ATM mediates constitutive NF-κB activation in high-risk myelodysplastic syndrome and acute myeloid leukemia

Abstract

The anti-apoptotic transcription factor nuclear factor-jB (NF-jB) is constitutively activated in CD34 þ myeloblasts from high-risk myelodysplastic syndrome (MDS) and acute myeloid leukemia (AML) patients. Inhibition of NF-jB by suppressing the canonical NF-jB activation pathway, for instance by knockdown of the three subunits of the inhibitor of NF-jB (IjB) kinase (IKK) complex (IKK1, IKK2 and NEMO) triggers apoptosis in such cells. Here, we show that an MDS/AML model cell line exhibits a constitutive interaction, within the nucleus, of activated, S1981-phosphorylated ataxia telangiectasia mutated (ATM) with NEMO. Inhibition of ATM with two distinct pharmacological inhibitors suppressed the activating autophosphorylation of ATM, blocked the interaction of ATM and NEMO, delocalized NEMO as well as another putative NF-jB activator, PIDD, from the nucleus, abolished the activating phosphorylation of the catalytic proteins of the IKK complex (IKK1/2 on serines 176/180), enhanced the expression of IjBa and caused the relocalization of NF-jB from the nucleus to the cytoplasm, followed by apoptosis. Knockdown of ATM with small-interfering RNAs had a similar effect that could not be enhanced by knockdown of NEMO, PIDD and the p65 NF-jB subunit, suggesting that an ATM inhibition/ depletion truly induced apoptosis through inhibition of the NF-jB system. Pharmacological inhibition of ATM also induced the nucleocytoplasmic relocalization of p65 in malignant myeloblasts purified from patients with highrisk MDS or AML, correlating with the induction of apoptosis. Altogether, these results support the contention that constitutively active ATM accounts for the activation of NF-jB in high-risk MDS and AML.

Histone Deacetylase Inhibitors Activate NF-κB in Human Leukemia Cells through an ATM/NEMO-related Pathway

“…They also provide further evidence of an important functional association between HDACI-induced ROS and DNA damage, as well as support for the notion that NF-B activation plays a major role in protecting cells, via Mn-SOD2 induction, from genomic damage and apoptosis (76). The present findings now integrate previous observations implicating HDACI-related ROS generation and DNA damage with emerging evidence linking the prosurvival NF-B pathway to the DNA damage response (20,54). The recent identification of NEMO as an ATM substrate thus provides a connection between HDACI-mediated DNA damage responses and a nuclear-to-cytoplasmic signaling cascade that activates the IKK/NF-B system (20,53).…”

“…DNA damage-mediated NF-B activation is dependent upon interactions between the ATM kinase and IKK␥ (NEMO) (20,54). Phosphorylation of ATM, one of the initial kinases activated in response to DNA damage (55), was monitored in cells exposed to LBH-589.…”

Nuclear initiated NF-κB signaling: NEMO and ATM take center stage

“…In addition to normal physiological DSBs that can lead to ATM-NEMO-dependent NF-κB activation, a recent study by Grosjean-Raillard et al [75] provides compelling evidence that ATM-NEMO-NF-κB signaling is constitutively activated in certain acute myeloid leukemia (AML) cell lines and more significantly a high percentage of primary myelodysplastic syndrome (MDS) and AML patient samples. Using the P39 AML cell line, the authors showed that ATM is constitutively active, NEMO and PIDD are constitutively nuclear, and an ATM-NEMO nuclear complex is also detectable.…”

IPO3-mediated Nonclassical Nuclear Import of NF-κB Essential Modulator (NEMO) Drives DNA Damage-dependent NF-κB Activation

“…Although the role of nuclear NEMO was originally discovered in the context of genotoxic stress-induced NF-B signaling (14), recent studies have further implicated its potential role in mediating additional processes, including the pathogenesis of myeloid dysplastic syndrome and acute myeloid leukemia (35), resistance to histone deacetylase inhibitors (36), and premature aging syndromes (37,38). Adding to the classical importin ␣-dependent nuclear import pathway mediating the nuclear import of some of the NF-B family members (76 -79), coupled with the recent identification of the Ran-GDP/ankyrin repeat ("RaDAR") import pathway for the IB family of proteins (49), our current identification of the IPO3 nonclassical import pathway in regulation of NEMO nuclear import not only expands our fundamental understanding of the nuclear trafficking aspects of the NF-B signaling system but also points to new therapeutic strategies against cancer resistance as well as the aforementioned medical conditions by targeting the NF-B system-related nuclear import mechanisms.…”

“…Once the IKK complex is active, IB is phosphorylated and degraded to release NF-B to the nucleus via the canonical signaling cascade. Under genotoxic and oxidative stress circumstances, activated IKK and/or NF-B have been shown to modulate apoptosis (16 -18, 23-27), DNA repair (28,29), cell cycle arrest (30,31), and synthesis of inflammatory mediators (32,33), thereby contributing to oncogenesis (34,35), drug resistance (36), and premature aging (37,38).…”