The downregulation of the RNA-binding protein Staufen2 in response to DNA damage promotes apoptosis

Abstract

Staufen2 (Stau2) is an RNA-binding protein involved in cell fate decision by controlling several facets of mRNA processing including localization, splicing, translation and stability. Herein we report that exposure to DNA-damaging agents that generate replicative stress such as camptothecin (CPT), 5-fluoro-uracil (5FU) and ultraviolet radiation (UVC) causes downregulation of Stau2 in HCT116 colorectal cancer cells. In contrast, other agents such as doxorubicin and ionizing radiation had no effect on Stau2 expression. Consistently, Stau2 expression is regulated by the ataxia telangiectasia and Rad3-related (ATR) signaling pathway but not by the DNA-PK or ataxia telangiectasia mutated/checkpoint kinase 2 pathways. Stau2 downregulation is initiated at the level of transcription, independently of apoptosis induction. Promoter analysis identified a short 198 bp region which is necessary and sufficient for both basal and CPT-regulated Stau2 expression. The E2F1 transcription factor regulates Stau2 in untreated cells, an effect that is abolished by CPT treatment due to E2F1 displacement from the promoter. Strikingly, Stau2 downregulation enhances levels of DNA damage and promotes apoptosis in CPT-treated cells. Taken together our results suggest that Stau2 is an anti-apoptotic protein that could be involved in DNA replication and/or maintenance of genome integrity and that its expression is regulated by E2F1 via the ATR signaling pathway.

STAU2 Protein Level is Controlled by Caspases and the CHK1 Pathway and Regulates Cell Cycle Progression in the Non-transformed hTERT-RPE1 Cells

“…This loop likely contributes to the ne-tuning of cell proliferation in changing cell environment. The regulation of STAU2 at the protein level is in addition to that already observed at the transcriptional level by the transcription factor E2F1 [25]. Regulation of STAU2 by the E2F1 and CHK1 pathways that induce and facilitate S phase progression and DNA surveillance suggests a role for STAU2 in pathways that merge with mechanisms of DNA replication and/or DNA maintenance during S phase.…”

“…The hyper-proliferative phenotype that results from the misregulation of these RNAbinding proteins is often followed by an accumulation of DNA damage due to the loss of cell cycle checkpoints [41,42]. Accumulation of DNA damages are indeed observed in STAU2-KO hTERT-RPE1 cells (Additional Fig S4) and in RNAi-mediated STAU2 knockdown in HCT116 cells [25]. Oncogenic transformation may also explain why tumor cells are not affected by STAU2 depletion.…”

“…2A) that disappeared in STAU2-KO cells (not shown), suggesting a partial cleavage of STAU2 by speci c peptidases in unstressed cells. Therefore, as STAU2 functions are linked to cell proliferation and apoptosis [25], we asked whether caspases, whose activities are, among others, linked to these processes [26], can modulate the steady-state levels of STAU2 in hTERT-RPE1 and HCT116 cells. Interestingly, the pan-caspase inhibitor ZVAD-FMK increased the steady-state levels of STAU2 indicating that caspases contribute to STAU2 degradation in unstressed cells (Fig.…”

“…STAU2 is also linked to the DNA damage response and the apoptotic pathway since STAU2 depletion causes an accumulation of DNA damage and facilitates apoptosis in the HCT116 cancer cell line [25]. In addition, induction of singlestranded break causes the inhibition of STAU2 transcription as a consequence of delocalization of the transcription factor E2F1 from the STAU2 promoter [25].…”

RNA toxicity and foci formation in microsatellite expansion diseases

“…Evidence to support such notion has been observed in Myotonic dystrophy type 1 (DM1), Spinocerebellar ataxia type 8 or 10 (SCA8/10), C9orf72-amyotrophic lateral sclerosis/frontotemporal dementia (C9orf72-ALS/FTD) and Fuchs endothelial corneal dystrophy (FECD) [37,51,69–71]. RBPs also participate in cellular processes such as DNA repair, transcription regulation, RNA processing/transport/localization, microRNA (miRNA) processing, protein quality control and apoptosis [72–74]. Disruption of such processes by foci sequestration may further exacerbate neuronal toxicity.…”