Transcriptome analysis of human OXR1 depleted cells reveals its role in regulating the p53 signaling pathway

Purpose: The oxidation resistance gene 1 (OXR1) is crucial for protecting against oxidative stress, limiting neurodegeneration and maintaining normal lifespan in eukaryotes. However, the molecular function of OXR1 is still unknown. Previously we showed that human OXR1 regulates expression of antioxidant genes GPX2 and HO-1 via the p21 signaling pathway. To examine the role of hOXR1 in global transcription regulation during cellular stress, we employed RNA sequencing to investigate the transcription profile in hOXR1 depleted HeLa cells. Methods: Control siRNA (siCon) and human OXR1 siRNA (siOXR1) transfected HeLa cells were either harvested directly (siCon_NT, siOXR1_NT) or exposed to 0.5 mM H2O2 for 1 h and then harvested immediately without recovery (siCon_R0h, siOXR1_R0h). Total RNA pooled from duplicate samples was used for RNA sequencing on an Illumina HiSeq2000 platform. The sequence reads that passed quality filters were analyzed at gene level. The Blast2GO program was used to generate gene ontology (GO) annotation of differentially expressed genes (DEGs).The WEGO software was used to further perform GO functional classification and to predict pathways affected. qRT–PCR validation was performed using SYBR Green assays. Results: In total, in non-treated and hydrogen peroxide exposed cells, hOXR1 depletion results in the down-regulation of 554 genes and the up-regulation of 253 genes. These differentially expressed genes include transcription factors (i.e. HIF1A, SP6, E2F8 and TCF3) and numerous genes of the p53 signaling pathway involved in cell-cycle arrest (i.e. cyclin D, CDK6 and p21) and apoptosis (i.e. CytC and CASP9). Western blot analysis reveals that hOXR1 suppresses CASP9 protein expression and reduces post-translational cleavage into its active form. After exposure to hydrogen peroxide (1 h), 56 early response genes were up-regulated in hOXR1 depleted cells, in which 38 of these genes were not induced in control cells. In addition, a subset of the commonly up-regulated early response genes showed a stronger induction in hOXR1 depleted cells (i.e. FOS, JUN and DUSP1). Out of a total of 52 differentially expressed transcription factors in hOXR1 depleted cells under normal physiology and oxidative stress condition, 14 genes (including HIF1A, STAT5A, E2F8 and TCF3) are differentially regulated under H2O2 treatment in hOXR1 silenced cells as compared to control cells. Finally, we demonstrate that hOXR1 depleted cells undergo cell cycle arrest in G2/M phase during oxidative stress. Conclusions: Human OXR1 is important for regulation of the early stress response to oxidative stress in HeLa cells. HOXR1 modulates the p53 signaling pathway via regulation of genes involved in cell cycle arrest, apoptosis and anti-oxidation. Further, hOXR1 regulates numerous transcription factors of importance for cellular stress responses. In summary, hOXR1 may act as a sensor of cellular oxidative stress to regulate the transcriptional networks required to detoxify reactive oxygen species (ROS) and modulate cell cycle arrest and cell death (apoptosis). Overall design: The mRNA profiles of hOXR1 depleted and control Hela cells with or without H2O2 treatment 1 h were generated by RNA sequencing using Illumina Hiseq 2000.

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Yang M, Lin X, Rowe A, Rognes T, Eide L, Bjørås M