Increased protein stability causes DNA methyltransferase 1 dysregulation in breast cancer.
We report that DNA methyltransferase 1 (DNMT1) expression is dysregulated in breast cancer. The elevated protein levels are not a result of increased mRNA levels, but rather an increase in protein half-life. We found that DNMT1 protein levels were elevated in breast cancer tissues and in MCF-7 breast cancer cells relative to normal human mammary epithelial cells (HMECs) without a concomitant increase in DNMT1 mRNA or proliferative fraction. Although DNMT1 mRNA levels were properly S-phase-regulated in both cell types, DNMT1 protein levels did not follow S-phase fraction in MCF-7 cells. Rather, an increase in DNMT1 protein stability was found for MCF-7 cells relative to HMECs, and a destruction domain was mapped to the N-terminal 120 amino acids of DNMT1, which was required for its proper ubiquitination and degradation in HMECs. Furthermore, overexpression of DNMT1 with this deleted destruction domain in HMECs resulted in significantly increased genomic 5-methylcytosine levels relative to overexpression of the full-length protein. The regulation of DNMT1 destruction via this domain may be dysfunctional in cancer cells leading to subsequent cytosine hypermethylation in the genome.
Agoston
Agoston T
AT
Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University, School of Medicine, Baltimore, Maryland 21231-1000, USA.
Argani
Pedram
P
Yegnasubramanian
Srinivasan
S
De Marzo
Angelo M
AM
Ansari-Lari
Mohammad Ali
MA
Hicks
Jessica L
JL
Davidson
Nancy E
NE
Nelson
William G
WG
D000595:Amino Acid Sequence; D001943:Breast Neoplasms / Q000201:enzymology* / Q000378:metabolism / Q000473:pathology; D002460:Cell Line; D045744:Cell Line, Tumor; D049109:Cell Proliferation; D004248:DNA (Cytosine-5-)-Methyltransferases / Q000096:biosynthesis / Q000737:chemistry* / Q000235:genetics / Q000378:metabolism*; D006801:Humans; D008969:Molecular Sequence Data; D020871:RNA Stability; D012333:RNA, Messenger / Q000096:biosynthesis
D012333:RNA, Messenger; D004248:DNA (Cytosine-5-)-Methyltransferases