α-catenin SUMOylation Inhibits Breast Cancer Progression

As the focus protein in this paper,α-catenin,is one of the catenin protein family members.α-catenin is encoded by CTNNA1.α-catenin is down-regulated or lost in a wide range of tumor types,which associate with higher tumor malignancy.α-catenin is frequently down-regulated in human skin cance,and an α-catenin-knockout skin squamous cell carcinoma mouse model showed up-regulation of many NF-κB downstream genes.In E-cadherin-negative basal-like breast cancer,down-regulating of α-catenin lead to NF-κB hyperactivated,which promote progress of breast cancer.SUMOylation is a post-translational modification which often affects physical and chemical properties of target proteins,thus regulating substrate proteins related signaling.A computer analysis of proteins mass spectrometry and the α-catenin protein sequence reveals two conserved SUMOylation sites.Therefore,we hypothesized that α-catenin is a target of SUMO.The main works of the paper are as follows:1.We observed that α-catenin is a target of SUMO using immunoprecipitation assay in HEK293 T cells.In addition,SUMOylation level of α-catenin was enhanced by Ubc9 and deSUMOylated by SENP1.And we found that endougenous α-catenin interacted with IκBα.So,we believe that α-catenin is modified by SUMO.We also found α-catenin SUMOylation site was its lysine 870 using site mutation assay.2.SUMOylation did not affect subcellular distribution between WT α-catenin and mutant.However,expected α-catenin-SUMO1 band was mainly evident in the cytoplasm.We also observed that both WT α-catenin and the K870 R α-catenin mutant were degraded at a similar rate.3.α-catenin SUMOylation mutant showed significantly reduced inhibition of NF-κB signaling using gene reportor assay.In addition,we found that SUMOylation enhanced interaction between α-catenin and IκBα using immunoprecipitation assay.4.Cell growth assay,Transwell assay and colony formation assay demonstrated that SUMOylation deficient α-catenin showed reduced inhibiton of cell growth and migration.Additionally,α-catenin SUMOylation mutant showed impared tumor suppression activity in 4T1/Luc cells in BALB/c mice.Collectively,our data identified a new mechanistic pathway for the regulation of α-catenin SUMOylation and NF-κB signaling,one that is based on the regulation of interaction between α-catenin and IκBα by direct SUMOylation of α-catenin.