Altered expression of microRNAs in the response to ER stress

MicroRNAs, a class of small noncoding RNAs, play key roles in diverse biological and pathological processes. ER stress, resulting from the accumulation of unfolded or misfolded proteins in the ER lumen, is triggered by various physiological events and pathological insults. Here, using RNA deep sequencing analysis, we found that the expression of some microRNAs was altered in HeLa and HEK293 cells under ER stress. Protein and RNA levels of DGCR8, Drosha, Exportin-5, Dicer, and Ago2 showed no significant alteration in ER-stressed cells, which suggested that the change in microRNA expression might not be caused by the microRNA biogenesis pathway but by other, unknown factors. Real-time PCR assays confirmed that hsa-miR-423-5p was up-regulated, whereas hsa-miR-221-3p and hsa-miR-452-5p were down-regulated, in both HeLa and HEK293 cells under ER stress. Luciferase activity and Western blot assays verified that CDKN1A was a direct target of hsa-miR-423-5p and that CDKN1B was a direct target of hsa-miR-221-3p and hsa-miR-452-5p. We speculated that by regulating their targets, microRNAs might function cooperatively as regulators in the adaptive response to ER stress.