Alu- and 7SL RNA Analogues Suppress MCF-7 Cell Viability through Modulating the Transcription of Endoplasmic Reticulum Stress Response Genes

Abstract

11% of the human genome is composed of Alu-retrotransposons, whose transcription by RNA polymerase III (Pol III) leads to the accumulation of several hundreds to thousands of Alu-RNA copies in the cytoplasm. Expression of Alu-RNA Pol III is significantly increased at various levels of stress, and the increase in the Alu-RNA level is accompanied by a suppression of proliferation, a decrease in viability, and induction of apoptotic processes in human cells. However, the question about the biological functions of Pol III Alu-transcripts, as well as their mechanism of action, remains open. In this work, analogues of Alu-RNA and its evolutionary ancestor, 7SL RNA, were synthesized. Transfection of human breast adenocarcinoma MCF-7 cells with the Alu-RNA and 7SL RNA analogues is accompanied by a decrease in viability and by induction of proapoptotic changes in these cells. The analysis of the combined action of these analogues and actinomycin D or tamoxifen revealed that the decreased viability of MCF-7 cells transfected with Alu-RNA and 7SL RNA was due to the modulation of transcription. A whole transcriptome analysis of gene expression revealed that increased gene expression of the transcription regulator NUPR1 (p8), as well as the transcription factor DDIT3 (CHOP), occurs under the action of both the Alu- and 7SL RNA analogues on MCF-7 cells. It has been concluded that induction of proapoptotic changes in human cells under the influence of the Alu-RNA and 7SL RNA analogues is related to the transcriptional activation of the genes of cellular stress factors, including the endoplasmic reticulum stress response factors.

Evolution of cellular stress response mechanisms

“…Nearly half of the human and other animal genomes are susceptible to transposition between different genomic loci (Finley, 2018). For example, Alu-retrotransposons comprise 11% of the human genome (Baryakin et al, 2013). Transcription of Alu-RNA and its evolutionary ancestor 7SL-RNA by RNA…”

“…Stress-induced transcription of these elements may be accompanied by an increase in the rate of their genomic transposition. It has been suggested that Alu/7SL transcripts contribute to the activation of key CSR functions such as cell cycle checkpoints and apoptosis (Baryakin et al, 2013).…”

Transposable elements, circular RNAs and mitochondrial transcription in age-related genomic regulation

“…Non-specific effects of Alu (i.e. effects that mirror those of 7SL RNA, from which Alu is believed to be derived) are observed (Baryakin et al, 2013;Herbert, 2019). Specifically, MCF-7 cells transfected with either Alu or 7SL RNA do not robustly induce interferon-inducible gene expression, but do show modulation of pro-apoptotic changes in expression of genes such as NUPR1, DDIT3 and FOXRED2 (Baryakin et al, 2013).…”

Alu RNA Modulates the Expression of Cell Cycle Genes in Human Fibroblasts

“…An early study based on the transient transfection of HeLa cells with Alu -carrying plasmids showed an Alu -dependent inhibition of cell proliferation, yet this effect could not be demonstrated to be caused by Alu RNA [29]. More recently, Alu and 7SL RNA transfection into MCF7 breast adenocarcinoma cells was found to entail a decrease in viability and an induction of pro-apoptotic changes [30]. In another recent study, Alu RNA transfection into the SW480 colorectal cancer cell line was instead found to be without effect on cell viability and cell cycle distribution, yet to induce epithelial-to-mesenchymal transition [27].…”

“…Recently, Di Ruocco et al [27] found no perturbation of cell cycle distribution of colorectal cancer cells in response to the transient transfection of a synthetic Alu . On the other hand, Sakamoto et al [29] previously found that HeLa cell growth was inhibited after the transient transfection of endogenous and synthetic Alu sequences, and Baryakin et al [30] showed that the transient transfection of an Alu -RNA analogue suppresses cell proliferation and induces apoptosis of breast cancer cells. In line with this, Hu et al [31] reported an inhibition of stem cell proliferation after the microinjection of an AluSx overexpressing vector in Ntera2 cells; Morales-Hernandèz et al [32] showed that the transient transfection of the NANOG Alu sequence (localized upstream of the NANOG gene) repressed the expression of the pluripotency genes OCT4 and NANOG in Ntera cells; and Castelnuovo et al [33] reported a differentiation-promoting effect of an Alu -like RNA in neuroblastoma cells.…”