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

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.