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Title: BTK blocks the inhibitory effects of MDM2 on p53 activity
Authors: Rada, M
Althubiti, M
Ekpenyong-Akiba, A.E
Lee, K.-G
Lam, K.P 
Fedorova, O
Barlev, N.A
Macip, S
Keywords: Bruton tyrosine kinase
protein MDM2
protein p53
amino terminal sequence
controlled study
DNA damage
enzyme activity
human cell
protein binding
protein domain
protein function
protein phosphorylation
transcription regulation
Issue Date: 2017
Citation: Rada, M, Althubiti, M, Ekpenyong-Akiba, A.E, Lee, K.-G, Lam, K.P, Fedorova, O, Barlev, N.A, Macip, S (2017). BTK blocks the inhibitory effects of MDM2 on p53 activity. Oncotarget 8 (63) : 106639-106647. ScholarBank@NUS Repository.
Rights: Attribution 4.0 International
Abstract: p53 is a tumour suppressor that is activated in response to various types of stress. It is regulated by a complex pattern of over 50 different post-translational modifications, including ubiquitination by the E3 ligase MDM2, which leads to its proteasomal degradation. We have previously reported that expression of Bruton's Tyrosine Kinase (BTK) induces phosphorylation of p53 at the N-terminus, including Serine 15, and increases its protein levels and activity. The mechanisms involved in this process are not completely understood. Here, we show that BTK also increases MDM2 and is necessary for MDM2 upregulation after DNA damage, consistent with what we have shown for other p53 target genes. Moreover, we found that BTK binds to MDM2 on its PH domain and induces its phosphorylation. This suggested a negative regulation of MDM2 functions by BTK, supported by the fact BTK expression rescued the inhibitory effects of MDM2 on p53 transcriptional activity. Indeed, we observed that BTK mediated the loss of the ubiquitination activity of MDM2, a process that was dependent on the phosphorylation functions of BTK. Our data together shows that the kinase activity of BTK plays an important role in disrupting the MDM2-p53 negative feedback loop by acting at different levels, including binding to and inactivation of MDM2. This study provides a potential mechanism to explain how BTK modulates p53 functions. @ Rada et al.
Source Title: Oncotarget
ISSN: 19492553
DOI: 10.18632/oncotarget.22543
Rights: Attribution 4.0 International
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