miR-133a Promotes TRAIL Resistance in Glioblastoma via Suppressing Death Receptor 5 and Activating NF-κB Signaling.

Recombinant tumor necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL), as a novel cancer therapeutic, is being tested in phase II and III clinical trials; however, TRAIL resistance remains a big obstacle preventing its clinical application. Considering that TRAIL-induced apoptosis through death receptors DR4 and DR5, their activation may be an alternative pathway to suppress TRAIL resistance. In this study, a negative correlation between DR5 expression and TRAIL resistance was observed, and miR-133a was predicted to be the most promising candidate to suppress DR5 expression. Further investigation demonstrated that miR-133a knockdown dramatically suppressed TRAIL resistance in glioblastoma in vitro and in vivo. An NF-κB family member, phosphorylated IκBα (P-IκBα), was shown to be stimulated by miR-133a, leading to the activation of this signaling. Finally, miR-133a was found to be inversely correlated with DR5 expression in human clinical specimens. In conclusion, our data demonstrate that miR-133a promotes TRAIL resistance in glioblastoma by suppressing DR5 expression and activating NF-κB signaling.

Usp5 functions as an oncogene for stimulating tumorigenesis in hepatocellular carcinoma.

As deubiquitinases, several ubiquitin specific protease members have been reported to mediate tumorigenesis. Although ubiquitin specific protease 5 (Usp5) was previously demonstrated to suppress p53 transcriptional activity and DNA repair, its role in carcinogenesis remains elusive. In this study, we sought to define a novel role of Usp5 in tumorigenesis. It was found that Usp5 was significantly upregulated in hepatocellular carcinoma (HCC) cells and most clinical specimens. Further functional investigation also showed that Usp5 knockdown suppressed cell proliferation, migration, drug resistance and induced apoptosis; on the other hand, Usp5 overexpression promoted colony formation, migration, drug resistance and tumorigenesis. Additionally, the inactivated p14ARF-p53 signaling was observed in Usp5 overexpressed HCC cells, while this signaling was activated by Usp5 knockdown. Therefore, our data demonstrated that Usp5 contributed to hepatocarcinogenesis by acting as an oncogene, which provides new insights into the pathogenesis of HCC and explores a promising molecular target for HCC diagnosis and therapy.

Ubiquitin specific peptidase 5 mediates Histidine-rich protein Hpn induced cell apoptosis in hepatocellular carcinoma through P14-P53 signaling.

Hpn is a small histidine-rich cytoplasmic protein from Helicobacter pylori and has been recognized as a high-risk factor for several cancers including gastric cancer, colorectal cancer, and MALT lymphoma. However, the relationship between Hpn and cancers remains elusive. In this study, we discovered that Hpn protein effectively suppressed cell growth and induced apoptosis in hepatocellular carcinoma (HCC). A two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomics was performed to find the molecular targets of Hpn in HCC cells. It was identified that twelve proteins were differentially expressed, with USP5 being one of the most significantly downregulated protein. The P14ARF -P53 signaling was activated by USP5 knockdown in HCC cells. Furthermore, USP5 overexpression significantly rescued the suppressive effect of Hpn on the viability of HCC cells. In conclusion, our study suggests that Hpn plays apoptosis-inducing roles through suppressing USP5 expression and activating the P14ARF -P53 signaling. Therefore, Hpn may be a potential candidate for developing novel anti-HCC drugs.

The lncRNA H19 promotes epithelial to mesenchymal transition by functioning as miRNA sponges in colorectal cancer.

Recently, the long non-coding RNA (lncRNA) H19 has been identified as an oncogenic gene in multiple cancer types and elevated expression of H19 was tightly linked to tumorigenesis and cancer progression. However, the molecular basis for this observation has not been characterized in colorectal cancer (CRC) especially during epithelial to mesenchymal transition (EMT) progression. In our studies, H19 was characterized as a novel regulator of EMT in CRC. We found that H19 was highly expressed in mesenchymal-like cancer cells and primary CRC tissues. Stable expression of H19 significantly promotes EMT progression and accelerates in vivo and in vitro tumor growth. Furthermore, by using bioinformatics study and RNA immunoprecipitation combined with luciferase reporter assays, we demonstrated that H19 functioned as a competing endogenous RNA (ceRNA) for miR-138 and miR-200a, antagonized their functions and led to the de-repression of their endogenous targets Vimentin, ZEB1, and ZEB2, all of which were core marker genes for mesenchymal cells. Taken together, these observations imply that the lncRNA H19 modulated the expression of multiple genes involved in EMT by acting as a competing endogenous RNA, which may build up the missing link between the regulatory miRNA network and EMT progression.

Hotair mediates hepatocarcinogenesis through suppressing miRNA-218 expression and activating P14 and P16 signaling.

BACKGROUND & AIMS: Long non-coding RNA Hotair has been considered as a pro-oncogene in multiple cancers. Although there is emerging evidence that reveals its biological function and the association with clinical prognosis, the precise mechanism remains largely elusive. METHODS: We investigated the function and mechanism of Hotair in hepatocellular carcinoma (HCC) cell models and a xenograft mouse model. The regulatory network between miR-218 and Hotair was elucidated by RNA immunoprecipitation and luciferase reporter assays. Finally, the correlation between Hotair, miR-218 and the target gene Bmi-1 were evaluated in 52 paired HCC specimens. RESULTS: In this study, we reported that Hotair negatively regulated miR-218 expression in HCC, which might be mediated through an EZH2-targeting-miR-218-2 promoter regulatory axis. Further investigation revealed that Hotair knockdown dramatically inhibited cell viability and induced G1-phase arrest in vitro and suppressed tumorigenicity in vivo by promoting miR-218 expression. Oncogene Bmi-1 was shown to be a functional target of miR-218, and the main downstream targets signaling, P16(Ink4a) and P14(ARF), were activated in Hotair-suppressed tumorigenesis. In primary human HCC specimens, Hotair and Bmi-1 were concordantly upregulated whereas miR-218 was downregulated in these tissues. Furthermore, Hotair was inversely associated with miR-218 expression and positively correlated with Bmi-1 expression in these clinical tissues. CONCLUSION: Hotair silence activates P16(Ink4a) and P14(ARF) signaling by enhancing miR-218 expression and suppressing Bmi-1 expression, resulting in the suppression of tumorigenesis in HCC.

Identification of miRNAs that specifically target tumor suppressive KLF6-FL rather than oncogenic KLF6-SV1 isoform.

The Krüppel like factor 6 (KLF6) gene encodes multiple protein isoforms derived from alternative mRNA splicing, most of which are intimately involved in hepatocarcinogenesis and tumor progression. Recent bioinformatics analysis shows that alternative mRNA splicing of the KLF6 gene produces around 16 alternatively spliced variants with divergent or even opposing functions. Intriguingly, the full-length KLF6 (KLF6-FL) is a tumor suppressor gene frequently inactivated in liver cancer, whereas KLF6 splice variant 1 (KLF6-SV1) is an oncogenic isoform with antagonistic function against KLF6-FL. Compelling evidence indicates that miRNA, the small endogenous non-coding RNA (ncRNA), acts as a vital player in modulating a variety of cellular biological processes through targeting different mRNA regions of protein-coding genes. To identify the potential miRNAs specifically targeting KLF6-FL, we utilized bioinformatics analysis in combination with the luciferase reporter assays and screened out two miRNAs, namely miR-210 and miR-1301, specifically targeted the tumor suppressive KLF6-FL rather than the oncogenic KLF6-SV1. Our in vitro experiments demonstrated that stable expression of KLF6-FL inhibited cell proliferation, migration and angiogenesis while overexpression of miR-1301 promoted cell migration and angiogenesis. Further experiments demonstrated that miR-1301 was highly expressed in liver cancer cell lines as well as clinical specimens and we also identified the potential methylation and histone acetylation for miR-1301 gene. To sum up, our findings unveiled a novel molecular mechanism that specific miRNAs promoted tumorigenesis by targeting the tumor suppressive isoform KLF6-FL rather than its oncogenic isoform KLF6-SV1.

MicroRNA-218 inhibits melanogenesis by directly suppressing microphthalmia-associated transcription factor expression.

The microphthalmia-associated transcription factor (MITF) is a pivotal regulator of melanogenic enzymes for melanogenesis, and its expression is modulated by many transcriptional factors at the transcriptional level or post-transcriptional level through microRNAs (miRNAs). Although several miRNAs modulate melanogenic activities, there is no evidence of their direct action on MITF expression. Out of eight miRNAs targeting the 3'-UTR of Mitf predicted by bioinformatic programs, our results show miR-218 to be a novel candidate for direct action on MITF expression. Ectopic miR-218 dramatically reduced MITF expression, suppressed tyrosinase activity, and induced depigmentation in murine immortalized melan-a melanocytes. MiR-218 also suppressed melanogenesis in human pigmented skin organotypic culture (OTC) through the repression of MITF. An inverse correlation between MITF and miR-218 expression was found in human primary skin melanocytes and melanoma cell lines. Taken together, our findings demonstrate a novel mechanism involving miR-218 in the regulation of the MITF pigmentary process and its potential application for skin whitening therapy.

1,3,5-Trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone directly targets heat shock protein 27 in hepatocellular carcinoma.

We previously showed that the small molecule 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone (TDP) induces apoptosis in hepatocellular carcinoma (HCC) by suppressing Hsp27 expression, although the mechanism is not fully understood. To investigate the functional association between TDP and Hsp27 protein in HCC, recombinant Hsp27 protein was incubated with TDP at room temperature, and assayed by mass spectrum (MS) and natural electrophoresis. TDP effectively stimulated Hsp27 to form aggregates ex vitro, leading to suppression of its chaperone activity. The aggregates were degraded by the ubiquitin-proteasome (UPS) pathway. TDP directly interacted with Asp17 and Phe55 in chain C of Hsp27 on the basis of bioinformatic prediction. In conclusion, Hsp27 is a direct target of TDP in its anti-cancer activity, which provides strong support for a clinical application.

Heat shock protein 27 mediates the effect of 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone on mitochondrial apoptosis in hepatocellular carcinoma.

Hepatocellular carcinoma (HCC) is a global public health problem which causes approximately 500,000 deaths annually. Considering that the limited therapeutic options for HCC, novel therapeutic targets and drugs are urgently needed. In this study, we discovered that 1,3,5-trihydroxy-13,13-dimethyl-2H-pyran [7,6-b] xanthone (TDP), isolated from the traditional Chinese medicinal herb, Garcinia oblongifolia, effectively inhibited cell growth and induced the caspase-dependent mitochondrial apoptosis in HCC. A two-dimensional gel electrophoresis and mass spectrometry-based comparative proteomics were performed to find the molecular targets of TDP in HCC cells. Eighteen proteins were identified as differently expressed, with Hsp27 protein being one of the most significantly down-regulated proteins induced by TDP. In addition, the following gain- and loss-of-function studies indicated that Hsp27 mediates mitochondrial apoptosis induced by TDP. Furthermore, a nude mice model also demonstrated the suppressive effect of TDP on HCC. Our study suggests that TDP plays apoptosis-inducing roles by strongly suppressing the Hsp27 expression that is specifically associated with the mitochondrial death of the caspase-dependent pathway. In conclusion, TDP may be a potential anti-cancer drug candidate, especially to cancers with an abnormally high expression of Hsp27.

Apoptosis induced by 1,3,6,7-tetrahydroxyxanthone in Hepatocellular carcinoma and proteomic analysis.

Gamboge is a traditional Chinese medicine and our previous study showed that gambogic acid and gambogenic acid suppress the proliferation of HCC cells. In the present study, another active component, 1,3,6,7-tetrahydroxyxanthone (TTA), was identified to effectively suppress HCC cell growth. In addition, our Hoechst-PI staining and flow cytometry analyses indicated that TTA induced apoptosis in HCC cells. In order to identify the targets of TTA in HCC cells, a two-dimensional gel electrophoresis was performed, and proteins in different expressions were identified by MALDA-TOF MS and MS/MS analyses. In summary, eighteen proteins with different expressions were identified in which twelve were up-regulated and six were down-regulated. Among them, the four most distinctively expressed proteins were further studied and validated by western blotting. The ß-tubulin and translationally controlled tumor protein were decreased while the 14-3-3σ and P16 protein expressions were up-regulated. In addition, TTA suppressed tumorigenesis partially through P16-pRb signaling. 14-3-3σ silence reversed the suppressive effect of cell growth and apoptosis induced by introducing TTA. In conclusion, TTA effectively suppressed cell growth through, at least partially, up-regulation of P16 and 14-3-3σ.

MiR-637 maintains the balance between adipocytes and osteoblasts by directly targeting Osterix.

Bone development is dynamically regulated by homeostasis, in which a balance between adipocytes and osteoblasts is maintained. Disruption of this differentiation balance leads to various bone-related metabolic diseases, including osteoporosis. In the present study, a primate-specific microRNA (miR-637) was found to be involved in the differentiation of human mesenchymal stem cells (hMSCs). Our preliminary data indicated that miR-637 suppressed the growth of hMSCs and induced S-phase arrest. Expression of miR-637 was increased during adipocyte differentiation (AD), whereas it was decreased during osteoblast differentiation (OS), which suggests miR-637 could act as a mediator of adipoosteogenic differentiation. Osterix (Osx), a significant transcription factor of osteoblasts, was shown to be a direct target of miR-637, which significantly enhanced AD and suppressed OS in hMSCs through direct suppression of Osx expression. Furthermore, miR-637 also significantly enhanced de novo adipogenesis in nude mice. In conclusion, our data indicated that the expression of miR-637 was indispensable for maintaining the balance of adipocytes and osteoblasts. Disruption of miR-637 expression patterns leads to irreversible damage to the balance of differentiation in bone marrow.