Human DNA-(Cytosine-5) Methyltransferase-PCNA Complex as a Target for p21 ^WAF1

TLDR

DNA-(cytosine-5) methyltransferase (MCMT) methylates newly replicated mammalian DNA, but the factors regulating this activity are unknown. MCMT binds PCNA via residues 163–174 at sites of newly replicated DNA without affecting its activity, and a p21(WAF1)-derived peptide disrupts this interaction, suggesting p21 may regulate methylation by blocking MCMT access to PCNA, as evidenced by inverse expression patterns of MCMT and p21 in SV40-transformed and nontransformed cells.

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.