hnRNP Q and hnRNP A1 Regulate the Translation of Cofilin in Response to Transient Oxygen-Glucose Deprivation in Hippocampal Neurons

RNF144A-VRK2-G3BP1 axis regulates stress granule assembly

Under the cellular stress, stress granules (SGs) help survival and proliferation of the cell. Unfortunately, the same SGs help unwanted cancer cells under stressful environment, including anti-cancer chemotherapy treatment. While SGs elevate the cancer cell's resistance to chemotherapy, the mechanism behind the formation of SGs in cancer cell under chemotherapy treatment is still to be revealed. Here, we identified that the level of VRK2 and the phosphorylation of its novel substrate, G3BP1, are reduced when the cellular stress was increased by sodium arsenite (SA) or cisplatin treatment. We also demonstrated that the level of RNF144A is increased in response to the stress and further downregulates VRK2 through proteasomal degradation in various types of cancer cells. Furthermore, inhibition of SG formation by the overexpression of VRK2 sensitized the cells to the stress and chemotherapy. Together, our study establishes an RNF144A-VRK2-G3BP1 axis that regulates SG formation and suggest its potential usage in anti-cancer therapy.

Evolutionary Analysis of the hnRNP Interactomes and Their Functions in Eukaryotes

The heterogeneous nuclear ribonucleoproteins (hnRNPs) are central regulators of several fundamental biological processes across eukaryotes. hnRNPs have been implicated in transcriptional and post-transcriptional regulation, telomere maintenance, stem cell maintenance, among other processes in major model organisms. Though hnRNPs are known to be conserved in eukaryotes, the evolutionary conservation/diversification of their functions across species is yet to be understood. To this end, the present work employed computational analyses to identify potential hnRNP orthologs in eighty eukaryotic species, and their interactors. Subsequently, a comprehensive analysis of the biological processes influenced by hnRNP interactomes showed alternative splicing and splicing regulation to be commonly associated with most species, while a few processes were uniquely associated with particular species. Further studies of the clustering patterns of the top-ranking hub nodes of the hnRNP protein networks revealed a notable clustering pattern of hnRNP K orthologs from five species. Subsequent analysis of the genes with overrepresented hnRNP K target sites within their untranslated regions showed hnRNP K orthologs from humans and Ciona intestanilis to potentially target transcripts involved in membrane-related processes. Remarkably, the hnRNP K ortholog from Lottia gigantea was found to possibly regulate other RNA-binding proteins (RBPs), suggesting a regulatory cascade involving hnRNPs and other RBPs. Further experimental studies in this regard would be of scientific and clinical importance, owing to the druggability of several human hnRNPs.

m6A-Induced lncRNA MEG3 Promotes Cerebral Ischemia-Reperfusion Injury Via Modulating Oxidative Stress and Mitochondrial Dysfunction by hnRNPA1/Sirt2 Axis

Ischemic stroke remains one of the major causes of serious disability and death globally. LncRNA maternally expressed gene 3 (MEG3) is elevated in middle cerebral artery occlusion/reperfusion (MCAO/R) rats and oxygen-glucose deprivation/reperfusion (OGD/R)-treated neurocytes cells. The objective of this study is to investigate the mechanism underlying MEG3-regulated cerebral ischemia/reperfusion (I/R) injury. MCAO/R mouse model and OGD/R-treated HT-22 cell model were established. The cerebral I/R injury was monitored by TTC staining, neurological scoring, H&E and TUNEL assay. The levels of MEG3, hnRNPA1, Sirt2 and other key molecules were detected by qRT-PCR and western blot. Mitochondrial dysfunction was assessed by transmission Electron Microscopy (TEM), JC-1 and MitoTracker staining. Oxidative stress was monitored using commercial kits. Bioinformatics analysis, RIP, RNA pull-down assays and RNA FISH were employed to detect the interactions among MEG3, hnRNPA1 and Sirt2. The m6A modification of MEG3 was assessed by MeRIP-qPCR. MEG3 promoted MCAO/R-induced brain injury by modulating mitochondrial fragmentation and oxidative stress. It also facilitated OGD/R-induced apoptosis, mitochondrial dysfunction and oxidative stress in HT-22 cells. Mechanistically, direct associations between MEG3 and hnRNPA1, as well as between hnRNPA1 and Sirt2, were observed in HT-22 cells. MEG3 regulated Sirt2 expression in a hnRNPA1-dependent manner. Functional studies showed that MEG3/Sirt2 axis contributed to OGD/R-induced mitochondrial dysfunction and oxidative stress in HT-22 cells. Additionally, METTL3 was identified as the m6A transferase responsible for the m6A modification of MEG3. m6A-induced lncRNA MEG3 promoted cerebral I/R injury via modulating oxidative stress and mitochondrial dysfunction by hnRNPA1/Sirt2 axis.