HnRNP E2 is downregulated in human oral cancer cells and the overexpression of hnRNP E2 induces apoptosis

Identification of HnRNP Family as Prognostic Biomarkers in Five Major Types of Gastrointestinal Cancer

BACKGROUND

Heterogeneous nuclear ribonucleoproteins (hnRNPs), a large family of RNAbinding proteins, have been implicated in tumor progression in multiple cancer types. However, the expression pattern and prognostic value of hnRNPs in five gastrointestinal (GI) cancers, including gastric, colorectal, esophageal, liver, and pancreatic cancer, remain to be investigated.

OBJECTIVE

The current research aimed to identify prognostic biomarkers of the hnRNP family in five major types of gastrointestinal cancer.

METHODS

Oncomine, Gene Expression Profiling Interactive Analysis (GEPIA), and Kaplan-Meier Plotter were used to explore the hnRNPs expression levels concerning clinicopathological parameters and prognostic values. The protein level of hnRNPU was validated by immunohistochemistry (IHC) in human tissue specimens. Genetic alterations of hnRNPs were analyzed using cBioportal, and Gene Ontology (GO) and Kyoto Encyclopedia of Genes and Genomes (KEGG) analyses were performed to illustrate the biological functions of co-expressed genes of hnRNPs.

RESULTS

The vast majority of hnRNPs were highly expressed in five types of GI cancer tissues compared to their adjacent normal tissues, and mRNA levels of hnRNPA2B1, D, Q, R, and U were significantly different in various GI cancer types at different stages. In addition, Kaplan-Meier analysis revealed that the increased hnRNPs expression levels were correlated with better prognosis in gastric and rectal cancer patients (log-rank p < 0.05). In contrast, patients with high levels of hnRNPs exhibited a worse prognosis in esophageal and liver cancer (log-rank p < 0.05). Using immunohistochemistry, we further confirmed that hnRNPU was overexpressed in gastric, rectal, and liver cancers. In addition, hnRNPs genes were altered in patients with GI cancers, and RNA-related processing was correlated with hnRNPs alterations.

CONCLUSION

We identified differentially expressed genes of hnRNPs in tumor tissues versus adjacent normal tissues, which might contribute to predicting tumor types, early diagnosis, and targeted therapies in five major types of GI cancer.

Heterogeneous Nuclear Ribonucleoprotein E2 (hnRNP E2) Is a Component of TDP-43 Aggregates Specifically in the A and C Pathological Subtypes of Frontotemporal Lobar Degeneration

TAR DNA-binding protein 43 (TDP-43) is the major component of the ubiquitin-positive protein aggregates seen in the majority of frontotemporal lobar degeneration and amyotrophic lateral sclerosis cases. TDP-43 belongs to the heterogeneous nuclear ribonucleoprotein (hnRNP) family that is involved in the regulation of RNA transcription, splicing, transport and translation. There are a great many hnRNPs, which often have overlapping functions and act cooperatively in RNA processing. Here we demonstrate that another hnRNP family member, hnRNP E2, shows a striking accumulation within dystrophic neurites and cytoplasmic inclusions in the frontal cortex and hippocampus of a subset of FTLD-TDP cases belonging to pathological subtypes A and C, where hnRNP E2 was found to co-localize with 87% of TDP-43 immunopositive inclusions. hnRNP E2-positive inclusions were not seen in FTLD-TDP cases with the C9orf72 expansion or in any other neurodegenerative disorders examined. This interaction with TDP-43 in specific FTLD subtypes suggests different underlying neurodegenerative pathways.

Poly(rC) binding protein 2 (PCBP2) promotes the viability of human gastric cancer cells by regulating CDK2

Survival rates for patients with gastric cancer, especially the advanced form, remain poor and the development of targeted treatments is hampered by a lack of efficient biological targets. Poly(rC) binding protein 2 (PCBP2) is an RNA-binding protein that contributes to mRNA stabilization, translational silencing and enhancement and it has been implicated as a promoter of gastric cancer growth. In the present study, we demonstrated that the expression level of PCBP2 was higher in human gastric cancer tissues compared to adjacent normal gastric tissues. A high level of PCBP2 was correlated with worse postoperative relapse-free survival and overall survival rates of gastric cancer patients. Small hairpin RNA-mediated depletion of PCBP2 dramatically decreased the viability of gastric cancer cells. Cyclin-dependent kinase 2 (CDK2) was positively regulated by PCBP2 via a direct 3' UTR binding pathway as determined using a ribonucleoprotein immunoprecipitation assay and a biotin pulldown assay. CDK2 mediated the promoting role of PCBP2. These results suggest that PCBP2 acts as an oncogene in human gastric cancer cells and that functionally depleting PCBP2 could be considered as a potential target for gastric cancer therapy.

High expression of PCBP2 is associated with progression and poor prognosis in patients with glioblastoma

BACKGROUND

Poly(C)-binding protein 2 (PCBP2) has been found to have ambiguous functions in a variety of cancers. However, the specific biological function of PCBP2 and its mechanism in glioblastoma remain unclear. We investigated the expression of PCBP2 in 143 glioblastoma specimens to explore the linkage between PCBP2 expression and clinicopathological parameters as well as clinical significance. Furthermore, the underlying mechanisms of PCBP2 on glioblastoma progression were discussed in vitro.

METHODS

The transcriptional and translational levels of PCBP2 in 143 glioblastoma patients were detected by quantitative Real-time PCR (qRT-PCR) and western blot. The association of prognostic outcomes and PCBP2 expression was evaluated using Kaplan-Meier analysis.

RESULTS

PCBP2 expression was markedly increased in higher stages of glioblastoma compared with those in lower stages (P<0.001). High expression of PCBP2 was associated with higher clinical stage and histological grade (P<0.001). Further research suggested that PCBP2 upregulation was connected with poorer prognosis in patients with glioblastoma (P<0.001). Moreover, PCBP2 knockdown could significantly decreased the colony formation and invasion capability of glioblastoma cells (P<0.01). Conversely, PCBP2 overexpression could increase the colony formation and invasion capability (P<0.01).

CONCLUSION

These findings indicated that PCBP2 might be a novel prognostic biomarker and a potential therapeutic target of glioblastoma.

RNA-binding Protein PCBP2 Regulates p73 Expression and p73-dependent Antioxidant Defense

TAp73, a member of the p53 family tumor suppressors, plays a critical rule in tumor suppression and neuronal development. However, how p73 activity is controlled at the posttranscriptional level is not well understood. Here, we showed that TAp73 activity is regulated by RNA-binding protein PCBP2. Specifically, we found that knockdown or knock-out of PCBP2 reduces, whereas ectopic expression of PCBP2 increases, TAp73 expression. We also showed that PCBP2 is necessary for p73 mRNA stability via the CU-rich elements in p73 3'-UTR. To uncover the biological relevance of PCBP2-regulated TAp73 expression, we showed that ectopic expression of PCBP2 inhibits, whereas knockdown or knock-out of PCBP2 increases, the production of reactive oxygen species (ROS) in a TAp73-dependent manner. Additionally, we found that glutaminase 2 (GLS2), a modulator of p73-dependent antioxidant defense, is also involved in PCBP2-regulated ROS production. Moreover, we generated PCBP2-deficient mice and primary mouse embryonic fibroblasts (MEFs) and showed that loss of PCBP2 leads to decreased p73 expression and, subsequently, increased ROS production and accelerated cellular senescence. Together, our data suggest that PCBP2 regulates p73 expression via mRNA stability and p73-dependent biological function in ROS production and cellular senescence.

β2-adrenergic receptor signaling promotes pancreatic ductal adenocarcinoma (PDAC) progression through facilitating PCBP2-dependent c-myc expression

The β2-adrenergic receptor (β2-AR) plays a crucial role in pancreatic ductal adenocarcinoma (PDAC) progression. In this report, we identified poly(rC)-binding protein 2 (PCBP2) as a novel binding partner for β2-AR using immunoprecipitation-mass spectrometry (IP-MS) approach. The association between β2-AR and PCBP2 was verified using reciprocal immunoprecipitation. Importantly, we found significant interaction and co-localization of the two proteins in the presence of β2-AR agonist in Panc-1 and Bxpc3 PDAC cells. β2-AR-induced recruitment of PCBP2 led to augmented protein level of c-myc in PDAC cells, likely as a result of enhanced internal ribosome entry segment (IRES)-mediated translation of c-myc. The activation of β2-AR accelerated cell proliferation and colony formation, while knockdown of PCBP2 or c-myc restrained the effect. Furthermore, overexpression of PCBP2 was observed in human PDAC cell lines and tissue specimens compared to the normal pancreatic ductal epithelial cells and the non-cancerous tissues respectively. Overexpression of β2-AR and PCBP2 was associated with advanced tumor stage and significantly worsened prognosis in patients with PDAC. Our results elucidate a new molecular mechanism by which β2-AR signaling facilitates PDAC progression through triggering PCBP2-dependent c-myc expression.

Regulation of Stem Cell Self-Renewal and Oncogenesis by RNA-Binding Proteins

Throughout their life span, multicellular organisms rely on stem cell systems. During development pluripotent embryonic stem cells give rise to all cell types that make up the organism. After birth, tissue stem cells maintain properly functioning tissues and organs under homeostasis as well as promote regeneration after tissue damage or injury. Stem cells are capable of self-renewal, which is the ability to divide indefinitely while retaining the potential of differentiation into multiple cell types. The ability to self-renew, however, is a double-edged sword; the molecular mechanisms of self-renewal can be a target of malignant transformation driving tumor development and progression. Growing lines of evidence have shown that RNA-binding proteins (RBPs) play pivotal roles in the regulation of self-renewal by modulating metabolism of coding and non-coding RNAs both in normal tissues and in cancers. In this review, we discuss our current understanding of tissue stem cell systems and how RBPs regulate stem cell fates as well as how the regulatory functions of RBPs contribute to oncogenesis.

Suppression of Poly(rC)-Binding Protein 4 (PCBP4) reduced cisplatin resistance in human maxillary cancer cells

Cisplatin plays an important role in the therapy for human head and neck cancers. However, cancer cells develop cisplatin resistance, leading to difficulty in treatment and poor prognosis. To analyze cisplatin-resistant mechanisms, a cisplatin-resistant cell line, IMC-3CR, was established from the IMC-3 human maxillary cancer cell line. Flow cytometry revealed that, compared with IMC-3 cells, cisplatin more dominantly induced cell cycle G2/M arrest rather than apoptosis in IMC-3CR cells. That fact suggests that IMC-3CR cells avoid cisplatin-induced apoptosis through induction of G2/M arrest, which allows cancer cells to repair damaged DNA and survive. In the present study, we specifically examined Poly(rC)-Binding Protein 4 (PCBP4), which reportedly induces G2/M arrest. Results showed that suppression of PCBP4 by RNAi reduced cisplatin-induced G2/M arrest and enhanced apoptosis in IMC-3CR cells, resulting in the reduction of cisplatin resistance. In contrast, overexpression of PCBP4 in IMC-3 cells induced G2/M arrest after cisplatin treatment and enhanced cisplatin resistance. We revealed that PCBP4 combined with Cdc25A and suppressed the expression of Cdc25A, resulting in G2/M arrest. PCBP4 plays important roles in the induction of cisplatin resistance in human maxillary cancers. PCBP4 is a novel molecular target for the therapy of head and neck cancers, especially cisplatin-resistant cancers.

Identification of Gene and MicroRNA Signatures for Oral Cancer Developed from Oral Leukoplakia

In clinic, oral leukoplakia (OLK) may develop into oral cancer. However, the mechanism underlying this transformation is still unclear. In this work, we present a new pipeline to identify oral cancer related genes and microRNAs (miRNAs) by integrating both gene and miRNA expression profiles. In particular, we find some network modules as well as their miRNA regulators that play important roles in the development of OLK to oral cancer. Among these network modules, 91.67% of genes and 37.5% of miRNAs have been previously reported to be related to oral cancer in literature. The promising results demonstrate the effectiveness and efficiency of our proposed approach.

The RNA-binding protein PCBP2 facilitates gastric carcinoma growth by targeting miR-34a

Gastric carcinoma is the fourth most common cancer worldwide, with a high rate of death and low 5-year survival rate. However, the mechanism underling gastric cancer is still not fully understood. Here in the present study, we identify the RNA-binding protein PCBP2 as an oncogenic protein in human gastric carcinoma. Our results show that PCBP2 is up-regulated in human gastric cancer tissues compared to adjacent normal tissues, and that high level of PCBP2 predicts poor overall and disease-free survival. Knockdown of PCBP2 in gastric cancer cells inhibits cell proliferation and colony formation in vitro, whereas opposing results are obtained when PCBP2 is overexpressed. Our in vivo subcutaneous xenograft results also show that PCBP2 can critically regulate gastric cancer cell growth. In addition, we find that PCBP2-depletion induces apoptosis in gastric cancer cells via up-regulating expression of pro-apoptotic proteins and down-regulating anti-apoptotic proteins. Mechanically, we identify that miR-34a as a target of PCBP2, and that miR-34a is critically essential for the function of PCBP2. In summary, PCBP2 promotes gastric carcinoma development by regulating the level of miR-34a.

A screen identifies the oncogenic micro-RNA miR-378a-5p as a negative regulator of oncogene-induced senescence

Oncogene-induced senescence (OIS) can occur in response to hyperactive oncogenic signals and is believed to be a fail-safe mechanism protecting against tumorigenesis. To identify new factors involved in OIS, we performed a screen for microRNAs that can overcome or inhibit OIS in human diploid fibroblasts. This screen led to the identification of miR-378a-5p and in addition several other miRNAs that have previously been shown to play a role in senescence. We show that ectopic expression of miR-378a-5p reduces the expression of several senescence markers, including p16^INK4A and senescence-associated β-galactosidase. Moreover, cells with ectopic expression of miR-378a-5p retain proliferative capacity even in the presence of an activated Braf oncogene. Finally, we identified several miR-378a-5p targets in diploid fibroblasts that might explain the mechanism by which the microRNA can delay OIS. We speculate that miR-378a-5p might positively influence tumor formation by delaying OIS, which is consistent with a known pro-oncogenic function of this microRNA.

RNA-binding protein PCBP2 modulates glioma growth by regulating FHL3

PCBP2 is a member of the poly(C)-binding protein (PCBP) family, which plays an important role in posttranscriptional and translational regulation by interacting with single-stranded poly(C) motifs in target mRNAs. Several PCBP family members have been reported to be involved in human malignancies. Here, we show that PCBP2 is upregulated in human glioma tissues and cell lines. Knockdown of PCBP2 inhibited glioma growth in vitro and in vivo through inhibition of cell-cycle progression and induction of caspase-3-mediated apoptosis. Thirty-five mRNAs were identified as putative PCBP2 targets/interactors using RIP-ChIP protein-RNA interaction arrays in a human glioma cell line, T98G. Four-and-a-half LIM domain 3 (FHL3) mRNA was downregulated in human gliomas and was identified as a PCBP2 target. Knockdown of PCBP2 enhanced the expression of FHL3 by stabilizing its mRNA. Overexpression of FHL3 attenuated cell growth and induced apoptosis. This study establishes a link between PCBP2 and FHL3 proteins and identifies a new pathway for regulating glioma progression.

Translational control in cancer etiology

The link between perturbations in translational control and cancer etiology is becoming a primary focus in cancer research. It has now been established that genetic alterations in several components of the translational apparatus underlie spontaneous cancers as well as an entire class of inherited syndromes known as "ribosomopathies" associated with increased cancer susceptibility. These discoveries have illuminated the importance of deregulations in translational control to very specific cellular processes that contribute to cancer etiology. In addition, a growing body of evidence supports the view that deregulation of translational control is a common mechanism by which diverse oncogenic pathways promote cellular transformation and tumor development. Indeed, activation of these key oncogenic pathways induces rapid and dramatic translational reprogramming both by increasing overall protein synthesis and by modulating specific mRNA networks. These translational changes promote cellular transformation, impacting almost every phase of tumor development. This paradigm represents a new frontier in the multihit model of cancer formation and offers significant promise for innovative cancer therapies. Current research, in conjunction with cutting edge technologies, will further enable us to explore novel mechanisms of translational control, functionally identify translationally controlled mRNA groups, and unravel their impact on cellular transformation and tumorigenesis.

BRCA1/p220 loss triggers BRCA1-IRIS overexpression via mRNA stabilization in breast cancer cells

BRCA1/p220-assocaited and triple negative/basal-like (TN/BL) tumors are aggressive and incurable breast cancer diseases that share among other features the no/low BRCA1/p220 expression. Here we show that BRCA1/p220 silencing in normal human mammary epithelial (HME) cells reduces expression of two RNA-destabilizing proteins, namely AUF1 and pCBP2, both proteins bind and destabilize BRCA1-IRIS mRNA. BRCA1-IRIS overexpression in HME cells triggers expression of several TN/BL markers, e.g., cytokeratins 5 and 17, p-cadherin, EGFR and cyclin E as well as expression and activation of the pro-survival proteins; AKT and survivin. BRCA1-IRIS silencing in the TN/BL cell line, SUM149 or restoration of BRCA1/p220 expression in the mutant cell line, HCC1937 reduced expression of TN/BL markers, AKT and survivin and induced cell death. Collectively, we propose that BRCA1/p220 loss of expression or function triggers BRCA1-IRIS overexpression through a post-transcriptional mechanism, which in turn promotes formation of aggressive and invasive breast tumors by inducing expression of TN/BL and survival proteins.

Expression and mutation analysis of heterogeneous nuclear ribonucleoprotein G in human oral cancer

We previously reported that wild type (wt) hnRNP G exhibited tumor suppressive activity in human oral squamous cell carcinoma (HOSCC) cell lines lacking hnRNP G. Wt hnRNP G markedly inhibited the proliferation capacity, anchorage independency and in vivo tumorigenicity of HOSCC cells and notably enhanced the DNA repair capabilities of these cells. In the present study, we studied the genetic and expression states of hnRNP G in normal, premalignant and malignant human oral tissues to further understand the relationship between the hnRNP G alterations and the development of human oral cancer. To correlate the cancer development and the level of hnRNP G expression, we performed an immunohistochemistry staining of hnRNP G in normal, premalignant and malignant human oral tissues. Moreover, we examined the entire coding regions of hnRNP G from selected samples to understand the cause of the alterations of the gene expression. The expression of hnRNP G was notably decreased or completely abolished in 80% of premalignant-dysplastic and malignant oral epithelial tissues, whereas 100% of normal and 90% of hyperplastic non-dysplastic epithelium showed high level of hnRNP G in the nucleus of the basal cell layers. Approximately 80% of HOSCC lacking the expression of hnRNP G showed genetic alteration in hnRNP G, i.e., point mutation and exonic deletion. This study suggest that genetic alterations and aberrant expression of hnRNP G occurring during oral carcinogenesis might be useful markers for the early detection of human oral cancer.

The cancerous translation apparatus

Deregulations in translational control are critical features of cancer initiation and progression. Activation of key oncogenic pathways promotes rapid and dramatic translational reprogramming, not simply by increasing overall protein synthesis, but also by modulating specific mRNA networks that promote cellular transformation. Additionally, ribosomopathies caused by mutations in ribosome components alter translational regulation leading to specific pathological features, including cancer susceptibility. Exciting advances in our understanding of translational control in cancer have illuminated a striking specificity innate to the translational apparatus. Characterizing this specificity will provide novel insights into how cells normally utilize translational control to modulate gene expression, how it is deregulated in cancer, and how these processes can be targeted to develop new cancer therapies.

In vitro and in vivo reduction of sodium arsenite induced toxicity by aqueous garlic extract

BACKGROUND

Arsenic is ubiquitous in the environment, and chronic or acute exposure through food and water as well as occupational sources can contribute to a well-defined spectrum of disease. Despite arsenic being a health hazard and a well-documented human carcinogen, a safe, effective and specific preventive or therapeutic measure for treating arsenic induced toxicity still eludes us.

OBJECTIVE

This study was undertaken to evaluate the therapeutic efficacy of aqueous garlic (Allium sativum L.) extract (AGE) in terms of normalization of altered biochemical parameters particularly indicative of oxidative stress following sodium arsenite (NaAsO(2)) exposure and depletion of inorganic arsenic burden, in vitro and in vivo.

RESULTS

AGE (2mg/ml) co-administered with 10 microM NaAsO(2) attenuated arsenite induced cytotoxicity, reduced intracellular reactive oxygen species (ROS) level in human malignant melanoma cells (A375), human keratinocyte cells (HaCaT) and in cultured human normal dermal fibroblast cells. Moreover, AGE application in NaAsO(2) intoxicated Sprague-Dawley rats resulted in a marked inhibition of tissue lipid peroxide generation; enhanced level of total tissue sulfhydryl groups and glutathione; and also increased the activities of antioxidant enzymes, superoxide dismutase and catalase to near normal. An increase in blood ROS level and myeloperoxidase activity in arsenic-intoxicated rats was effectively prevented by AGE administration. AGE was also able to counter arsenic mediated incongruity in blood hematological variables and glucose level.

CONCLUSIONS

The restorative property of AGE was attributed to its antioxidant activity, chelating efficacy, and/or oxidizing capability of trivalent arsenic to its less toxic pentavalent form. Taken together, evidences indicate that AGE can be a potential protective regimen for arsenic mediated toxicity.