The interferon-regulated host factor hnRNPA0 modulates HIV-1 production by interference with LTR activity, mRNA trafficking, and programmed ribosomal frameshifting.

The interplay between host factors and viral components impacts viral replication efficiency profoundly. Members of the cellular heterogeneous nuclear ribonucleoprotein family (hnRNPs) have been extensively studied as HIV-1 host dependency factors, but whether they play a role in innate immunity is currently unknown. This study aimed to identify hnRNPA0 as a type I interferon (IFN)-repressed host factor in HIV-1-infected cells. Knockdown of hnRNPA0, a situation that mirrors conditions under IFN stimulation, increased LTR activity, export of unspliced HIV-1 mRNA, viral particle production, and thus, increased infectivity. Conversely, hnRNPA0 overexpression primarily reduced plasmid-driven and integrated HIV-1 long terminal repeat (LTR) activity, significantly decreasing total viral mRNA and protein levels. In addition, high levels of hnRNPA0 significantly reduced the HIV-1 programmed ribosomal frameshifting efficiency, resulting in a shift in the HIV-1 p55/p15 ratio. The HIV-1 alternative splice site usage remained largely unaffected by altered hnRNPA0 levels suggesting that the synergistic inhibition of the LTR activity and viral mRNA transcription, as well as impaired ribosomal frameshifting efficiency, are critical factors for efficient HIV-1 replication regulated by hnRNPA0. The pleiotropic dose-dependent effects under high or low hnRNPA0 levels were further confirmed in HIV-1-infected Jurkat cells. Finally, our study revealed that hnRNPA0 levels in PBMCs were lower in therapy-naive HIV-1-infected individuals compared to healthy controls. Our findings highlight a significant role for hnRNPA0 in HIV-1 replication and suggest that its IFN-I-regulated expression levels are critical for viral fitness allowing replication in an antiviral environment.IMPORTANCERNA-binding proteins, in particular, heterogeneous nuclear ribonucleoproteins (hnRNPs), have been extensively studied. Some act as host dependency factors for HIV-1 since they are involved in multiple cellular gene expression processes. Our study revealed hnRNPA0 as an IFN-regulated host factor, that is differently expressed after IFN-I treatment in HIV-1 target cells and lower expressed in therapy-naïve HIV-1-infected individuals. Our findings demonstrate the significant pleiotropic role of hnRNPA0 in viral replication: In high concentrations, hnRNPA0 limits viral replication by negatively regulating Tat-LTR transcription, retaining unspliced mRNA in the nucleus, and significantly impairing programmed ribosomal frameshifting. Low hnRNPA0 levels as observed in IFN-treated THP-1 cells, particularly facilitate HIV LTR activity and unspliced mRNA export, suggesting a role in innate immunity in favor of HIV replication. Understanding the mode of action between hnRNPA0 and HIV-1 gene expression might help to identify novel therapeutically strategies against HIV-1 and other viruses.

hnRNPA0 promotes MYB expression by interacting with enhancer lncRNA MY34UE-AS in human leukemia cells.

MYB is a key regulator of hematopoiesis and erythropoiesis, and dysregulation of MYB is closely involved in the development of leukemia, however the mechanism of MYB regulation remains still unclear so far. Our previous study identified a long noncoding RNA (lncRNA) derived from the -34 kb enhancer of the MYB locus, which can promote MYB expression, the proliferation and migration of human leukemia cells, and is therefore termed MY34UE-AS. Then the interacting partner proteins of MY34UE-AS were identified and studied in the present study. hnRNPA0 was identified as a binding partner of MY34UE-AS through RNA pulldown assay, which was further validated through RNA immunoprecipitation (RIP). hnRNPA0 interacted with MY34UE-AS mainly through its RRM2 domain. hnRNPA0 overexpression upregulated MYB and increased the proliferation and migration of K562 cells, whereas hnRNPA0 knockdown showed opposite effects. Rescue experiments showed MY34UE-AS was required for above mentioned functions of hnRNPA0. These results reveal that hnRNPA0 is involved in leukemia through upregulating MYB expression by interacting with MY34UE-AS, suggesting that the hnRNPA0/MY34UE-AS axis could serve as a potential target for leukemia treatment.

LncRNA LIMp27 Regulates the DNA Damage Response through p27 in p53-Defective Cancer Cells.

P53 inactivation occurs in about 50% of human cancers, where p53-driven p21 activity is devoid and p27 becomes essential for the establishment of the G1/S checkpoint upon DNA damage. Here, this work shows that the E2F1-responsive lncRNA LIMp27 selectively represses p27 expression and contributes to proliferation, tumorigenicity, and treatment resistance in p53-defective colon adenocarcinoma (COAD) cells. LIMp27 competes with p27 mRNA for binding to cytoplasmically localized hnRNA0, which otherwise stabilizes p27 mRNA leading to cell cycle arrest at the G0/G1 phase. In response to DNA damage, LIMp27 is upregulated in both wild-type and p53-mutant COAD cells, whereas cytoplasmic hnRNPA0 is only increased in p53-mutant COAD cells due to translocation from the nucleus. Moreover, high LIMp27 expression is associated with poor survival of p53-mutant but not wild-type p53 COAD patients. These results uncover an lncRNA mechanism that promotes p53-defective cancer pathogenesis and suggest that LIMp27 may constitute a target for the treatment of such cancers.

LncRNA miR205HG hinders HNRNPA0 translation: anti-oncogenic effects in esophageal carcinoma.

Esophageal carcinoma (ESCA) affects 4 450 000 people and causes approximately 400 000 deaths annually worldwide, making it the sixth most lethal and eighth most common cancer. Patients with ESCA are often diagnosed at the later stages in which cancer cell metastasis is the main factor contributing to the low 5-year survival rate (< 20%) of this disease. Long noncoding RNAs (lncRNAs) are a group of regulatory RNAs with a length of > 200 nucleotides but which fail to encode proteins. In this study, by using real-time quantitative PCR, we found that the expression of the miR205 host gene (miR205HG; a lncRNA) was downregulated in ESCA tumors when compared with normal esophageal tissues or adjacent normal tissues of tumors. Furthermore, we demonstrated that miR205HG modulates the expression of extracellular matrix-related genes in ESCA cells. In the transwell assay, downregulation of miR205HG contributes to migration and invasion of ESCA cells. In relation to the mechanism, our data show that miR205HG interacts with heterogeneous nuclear ribonucleoprotein A0 (HNRNPA0) mRNA and then hamper its translation by interacting with lin-28 homolog A (LIN28A). Altogether, we highlight that the miR205HG-HNRNPA0 axis is implicated in the migration and invasion of ESCA cells and that these members of this pathway may serve as therapeutic targets to inhibit metastasis of ESCA.

RNA-binding Protein, GADD45-alpha, p27Kip1, p53 and Genotoxic Stress Response in Relation to Chemoresistance in Cancer.

Genotoxic chemotherapeutics particularly cisplatin remain effective for clinical management of various malignancies including lung cancer. However, the development of chemoresistance leads to treatment failure. The mechanisms by which tumor cells acquire resistance to chemotherapy are multifaceted in nature and some remain to be fully elucidated. Recently, a potential role of RNA-binding protein hnRNPA0 in chemoresistance of p53-defective lung cancer cells was reported. Genotoxic (DNA damaging) chemotherapy was reported to activate hnRNPA0 which in turn post-transcriptionally regulated p27Kip1 and Gadd45-alpha by stabilizing their mRNAs. Regulation of p27Kip1 and Gadd45-alpha led to enforcement of G1/S and G2/M checkpoints thereby providing time for DNA repair and thus, resistance to chemotherapy. The identification of a signaling network involving the kinase MK2, hnRNPA0, p27Kip1 and Gadd45-alpha that may predict response to chemotherapy is an interesting finding. Further studies are now needed to gain additional insights as to whether this network is restricted only to a subset of tumors or more broadly relevant across multiple tumor types.