PIWI proteins contribute to apoptosis during the UPR in human airway epithelial cells

Abstract

Small noncoding microRNAs (miRNAs) post-transcriptionally regulate a large portion of the human transcriptome. miRNAs have been shown to play an important role in the unfolded protein response (UPR), a cellular adaptive mechanism that is important in alleviating endoplasmic reticulum (ER) stress and promoting cell recovery. Another class of small noncoding RNAs, the Piwi-interacting RNAs (piRNAs) together with PIWI proteins, was originally shown to play a role as repressors of germline transposable elements. More recent studies, however, indicate that P-element induced WImpy proteins (PIWI proteins) and piRNAs also regulate mRNA levels in somatic tissues. Using genome-wide small RNA next generation sequencing, cell viability assays, and caspase activity assays in human airway epithelial cells, we demonstrate that ER stress specifically up-regulates total piRNA expression profiles, and these changes correlate with UPR-induced apoptosis as shown by up-regulation of two pro-apoptotic factor mRNAs, CHOP and NOXA. Furthermore, siRNA knockdown of PIWIL2 and PIWIL4, two proteins involved in piRNA function, attenuates UPR-related cell death, inhibits piRNA expression, and inhibits the up-regulation of CHOP and NOXA mRNA expression. Hence, we provide evidence that PIWIL2 and PIWIL4 proteins, and potentially the up-regulated piRNAs, constitute a novel epigenetic mechanism that control cellular fate during the UPR.

Biopathological Significance of PIWI–piRNA Pathway Deregulation in Invasive Breast Carcinomas

“…Regarding PIWIL4, lack of correlation between its level of expression and methylation status of its promoter suggests another mechanism of inactivation ( Figure S5 ). These results are in partial agreement with several mechanisms of deregulation recently mentioned in the literature, such as epigenetic inactivation of the PIWIL2 gene by hypermethylation of promoters CpG islands and delocalization of PIWI proteins into cytoplasmic stress bodies [ 58 ]. PIWIL2 variants constitute a complex regulatory network that could partly explain versatility of PIWI proteins and contradictory results in the literature.…”

SARS-CoV-2 may regulate cellular responses through depletion of specific host miRNAs

“…For these studies, we analyzed data from a previous next-generation sequencing analysis of 16HBE14o-cells and primary HBEs. The deep sequencing data are deposited in the Gene Expression Omnibus (GEO) at accession number GSE117629 ) ( 37 ).…”

“…Both the increased ER membrane and the protein folding demand can result in coronavirus-related ER stress and activation of a dedicated signaling pathway, the unfolded protein response (UPR). Importantly, the UPR has the ability to promote cellular survival by increasing ER membranes and folding capacity, but also has the ability to induce cell death if the stress is persistent ( 5 , 8 , 10 , 37 , 45 , 51 , 104 ).…”

“…miRNA expression profiles are often cell-type specific and differ between individuals, and importantly, can be affected by cellular stress responses ( 11 , 12 ). In our recent study, we demonstrated that exposure of human lung epithelial cells to endoplasmic reticulum stress (ER stress) results in a global reduction of miRNA expression levels ( 37 ) and may also lead to activation of a miRNA-based reduction of antigen presentation ( 7 ). Notably, ER stress and the downstream activation of stress responses has been reported during coronavirus infections ( 16 , 35 ), and has been proposed to facilitate SARS-CoV replication ( 16 ).…”

Application of Real-Time Cell Electronic Analysis System in Modern Pharmaceutical Evaluation and Analysis

“…RTCA also provides a great method to follow the effects of gene silencing on cell survival. Gebert et al [40] used the xCELLigence RTCA system for real-time monitoring of cell viability. Immortalized human bronchial epithelial cells (16HBE14o-) were used as an unfolded protein response (UPR) cell fate model to determine UPR-related apoptosis induced by pharmacological endoplasmic reticulum (ER) stress.…”