CABLES1 Deficiency Impairs Quiescence and Stress Responses of Hematopoietic Stem Cells in Intrinsic and Extrinsic Manners

Bone marrow (BM) niche cells help to keep adult hematopoietic stem cells (HSCs) in a quiescent state via secreted factors and induction of cell-cycle inhibitors. Here, we demonstrate that the adapter protein CABLES1 is a key regulator of long-term hematopoietic homeostasis during stress and aging. Young mice lacking Cables1 displayed hyperproliferation of hematopoietic progenitor cells. This defect was cell intrinsic, since it was reproduced in BM transplantation assays using wild-type animals as recipients. Overexpression and short hairpin RNA-mediated depletion of CABLES1 protein resulted in p21^Cip/waf up- and downregulation, respectively. Aged mice lacking Cables1 displayed abnormalities in peripheral blood cell counts accompanied by a significant reduction in HSC compartment, concomitant with an increased mobilization of progenitor cells. In addition, Cables1^−/− mice displayed increased sensitivity to the chemotherapeutic agent 5-fluorouracil due to an abnormal microenvironment. Altogether, our findings uncover a key role for CABLES1 in HSC homeostasis and stress hematopoiesis. Maintenance of hematopoietic stem cell quiescence is crucial for homeostasis. Using mutant mice and cross-transplant experiments, Louache and colleagues show that the adapter protein CABLES1 is required for stem cell quiescence under transplantation and regulates p21^Cip/waf protein level. In addition, CABLES1 is a niche-based regulator of hematopoietic stem cell responses to proliferative stress and during aging.