Phosphatase Wip1 negatively regulates neutrophil development through p38 MAPK-STAT1

Abstract

IntroductionPolymorphonuclear neutrophil granulocytes (PMNs or neutrophils) develop in the bone marrow (BM). They are fully equipped with a variety of granules, which contain proteases that enable the neutrophils to deliver lethal hits against invading microorganisms. 1,2 Although neutrophils are essential to host defense against intruding microorganisms and play a critical role in initiating inflammation and innate immunity, they also contribute to the pathology of various acute and chronic inflammatory conditions. 3,4 In this manner, means to properly control the development, homeostasis, and functional activities of neutrophils is of central importance to mounting robust host defense responses and simultaneously avoiding tissue damage. 5,6 However, the molecular mechanisms that accomplish this balanced effect remain poorly understood.Wild-type (WT) p53-induced phosphatase 1 (Wip1, also called PP2C␦), which is encoded by protein phophatase magnesiumdependent 1delta (PPm1D), is a serine/threonine protein phosphatase belonging to the type 2C␦ protein phosphatases. 7 It is activated by various stresses and involved in various cellular processes, such as tumorigenesis and aging. 8,9 Wip1, overexpressed in many cancers, is recognized as a novel oncogene inhibiting several p53-dependent tumor suppressor pathways, such as ATM-CHK2-p53 and p38 MAPK-p53 pathways as well as the NF-B pathway. [10][11][12][13] Currently, Wip1 is thought to be a promising drug target for cancer therapy. In the present study, after observing that Wip1 is specifically expressed in resting neutrophils among all immune cells and is up-regulated gradually during neutrophil maturation, we used Wip1-deficient mice to investigate the role of Wip1 in neutrophil development and homeostasis. Notably, Wip1-deficient mice displayed neutrophilia with significantly expanded granulocytic differentiation and hypermaturation phenotype in a cell-intrinsic and specific manner. Thus, phosphatase Wip1, as a key feedback regulator, negatively controls granulocytopoiesis and peripheral neutrophil homeostasis. Methods MiceC57BL/6 and CD45.1 ϩ mice were purchased from Beijing University Experimental Animal Center (Beijing, China). Wip1 Ϫ/Ϫ , p53 ϩ/Ϫ , and p38 ϩ/Ϫ mice were kindly provided by the Key Laboratory of Human Diseases Comparative Medicine, the Ministry of Public Health (Beijing, China). Wip1 Ϫ/Ϫ mice have been described 10,14 and backcrossed to the C57BL/6 background in our laboratory. Wip1 Ϫ/Ϫ and p53 ϩ/Ϫ mice were mated to obtain Wip1 Ϫ/Ϫ p53 Ϫ/Ϫ double-knockout mice. All mice were bred and maintained in specific pathogen-free conditions. Sex-matched littermate mice 6-12 weeks of age were mainly used for experiments unless otherwise noted. Complete or mixed chimeras were generated by transferring 1 to 2 ϫ 10 7 BM cells (BMCs) from either WT and/or Wip1KO mice into lethally irradiated mice. 15,16 Animal protocols were approved by the Animal Ethics Committee of the Institute of Zoology, Beijing, China. *G.L., X.H., and B.S. contributed equally to this st...

Wip1 deficiency impairs haematopoietic stem cell function via p53 and mTORC1 pathways

“…Recent studies suggest that Wip1 plays an important role in regulating certain physiological and pathological processes by dephosphorylating distinct downstream targets 21,[24][25][26]29,37 . In pancreatic islets, reduced Wip1 expression contributes to the aging-related decline in the proliferation and regenerative capacities of pancreatic islets via increased p38 activity 26 .…”

“…In the haematopoietic system, Wip1 deletion in mice results in a smaller thymus due to p53-dependent cell cycle arrest during the development of T cells 28 and enhanced maturation of neutrophils, which are mediated by p38 MAPK-STAT1-dependent pathways 29 . However, the role of Wip1 in regulating HSC homeostasis and aging remains unknown.…”

TSC1 controls macrophage polarization to prevent inflammatory disease

“…Protein concentration was determined using a BCA assay. Proteins samples were analysed on SDS polyacrylamide gel electrophoresis (SDS-PAGE) and transferred onto PVDF membranes (Millipore, CA) 60 . Each polyvinylidene fluoride membrane was blocked with TBST (100 mM Tris-HCl pH 7.5, 150 mM NaCl, 0.05% Tween20) with 5% non-fat dried milk for 1 h, then incubated with primary antibodies overnight on a shaker at 4°C.…”

The generation of neutrophils in the bone marrow is controlled by autophagy

“…Our data for the importance of p38 in the regulation of neutrophil differentiation are in agreement with previously published work demonstrating that the phosphatase Wip1 blocks the differentiation process of neutrophils through the inhibition of the p38 MAPK-STAT1 pathway. 54 In addition, neutropenia has been recognized as an important adverse event of rapamycin therapy, 55 pointing to the possibility that mTOR-regulated autophagy in neutrophil precursors is responsible for this phenomenon.…”