Identification of p53-R175H Q167 and R248 as Residues Most Involved in Its Interaction with Plakoglobin

Abstract

Background: The conformational p53-R175H is the most frequently occurring p53 mutant in cancers and a focus of mutant p53 targeted therapies. Plakoglobin is a dual cell adhesion and signaling protein with tumor suppressor activity. We previously showed that plakoglobin interacts with p53 and restores tumor suppressive activity of p53 mutants, including p53-R175H, in vitro. Method: Here, we used in silico modeling to predict the residues in p53-R175H that contribute the most to its interaction with plakoglobin, which identified p53-R175H Q167 and R248 as residues most involved in this interaction. To validate our in silico results, constructs were developed in which the predicted residues were substituted by alanine and transfected into the p53 null and plakoglobin deficient H1299 cells with or without plakoglobin. Transfectants expressing substituted residues were characterized using various biochemical and functional assays. Results: Co-immunoprecipitation and GST pull down assays showed a significant reduction in p53-R175H-plakoglobin association in p53-R175H-(Q167A, R248A and Q167A-R248A) transfectants. Despite the reduced interaction, in vitro invasion assays showed plakoglobin expression decreased invasiveness of all transfectants with the highest reduction in p53-R175H-R248A and R175H-Q167A-R248A expressing transfectants. Conclusion: These studies demonstrate, for the first time, the role of Q167 and R248 residues in p53-R175H's interaction with plakoglobin. The larger implication of these observations is the potential for exploring plakoglobin's interaction with p53-R175H mutant for the development of cancer therapeutics that restores the wild-type transcriptional activity/function of mutant p53s.