Over-expression of SUMO-1 induces the up-regulation of heterogeneous nuclear ribonucleoprotein A2/B1 isoform B1 (hnRNP A2/B1 isoform B1) and uracil DNA glycosylase (UDG) in hepG2 cells

Emerging roles of hnRNP A2B1 in cancer and inflammation

Heterogeneous nuclear ribonucleoproteins (hnRNPs) are a group of RNA-binding proteins with important roles in multiple aspects of nucleic acid metabolism, including the packaging of nascent transcripts, alternative splicing, transactivation of gene expression, and regulation of protein translation. As a core component of the hnRNP complex in mammalian cells, heterogeneous nuclear ribonucleoprotein A2B1 (hnRNP A2B1) participates in and coordinates various molecular events. Given its regulatory role in inflammation and cancer progression, hnRNP A2B1 has become a novel player in immune response, inflammation, and cancer development. Concomitant with these new roles, a surprising number of mechanisms deemed to regulate hnRNP A2B1 functions have been identified, including post-translational modifications, changes in subcellular localization, direct interactions with multiple DNAs, RNAs, and proteins or the formation of complexes with them, which have gradually made hnRNP A2B1 a molecular target for multiple drugs. In light of the rising interest in the intersection between cancer and inflammation, this review will focus on recent knowledge of the biological roles of hnRNP A2B1 in cancer, immune response, and inflammation.

Focus on DNA Glycosylases-A Set of Tightly Regulated Enzymes with a High Potential as Anticancer Drug Targets

Cancer is the second leading cause of death with tens of millions of people diagnosed with cancer every year around the world. Most radio- and chemotherapies aim to eliminate cancer cells, notably by causing severe damage to the DNA. However, efficient repair of such damage represents a common mechanism of resistance to initially effective cytotoxic agents. Thus, development of new generation anticancer drugs that target DNA repair pathways, and more particularly the base excision repair (BER) pathway that is responsible for removal of damaged bases, is of growing interest. The BER pathway is initiated by a set of enzymes known as DNA glycosylases. Unlike several downstream BER enzymes, DNA glycosylases have so far received little attention and the development of specific inhibitors of these enzymes has been lagging. Yet, dysregulation of DNA glycosylases is also known to play a central role in numerous cancers and at different stages of the disease, and thus inhibiting DNA glycosylases is now considered a valid strategy to eliminate cancer cells. This review provides a detailed overview of the activities of DNA glycosylases in normal and cancer cells, their modes of regulation, and their potential as anticancer drug targets.

SUMO1 promotes the proliferation and invasion of non-small cell lung cancer cells by regulating NF-κB

Background

Our previous study showed that SUMO1 expression is closely related to progression in non‐small cell lung cancer (NSCLC); however, the function of SUMO1 in NSCLC has not yet been well elucidated.

Methods

SUMO1 was enhanced or silenced in two NSCLC cell lines by using either forced SUMO1 expression or short hairpin RNA against SUMO1 lentiviral vectors, respectively. The biological functions of SUMO1 in NSCLC were investigated through colony‐formation, cell proliferation, and invasion assays, and cell cycle analysis. NF‐κB expression was detected in the overexpressed and silenced SUMO1 cell lines. Immunohistochemistry was used to detect an association between SUMO1 and NF‐κB in the cancer and adjacent tissues of 168 patients with lung cancer.

Results

Overexpressed SUMO1 promoted the proliferation rate, colony formation ability, invasion, and NF‐κB expression in an A549 cell line. Conversely, SUMO1 depletion inhibited the cell growth rate, colony formation ability, invasion, and NF‐κB expression in a Calu‐1 cell line. SUMO1 expression was significantly correlated with NF‐κB expression in lung adenocarcinoma and squamous carcinoma patients (r > 0.5, P < 0.001).

Conclusion

Our results provide evidence that SUMO1 promotes the proliferation and invasion of NSCLC cells by regulating NF‐κB.

SUMO-1 Gene Silencing Inhibits Proliferation and Promotes Apoptosis of Human Gastric Cancer SGC-7901 Cells

Background: It has been reported that blocking small ubiquitin-like modifier (SUMO) conjugation by silencing SUMO gene remarkably decreased tumor growth in vivo. However, few studies have examined the relationship between SUMO gene silencing and gastric cancer (GC). The study aims to explore the effects of SUMO-1 gene silencing on GC cell proliferation and apoptosis. Methods: GC cells were cultured and divided into 5 groups: the blank group (without any transfection or treatment), the empty vector group (transfected with empty vector), the shRNA-SUMO-1-1 group (transfected with shRNA-SUMO-1-1 plasmid), the shRNA-SUMO-1-2 group (transfected with shRNA-SUMO-1-2 plasmid), and the shRNA-SUMO-1-3 group (transfected with shRNA-SUMO-1-3 plasmid). Cell Counting Kit-8 (CCK-8) assay was performed to examine cell proliferation. Annexin V/PI staining combined with flow cytometry were used to detect cell apoptosis. Quantitative real-time polymerase chain reaction (qRT-PCR) and Western blotting were employed to measure the mRNA and protein expressions of SUMO-1, P53, Bcl-2 and c-myc, respectively. Results: SUMO-1 mRNA and protein expressions were decreased after transfecting with shRNA-SUMO-1. Compared with the blank group, the shRNA-SUMO-1-1 group presented a remarkable decreased proliferation of SGC-7901 cells. Significant increase in cell apoptosis rate was observed. Bcl-2, c-myc and P53 expressions were declined after transfecting with shRNA-SUMO plasmid. Conclusion: Our study provided evidence that SUMO-1 gene silencing could decrease proliferation and promote apoptosis in GC cells.

Bortezomib inhibits Burkitt's lymphoma cell proliferation by downregulating sumoylated hnRNP K and c-Myc expression

Bortezomib (Velcal) was the first proteasome inhibitor to be approved by the US Food and Drug Administration to treat patients with relapsed/refractory multiple myelomas. Previous studies have demonstrated that bortezomib inhibits tumor cell proliferation and induces apoptosis by blocking the nuclear factor (NF)-κB pathway. However, the exact mechanism by which bortezomib induces cancer cell apoptosis is still not well understood. In this study, we found that bortezomib significantly inhibited cell proliferation in both human Burkitt's lymphoma CA46 and Daudi cells. Through proteomic analysis, we found that bortezomib treatment changed the expression of various proteins in distinct functional categories including unfolding protein response (UPS), RNA processing, protein targeting and biosynthesis, apoptosis, and signal transduction. Among the proteins with altered expression, hnRNP K, hnRNP H, Hsp90α, Grp78, and Hsp7C were common to both Daudi and CA46 cells. Interestingly, bortezomib treatment downregulated the expression of high-molecular-weight (HMw) hnRNP K and c-Myc but upregulated the expression of low-molecular-weight (LMw) hnRNP K. Moreover, cell proliferation was significantly correlated with high expression of HMw hnRNP K and c-Myc. HMw and LMw hnRNP K were identified as sumoylated and desumoylated hnRNP K, respectively. Using transient transfection, we found that sumoylated hnRNP K increased c-Myc expression at the translational level and contributed to cell proliferation, and that Lys422 of hnRNP K is the candidate sumoylated residue. Our results suggest that besides inhibiting the ubiquitin-proteasome pathway, bortezomib may inhibit cell proliferation by downregulating sumoylated hnRNP K and c-Myc expression in Burkitt's lymphoma cells.

Base Excision Repair, a Pathway Regulated by Posttranslational Modifications

Base excision repair (BER) is an essential DNA repair pathway involved in the maintenance of genome stability and thus in the prevention of human diseases, such as premature aging, neurodegenerative diseases, and cancer. Protein posttranslational modifications (PTMs), including acetylation, methylation, phosphorylation, SUMOylation, and ubiquitylation, have emerged as important contributors in controlling cellular BER protein levels, enzymatic activities, protein-protein interactions, and protein cellular localization. These PTMs therefore play key roles in regulating the BER pathway and are consequently crucial for coordinating an efficient cellular DNA damage response. In this review, we summarize the presently available data on characterized PTMs of key BER proteins, the functional consequences of these modifications at the protein level, and also the impact on BER in vitro and in vivo.

hnRNPA2/B1 activates cyclooxygenase-2 and promotes tumor growth in human lung cancers

Cyclooxygenase-2 (COX-2) is highly expressed in tumor cells and has been regarded as a hallmarker for cancers, but the excise regulatory mechanism of COX-2 in tumorigenesis remains largely unknown. Here, we pulled down and identified a novel COX-2 regulator, heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNPA2/B1), which could specifically bind to COX-2 core promoter and regulate tumor growth in non-small-cell lung cancers (NSCLCs). Knockdown of hnRNPA2/B1 by shRNA or siRNA downregulated COX-2 expression and prostaglandin E2 (PGE2) production, and suppressed tumor cell growth in NSCLC cells in vitro and in vivo. Conversely, overexpression of hnRNPA2/B1 up-regulated the levels of COX-2 and PGE2 and promoted tumor cell growth. We also showed that hnRNPA2/B1 expression was positively correlated with COX-2 expression in NSCLC cell lines and tumor tissues, and the up-regulated expression of hnRNPA2/B1 and COX-2 predicted worse prognosis in NSCLC patients. Furthermore, we demonstrated that the activation of COX-2 expression by hnRNPA2/B1 was mediated through the cooperation with p300, a transcriptional co-activator, in NSCLC cells. The hnRNPA2/B1 could interact with p300 directly and be acetylated by p300. Exogenous overexpression of p300, but not its histone acetyltransferase (HAT) domain deletion mutation, augmented the acetylation of hnRNPA2/B1 and enhanced its binding on COX-2 promoter, thereby promoted COX-2 expression and lung cancer cell growth. Collectively, our results demonstrate that hnRNPA2/B1 promotes tumor cell growth by activating COX-2 signaling in NSCLC cells and imply that the hnRNPA2/B1/COX-2 pathway may be a potential therapeutic target for human lung cancers.

Transient protection from heat-stress induced apoptotic stimulation by metastasis-associated protein 1 in pachytene spermatocytes

BACKGROUND

Deregulated thermal factors have been frequently implicated in the pathogenesis of male infertility, but the molecular basis through which certain responses are directed remain largely unknown. We previously reported that overexpression of exogenous Metastasis-associated protein 1 (MTA1) protects spermatogenic tumor cells GC-2spd (ts) against heat-induced apoptosis. To further dissect the underlying mechanism, we addressed here the fine coordination between MTA1 and p53 in pachytene spermatocytes upon hyperthermal stimulation.

METHODOLOGY/PRINCIPAL FINDINGS

High level of MTA1 expression sustained for 1.5 h in primary spermatocytes after heat stress before a notable decrease was detected conversely correlated to the gradual increase of acetylation status of p53 and of p21 level. Knockdown of the endogenous MTA1 in GC-2spd (ts) elevated the acetylation of p53 by diminishing the recruitment of HDAC2 and thereafter led to a dramatic increase of apoptosis after heat treatment. Consistent with this, in vivo interference of MTA1 expression in the testes of C57BL/6 mice also urged an impairment of the differentiation of spermatocytes and a disruption of Sertoli cell function due to the elevated apoptotic rate after heat stress. Finally, attenuated expression of MTA1 of pachytene spermatocytes was observed in arrested testes (at the round spermatid level) of human varicocele patients.

CONCLUSIONS

These data underscore a transient protective effect of this histone modifier in primary spermatocytes against heat-stress, which may operate as a negative coregulator of p53 in maintenance of apoptotic balance during early phase after hyperthermal stress.

Anti-inflammatory effect of insulin in the human hepatoma cell line HepG2 involves decreased transcription of IL-6 target genes and nuclear exclusion of FOXO1

The liver is an important target for interleukin-6 (IL-6) action leading to an increased inflammatory response with impaired insulin signaling and action. The aims of this study are to address if insulin is anti-inflammatory and attenuates IL-6-induced inflammation in the human hepatoma cell line HepG2 and if this involves signal transducer and activator of transcription 3 (STAT3) signal transduction. It was found that insulin significantly reduced IL-6-induced gene transcription of serum amyloid 1 (SAA1), serum amyloid 2 (SAA2), haptoglobin, orosomucoid, and plasmin activator inhibitor-1 (PAI-1). However, the authors did not find any evidence that insulin inhibited IL-6 signal transduction, i.e., no effect of insulin was detected on STAT3 phosphorylation or its translocation to cell nucleus. The potential role of PKCδ was also analyzed but no evidence of its involvement was found. Taken together, these results suggest that the anti-inflammatory effect of insulin on IL-6 action is exerted at the level of the transcriptional activation of the genes. Further analysis revealed that insulin regulates nuclear localization of FOXO1, which is an important co-activator for STAT3 mediated transcription. Insulin induced nuclear exit and Thr24 phosphorylation of FOXO1, thus, inhibiting STAT3-mediated transcription.

Role of SUMO-1, MDM2 and P53 in 5-flurouracil-induced apoptosis of HepG2 cells

AIM: To investigate the role of small ubiquitin-like modifier-1 (SUMO-1), murine double minute gene 2 (MDM2) and P53 in 5-flurouracil (5-Fu)-induced apoptosis of HepG2 cells.

METHODS: Non-transfected HepG2 cells and HepG2 cells transfected with pMDM2 and pSUMO-1 plasmids, alone or both, were treated with different concentrations of 5-Fu for 36 hours. The expression of endogenous P53 protein in HepG2 cells was detected by Western blot.

RESULTS: Treatment with 5-Fu significantly increased the relative expression level of endogenous P53 protein and the apoptosis rate of HepG2 cells in a concentration-dependent manner (90.15% ± 4.22% vs 11.27% ± 1.18%, 33.61% ± 3.15% vs 3.22% ± 0.60%, both P < 0.05). Cells transfected with the pMDM2 plasmid had an apparent resistance to 5-Fu-induced apoptosis of HepG2 cells. The relative expression level of P53 protein and the apoptosis rate in cells transfected with the pMDM2 plasmid were much lower than those in non-transfected cells treated with the same concentration of 5-Fu (51.80% ± 0.78% vs 90.15% ± 4.22%; 20.45% ± 2.23% vs 33.61% ± 3.15%, both P < 0.05). No significant differences were noted in the relative expression level of P53 protein and the apoptosis rate between cells co-transfected with the pSUMO-1 and pMDM2 plasmids and non-transfected cells (78.85% ± 2.43% vs 51.80% ± 0.78%, 29.83% ± 0.53% vs 20.45% ± 2.23%, both P < 0.05).

CONCLUSION: SUMO-1 could inhibit MDM2-induced degradation of P53 protein and enhance the nuclear expression of P53, thus promoting 5-Fu-induced cell apoptosis and elevating chemosensitivity.

Up-regulation and subcellular localization of hnRNP A2/B1 in the development of hepatocellular carcinoma

Background

Hepatocellular carcinoma (HCC) is one of the world's leading causes of death among cancer patients. It is important to find a new biomarker that diagnoses HCC and monitors its treatment. In our previous work, we screened a single-chain antibody (scFv) N14, which could specifically recognize human HepG2 HCC cells but not human non-cancerous liver LO2 cells. However, the antigen it recognized in the cells remained unknown.

Methods

Recombinant scFv N14 antibody was expressed as an active antibody. Using this antibody with a combination of immunological and proteomic approaches, we identified the antigen of scFv N14 antibody as the heterogeneous nuclear ribonucleoprotein A2/B1 (hnRNP A2/B1). The expression of hnRNP A2/B1 in HCC cells was then investigated by semi-quantitative RT-PCR and immunohistochemistry.

Results

We found that the up-regulation of hnRNP A2/B1 was measured at both transcriptional and translational levels in rat HCC cells but not in rat hepatic cells. We also found that in various human hepatic tissues, hnRNP A2/B1 was highly expressed in both human hepatitis virus positive liver tissues and human HCC tissues but not in normal liver tissues. Interestingly, we observed that the localization of hnRNP A2/B1 in HCC cells was altered during the development of HCC. In human hepatitis virus infected tissues hnRNP A2/B1 resides exclusively in the nuclei of hepatocytes. However, when the HCC progressed from a well differentiated to a poorly differentiated stage, hnRNP A2/B1 was increasingly localized in the cytoplasm. In contrast, the HCC tissues with hnRNP A2/B1 highly expressed in the nucleus decreased.

Conclusions

This work is the first to show that hnRNP A2/B1 is the antigen specifically recognized by the scFv N14 antibody in HCC cells. The over-expression of hnRNP A2/B1 was confirmed in cultured human and rat HCC cell lines, human virus related hepatitis liver tissues and human HCC tissues. The increased localization of hnRNP A2/B1 in the cytoplasm of HCC cells was revealed during the dedifferentiation of hepatocellular carcinoma. Therefore, we suggest that the increased expression and cytoplasmic localization of hnRNP A2/B1 can be used as a diagnostic biomarker to assess the risk of human liver cancer.

The intracellular delivery of a recombinant peptide derived from the acidic domain of PIAS3 inhibits STAT3 transactivation and induces tumor cell death

Signaling components, which confer an "addiction" phenotype on cancer cells, represent promising drug targets. The transcription factor signal transducers and activators of transcription 3 (STAT3) is constitutively activated in many different types of tumor cells and its activity is indispensible in a large fraction. We found that the expression of the endogenous inhibitor of STAT3, protein inhibitor of activated STAT3 (PIAS3), positively correlates with STAT3 activation in normal cells. This suggests that PIAS3 controls the extent and the duration of STAT3 activity in normal cells and thus prevents its oncogenic function. In cancer cells, however, the expression of PIAS3 is posttranscriptionally suppressed, possibly enhancing the oncogenic effects of activated STAT3. We delimited the interacting domains of STAT3 and PIAS3 and identified a short fragment of the COOH-terminal acidic region of PIAS3, which binds strongly to the coiled-coil domain of STAT3. This PIAS3 fragment was used to derive the recombinant STAT3-specific inhibitor rPP-C8. The addition of a protein transduction domain allowed the efficient internalization of rPP-C8 into cancer cells. This resulted in the suppression of STAT3 target gene expression, in the inhibition of migration and proliferation, and in the induction of apoptosis at low concentrations [half maximal effective concentration (EC(50)), <3 micromol/L]. rPP-C8 did not affect normal fibroblasts and represents an interesting lead for the development of novel cancer drugs targeting the coiled-coil domain of STAT3.