Mdm-2 binding and TAF(II)31 recruitment is regulated by hydrogen bond disruption between the p53 residues Thr18 and Asp21.
Analyses of five wild-type p53 containing cell lines revealed lineage specific differences in phosphorylation of Thr18 after treatment with ionizing (IR) or ultraviolet (UV) radiation. Importantly, Thr18 phosphorylation correlated with induction of the p53 downstream targets p21(Waf1/Cip1) (p21) and Mdm-2, suggesting a transactivation enhancing role. Thr18 phosphorylation has been shown to abolish side-chain hydrogen bonding between Thr18 and Asp21, an interaction necessary for stabilizing alpha-helical conformation within the transactivation domain. Mutagenesis-derived hydrogen bond disruption attenuated the interaction of p53 with the transactivation repressor Mdm-2 but had no direct effect on the interaction of p53 with the basal transcription factor TAF(II)31. However, prior incubation of p53 mutants with Mdm-2 modulated TAF(II)31 interaction with p53, suggesting Mdm-2 blocks the accessibility of p53 to TAF(II)31. Consistently, p53-null cells transfected with hydrogen bond disrupting p53 mutants demonstrated enhanced endogenous p21 expression, whereas p53/Mdm-2-double null cells exhibited no discernible differences in p21 expression. We conclude disruption of intramolecular hydrogen bonding between Thr18 and Asp21 enhances p53 transactivation by modulating Mdm-2 binding, facilitating TAF(II)31 recruitment.
Jabbur
James R
JR
Department of Pathology, The University of Texas M.D. Anderson Cancer Center, Houston, Texas, TX 77030, USA.
Tabor
Amy D
AD
Cheng
Xiaodong
X
Wang
Hua
H
Uesugi
Motonari
M
Lozano
Guillermina
G
Zhang
Wei
W
D000595:Amino Acid Sequence; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins / Q000502:physiology; D004249:DNA Damage; D006801:Humans; D006860:Hydrogen Bonding; D008969:Molecular Sequence Data; D009687:Nuclear Proteins; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D051736:Proto-Oncogene Proteins c-mdm2; D035381:TATA-Binding Protein Associated Factors; D013912:Threonine / Q000378:metabolism; D015534:Trans-Activators / Q000378:metabolism*; D035362:Transcription Factor TFIID; D015533:Transcriptional Activation; D016159:Tumor Suppressor Protein p53 / Q000737:chemistry* / Q000378:metabolism / Q000528:radiation effects; D014466:Ultraviolet Rays
C493956:CDKN1A protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016213:Cyclins; D009687:Nuclear Proteins; D011518:Proto-Oncogene Proteins; C106849:TAF9 protein, human; D035381:TATA-Binding Protein Associated Factors; D015534:Trans-Activators; D035362:Transcription Factor TFIID; D016159:Tumor Suppressor Protein p53; D013912:Threonine; C497206:MDM2 protein, human; D051736:Proto-Oncogene Proteins c-mdm2