DRP004318
Phf6 restricts the self-renewal of hematopoietic stem cells via regulation of Nr4a1 expression
Recurrent inactivating mutations have been identified in various hematological malignancies in the X-linked PHF6 gene. However, it is currently unknown how PHF6 regulates normal hematopoiesis and how inactivation of PHF6 contributes to leukemogenesis. To get insight into this, we generated a mouse line carrying floxed Phf6 allele and inactivated Phf6 in hematopoietic cells at various developmental stages. Vav1-Cre mediated fetal Phf6 deletion promoted the proliferation of hematopoietic stem cell (HSC) in vitro and reconstitution capacity of adult HSCs without affecting the HSC pool size in donor mice. Phf6 deletion in postnatal or adult stages with Mx1-Cre; Phf6fl/y mice demonstrated that cycling HSCs efficiently acquires competitive advantage upon Phf6 deletion in compared with dormant HSCs.  Although inducible Phf6 deletion with RosaCreERT deletor in competitively engrafted recipients did not increase chimerism of Phf6d/y cells in primary recipients, Phf6d/y cells strikingly outcompeted competitors upon secondary transplantation. These data exhibit that Phf6 loss augments HSC self-renewal only in stress conditions. Moreover, expression profiling and molecular analysis revealed that negative enrichment of gene set for TNFa in Phf6d/y HSCs, reduced expression of Nr4a1 which is known to be induced by TNFa signaling pathway and NR4A1 is direct down-stream target of PHF6.  Beside, loss- and gain-of-function analysis revealed Nr4a1 negatively regulates HSCs proliferation as Phf6 does.  Our findings demonstrate that Phf6 is a novel negative regulator of HSC self-renewal and imply a role of inactivating PHF6 mutations in leukemogenesis.