Bone marrow failure, somatic rescue by p53 inactivation, and enhanced leukemogenesis in germ line ERCC6L2 disease

Abstract

<p>Recessively inherited loss-of-function mutations in excision repair cross-complementing 6–like 2 (<em>ERCC6L2</em>) cause a bone marrow failure (BMF) syndrome characterized by moderate cytopenias, frequent somatic <em>TP53</em> mutations, and a propensity to develop myeloid malignancies. The pathophysiology and molecular mechanisms underlying the BMF syndrome as well as its association with <em>TP53</em>-mutant clonal hematopoiesis and myeloid malignancies have remained poorly understood. Using novel preclinical in vitro and in vivo model systems, we demonstrate that Ercc6l2 maintains the competitive fitness of hematopoietic stem and progenitor cells (HSPCs) by mitigating replication stress. Sustained replication stress and DNA damage in Ercc6l2-deficient HSPCs cause p53 pathway activation followed by cell cycle arrest and apoptosis. Moreover, Ercc6l2 deficiency results in decreased expression of master hematopoietic regulators <em>Runx1</em> and <em>Gata1</em> in HSPCs. Altogether, loss of Ercc6l2 leads to reduced HSPC numbers, bone marrow hypocellularity, and cytopenias. Notably, somatic <em>Trp53</em> mutations restore cellular fitness of Ercc6l2-deficient HSPCs by abrogating p53 pathway activation and restoring <em>Runx1</em> and <em>Gata1</em> expression, thereby correcting the BMF phenotype. However, p53 loss fails to normalize replication stress, allowing for the accumulation of DNA damage over time, which increases the likelihood for leukemic transformation. Our data uncover the pathogenesis of ERCC6L2 disease and provide a prototypic example of clonal compensation in BMF syndromes, in which somatic mutations in leukemia-associated genes, in this case <em>TP53</em>, transiently improve blood cell production at, however, the expense of increasing leukemogenic potential.</p>