Proliferating cell nuclear antigen (PCNA) has been described as a “ringmaster” of the genome because of its essential roles in DNA replication and repair. Interestingly, in addition to DNA replication and repair PCNA is involved in cell cycle progression and apoptosis and interacts with <20 proteins. Because of these abundant interactions, the post-translational modification of PCNA has been implicated for many years, and reports of phosphorylation, acetylation, ubiquitination, and sumoylation have surfaced in efforts to explain how this complex molecule can function in so many processes. Recently, we performed the first detailed structural analysis of a specific PCNA isoform found in malignant cells and found that this isoform did not harbor these modifications, but instead showed the presence of fairly novel post-translational modification, methyl esterification. Consistent with this modification, we have also observed a charge shift for PCNA following DNA damage by 2D electrophoresis and have identified a corresponding increase in PCNA-dependent carboxyl methyl transferase activity in cell extracts following DNA damage. Taken together this data supports the presence of a unique signaling mechanism occurring malignant cells. Using LC-MS/MS techniques, we will elucidate the structural differences to PCNA following DNA damage both in vitro and in vivo using a metabolic labeling/SILAC approach. Additionally, progress into the identification of enzyme(s) responsible for methyl esterifying PCNA in response to DNA damage and their potential as a therapeutic targets will be discussed.

98th AACR Annual Meeting-- Apr 14-18, 2007; Los Angeles, CA