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Phosphorylation of p53: a novel pathway for p53 inactivation in human T-cell lymphotropic virus type 1-transformed
C A Pise-Masison1, M Radonovich, K Sakaguchi
1Virus Tumor Biology Section, Laboratory of Receptor Biology and Gene Expression, National Cancer Institute, National Institutes of Health, Bethesda, Maryland 20892-5055, USA.
Abstract:
Inhibition of p53 function, through either mutation or interaction with viral or cellular transforming proteins, correlates strongly with the oncogenic potential. Only a small percentage of human T-cell lymphotropic virus type 1 (HTLV-1)-transformed cells carry p53 mutations, and mutated p53 genes have been found in only one-fourth of adult T-cell leukemia cases. In previous studies, we demonstrated that wild-type p53 is stabilized and transcriptionally inactive in HTLV-1-transformed cells. Further, the viral transcriptional activator Tax plays a role in both the stabilization and inactivation of p53 through a mechanism involving the first 52 amino acids of p53. Here we show for the first time that phosphorylation of p53 inactivates p53 by blocking its interaction with basal transcription factors. Using two-dimensional peptide mapping, we demonstrate that peptides corresponding to amino acids 1 to 19 and 387 to 393 are hyperphosphorylated in HTLV-1-transformed cells. Moreover, using antibodies specific for phosphorylated Ser15 and Ser392, we demonstrate increased phosphorylation of these amino acids. Since HTLV-1 p53 binds DNA in a sequence-specific manner but fails to interact with TFIID, we tested whether phosphorylation of the N terminus of p53 affected p53-TFIID interaction. Using biotinylated peptides, we show that phosphorylation of Ser15 alone inhibits p53-TFIID interaction. In contrast, phosphorylation at Ser15 and -37 restores TFIID binding and blocks MDM2 binding. Our studies provide evidence that HTLV-1 utilizes the posttranslational modification of p53 in vivo to inactivate function of the tumor suppressor protein.
Insights
Human T-cell lymphotropic virus type 1 (HTLV-1) inactivates the tumor suppressor protein p53 through phosphorylation. This posttranslational modification prevents p53 from interacting with transcription factors, contributing to cancer development.
Area of Science:
- Oncology
- Virology
- Molecular Biology
Background:
- p53 tumor suppressor function is critical for preventing oncogenesis.
- HTLV-1 infection is linked to cancer, but the mechanism of p53 inactivation is not fully understood.
- Wild-type p53 is stabilized and transcriptionally inactive in HTLV-1-transformed cells, involving the viral Tax protein.
Purpose of the Study:
- To investigate the role of p53 phosphorylation in HTLV-1-mediated oncogenesis.
- To identify specific phosphorylation sites on p53 in HTLV-1-transformed cells.
- To elucidate how p53 phosphorylation affects its interaction with transcription factors.
Main Methods:
- Two-dimensional peptide mapping to identify hyperphosphorylated peptides.
- Western blot analysis using antibodies specific for phosphorylated serine residues (Ser15, Ser392).
- Biotinylated peptide assays to assess p53 interaction with TFIID and MDM2.
Main Results:
- Peptides corresponding to amino acids 1-19 and 387-393 of p53 are hyperphosphorylated in HTLV-1-transformed cells.
- Increased phosphorylation at Ser15 and Ser392 of p53 was observed.
- Phosphorylation of Ser15 inhibits p53 interaction with TFIID, while phosphorylation at Ser15 and Ser37 restores TFIID binding and blocks MDM2 binding.
Conclusions:
- HTLV-1 utilizes p53 phosphorylation as a mechanism to inactivate its tumor suppressor function.
- Posttranslational modification of p53 by HTLV-1 is crucial for viral oncogenesis.
- Targeting p53 phosphorylation could be a therapeutic strategy against HTLV-1-associated cancers.