DNA (cytosine-5)-methyltransferase 1 as a mediator of mutant p53-determined p16(ink4A) down-regulation.
In cancer, gene silencing via hypermethylation is as common as genetic mutations in p53. Understanding the relationship between mutant p53 and hypermethylation of other tumor suppressor genes is essential when elucidate mechanisms of tumor development. In this study, two isogenic human B lymphoblast cell lines with different p53 status include TK6 containing wild-type p53 and WTK1 with mutant p53 were used and contrasted. Lower levels of p16(ink4A) protein were detected in WTK1 cells than in TK6 cells, which were accompanied by increased DNA (cytosine-5)-methyltransferase 1 (DNMT1) gene expression as well as hypermethylation of the p16 ( ink4A ) promoter. siRNA experiments to transiently knock down wild-type p53 in TK6 cells resulted in increase of DNMT1 expression as well as decrease of p16(ink4A) protein. Conversely, siRNA knockdown of mutant p53 in WTK1 cells did not alter either DNMT1 or p16(ink4A) protein levels. Furthermore, loss of suppression function of mutant p53 to DNMT1 in WTK1 was caused by the attenuation of its binding ability to the DNMT1 promoter. In summary, we provide evidences to elucidate the relationship between mutant p53 and DNMT1. Our results indicate that mutant p53 loses its ability to suppress DNMT1 expression, and thus enhances methylation levels of the p16 ( ink4A ) promoter and subsequently down-regulates p16(ink4A )protein.
Guo
Zhanjun
Z
Radiation Biology and Oncology Branches, Center for Cancer Research, National Cancer Institute, National Institutes of Health, Bethesda, MD, 20892, USA.
Tsai
Mong-Hsun
MH
Shiao
Yih-Horng
YH
Chen
Li-Han
LH
Wei
Mei-Ling
ML
Lv
Xing
X
Gius
David
D
Little
John B
JB
Mitchell
James B
JB
Chuang
Eric Y
EY
D001402:B-Lymphocytes / Q000378:metabolism*; D045744:Cell Line, Tumor; D019941:Cyclin-Dependent Kinase Inhibitor p16 / Q000235:genetics / Q000378:metabolism*; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000235:genetics / Q000378:metabolism*; D019175:DNA Methylation; D015536:Down-Regulation; D006801:Humans; D009154:Mutation; D009369:Neoplasms / Q000235:genetics / Q000378:metabolism*; D011401:Promoter Regions, Genetic / Q000235:genetics; D034741:RNA, Small Interfering / Q000235:genetics; D016159:Tumor Suppressor Protein p53 / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*
D019941:Cyclin-Dependent Kinase Inhibitor p16; D034741:RNA, Small Interfering; D016159:Tumor Suppressor Protein p53; D000076123:DNA (Cytosine-5-)-Methyltransferase 1; D004248:DNA (Cytosine-5-)-Methyltransferases; C000619380:DNMT1 protein, human