The DEAD-box RNA helicase 51 controls non-small cell lung cancer proliferation by regulating cell cycle progression via multiple pathways

Where all the Roads Meet? A Crossover Perspective on Host Factors Regulating SARS-CoV-2 infection

COVID-19 caused by SARS-CoV-2 is the latest pandemic which has thrown the world into an unprecedented social and economic uncertainties along with huge loss to humanity. Identification of the host factors regulating the replication of SARS-CoV-2 in human host may help in the development of novel anti-viral therapies to combat the viral infection and spread. Recently, some research groups used genome-wide CRISPR/Cas screening to identify the host factors critical for the SARS-CoV-2 replication and infection. A comparative analysis of these significant host factors (p < 0.05) identified fifteen proteins common in these studies. Apart from ACE2 (receptor for SARS-CoV-2 attachment), other common host factors were CSNK2B, GDI2, SLC35B2, DDX51, VPS26A, ARPP-19, C1QTNF7, ALG6, LIMA1, COG3, COG8, BCOR, LRRN2 and TLR9. Additionally, viral interactome of these host factors revealed that many of them were associated with several SARS-CoV-2 proteins as well. Interestingly, some of these host factors have already been shown to be critical for the pathogenesis of other viruses suggesting their crucial role in virus-host interactions. Here, we review the functions of these host factors and their role in other diseases with special emphasis on viral diseases.

Knockdown of DEAD-box 51 inhibits tumor growth of esophageal squamous cell carcinoma via the PI3K/AKT pathway

BACKGROUND

Esophageal squamous cell carcinoma (ESCC) is one of the most prevalent malignancies that seriously threaten people’s health worldwide. DEAD-box helicase 51 (DDX51) is a member of the DEAD-box (DDX) RNA helicase family, and drives or inhibits tumor progression in multiple cancer types.

AIM

To determine whether DDX51 affects the biological behavior of ESCC.

METHODS

The expression of DDX51 in ESCC tumor tissues and adjacent normal tissues was detected by Immunohistochemistry (IHC) analyses and quantitative PCR (qPCR). We knocked down DDX51 in ESCC cell lines by using a small interfering RNA (siRNA) transfection. The proliferation, apoptosis, and mobility of DDX51 siRNA-transfected cells were detected. The effect of DDX51 on the phosphoinositide 3-kinase (PI3K)/AKT pathway was investigated by western blot analysis. A mouse xenograft model was established to investigate the effects of DDX51 knockdown on ESCC tumor growth.

RESULTS

DDX51 exhibited high expression in ESCC tissues compared with normal tissues and represented a poor prognosis in patients with ESCC. Knockdown of DDX51 induced inhibition of ESCC cell proliferation and promoted apoptosis. Moreover, DDX51 siRNA-expressing cells also exhibited lower migration and invasion rates. Investigations into the underlying mechanisms suggested that DDX51 knockdown induced inactivation of the PI3K/AKT pathway, including decreased phosphorylation levels of phosphate and tensin homolog, PI3K, AKT, and mammalian target of rapamycin. Rescue experiments demonstrated that the AKT activator insulin-like growth factor 1 could reverse the inhibitory effects of DDX51 on ESCC malignant development. Finally, we injected DDX51 siRNA-transfected TE-1 cells into an animal model, which resulted in slower tumor growth.

CONCLUSION

Our study suggests for the first time that DDX51 promotes cancer cell proliferation by regulating the PI3K/AKT pathway; thus, DDX51 might be a therapeutic target for ESCC.

The TSN1 Binding Protein RH31 Is a Component of Stress Granules and Participates in Regulation of Salt-Stress Tolerance in Arabidopsis

Tudor staphylococcal nucleases (TSNs) are evolutionarily conserved RNA binding proteins, which include redundant TSN1 and TSN2 in Arabidopsis. It has been showed TSNs are the components of stress granules (SGs) and regulate plant growth under salt stress. In this study, we find a binding protein of TSN1, RH31, which is a DEAD-box RNA helicase (RH). Subcellular localization studies show that RH31 is mainly located in the nucleus, but under salinity, it translocates to the cytoplasm where it accumulates in cytoplasmic granules. After cycloheximide (CHX) treatment which can block the formation of SGs by interfering with mRNP homeostasis, these cytoplasmic granules disappeared. More importantly, RH31 co-localizes with SGs marker protein RBP47. RH31 deletion results in salt-hypersensitive phenotype, while RH31 overexpression causes more resistant to salt stress. In summary, we demonstrate that RH31, the TSN1 binding protein, is a component of plant SGs and participates in regulation of salt-stress tolerance in Arabidopsis.

DEAD-Box RNA Helicases in Cell Cycle Control and Clinical Therapy

Cell cycle is regulated through numerous signaling pathways that determine whether cells will proliferate, remain quiescent, arrest, or undergo apoptosis. Abnormal cell cycle regulation has been linked to many diseases. Thus, there is an urgent need to understand the diverse molecular mechanisms of how the cell cycle is controlled. RNA helicases constitute a large family of proteins with functions in all aspects of RNA metabolism, including unwinding or annealing of RNA molecules to regulate pre-mRNA, rRNA and miRNA processing, clamping protein complexes on RNA, or remodeling ribonucleoprotein complexes, to regulate gene expression. RNA helicases also regulate the activity of specific proteins through direct interaction. Abnormal expression of RNA helicases has been associated with different diseases, including cancer, neurological disorders, aging, and autosomal dominant polycystic kidney disease (ADPKD) via regulation of a diverse range of cellular processes such as cell proliferation, cell cycle arrest, and apoptosis. Recent studies showed that RNA helicases participate in the regulation of the cell cycle progression at each cell cycle phase, including G1-S transition, S phase, G2-M transition, mitosis, and cytokinesis. In this review, we discuss the essential roles and mechanisms of RNA helicases in the regulation of the cell cycle at different phases. For that, RNA helicases provide a rich source of targets for the development of therapeutic or prophylactic drugs. We also discuss the different targeting strategies against RNA helicases, the different types of compounds explored, the proposed inhibitory mechanisms of the compounds on specific RNA helicases, and the therapeutic potential of these compounds in the treatment of various disorders.

RNA Helicases as Shadow Modulators of Cell Cycle Progression

The progress of the cell cycle is directly regulated by modulation of cyclins and cyclin-dependent kinases. However, many proteins that control DNA replication, RNA transcription and the synthesis and degradation of proteins can manage the activity or levels of master cell cycle regulators. Among them, RNA helicases are key participants in RNA metabolism involved in the global or specific tuning of cell cycle regulators at the level of transcription and translation. Several RNA helicases have been recently evaluated as promising therapeutic targets, including eIF4A, DDX3 and DDX5. However, targeting RNA helicases can result in side effects due to the influence on the cell cycle. In this review, we discuss direct and indirect participation of RNA helicases in the regulation of the cell cycle in order to draw attention to downstream events that may occur after suppression or inhibition of RNA helicases.

MAT2B promotes proliferation and inhibits apoptosis in osteosarcoma by targeting epidermal growth factor receptor and proliferating cell nuclear antigen

Osteosarcoma (OS) is the most commonly diagnosed bone tumor in young people with poor prognosis. At present, the mechanisms underlying tumorigenesis in OS are not well understood. The methionine adnosyltransferase 2B (MAT2B) gene encodes the regulatory subunit of methionine adenosyltransferase (MAT). Recent studies demonstrated that it is highly expressed in a number of human malignancies; however, is undefined in OS. In the present study, MAT2B expression was investigated in tumor samples and cell lines. In vivo and in vitro, lentivirus‑mediated small hairpin RNA was constructed to target the MAT2B gene and examine the role of MAT2B in OS proliferation. Microarray analysis was performed to examine the possible downstream molecular target of MAT2B in OS. MAT2B was markedly increased in OS specimens compared with the normal bone tissues, and it was additionally abundantly expressed in OS cell lines. Inhibition of MAT2B expression caused a marked decrease in proliferation and significant increase in apoptosis. In vivo, MAT2B silencing significantly inhibited OS cell growth. Microarray analysis suggested that epidermal growth factor receptor (EGFR) and proliferating cell nuclear antigen (PCNA) may function as downstream targets of MAT2B in OS, as confirmed by reverse transcription‑quantitative polymerase chain reaction assays and western blotting. Collectively, these results suggested that MAT2B serves a critical role in the proliferation of OS by regulating EGFR and PCNA and that it may be a potential therapeutic target and prognostic factor of OS.

DDX51 gene promotes proliferation by activating Wnt/β-catenin signaling in breast cancer

Breast cancer was a malignant tumor seriously threatening the life of women in the world. But the prognosis of breast cancer patients was not so satisfactory due to the limited effective therapeutics. The heterogeneity decided that more than one gene or one signaling pathway was responsible for the initiation or progression of breast cancer. DDX51 gene was a member of RNA helicases family in charge of regulation of RNA metabolism. And DDX51 gene was shown to promote proliferation in NSCLC. But we firstly reported the abundant expression of DDX51 gene in both the breast cancer tissues and cell lines in this study. And DDX51 expression was shown to be associated with TNM stage and prognosis in breast cancer patients. When DDX51 was successfully knocked down, either proliferation or DNA synthesis of MCF-7 cells was inhibited. But the ability of migration and invasion of MCF-7 cells was not affected by DDX51 gene. Furthermore, DDX51 knockdown was accompanied by inhibition of Wnt/β-catenin signaling because expression of critical members such as β-catenin, cyclin D1, TCF/LEF, and DKK1 were all affected. Therefore, this study proved that DDX51 gene promoted proliferation in MCF-7 cells by regulating Wnt/β-catenin signaling pathway and showed clinical significance in breast cancer. This study provides us a new promising hope for treatment of patients with breast cancer.

"Stealth dissemination" of macrophage-tumor cell fusions cultured from blood of patients with pancreatic ductal adenocarcinoma

Here we describe isolation and characterization of macrophage-tumor cell fusions (MTFs) from the blood of pancreatic ductal adenocarcinoma (PDAC) patients. The MTFs were generally aneuploidy, and immunophenotypic characterizations showed that the MTFs express markers characteristic of PDAC and stem cells, as well as M2-polarized macrophages. Single cell RNASeq analyses showed that the MTFs express many transcripts implicated in cancer progression, LINE1 retrotransposons, and very high levels of several long non-coding transcripts involved in metastasis (such as MALAT1). When cultured MTFs were transplanted orthotopically into mouse pancreas, they grew as obvious well-differentiated islands of cells, but they also disseminated widely throughout multiple tissues in "stealth" fashion. They were found distributed throughout multiple organs at 4, 8, or 12 weeks after transplantation (including liver, spleen, lung), occurring as single cells or small groups of cells, without formation of obvious tumors or any apparent progression over the 4 to 12 week period. We suggest that MTFs form continually during PDAC development, and that they disseminate early in cancer progression, forming "niches" at distant sites for subsequent colonization by metastasis-initiating cells.

Liquid biopsies in lung cancer-time to implement research technologies in routine care?

Lung cancer is the leading cause of cancer mortality. A substantial progress in the understanding of lung cancer biology has resulted in several promising targeted therapies for advanced disease. Druggable targets today include point mutations such as EGFR, BRAF and re-arrangements in genes such as ALK and ROS1. Liquid biopsies collecting e.g., circulating tumor DNA (ctDNA) reflects overall tumor information and is not biased by analyzing of only a small fraction of the tumor and is always accessible in contrast to the lung cancer tissue. Technological advances in detection of low frequency mutation variants in ctDNA have made it the dominating liquid biopsy platform in terms of utility and sensitivity. Circulating DNA or RNA may possible be used to define populations with higher risk of developing lung cancer, thus reducing screening cohorts and increasing the positive predictive value of screening. Blood based-tests may also aid to identify genetic alterations several weeks prior to radiologically verified recurrence and may be of great value in the follow-up of lung cancer patients. Besides being an alternative to invasive biopsies in selected cases, liquid biopsies offer a unique possibility to monitor treatment response following medical treatment as well as treatment response and resistance development after targeted therapy, giving a possibility to modify the treatment after the genetic profile of the tumor. Ideally, genetic alterations found in ctDNA could be tracked in real-time discriminating between fast-growing life-threatening tumors from more indolent slow growing tumors or premalignant growth that are of no concern for the wellbeing of the patient. This review focuses on future perspectives of liquid biopsies in lung cancer care for different clinical settings and present current technological platforms for further discussion of possible strategies for implementation of liquid biopsies in lung cancer.

Hypomethylation agent decitabine restores drug sensitivity by depressing P-glycoprotein activity through MAPK signaling pathway

The multidrug resistance (MDR) continues to be an obstacle in the treatment of both hematological and solid tumors. Hypomethylation agent, decitabine (5-Aza-dC), is an experimental agent in MDR therapy, while the mechanism is not very clear. In the present study, we demonstrated 5-Aza-dC may reverse MDR induced by P-glycoprotein (P-gp) coded by mdr1 gene in both hematologic K562/ADR cells and solid tumor MCF-7/ADR cells with time and dose-dependent manner. 5-Aza-dC significantly increased drug sensitivity in patients' leukemic cells which had higher expression of mdr1 gene. Both total protein and membrane P-gp expression were up-regulated with 5-Aza-dC treatment in K562/ADR and MCF-7/ADR cells. However, accumulation of adriamycin and rhodamine 123 were increased which suggested the depression of P-gp activity. Gene expression profiling was performed and activation of MAPK signaling pathway was identified as the most significant change affected by 5-Aza-dC. Inhibition of MAPK pathway could increase P-gp activity. Our data suggested that hypomethylation agent decitabine restores drug sensitivity in the P-gp-induced MDR phenotype by depressing of P-gp activity as drug pump partly through MAPK signaling pathway.

Live kinase B1 maintains CD34+CD38- AML cell proliferation and self-renewal

Live kinase B1 (LKB1) has been recognized as a tumor suppressor in many human cancers; however, LKB1 maintains self-renewal of hematopoietic stem cells (HSCs). The existence of leukemia stem cells (LSCs) is responsible for drug resistance and leukemia relapse. In acute myeloid leukemia (AML), CD34⁺CD38^- fraction is the most enriched compartment for LSCs. We found that LKB1 was upregulated in CD34⁺CD38^- AML cells. LKB1 downregulation suppressed the long-term proliferation of CD34⁺CD38^- AML cells, induced CD34⁺CD38^- AML cells into G2/M phase, and enhanced the sensitivity of CD34⁺CD38^- AML cells to chemotherapy. Furthermore, LKB1 downregulation in CD34⁺CD38^- AML cells inhibited tumor formation in NOD-SCID mice. Downregulation of LKB1 gene makes LSCs partly loose the characters as stem cells. Gene expression microarray showed that MAPK/ERK pathway was implicated in the regulation of CD34⁺CD38^- AML cell proliferation by LKB1. Together, these findings demonstrate that LKB1 plays an important role in the maintenance of LSCs, which may be responsible for drug resistance and AML relapse.