E3 ubiquitin ligase Cbl-b activates the p53 pathway by targeting Siva1, a negative regulator of ARF, in FLT3 inhibitor-resistant acute myeloid leukemia

Abstract

Previous clinical studies have shown that the presence of receptor tyrosine kinase (RTK) FLT3 with activating mutation, FLT3-ITD (internal tandem duplication), translates into poor prognosis in acute myeloid leukemia (AML). 1 Several tyrosine kinase inhibitors (TKIs) of constitutively active FLT3 have been developed and tested in clinical trials. 1 So far, these small molecule inhibitors have resulted in only modest improvement in AML patients because of, in part, the presence of leukemic blasts showing resistance against FLT3 inhibitors. 2 Thus, devising an improved therapeutic strategy to overcome AML resistance to FLT3 inhibitors could improve the likelihood of achieving long-term survival of AML patients.Tumor suppressor p53 is a critical gatekeeper for cell growth and division, and regulates a large number of downstream targets in response to various oncogenes and genotoxic stresses, ultimately suppressing tumorigenesis. 3 Although mutations in the tumor suppressor p53 gene (TP53) are found in only about 5-10% of AML patients, inactivation of wild-type p53 protein frequently occurs through overexpression of its negative regulatory molecule, murine double minute 2 (MDM2), which targets p53 for ubiquitin-mediated degradation. 3 On genotoxic stimuli such as irradiation, p53 is phosphorylated and the interaction between p53 and MDM2 is blocked, which leads to an increased level of p53 and eventually inhibition of the growth of tumor cells. Recent studies have shown that FLT3-ITD blocks p53 activation in AML, and restoration of p53 activities sensitizes AML blasts to FLT3 inhibitor treatment. 4,5 In addition, BA/F3 cells expressing FLT3-ITD (BA/F3-FLT3-ITD) were resistant to FLT3 inhibitor PKC412 on being transfected with lentivirus encoding shRNA targeting p53. 4 This suggests that FLT3-ITD + AML cells acquire resistance to FLT3 inhibitors, at least in part, by inactivation of p53, which provides a rationale to target p53 and its regulatory network for overcoming AML resistance to FLT3 inhibitors.First, we tested whether activation of p53 by Nutlin-3 could be exploited for overcoming resistance of FLT3-ITD AML cells to FLT3 inhibitors. Nutlin-3 is a highly specific, nonConflict of Interest: The authors declare no conflict of interest. HHS Public Access Author ManuscriptAuthor Manuscript Author ManuscriptAuthor Manuscript genotoxic MDM2 antagonist and functions as a competitive inhibitor of the p53-MDM2 interaction. 6 As shown in Figure 1a, Nutlin-3 was able to significantly suppress the growth of the AML cell line MOLM13-R-PKC412 that is resistant to the FLT3 inhibitor PKC412. Another PKC412-resistant AML cell line MV4-11R-PKC412 that was generated from PKC412-sensitive MV4-11 harboring mutant form of p53 (ref.7) was resistant to Nutlin-3. Consistently, Nutlin-3 increased the level of p53 and regulated the expression of well-known p53 target genes, p21 and Axl, 3 in MOLM13-R-PKC412 (wild-type p53) but not in MV4-11R-PKC412 (mutant p53) ( Figure 1b). In primary AML blasts from patients that showed intrinsic re...

Clinical resistance to crenolanib in acute myeloid leukemia due to diverse molecular mechanisms

“…TP53 pathway mutations are mutually exclusive with FLT3 mutations in de novo AML and were shown to be related to FLT3 inhibitor resistance 34,35 . Interestingly, we observed one TP53 mutation and one PPM1D mutation that co-occurred with FLT3 -ITD and/or FLT3 TKD in two individual patients with crenolanib poor response.…”

MicroRNA-29b-2-5p inhibits cell proliferation by directly targeting Cbl-b in pancreatic ductal adenocarcinoma

“…MDM2 inhibits p53 activity in the cytoplasm, promotes p53 degradation and prevents p53 from entering the nucleus and exerts its function [ 45 ]. Moreover, previous studies reported that Cbl-b could target Siva 1 and upregulate p53 in lymphoma [ 46 ].…”

Siva-1 emerges as a tissue-specific oncogene beyond its classic role of a proapoptotic gene

“…Additionally, a protective mechanism preserving p53 levels was demonstrated in acute myeloid leukemia: E3 ubiquitin ligase Cbl-b ubiquitinates Siva-1 leading to its degradation and stabilization of p53 levels. 40 , 41 Further, Siva-1 has a specific p53-independent function in the monoubiquitination of PCNA (proliferating cell nuclear antigen). It binds E3 ubiquitin ligase RAD18 and promotes its E3 PCNA ligase activity.…”