Mechanisms Of USP2a-mediated Regulation Of Metastasis By Facilitating TGF-β Induced Epithelial-mesenchymal Transition

Cancer is the second leading cause of death worldwide and accounts for nearly nine million deaths each year.Because of atypical symptoms of cancers,the cancer cells are often found to metastasize into nearby lymph nodes or tissues and colonize in the same organs or distant parts of the body along with the diagnosis of cancers,and such metastasis is believed to be responsible for up to 90%of solid tumor-associated deaths.In the process of tumor metastasis,epithelial-mesenchymal transition(EMT)is considered as a key step in the tumor progression.EMT has been reported to be involved in the development of multiple malignancies,like breast cancer,colorectal cancer,prostate cancer and lung cancer.Previous studies have shown that TGF-β regulates a variety of biological processes,including cell proliferation,development and immune responses.TGF-βplays a dual role in the tumorigenesis and tumor progression.Early in the tumor initiation,TGF-β functions as a tumor suppressor to induce apoptosis and cell cycle arrest.Along with the tumor progression,TGF-β facilitates metastasis by promoting EMT of tumor cells.However,the regulatory mechanism remains unknown.In this study,we have characterized the role of USP2a in promoting metastasis by facilitating TGF-β triggered signaling.Overexpression of USP2a potentiated TGF-β-mediated activation of SMAD2/3/4 reporter,expression of p15,p21 or p27,and phosphorylation of SMAD2.Knockdown of USP2a significantly inhibited TGF-β-mediated activation of SMAD2/3/4 reporter,expression of p15,p21 or p27,and phosphorylation of SMAD2.USP2a interacts with TGFBR1 and TGFBR2 upon TGF-β stimulation and removes K33-linked polyubiquitin chains from Lys502 of TGFBR1,promoting the recruitment of SMAD2/3.Simultaneously,TGFBR2 phosphorylates Ser207/225 of USP2a,leading to the disassociation of SMAD2/3 from TGFBR1.The phosphorylation of USP2a and SMAD2 is positively correlated in human tumor biopsies and USP2a is hyper-phosphorylated in lung adenocarcinomas with lymph nodes invasion.Depletion or pharmacologic inhibition of USP2a significantly inhibited TGF-β-mediated activation of SMAD2/3/4 reporter,phosphorylation of SMAD2,and expression of EMT associatated genes.Results from mouse model shows that depletion or pharmacologic inhibition of USP2a dampens lung metastasis of tumor cells,and improve the survival of the tumor mice.The results of this study reveal the new mechanisms of TGF-β trigured signaling and the new function of USP2a as a tumor metastasis promoting factor.Our findings have characterized a previously unknown role of USP2a as a potential target for treatment of metastatic cancers.