SMAD4 and hepatocellular carcinoma: Given that it is ubiquitination, rather than phosphorylation, which tightly controls the protein abundance and function of Smad4 (Dupont et al., 2009; Liang et al., 2004; Wan et al., 2005; Zhou et al., 2017), we conducted a functional RNA interference screen to globally profile the contribution of ubiquitin‐specific proteases (USPs), the major subfamily of deubiquitinating enzymes (DUBs), to the transcriptional activity of Smad4 in HCC models.