PHF6 Expression Levels Impact Human Hematopoietic Stem Cell Differentiation

Abstract

Transcriptional control of hematopoiesis involves complex regulatory networks and functional perturbations in one of these components often results in malignancies. Loss-of-function mutations in PHF6 , encoding a presumed epigenetic regulator, have been primarily described in T cell acute lymphoblastic leukemia (T-ALL) and the first insights into its function in normal hematopoiesis only recently emerged from mouse modeling experiments. Here, we investigated the role of PHF6 in human blood cell development by performing knockdown studies in cord blood and thymus-derived hematopoietic precursors to evaluate the impact on lineage differentiation in well-established in vitro models. Our findings reveal that PHF6 levels differentially impact the differentiation of human hematopoietic progenitor cells into various blood cell lineages, with prominent effects on lymphoid and erythroid differentiation. We show that loss of PHF6 results in accelerated human T cell development through reduced expression of NOTCH1 and its downstream target genes. This functional interaction in developing thymocytes was confirmed in vivo using a phf6 -deficient zebrafish model that also displayed accelerated developmental kinetics upon reduced phf6 or notch1 activation. In summary, our work reveals that appropriate control of PHF6 expression is important for normal human hematopoiesis and provides clues towards the role of PHF6 in T-ALL development.

PHF6 Mutations in Hematologic Malignancies

“…Supporting a fundamental role for PHF6 in general development, PHF6-homozygous knockout mice die perinatally (9). However, scientists have also developed various knockout models in mice to explore the role of PHF6 in hematopoiesis (8,(10)(11)(12)(13). McRae et al showed that germline deletion of murine PHF6 is lethal in males whereas heterozygous females survived to adulthood (10).…”

“…Supporting a fundamental role for PHF6 in general development, PHF6- homozygous knockout mice die perinatally ( 9 ). However, scientists have also developed various knockout models in mice to explore the role of PHF 6 in hematopoiesis ( 8 , 10 – 13 ). McRae et al.…”

“…However, conditional knockout of PHF6 does show a mild reduction in double-negative DN2 and DN3 thymic progenitors and decreased numbers of peripheral blood CD4 and CD8 positive T-cells in 8-week-old mice ( 10 , 11 , 13 ). Moreover, knockdown studies in cord blood and thymus-derived hematopoietic precursors showed that PHF6 loss fosters a preferential differentiation of B-lymphocytes, reduced erythroid development, and accelerated T-cell development via downregulation of NOTCH1 ( 8 ).…”

“…PHF6 contains two imperfect PHD-like zinc finger domains, two nuclear localization signals as well as a nucleolar localization sequence (Figure 1) (2,(4)(5)(6). Expression of PHF6 is found in almost all tissues, with particularly high expression in the brain/developing central nervous system as well as in all hematopoietic subpopulations (high levels in CD34+ precursor cells and B-cells; low levels in NK-cells and monocytes) implicating a role for PHF6 in a variety of functions including neurogenesis and hematopoiesis (2,7,8).…”

Uncovering perturbations in human hematopoiesis associated with healthy aging and myeloid malignancies at single cell resolution

“…HSPCs from the patient with MDS showed an increased levels of transcription factors involved in the prevention of erythropoiesis such as JUN, YBX1, LMO2, and LYL1 (36,37). On the other hand, the expression of genes such as SLC25A6, EPSTI1 and PHF6, which play a prominent role in the promotion of erythroid differentiation, failed to raise in HSPCs from this patient (38,39). Despite these changes, we observed that essential drivers of erythropoiesis (GATA1, and KLF1) as well as erythroid specific markers (AHSP, CA1, and HBB) followed trends similar to those of healthy HSPCs, which is in agreement with the apparently normal progression of differentiation at the progenitor stages.…”