MAPK1 and head and neck squamous cell carcinoma: Furthermore, inhibition of Erk phosphorylation by PI3Kα inhibitor was revealed to be mediated by GAB1, as evidenced by the observation that the phosphorylation of GAB1 and Erk remained largely unchanged upon CYH33 treatment in HNSCC cells and xenografts overexpressing myristoylated GAB1.