Inhibition of DEK contributes to the tolerance of replication stress and restores HSC function in Fanconi anemia [13-CUT-Tag]

Replication stress drives functional decline in HSCs and is a major driver of BM failure in Fanconi anemia (FA). At present, how HSCs respond and counteract replication stress remains largely unknown. Using integrated multi-omics, we demonstrate that global chromatin relaxation is a prerequisite for the activation of stress-responsive genes and replication fork stabilization/progression in HSCs under replication stress. The reduced DEK (a chromatin architectural protein) contributes to the chromatin relaxation in HSCs, whereas DEK-overexpressed HSCs are confronted with a strong replication challenge, resulting in impaired HSC maintenance and hematopoiesis. Fancd2 deletion induces DEK expression and causes replication stress in HSCs, while haploinsufficiency of DEK promotes chromatin opening in Fancd2-deficient HSCs and substantially recovers HSC function. Notably, DEK expression is abnormally up-regulated in bone marrow (BM) CD34+ cells from FA patients. Inhibition of DEK significantly restores the proliferation capacity in vitro and engraftment in vivo of BM CD34+ cells from FA patients. At the molecular level, we identify that the transcriptional factor ATF2 directly promotes DEK transcription, mainly relying on the phosphorylated ATF2 (Thr69/71). Wild-type HSCs reduces DEK expression to counteract replication stress through the ATR kinase to phosphorylate ATF2 at Ser490/498. However, Fancd2 deficiency induces hyper-phosphorylation of p38 that further phosphorylates ATF2 at Thr69/71, causing DEK accumulation in HSCs. Collectively, our findings provide the first evidence of a functional link between chromatin relaxation and replication stress tolerance in HSCs, and highlight DEK as a potential molecular target for FA.