PFKFB3 and esophageal squamous cell carcinoma: Furthermore, to ascertain the function of K302 in regulating PFKFB3, FLAG-tagged PFKFB3 wild-type (WT) or K302A was exogenously expressed in ESCC cells; intriguingly, the PFKFB3 K302A mutant showed an extended half-life (Fig. 4j, Supplementary Fig. 4l), indicating that K302 is an important ubiquitination site responsible for PFKFB3 stability.