Isoform specific FBXW7 mediates NOTCH1 Abruptex mutation C1133Y deregulation in oral squamous cell carcinoma

Our group previously identified that the NOTCH1 Abruptex domain contains the most mutations in Chinese OSCC patients, including a hotspot mutation (C1133Y). FBXW7 is an E3 ubiquitin ligase that regulates a network of proteins, including NOTCH1, via degradation. In this study, we first described the co-localization of isoform specific FBXW7-FBXW7β and NOTCH1(C1133Y) mutation in the same cytoplasmic sites. Gain- and loss-of-function assays were performed to examine the tumor suppressor role of FBXW7β in the proliferation and invasion of OSCC cells. The co-expression of NOTCH1(C1133Y) and FBXW7β significantly attenuated tumor growth. Meanwhile, FBXW7β reversed the oncogenic phenotype and the activation of the AKT/ERK/NFκB pathway induced by NOTCH1(C1133Y) mutation. FBXW7β downregulated the stability of NOTCH1(C1133Y) protein and promoted protein ubiquitination. This was the first time that we selected a NOTCH1 hotspot mutation detected in clinical samples and identified the function of FBXW7β that mediated NOTCH1 mutation degradation in OSCC. The newly identified interaction between FBXW7β and NOTCH1(C1133Y) protein provides new insights into the progression of OSCC, especially regarding Abruptex domain mutations, and represents a valuable target for OSCC therapy.