SKP2 and hepatocellular carcinoma: The regulation of LKB1 activity by ubiquitination was also observed in a recent study, whereby Lee et al. showed that K63 linkage of LKB1 mediated by E3 ligase Skp2 dictates the complex integrity and kinase activity of LKB1.18 However, the LKB1 kinase activity maintained by K63 linkage confers LKB1 with the oncogenic activity in hepatocellular carcinoma (HCC) models.18 In our study, we showed that SKP2 was not responsible for the LKB1 K6-linked ubiquitination (Supplementary Fig. S4e), suggesting that the K6 linkage on LKB1 utilized some other E3 ubiquitin ligase(s) instead of SKP2.