MicroRNA 520b Mediates ATF5 Expression under Diverse Cellular Stress in Cancer Cells

Abstract

ATF5 is a widely expressed transcription factor that modulates cell survival, proliferation, and differentiation. It is upregulated during such diverse stresses as endoplasmic reticulum stress, amino acid deprivation, and oxidative stress. We had previously found that ATF5 is elevated and acts as a survival factor in several cancer cell lines compared to non‐transformed cells. Cellular stress pathways are implicated in cancer progression, treatment resistance, and metastasis, and upregulation of ATF5 has been implicated in each of these areas for several cancer types, including breast cancer. While the regulation of ATF5 expression is not fully understood, we hypothesize that microRNA (miRNA) play a role in regulating ATF5 under diverse cellular stress conditions. We used in silico analysis to identify potential miRNA candidates (129‐5p, 433‐3p, and 520b) and verified the ability of these candidates to interact with the ATF5 3′ untranslated region (UTR) by luciferase assay. In addition, miRNA were transfected into HeLa human cervical carcinoma cells and their capacity to regulate ATF5 expression was assessed under a variety of cellular stresses. Expression levels of ATF5 protein, ATF5 mRNA, and candidate miRNA were assessed by either Western blot analysis or RT‐qPCR. Of the three miRNA candidates, only miRNA 520b reversed the upregulation of ATF5 under diverse stress conditions in HeLa cells, resulting in a significant reduction (p<0.05) in ATF5 protein expression (~ 40% decrease) compared to control. Under stress conditions in non‐transfected HeLa cells, a rapid and significant decrease (p<0.05) in miRNA 520b (~70% reduction) was observed. This inversely correlated with a significant increase (p<0.05) in ATF5 mRNA (~2‐fold) and increased levels of protein expression (>2‐fold) in cells exposed to stress. Additionally, preliminary data indicate that the ability of miR‐520b to regulate ATF5 is also observed in other cell lines including MCF7 and MDA‐MD‐231 human breast adenocarcinoma cells. Further studies are warranted to determine the mechanism underlying the depressed levels of miRNA 520b under stress, and whether the upregulation of ATF5 in this context leads to enhanced cell survival. Our findings reveal a novel cellular stress‐activated mechanism of ATF5 regulation in cervical carcinoma and breast adenocarcinoma cells, which may lead to novel therapeutic interventions for breast and other cancers in the future.Support or Funding InformationThis work was supported by grants from the National Science Foundation Graduate Research Fellowship Program (grant DGE‐1347973 to Kari Gaither), and the Health Sciences and Services Authority of Spokane, Washington (grant WSU002292 to College of Pharmacy and Pharmaceutical Sciences, Washington State University).This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.