β-Catenin Inhibits Promyelocytic Leukemia Protein Tumor Suppressor Function in Colorectal Cancer Cells

Background & AimsLoss of promyelocytic leukemia protein (PML) nuclear body (NB) formation has been reported in colorectal and other solid tumors. However, genetic alteration of PML is rarely observed in these tumors; the exact mechanisms that mediate loss of PML function are not known.MethodsWe previously used a comprehensive shotgun mass spectrometry approach to identify PML as 1 of 70 proteins that coimmunoprecipitate with anti–T-cell factor 4 in DLD-1 and HCT116 colorectal cancer cell lines; we investigated the effects of altered β-catenin expression on PML function in these cells.Resultsβ-catenin specifically interacted with the product of PML transcript variant IV (PML-IV) through the armadillo repeat domain of β-catenin. Overexpression of β-catenin in colorectal cancer cells disrupted the subcellular compartmentalization of PML-IV, whereas knockdown of β-catenin restored formation of PML-NB. Modification of PML by the small ubiquitin-related modifier (SUMO) is required for proper assembly of PML-NB. β-catenin inhibited Ran-binding protein 2–mediated SUMOylation of PML-IV.Conclusionsβ-catenin interacts with PML isoform IV and disrupts PML-IV function and PML-NB formation by inhibiting Ran-binding protein 2–mediated SUMO modification of PML-IV. These findings indicate the involvement of a posttranslational mechanism in disruption of PML-NB organization in cancer cells and provide more information about the oncogenic functions of β-catenin.