NDRG3 is a novel regulator of T and B cell development with phosphorylation-specific activity and phenotypes.

Abstract

Abstract Common lymphoid progenitors (CLPs) in the bone marrow give rise to both T and B cells, but the mechanisms underpinning downstream cell fate decisions have yet to be fully elucidated. We have identified N-Myc Downstream Regulated Gene 3 (NDRG3) - a highly conserved regulator of Wnt/B-catenin signaling - as a novel regulator of lymphocyte cell fate decisions and a substrate of Akt kinase. To determine the effect of NDRG3 phosphorylation, hematopoietic stem cells (HSCs) overexpressing a phospho-null (S331A) or phospho-mimetic (S331E) mutant of NDRG3 were transferred into lethally irradiated mice followed by analysis of the reconstituted immune populations. S331A-expressing cells developed a 3:1 preference for the T cell fate while those expressing S331E had a 9:1 preference for the B cell fate. To further probe the effects of NDRG3 phosphorylation, we developed a mouse model that utilizes IL-7Ra-driven Cre to express phospho-null NDRG3-S331A from the endogenous locus. NDRG3-S331A expressing thymocytes displayed a faster transition through the preTCR and TCR checkpoints. Given the importance of TCF1 in thymocyte development, NDRG3-S331A mice were crossed to TCF1-GFP and TCF1-RE-GFP reporter mice to examine effects on the Wnt/TCF1 signaling pathway. In the spleen, T cells were increase at the expense of B cells. Within the B cell population, NDRG3-S331A cells exhibited a 4:1 preference for the marginal zone to follicular B cell fate that was associated with increased levels of IRF4 and IRF8 transcription factors, which are necessary for proper B cell development. These data reveal that NDRG3 controls the developmental kinetics and pathways governing T and B cell development and maturation in a phosphorylation-dependent manner. Supported by NIH grant R01 AI089805 and a training fellowship from the Burroughs Wellcome Fund.