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Nupr1 regulates the quiescence threshold of HSC
niche occupied by WT HSC was ablated, providing a niche vacuum into which donor Nupr1-/- HSC could enter. The dominance of Nupr1-/- HSC is a consequence of faster turnover rates of these cells over their WT counterparts. In a previous study, loss of Dnmt3a also led to clonal dom- inance of HSC, although accompanied by a failure of hematopoiesis due to a dramatic block in differentia- tion.4,49 Thus, the engraftment advantage caused by loss of Nupr1 might have prospective translational implica- tions for HSC transplantation, since a faster recovery of hematopoiesis in HSC transplant hosts definitely reduces infection risks in patients.50,51
In our models, Nupr1 regulated hematopoietic homeo- stasis via targeting the p53 pathway. p53 is essential for regulating hematopoietic homeostasis.27 It is unknown whether NUPR1 interacts directly with p53 in the context of HSC, as commercial antibodies suitable for protein-pro- tein interaction assays are not currently available. NUPR1 and p53 interacted directly in human breast epithelial cells.22 Knocking out p53 in HSC can promote HSC expan- sion, but directly targeting p53 caused HSC apoptosis and tumorigenesis.52 Thus, Nupr1 might behave as an upstream regulator of p53 signaling and uniquely regulate cell quies- cence in the context of HSC. In a previous study, Mdm2 was found to be a key repressive regulator of p53 signaling. MDM2 degrades p53 protein by promoting p53 ubiquiti- nation.46,53 Complete deletion of Mdm2 will lead to embry- onic death because of the excess expression of p53.46 This embryonic lethality can, however, be rescued by a combi- nation of Trp53-/-, indicating its essential role of negative regulation of p53. We, therefore, crossed the Nupr1-/- mice with Mdm2+/- mice in order to upregulate p53 expression indirectly. The level of p53 expression is expectedly elevat- ed in Nupr1-/-Mdm2+/- HSC; however, it is even higher than
that in WT mice (Figure 5C, D). A decreased level of MDM2 and increased p53 activity in HSC reduce the abil- ity of competitiveness.26 Thus, it is possible that the down- regulating effect of Nupr1 on p53 level is mild, while the upregulation of p53 level by haploid deletion of Mdm2 is dramatic. Consequently, the competitiveness of Nupr1-/- Mdm2+/- HSC failed to reach WT level in the rescue assay.
In conclusion, loss of Nupr1 in HSC promotes engraft- ment by tuning the quiescence threshold of HSC via regu- lation of the p53 checkpoint pathway. Our study unveils the prospect of shortening the engraftment time-window in HSC transplantation by targeting the intrinsic machin- ery controlling HSC quiescence.
Disclosures
No conflicts of interest to disclose.
Contributions
TJW and CXX performed research, analyzed data and wrote the paper; YD and QTW analyzed RNA-sequencing data; SH, FD, KTW, XFL, LJL, YG and YXG performed experiments; JD, TC and HC discussed the manuscript; JYW designed the research, and wrote the manuscript.
Funding
This work was supported by grants from the National Natural Science Foundation of China (31900814, 81925002, 81922002), Strategic Priority Research Program of the Chinese Academy of Sciences (XDA16010601), Key Research & Development Program of Guangzhou Regenerative Medicine and Health Guangdong Laboratory (2018GZR110104006), CAS Key Research Program of Frontier Sciences (QYZDB-SSW-SM057), and Science and Technology Planning Project of Guangdong Province (2017B030314056).
References
1. Cheshier SH, Morrison SJ, Liao X, Weissman IL. In vivo proliferation and cell cycle kinetics of long-term self-renewing hematopoietic stem cells. Proc Natl Acad Sci U S A. 1999;96(6):3120-3125.
2. Wilson A, Laurenti E, Oser G, et al. Hematopoietic stem cells reversibly switch from dormancy to self-renewal during homeostasis and repair. Cell. 2008;135(6): 1118-1129.
3.Rodrigues NP, Janzen V, Forkert R, et al. Haploinsufficiency of GATA-2 perturbs adult hematopoietic stem-cell homeostasis. Blood. 2005;106(2):477-484.
4. Challen GA, Sun D, Jeong M, et al. Dnmt3a is essential for hematopoietic stem cell dif- ferentiation. Nat Genet. 2011;44(1):23-31.
5. Mayle A, Yang L, Rodriguez B, et al. Dnmt3a loss predisposes murine hematopoietic stem cells to malignant transformation. Blood. 2015;125(4):629- 638.
6. Santaguida M, Schepers K, King B, et al. JunB protects against myeloid malignancies by limiting hematopoietic stem cell prolif- eration and differentiation without affect- ing self-renewal. Cancer Cell. 2009;15(4): 341-352.
7. Takubo K, Goda N, Yamada W, et al. Regulation of the HIF-1alpha level is essen- tial for hematopoietic stem cells. Cell Stem Cell. 2010;7(3):391-402.
8.Tesio M, Tang Y, Mudder K, et al.
Hematopoietic stem cell quiescence and function are controlled by the CYLD- TRAF2-p38MAPK pathway. J Exp Med. 2015;212(4):525-538.
9. Laurenti E, Frelin C, Xie S, et al. CDK6 lev- els regulate quiescence exit in human hematopoietic stem cells. Cell Stem Cell. 2015;16(3):302-313.
10. Mallo GV, Fiedler F, Calvo EL, et al. Cloning and expression of the rat p8 cDNA, a new gene activated in pancreas during the acute phase of pancreatitis, pancreatic develop- ment, and regeneration, and which pro- motes cellular growth. J Biol Chem. 1997;272(51):32360-32369.
11. Ree AH, Tvermyr M, Engebraaten O, et al. Expression of a novel factor in human breast cancer cells with metastatic poten- tial. Cancer Res. 1999;59(18):4675-4680.
12. Ree AH, Pacheco MM, Tvermyr M, Fodstad O, Brentani MM. Expression of a novel factor, com1, in early tumor progres- sion of breast cancer. Clin Cancer Res. 2000;6(5):1778-1783.
13. Ito Y, Yoshida H, Motoo Y, et al. Expression and cellular localization of p8 protein in thyroid neoplasms. Cancer Lett. 2003;201 (2):237-244.
14. Mohammad HP, Seachrist DD, Quirk CC, Nilson JH. Reexpression of p8 contributes to tumorigenic properties of pituitary cells and appears in a subset of prolactinomas in transgenic mice that hypersecrete luteiniz- ing hormone. Mol Endocrinol. 2004;18(10): 2583-2593.
15. Brannon KM, Million Passe CM, White CR, Bade NA, King MW, Quirk CC. Expression of the high mobility group A family mem- ber p8 is essential to maintaining tumori- genic potential by promoting cell cycle dys- regulation in LbetaT2 cells. Cancer Lett. 2007;254(1):146-155.
16. Jiang WG, Davies G, Martin TA, Kynaston H, Mason MD, Fodstad O. Com-1/p8 acts as a putative tumour suppressor in prostate cancer. Int J Mol Med. 2006;18(5):981-986.
17.Malicet C, Lesavre N, Vasseur S, Iovanna JL. p8 inhibits the growth of human pancre- atic cancer cells and its expression is induced through pathways involved in growth inhibition and repressed by factors promoting cell growth. Mol Cancer. 2003;2:37.
18. Malicet C, Giroux V, Vasseur S, Dagorn JC, Neira JL, Iovanna JL. Regulation of apopto- sis by the p8/prothymosin alpha complex. Proc Natl Acad Sci U S A. 2006;103(8):2671- 2676.
19. Vasseur S, Hoffmeister A, Garcia-Montero A, et al. p8-deficient fibroblasts grow more rapidly and are more resistant to adri- amycin-induced apoptosis. Oncogene. 2002;21(11):1685-1694.
20. Carracedo A, Lorente M, Egia A, et al. The stress-regulated protein p8 mediates cannabinoid-induced apoptosis of tumor cells. Cancer Cell. 2006;9(4):301-312.
21. Gironella M, Malicet C, Cano C, et al. p8/nupr1 regulates DNA-repair activity after double-strand gamma irradiation-
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