Mdm2 Is Required for Survival of Hematopoietic Stem Cells/Progenitors via Dampening of ROS-Induced p53 Activity

Abstract

Summary Mdm2 is an E3 ubiquitin ligase that targets p53 for degradation. p53515C (encoding p53R172P) is a hypomorphic allele of p53 that rescues the embryonic lethality of Mdm2−/− mice. Mdm2−/− p53515C/515C mice, however, die by postnatal day 13 due to hematopoietic failure. Hematopoietic stem cells and progenitors of Mdm2−/− p53515C/515C mice were normal in fetal livers but were depleted in postnatal bone marrows. After birth, these mice had elevated reactive oxygen species (ROS) thus activating p53R172P. In the absence of Mdm2, stable p53R172P induced ROS, and cell cycle arrest, senescence and cell death in the hematopoietic compartment. This phenotype was partially rescued with antioxidant treatment and upon culturing of hematopoietic cells in methycellulose at 3% oxygen. p16 was also stabilized due to ROS, and its loss increased cell cycling, and partially rescued hematopoiesis and survival. Thus, Mdm2 is required to control ROS-induced p53 levels for sustainable hematopoiesis.

Stem cells and the impact of ROS signaling

“…Indirectly modulated by APE/REF1 and KEAP1, the oxidation of which results in NRF2 activation and inactivation, respectively (Itoh et al, 1999;Motohashi and Yamamoto, 2004) Can regulate the transcription of antioxidant enzymes (Venugopal and Jaiswal, 1996) Control of stem cell fate by protecting NSCs, ISCs and MSCs from oxidative damage (Hochmuth et al, 2011;Tsai et al, 2013) p53 Redox sensor whose DNA-binding capacity is impaired by oxidation (direct) or maintained by interaction with oxidized APE/REF1 (indirect) (Parks et al, 1997) Regulates transcription of antioxidants and pro-oxidant enzymes (Polyak et al, 1997) p53 controls ROS levels in postnatal BM (Abbas et al, 2010); p53 activity regulates stem cell fate and selfrenewal in HSCs and ESCs (Liu et al, 2009a;TeKippe et al, 2003) Different types of enzymes and transcription factors are regulated by ROS and can, in turn, regulate ROS with varying outcomes in different stem cell populations. AKT, protein kinase B; ASK1, mitogen-activated protein kinase kinase kinase 5 (MAP3K5); BID, BH3 interacting domain death agonist; BM, XXXXXX; Cys, cysteine; ESC, embryonic stem cell; GPX1, glutathione peroxidase 1; HSC, hematopoietic stem cell; ISC, XXXX: JNK, Jun kinase; KEAP1, kelch-like ECH-associated protein 1; NOX, NADPH oxidase; NRF2, nuclear factor erythroid 2; MSC, mesenchymal stem cells; NSC, neural stem cell; OCT4, POU domain, class 5, transcription factor 1 (POU5F1); p53, transformation related protein 53; PI3K, phosphatidylinositol 3-kinase; ROS, reactive oxygen species; SOD2, superoxide dismutase 2; TFs, transcription factors.…”

Reliability of ROS and RNS detection in hematopoietic stem cells − potential issues with probes and target cell population

“…In response to oxidative stress, ATM-dependent inhibition of mTOR maintains quiescence of HSCs by repressing ROS production and mitogenesis (Chen et al, 2008a;Ditch and Paull, 2012). In addition, ROS induce activation of p53, which triggers apoptosis or the expression of the anti-oxidative defense enzymes in LSK cells (Abbas et al, 2010). Hypoxia-inducible factor 1-alpha (HIF1α) has also been implicated in a negative feedback loop of ROS regulation (Honma et al, 2013;Simsek et al, 2010;Takubo et al, 2010); ROS-stabilized HIFα (Piccoli et al, 2007a) induces adaptive metabolic responses that ensure redox homeostasis (Cam et al, 2010), such as inhibition of mTOR signaling and mitochondrial activity (Cam et al, 2010), as well as activation of glycolytic metabolism .…”

“…DCFH 2 has also been used as a general indicator of the redox status of HSCs and HPCs (Abbas et al, 2010;Chen et al, 2008a;Chuikov et al, 2010;Fan et al, 2007;Hosokawa et al, 2007;Jang and Sharkis, 2007;Jung et al, 2013;Juntilla et al, 2010;Liu et al, 2009;Pazhanisamy et al, 2011;Piccoli et al, 2007a;Shao et al, 2014;Yahata et al, 2011) (Table 1) (Folkes et al, 2009). Second, the efficiency of oxidation of the intermediate DCFH 2 probe radical into the final product depends on the environmental oxygen concentration (Wrona and Wardman, 2006).…”

Hyperactivation of Mammalian Target of Rapamycin Complex 1 (mTORC1) Promotes Breast Cancer Progression through Enhancing Glucose Starvation-induced Autophagy and Akt Signaling

“…However, the alterations of Tsc1 or Tsc2 and their potential roles and mechanisms in the development and progression of breast and other tissue malignancies are not well documented. Bioinformatics analysis of several datasets in the Oncomine databases (26) showed significantly decreased expression levels of Tsc1 mRNA in human breast cancer samples compared with that of normal breast tissues (Fig. 1A).…”

“…Tsc1 is down-regulated in human breast cancers, and Tsc1 deletion increases multiplication, proliferation, migration, and invasion of primary mouse mammary tumor cells. A, microarray data of the relative expression levels of Tsc1 in human invasive breast ductal carcinoma versus normal breast tissues were extracted from Oncomine (26). The analyzed datasets include Radvanyi Breast, Richardson Breast 2, The Cancer Genome Atlas Breast, and Curtis Breast (see "Experimental Procedures" for information on the datasets).…”