Pml and TAp73 interacting at nuclear body mediate imatinib‐induced p53‐independent apoptosis of chronic myeloid leukemia cells

Abstract

Bcr-abl signals for leukemogenesis of chronic myeloid leukemia (CML) and activates ras. Since the function of promyelocytic leukemia protein (pml) is provoked by ras to promote apoptosis and senescence in untransformed cells, the function is probably masked in CML. Imatinib specifically inhibits bcr-abl and induces apoptosis of CML cells. As reported previously, p53 wild CML was more resistant to imatinib than that lacking p53. Here, we searched for an imatinib-induced p53 independent proapoptotic mechanism. We found imatinib up-regulated phosphorylation of p38 mitogen-activated protein kinase (MAPK), checkpoint kinase 2 (chk2) and transactivation-competent (TA) p73; expression of pml and bax; formation of PML-nuclear body (NB); and co-localization of TAp73/PML-NB in p53-nonfunctioning K562 and p53 mutant Meg-01 CML cells, but not in BCR-ABL -HL60 cells. In K562 cells, with short interfering RNAs (siRNAs), knockdown of pml led to dephosphorylation of TAp73. Knockdown of either pml or TAp73 abolished the imatinib-induced apoptosis. Inhibition of p38 MAPK with SB203580 led to dephosphorylation of TAp73, abolishment of TAp73/PML-NB co-localization, and the subsequent apoptosis. Conversely, interferon a-2a (IFNa), which increased phosphrylated TAp73 and TAp73/PML-NB co-localization, increased additively apoptosis with imatinib. The imatinibinduced TAp73/PML-NB co-localization was accompanied by coimmpunoprecipitation of TAp73 with pml. The imatinib-induced co-localization was also found in primary CML cells from 3 of 6 patients, including 2 with p53 mutant and one with p53 wild . A novel p53-independent proapoptotic mechanism using p38 MAPK /pml/ TAp73 axis with a step processing at PML-NB and probably with chk2 and bax being involved is hereby evident in some imatinibtreated CML cells. ' UICCKey words: p38 MAPK; pml; p73; nuclear body; chronic myeloid leukemia; imatinib The oncogenic bcr-abl tyrosine kinase resulting from the Philadelphia chromosome (Ph) signals for leukemogenesis of CML. Imatinib mesylate, a specific inhibitor of c-abl and bcr-abl, induces apoptosis of CML cells and has created a revolutionary success in CML treatment. 1 Imatinib down-regulates various antiapoptotic signals including bcl-X L , Akt kinase and NFjB in CML cells. 2 Nevertheless, the proapoptotic mechanism elicited by imatinib has not been well-defined. p53 generally generates an important proapoptotic effect on cells under genotoxic and non-genotoxic stress. However, the p53 level in the imatinib-treated CML cells was reduced and failed to accumulate in response to DNA damage. This is explained by the fact that constitutive phosphorylation of p53 at serine 20 is inhibited by imatinib. 3 Besides, CML cells with wild type p53 are more resistant to imatinib than those lacking p53. 3 Therefore, we rationalized the existence of an imatinib-induced p53-independent proapoptotic mechanism.p73 is a homologue of the p53 tumor suppressor and induces apoptosis by different mechanisms. 4,5 Unlike p53, there are several different isomers of p73 ...

p53 Gene (NY-CO-13) Levels in Patients with Chronic Myeloid Leukemia: The Role of Imatinib and Nilotinib

“…Additionally, Liu et al’s study illustrated that imatinib might induce the pre-apoptotic pathway independent of p53 activation through activation of specific signal pathways such as mitogen-activated protein kinase p38 (MAPK) and PML-nuclear body. So that p53-independent pathway might be an alternative pathway for the action of imatinib during therapy of patients with CML [ 26 ]. This detection may explain the low levels of p53 in imatinib-treated patients compared to nilotinib-treated patients as revealed in our study.…”

PML nuclear bodies: Assembly and oxidative stress-sensitive sumoylation

“…131 In various settings, interferon-triggered cancer cell apoptosis or senescence involves PML and p53. [132][133][134][135][136] Similarly, both PML and sumoylation of DAXX were shown to be critical for interferon-triggered apoptosis in B cells. 137 Thus, the PML interferon crosstalks are not limited to antiviral effects.…”

Post-translational modifications of PML: consequences and implications

“…In addition, following DNA damage, Chk2 and p53 are enriched in PML NBs, where PML promotes Chk2 autophosphorylation, phosphorylation of p53 by Chk2 at Ser20 and subsequent stabilization of p53 (Louria-Hayon et al, 2003; Yang et al, 2006). Imatinib, a drug used to treat chronic myeloid leukemia (CML), induces TAp73 (a p53 family member) phosphorylation and localization to PML NBs in a p38- and PML-dependent manner in CML cells (Liu et al, 2009). …”