Retinoblastoma pathway dysregulation causes DNA methyltransferase 1 overexpression in cancer via MAD2-mediated inhibition of the anaphase-promoting complex.
We have examined the mechanism of normal DNA methyltransferase 1 (DNMT1) degradation as well as its mechanism of dysregulation in cancer. We have previously reported that DNMT1 protein levels were elevated and abnormally stabilized because of defective degradation through its N-terminal destruction domain. Here, we report that DNMT1 was abnormally stabilized in several cancer cell lines and that, in cells with normal DNMT1 destruction, depletion of CDC20 or FZR1 (two substrate recognition adaptor components of the anaphase-promoting complex) resulted in stabilization of DNMT1 that was partially dependent on the N-terminal destruction domain, thus implicating this cell cycle regulator in the destruction of DNMT1. MAD2, an inhibitor of CDC20, was shown to stabilize DNMT1 levels, and overexpression of MAD2, a consequence of retinoblastoma (RB) pathway dysregulation, was shown to correlate with impaired G(1) phase DNMT1 destruction and RB inactivation by hyperphosphorylation in several normal and cancer cell lines. Furthermore, in a series of 85 cases of human breast cancer, a moderately strong, but highly significant, correlation between MAD2 and DNMT1 immunohistochemical staining was observed, yielding a Spearman rank order correlation coefficient of 0.37 (P<0.001). This suggests that RB pathway inactivation, a common dysfunction in cancer cells, may be the underlying cause of DNMT1 dysregulation.
Agoston
Agoston T
AT
Sidney Kimmel Comprehensive Cancer Center, The Johns Hopkins University, School of Medicine, Baltimore, MD, USA.
Argani
Pedram
P
De Marzo
Angelo M
AM
Hicks
Jessica L
JL
Nelson
William G
WG
D064173:Anaphase-Promoting Complex-Cyclosome; D001943:Breast Neoplasms / Q000378:metabolism; D002135:Calcium-Binding Proteins / Q000378:metabolism*; D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins / Q000378:metabolism*; D015254:DNA Modification Methylases / Q000378:metabolism*; D005260:Female; D006801:Humans; D015151:Immunoblotting; D007150:Immunohistochemistry; D064246:Mad2 Proteins; D009369:Neoplasms / Q000378:metabolism*; D034741:RNA, Small Interfering; D012097:Repressor Proteins / Q000378:metabolism*; D016160:Retinoblastoma Protein / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction; D014162:Transfection; D043743:Ubiquitin-Protein Ligase Complexes / Q000378:metabolism*
D002135:Calcium-Binding Proteins; D064199:Cdc20 Proteins; D064200:Cdh1 Proteins; D018797:Cell Cycle Proteins; C577584:FZR1 protein, human; C577697:MAD2L1 protein, human; D064246:Mad2 Proteins; D034741:RNA, Small Interfering; D012097:Repressor Proteins; D016160:Retinoblastoma Protein; C577488:CDC20 protein, human; D015254:DNA Modification Methylases; D043743:Ubiquitin-Protein Ligase Complexes; D064173:Anaphase-Promoting Complex-Cyclosome