PSF knockdown enhances apoptosis via downregulation of LC3B in human colon cancer cells

Assessment of an Anticancer Effect of the Simultaneous Administration of MM-129 and Indoximod in the Colorectal Cancer Model

(1) Background: The purpose of the given study was to examine the antitumor activity of the simultaneous administration of MM-129, a 1,2,4-triazine derivative, and indoximod (IND), the kynurenine pathway inhibitor, toward colon cancer. (2) Methods: The efficiency of the co-administration of the studied compounds was assessed in xenografted zebrafish embryos. Then, the effects of the combined administration of compounds on cellular processes such as cell viability, apoptosis, and intracellular signaling pathways were evaluated. In vitro studies were performed using two colorectal cancer cell lines, namely, DLD-1 and HT-29. (3) Results: The results indicated that the simultaneous application of MM-129 and indoximod induced a stronger inhibition of tumor growth in zebrafish xenografts. The combination of these compounds intensified the process of apoptosis by lowering the mitochondrial potential, enhancing the externalization of phosphatidylserine (PS) and activation of caspases. Additionally, the expression of protein kinase B (AKT) and indoleamine 2,3-dioxygenase-(1IDO1) was disrupted under the applied compound combination. (4) Conclusions: Simultaneous targeting of ongoing cell signaling that promotes tumor progression, along with inhibition of the kynurenine pathway enzyme IDO1, results in the enhancement of the antitumor effect of the tested compounds against the colon cancer cells.

AGO-RBP crosstalk on target mRNAs: Implications in miRNA-guided gene silencing and cancer

MicroRNAs (miRNAs) and RNA-binding proteins (RBPs) are important regulators of mRNA translation and stability in eukaryotes. While miRNAs can only bind their target mRNAs in association with Argonaute proteins (AGOs), RBPs directly bind their targets either as single entities or in complex with other RBPs to control mRNA metabolism. miRNA binding in 3' untranslated regions (3' UTRs) of mRNAs facilitates an intricate network of interactions between miRNA-AGO and RBPs, thus determining the fate of overlapping targets. Here, we review the current knowledge on the interplay between miRNA-AGO and multiple RBPs in different cellular contexts, the rules underlying their synergism and antagonism on target mRNAs, as well as highlight the implications of these regulatory modules in cancer initiation and progression.

RNA processing genes characterize RNA splicing and further stratify colorectal cancer

Objectives

Due to the limited evaluation of the prognostic value of RNA processing genes (RPGs), which are regulators of alternative splicing events (ASEs) that have been shown to be associated with tumour progression, this study sought to determine whether colorectal cancer (CRC) could be further stratified based on the expression pattern of RPGs.

Materials and Methods

The gene expression profiles of CRCs were collected from TCGA (training set) and three external validation cohorts, representing 1060 cases totally. Cox regression with least absolute shrinkage and selection operator (LASSO) penalty was used to develop an RNA processing gene index (RPGI) risk score. Kaplan‐Meier curves, multivariate Cox regression and restricted mean survival (RMS) analyses were harnessed to evaluate the prognostic value of the RPGI.

Results

A 22‐gene RPGI signature was developed, and its risk score served as a strong independent prognostic factor across all data sets when adjusted for major clinical variables. Moreover, ASEs for certain genes, such as FGFR1 and the RAS oncogene family, were significantly correlated with RPGI. Expression levels of genes involved in splicing‐ and tumour‐associated pathways were significantly correlated with RPGI score. Furthermore, a combination of RPGI with age and tumour stage resulted in significantly improved prognostic accuracy.

Conclusions

Our findings highlighted the prognostic value of RPGs for risk stratification of CRC patients and provide insights into specific ASEs associated with the development of CRC.

The MNK1/2-eIF4E Axis as a Potential Therapeutic Target in Melanoma

: Melanoma is a type of skin cancer that originates in the pigment-producing cells of the body known as melanocytes. Most genetic aberrations in melanoma result in hyperactivation of the mitogen activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K) pathways. We and others have shown that a specific protein synthesis pathway known as the MNK1/2-eIF4E axis is often dysregulated in cancer. The MNK1/2-eIF4E axis is a point of convergence for these signaling pathways that are commonly constitutively activated in melanoma. In this review we consider the functional implications of aberrant mRNA translation in melanoma and other malignancies. Moreover, we discuss the consequences of inhibiting the MNK1/2-eIF4E axis on the tumor and tumor-associated cells, and we provide important avenues for the utilization of this treatment modality in combination with other targeted and immune-based therapies. The past decade has seen the increased development of selective inhibitors to block the action of the MNK1/2-eIF4E pathway, which are predicted to be an effective therapy regardless of the melanoma subtype (e.g., cutaneous, acral, and mucosal).

SFPQ is involved in regulating arsenic-induced oxidative stress by interacting with the miRNA-induced silencing complexes

Arsenic exposure contributed to the development of human diseases. Arsenic exerted multiple organ toxicities mainly by triggering oxidative stress. However, the signaling pathway underlying oxidative stress is unclear. We previously found that the expression of SFPQ, a splicing factor, was positively associated with urinary arsenic concentration in an arsenic-exposed population, suggesting an oxidative stress regulatory role for SFPQ. To test this hypothesis, we established cell models of oxidative stress in human hepatocyte cells (L02) treated with NaAsO₂. Reactive oxygen species (ROS) synthesis displayed a time- and dose-dependent increase with NaAsO₂ treatment. SFPQ suppression resulted in a 36%-53% decrease in ROS generation, leading to enhanced cellular damage determined by 8-OHdG, comet tail moment, and micronucleus analysis. Particularly, SFPQ deficiency attenuated expression of the oxidase genes DUOX1, DUOX2, NCF2, and NOX2. A fluorescent-based RNA electrophoretic mobility shift assay (FREMSA) and dual-luciferase reporter system revealed that miR-92b-5p targeted DUOX2 mRNA degradation. An RNA immunoprecipitation assay showed an interaction between SFPQ and miR-92b-5p of the miRNA-induced silencing complex (miRISC). Notably, NaAsO₂ treatment diminished the interaction between SFPQ and miR92b-5p, accompanied by decreased binding between miR-92b-5p and 3'-UTR of DUOX2. However, SFPQ deficiency suppressed the dissociation of miR-92b-5p from 3'-UTR of DUOX2, indicating that miR-92b-5p regulated the SFPQ-dependent DUOX2 expression. Taken together, we reveal that SFPQ responds to arsenic-induced oxidative stress by interacting with the miRISC. These findings offer new insight into the potential role of SFPQ in regulating cellular stress response.

Splicing factor proline- and glutamine-rich (SFPQ) protein regulates platinum response in ovarian cancer-modulating SRSF2 activity

In epithelial ovarian cancer (EOC), response to platinum (PT)-based chemotherapy dictates subsequent treatments and predicts patients' prognosis. Alternative splicing is often deregulated in human cancers and can be altered by chemotherapy. Whether and how changes in alternative splicing regulation could impact on the response of EOC to PT-based chemotherapy is still not clarified. We identified the splicing factor proline and glutamine rich (SFPQ) as a critical mediator of response to PT in an unbiased functional genomic screening in EOC cells and, using a large cohort of primary and recurrent EOC samples, we observed that it is frequently overexpressed in recurrent PT-treated samples and that its overexpression correlates with PT resistance. At mechanistic level, we show that, under PT treatment, SFPQ, in complex with p54^nrb, binds and regulates the activity of the splicing factor SRSF2. SFPQ/p54^nrb complex decreases SRSF2 binding to caspase-9 RNA, favoring the expression of its alternative spliced antiapoptotic form. As a consequence, SFPQ/p54^nrb protects cells from PT-induced death, eventually contributing to chemoresistance. Overall, our work unveils a previously unreported SFPQ/p54^nrb/SRSF2 pathway that in EOC cells plays a central role in regulating alternative splicing and PT-induced apoptosis and that could result in the design of new possible ways of intervention to overcome PT resistance.

Interaction of HIV-1 integrase with polypyrimidine tract binding protein and associated splicing factor (PSF) and its impact on HIV-1 replication

Background

The different interactions between viral proteins and cellular host proteins are required for efficient replication of HIV-1. Various reports implicated host cellular proteins as a key factor that either interact directly with HIV-1 integrase (IN) or get involved in the integration process of virus resulting in the modulation of integration step. Polypyrimidine tract binding protein and associated splicing factor (PSF) has diverse functions inside the cell such as transcriptional regulation, DNA repair, acts as nucleic acids binding protein and regulate replication and infectivity of different viruses.

Results

The protein binding study identified the association of host protein PSF with HIV-1 integrase. The siRNA knockdown (KD) of PSF resulted in increased viral replication in TZM-bl cells, suggesting PSF has negative influence on viral replication. The quantitative PCR of virus infected PSF knockdown TZM-bl cells showed more integrated DNA and viral cDNA as compared to control cells. We did not observe any significant difference between the amount of early reverse transcription products as well as infectivity of virus in the PSF KD and control TZM-bl cells. Molecular docking study supported the argument that PSF hinders the binding of viral DNA with IN.

Conclusion

In an attempt to study the host interacting protein of IN, we have identified a new interacting host protein PSF which is a splicing factor and elucidated its role in integration and viral replication. Experimental as well as in silico analysis inferred that the host protein causes not only change in the integration events but also targets the incoming viral DNA or the integrase-viral DNA complex. The role of PSF was also investigated at early reverse transcript production as well as late stages. The PSF is causing changes in integration events, but it does not over all make any changes in the virus infectivity. MD trajectory analyses provided a strong clue of destabilization of Integrase-viral DNA complex occurred due to PSF interaction with the conserved bases of viral DNA ends that are extremely crucial contact points with integrase and indispensable for integration. Thus our study emphasizes the negative influence of PSF on HIV-1 replication.

Electronic supplementary material

The online version of this article (10.1186/s12977-019-0474-1) contains supplementary material, which is available to authorized users.

The PTB-Associated Splicing Factor/Peroxisome Proliferator-Activated Receptor Gamma Axis Regulates Autophagosome Formation in Human Pancreatic Cancer Cells

Peroxisome proliferator-activated receptor gamma (PPARγ) is a nuclear receptor that plays a major regulatory role in metabolic function. It is overexpressed in many types of cancer cells, suggesting that regulation of PPARγ may also affect carcinogenesis. Our previous study suggested that PTB-associated splicing factor (PSF) is a PPARγ-interacting protein and growth regulator of colon cancer cells. In addition, PSF has been shown to be involved in several important regulatory steps of cancer cell proliferation. In this study, we aimed to investigate the relationships between PSF and PPARγ in pancreatic cancer by evaluating the effects of PSF expression in pancreatic cancer cell lines. PSF expression affected the expression of PPARγ, and knockdown of PSF using specific small-interfering RNA (siRNA) significantly suppressed the proliferation of pancreatic cancer cells. Furthermore, PSF knockdown induced cell growth inhibition and autophagosome formation through inhibition of PPARγ. Interestingly, Panc-1 cells were more susceptible to PSF knockdown-induced autophagy than MIA-PaCa-2 cells. Thus, our data indicated that PSF was an important regulator of autophagy and played critical roles in the survival and growth of pancreatic cancer cells. The PSF-PPARγ axis may play a role in the control of pancreatic cancer pathogenesis. This study is the first to describe the effects of PSF on pancreatic cancer cell growth and autophagy associated with PPARγ.

PSF: nuclear busy-body or nuclear facilitator?

PTB-associated splicing factor (PSF) is an abundant and essential nucleic acid-binding protein that participates in a wide range of gene regulatory processes and cellular response pathways. At the protein level, PSF consists of multiple domains, many of which remain poorly characterized. Although grouped in a family with the proteins p54nrb/NONO and PSPC1 based on sequence homology, PSF contains additional protein sequence not included in other family members. Consistently, PSF has also been implicated in functions not ascribed to p54nrb/NONO or PSPC1. Here, we provide a review of the cellular activities in which PSF has been implicated and what is known regarding the mechanisms by which PSF functions in each case. We propose that the complex domain arrangement of PSF allows for its diversity of function and integration of activities. Finally, we discuss recent evidence that individual activities of PSF can be regulated independently from one another through the activity of domain-specific co-factors.

Long non-coding RNAs drive metastatic progression in melanoma (Review)

Metastatic melanoma is the leading cause of skin-cancer related deaths and while in recent years some progress has been made with targeted therapies, there remains an urgent unmet need for novel therapeutic treatments and reliable diagnostic, prognostic and predictive biomarkers. The emergence of next generation sequencing (NGS) has seen a growing appreciation for the role played by non-coding genomic transcripts in regulating gene expression and by extension impacting on disease progression. The long non-coding RNAs (lncRNAs) represent the most enigmatic of these new regulatory molecules. Our understanding of how lncRNAs regulate biological functions and their importance to disease aetiology, while still limited, is rapidly improving, in particular with regards to their role in cancer. Herein we review the identification of several lncRNAs shown to impact on melanoma disease progression and discuss how these molecules are operating at the molecular level.