A Direct Interaction Between P53-Binding Protein 1 and Minichromosome Maintenance Complex in Hepg2 Cells

Abstract

Background/Aims: Hepatocellular carcinoma (HCC) is the second leading cause of cancer-related deaths worldwide. DNA damage repair in cancer cells is a promising approach for the treatment of cancers. We aimed to explore the potential interaction between p53-binding protein 1 (53BP1) and minichromosome maintenance (MCMs) proteins during DNA damage in human hepatoma HepG2 cells. Methods: The recombinant vectors of 53BP1 and MCMs with tags were constructed and transfected into HepG2 cells. Immunoprecipitation (IP) and mass spectrometry (MS) were performed to identify the possible interactions between 53BP1 and MCMs, and glutathione S-transferase (GST) pull-down assay was carried out to detect the direct interaction. Moreover, the expressions of MCM2 and MCM6 were suppressed by specific short hairpin RNAs (shRNAs), and then the chromatin fraction and foci formation of 53BP1 were examined under the condition of DNA damage. Results: The results showed that MCM2/3/5/6 was immunoprecipitated against the hemaglutinin (HA)-tagged 53BP1 in HepG2 cell nuclei. GST results revealed that there was a direct interaction between 53BP1 and MCMs complex. Moreover, the non-chromatin level of 53BP1 was significantly increased by down-regulation of MCM2 or MCM6, but was statistically decreased the chromatin level. Furthermore, we observed that knockdown of MCM2 or MCM6 could statistically inhibit the foci formation of 53BP1 in HepG2 cell nuclei upon bleomycin-induced DNA damage (P < 0.01). Conclusion: Our results suggest that there is a direct interaction between 53BP1 and MCMs, which is essential for 53BP1 chromatin fraction and foci formation in hepatoma HepG2 cells.