Rad9 modulates the P21WAF1 pathway by direct association with p53.
BACKGROUND
Previous studies suggest that human RAD9 (hRad9), encoding a DNA damage checkpoint molecule, which is frequently amplified in epithelial tumor cells of breast, lung, head and neck cancer, participates in regulation of the tumor suppressor p53-dependent transactivation of pro-survival P21WAF1. This study examined the exact mechanism of the hRad9 function, especially through the phosphorylation of the C-terminus, in the transcription regulation of P21WAF1.


RESULTS
The transfection of phosphorylation-defective hRAD9 mutants of C-terminus resulted in reduction of the p53-dependent P21WAF1 transactivation; the knockdown of total hRad9 elicited an increased P21WAF1 mRNA expression. Immunoprecipitation and a ChIP assay showed that hRad9 and p53 formed a complex and both were associated with two p53-consensus DNA-binding sequences in the 5' region of P21WAF1 gene. The association was reduced in the experiment of phosphorylation-defective hRAD9 mutants.


CONCLUSIONS
The present study indicates the direct involvement of hRad9 in the p53-dependent P21WAF1 transcriptional mechanism, presumably via the phosphorylation sites, and alterations of the hRad9 pathway might therefore contribute to the perturbation of checkpoint activation in cancer cells.
Ishikawa
Kazuhiro
K
Department of Otolaryngology-Head and Neck Surgery, Jichi Medical University School of Medicine, Tochigi, Japan. kazu-ish@jichi.ac.jp <kazu-ish@jichi.ac.jp>
Ishii
Hideshi
H
Murakumo
Yoshiki
Y
Mimori
Koshi
K
Kobayashi
Masahiko
M
Yamamoto
Ken-ichi
K
Mori
Masaki
M
Nishino
Hiroshi
H
Furukawa
Yusuke
Y
Ichimura
Keiichi
K
D018797:Cell Cycle Proteins / Q000378:metabolism*; D047369:Chromatin Immunoprecipitation; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism*; D004249:DNA Damage / Q000235:genetics*; D005786:Gene Expression Regulation; D018816:Genes, cdc; D006801:Humans; D047468:Immunoprecipitation; D010766:Phosphorylation; D034622:RNA Interference; D015398:Signal Transduction / Q000235:genetics*; D016159:Tumor Suppressor Protein p53 / Q000378:metabolism*
C493956:CDKN1A protein, human; D018797:Cell Cycle Proteins; D050759:Cyclin-Dependent Kinase Inhibitor p21; D016159:Tumor Suppressor Protein p53; C069930:rad9 protein