. Furthermore, miR-374a directly targeted and suppressed multiple negative regulators of the Wnt/β-catenin signaling cascade, including WIF1, PTEN, and WNT5A. Notably, miR-374a was markedly upregulated in primary tumor samples from patients with distant metastases and was associated with poor metastasis-free survival. These results demonstrate that miR-374a maintains constitutively activated Wnt/β-catenin signaling and may represent a therapeutic target for early metastatic breast cancer.

miR-205 Targets PTEN and PHLPP2 to Augment AKT Signaling and Drive Malignant Phenotypes in Non–Small Cell Lung Cancer

AKT signaling is constitutively activated in various cancers, due in large part to loss-of-function in the PTEN and PHLPP phosphatases that act as tumor suppressor genes. However, AKT signaling is activated widely in non-small cell lung cancers (NSCLC) where genetic alterations in PTEN or PHLPP genes are rare, suggesting an undefined mechanism(s) for their suppression. In this study, we report upregulation of the oncomir microRNA (miR)-205 in multiple subtypes of NSCLC, which directly represses PTEN and PHLPP2 expression and activates both the AKT/FOXO3a and AKT/mTOR signaling pathways. miR-205 overexpression in NSCLC cells accelerated tumor cell proliferation and promoted blood vessel formation in vitro and in vivo. Conversely, RNA interference-mediated silencing of endogenous miR-205 abrogated these effects. The malignant properties induced by miR-205 in NSCLC cells were reversed by AKT inhibitors, FOXO3a overexpression, rapamycin treatment, or restoring PHLPP2 or PTEN expression. Mechanistic investigations revealed that miR-205 overexpression was a result of NF-κB-mediated transactivation of the miR-205 gene. Taken together, our results define a major epigenetic mechanism for suppression of PTEN and PHLPP2 in NSCLC, identifying a pivotal role for miR-205 in development and progression of this widespread disease.

MiR‐136 promotes apoptosis of glioma cells by targeting AEG‐1 and Bcl‐2

MicroRNAs have the capacity to coordinately repress multiple target genes and interfere with biological functions of the cell, such as proliferation and apoptosis. Here we report that miR‐136 is downregulated in human glioma, and that the miRNA promotes apoptosis of glioma cells induced by chemotherapy. Two anti‐apoptotic genes, AEG‐1 and Bcl‐2, are identified as targets of miR‐136, and restoration of AEG‐1 or Bcl‐2 expression suppresses miR‐136‐enhanced apoptosis. Therefore, miR‐136 might play a tumor‐suppressive role in human glioma and thereby might represent a potential therapeutic strategy.

Sp1 is upregulated in human glioma, promotes MMP-2-mediated cell invasion and predicts poor clinical outcome.

Sp1, the first identified transcription factor, has been reported to be associated with the development and progression of various human cancer types. However, the clinical significance and biological role of Sp1 in glioma are less well understood. In this study, we found that the expression of Sp1 was markedly elevated in glioma cell lines and tissues. Immunohistochemistry analysis revealed that the vast majority of 222 paraffin‐embedded archival glioma specimens tested displayed positive Sp1 expression, and 58.6% exhibited high‐level Sp1 expression. Statistical analysis suggested that the high Sp1 expression was correlated strongly with the WHO grading (p < 0.001) and survival status (p < 0.001) of glioma patients. Patients with lower Sp1 expression had better overall survival than those with higher Sp1 expression. Multivariate analysis suggested that Sp1 expression might be an independent prognostic indicator of the survival of patients with glioma. Furthermore, overexpression of Sp1 in glioma cells was found to increase their invasiveness, and in contrast, silencing Sp1 by siRNA caused an inhibition of cell invasion. Moreover, we demonstrated that the up‐regulation of Sp1 could increase activity and expression of MMP‐2. Collectively, our data suggest that Sp1 might represent a valuable prognostic marker for glioma and is involved in modulation of tumor invasion.

Sphingosine kinase 1 regulates the Akt/FOXO3a/Bim pathway and contributes to apoptosis resistance in glioma cells.

The aim of this study was to investigate the mechanism through which Sphingosine kinase-1 (SPHK1) exerts its anti-apoptosis activity in glioma cancer cells. We here report that dysregulation of SPHK1 alters the sensitivity of glioma to apoptosis both in vitro and in vivo. Further mechanistic study examined the expression of Bcl-2 family members, including Bcl-2, Mcl-1, Bax and Bim, in SPHK1-overexpressing glioma cells and revealed that only pro-apoptotic Bim was downregulated by SPHK1. Moreover, the transcriptional level of Bim was also altered by SPHK1 in glioma cells. We next confirmed the correlation between SPHK1 and Bim expression in primary glioma specimens. Importantly, increasing SPHK1 expression in glioma cells markedly elevated Akt activity and phosphorylated inactivation of FOXO3a, which led to downregulation of Bim. A pharmacological approach showed that these effects of SPHK1 were dependent on phosphatidylinositol 3-kinase (PI3K). Furthermore, effects of SPHK1 on Akt/FOXO3a/Bim pathway could be reversed by SPHK1 specific RNA interference or SPHK1 inhibitor. Collectively, our results indicate that regulation of the Akt/FOXO3a/Bim pathway may be a novel mechanism by which SPHK1 protects glioma cells from apoptosis, thereby involved in glioma tumorigenesis.

Sphingosine Kinase 1 Is Overexpressed and Promotes Proliferation in Human Thyroid Cancer

Sphingosine kinase 1 (SphK1), an oncogenic kinase, has been previously found to be elevated in various types of human cancer and play a role in tumor development and progression. Nevertheless, the biological and clinical significance of SphK1 in thyroid cancer is largely unknown. Here, we demonstrate that the expression of SphK1 is generally up-regulated in thyroid cancer and that its expression level is correlated with the degree of thyroid malignancy. Silencing SphK1 by specific RNA interference is able to suppress the proliferation of thyroid cancer cells, and SphK1 expression level is strongly associated with the expression of proliferation cell nuclear antigen in thyroid cancer tissues. Of particular note is that depletion of SphK1 results in dephosphorylation of protein kinase B and glycogen synthase kinase-3β and subsequent inactivation of β-catenin-T-cell factor/lymphoid enhancing factor transcriptional activity. Hence, taken together, our study has identified SphK1 as a proproliferative oncogenic kinase, an Akt/glycogen synthase kinase-3β/β-catenin activator, and probably a biomarker for thyroid cancer as well.

Aberrantly expressed miR-582-3p maintains lung cancer stem cell-like traits by activating Wnt/β-catenin signalling

Cancer stem cells (CSCs) are involved in tumorigenesis, tumour recurrence and therapy resistance and Wnt signalling is essential for the development of the biological traits of CSCs. In non-small cell lung carcinoma (NSCLC), unlike in colon cancer, mutations in β-catenin and APC genes are uncommon; thus, the mechanism underlying the constitutive activation of Wnt signalling in NSCLC remains unclear. Here we report that miR-582-3p expression correlates with the overall- and recurrence-free-survival of NSCLC patients, and miR-582-3p has an activating effect on Wnt/β-catenin signalling. miR-582-3p overexpression simultaneously targets multiple negative regulators of the Wnt/β-catenin pathway, namely, AXIN2, DKK3 and SFRP1. Consequently, miR-582-3p promotes CSC traits of NSCLC cells in vitro and tumorigenesis and tumour recurrence in vivo. Antagonizing miR-582-3p potently inhibits tumour initiation and progression in xenografted animal models. These findings suggest that miR-582-3p mediates the constitutive activation of Wnt/β-catenin signalling, likely serving as a potential therapeutic target for NSCLC.

IKBKE is over-expressed in glioma and contributes to resistance of glioma cells to apoptosis via activating NF-κB.

IκB kinase‐ε (IKBKE), a member of the IκB kinase (IKK) family, has been identified as an oncogenic protein and found to be up‐regulated in breast cancer, ovarian cancer and prostate cancer. Nonetheless, the expression status and functional significance of IKBKE in human glioma remain unexplored. For the first time, we have demonstrated that mRNA and protein levels of IKBKE were robustly up‐regulated in glioma cell lines and human primary glioma tissues. Immunohistochemistry analysis revealed that 53.5% (38/71) paraffin‐embedded archived glioma specimens exhibited high levels of IKBKE expression. Intriguingly, there was no significant difference in IKBKE expression among different grades of glioma. To understand the biological function of IKBKE in the development and progression of human glioma, glioma cells lines ectopically over‐expressing IKBKE were established and tested for their responsiveness to apoptotic inducers. Our data showed that IKBKE over‐expression inhibited cell apoptosis induced by UV irradiation or adriamycin and, in contrast, shRNAi‐mediated suppression of IKBKE increased the sensitivity of glioma cells to the apoptotic inducers. Importantly, we found that up‐regulated IKBKE could induce the expression of Bcl‐2 through activating NF‐κB signalling, and that, specifically, we identified IκB as a critical component for this signalling cascade. The current study suggests that up‐regulation of IKBKE may represent an important molecular hallmark that is biologically and clinically relevant to the development and progression, as well as the chemo‐ and radio‐resistance, of the disease. Copyright

Dengue Virus Subverts Host Innate Immunity by Targeting Adaptor Protein MAVS

ABSTRACT Dengue virus (DENV) is the most common mosquito-borne virus infecting humans and is currently a serious global health challenge. To establish infection in its host cells, DENV must subvert the production and/or antiviral effects of interferon (IFN). The aim of this study was to understand the mechanisms by which DENV suppresses IFN production. We determined that DENV NS4A interacts with mitochondrial antiviral signaling protein (MAVS), which was previously found to activate NF-κB and IFN regulatory factor 3 (IRF3), thus inducing type I IFN in the mitochondrion-associated endoplasmic reticulum membranes (MAMs). We further demonstrated that NS4A is associated with the N-terminal CARD-like (CL) domain and the C-terminal transmembrane (TM) domain of MAVS. This association prevented the binding of MAVS to RIG-I, resulting in the repression of RIG-I-induced IRF3 activation and, consequently, the abrogation of IFN production. Collectively, our findings illustrate a new molecular mechanism by which DENV evades the host immune system and suggest new targets for anti-DENV strategies. IMPORTANCE Type I interferon (IFN) constitutes the first line of host defense against invading viruses. To successfully establish infection, dengue virus (DENV) must counteract either the production or the function of IFN. The mechanism by which DENV suppresses IFN production is poorly understood and characterized. In this study, we demonstrate that the DENV NS4A protein plays an important role in suppressing interferon production through binding MAVS and disrupting the RIG-I–MAVS interaction in mitochondrion-associated endoplasmic reticulum membranes (MAMs). Our study reveals that MAVS is a novel host target of NS4A and provides a molecular mechanism for DENV evasion of the host innate immune response. These findings have important implications for understanding the pathogenesis of DENV and may provide new insights into using NS4A as a therapeutic and/or prevention target.

MicroRNA-542-3p Suppresses Tumor Cell Invasion via Targeting AKT Pathway in Human Astrocytoma

Background: MicroRNAs play important roles in regulating AKT pathway. Results: miR-542-3p suppresses glioblastoma cell invasion through directly inhibiting AKT1, ILK, and PIK3R1. Conclusion: miR-542-3p down-regulation contributes to aberrant activation of the AKT signaling, and miR-542-3p acts as a negative regulator in astrocytoma progression. Significance: Learning how miRNAs participate in AKT pathway is crucial for understanding its regulators and cancer therapy. The molecular mechanism underlying constitutive activation of AKT signaling, which plays essential roles in astrocytoma progression, is not fully characterized. Increasing numbers of studies have reported that microRNAs are involved in the malignant behavior of astrocytoma cells via directly targeting multiple oncogenes or tumor suppressors. Here, we found that microRNA (miR)-542-3p expression was decreased in glioblastoma cell lines and astrocytoma tissues, and reduced levels of miR-542-3p expression correlated with high histopathological grades and poor prognosis of astrocytoma patients. Exogenous miR-542-3p suppressed glioblastoma cell invasion through not only targeting AKT1 itself but also directly down-regulating its two important upstream regulators, namely, integrin-linked kinase and PIK3R1. Notably, overexpressing miR-542-3p decreased AKT1 phosphorylation and directly and indirectly repressed nuclear translocation and transactivation activity of β-catenin to exert its anti-invasive effect. Furthermore, the miR-542-3p expression level negatively correlated with AKT activity as well as levels of integrin-linked kinase and PIK3R1 in human astrocytoma specimens. These findings suggest that miR-542-3p acts as a negative regulator in astrocytoma progression and that miR-542-3p down-regulation contributes to aberrant activation of AKT signaling, leaving open the possibility that miR-542-3p may be a potential therapeutic target for high grade astrocytoma.