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Human DNA-(cytosine-5) methyltransferase-PCNA complex as a target for p21WAF1
1Chemical Carcinogenesis Laboratory, Institute of Molecular and Cell Biology, National University of Singapore, Kent Ridge Crescent, Singapore 119260, Republic of Singapore.
Abstract:
DNA-(cytosine-5) methyltransferase (MCMT) methylates newly replicated mammalian DNA, but the factors regulating this activity are unknown. Here, MCMT is shown to bind proliferating cell nuclear antigen (PCNA), an auxiliary factor for DNA replication and repair. Binding of PCNA requires amino acids 163 to 174 of MCMT, occurs in intact cells at foci of newly replicated DNA, and does not alter MCMT activity. A peptide derived from the cell cycle regulator p21(WAF1) can disrupt the MCMT-PCNA interaction, which suggests that p21(WAF1) may regulate methylation by blocking access of MCMT to PCNA. MCMT and p21(WAF1) may be linked in a regulatory pathway, because the extents of their expression are inversely related in both SV40-transformed and nontransformed cells.
Insights
DNA-(cytosine-5) methyltransferase (MCMT) binds to proliferating cell nuclear antigen (PCNA), a key factor in DNA replication. This interaction, potentially regulated by p21(WAF1), suggests a novel mechanism for controlling DNA methylation.
Area of Science:
- Molecular Biology
- Epigenetics
- Cell Biology
Background:
- DNA-(cytosine-5) methyltransferase (MCMT) is responsible for methylating newly replicated DNA in mammals.
- The regulatory factors controlling MCMT activity and its localization during DNA replication are currently unknown.
Purpose of the Study:
- To identify factors that regulate DNA-(cytosine-5) methyltransferase (MCMT) activity.
- To investigate the interaction between MCMT and other proteins involved in DNA replication and repair.
Main Methods:
- Co-immunoprecipitation assays to detect protein-protein interactions.
- Immunofluorescence microscopy to visualize protein localization in intact cells.
- Peptide inhibition assays to study regulatory mechanisms.
Main Results:
- MCMT was found to bind proliferating cell nuclear antigen (PCNA), an auxiliary factor for DNA replication and repair.
- PCNA binding involves specific amino acids (163-174) within MCMT and occurs at sites of newly replicated DNA.
- A peptide derived from p21(WAF1) disrupted the MCMT-PCNA interaction, suggesting p21(WAF1) may regulate MCMT access to PCNA.
- Expression levels of MCMT and p21(WAF1) were inversely correlated in different cell types.
Conclusions:
- PCNA is a binding partner for MCMT, localizing it to sites of DNA replication.
- The cell cycle regulator p21(WAF1) may play a role in modulating MCMT activity by interfering with its interaction with PCNA.
- A potential regulatory pathway linking MCMT and p21(WAF1) in mammalian DNA methylation is proposed.