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Summary: TGF-β has been demonstrated to promote tumor metastasis, and the regulatory mechanisms are poorly understood. Here, we report the role of USP2a in promoting metastasis by facilitating TGF-β-triggered signaling. 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/Ser225 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 node invasion. Depletion or pharmacologic inhibition of USP2a dampens TGF-β-triggered signaling and metastasis. Our findings have characterized an essential role of USP2a as a potential target for treatment of metastatic cancers. : Zhao et al. find that USP2a deconjugates K33-linked ubiquitination of TGFBR1 at Lys502 and is phosphorylated at Ser207/Ser225 by TGFBR2 after TGF-β stimulation. This allows R-SMAD recruitment to and subsequent disassociation from the TGFBR1/2 receptor complex. Keywords: USP2a, TGF-β, epithelial-to-mesenchymal transition, metastasis, ubiquitination, phosphorylation, SMAD2/3, TGFBR1/2, signaling transduction