Abstract 4350:MAPK1E322Ksomatic mutation promotes cell proliferation via positive feedback regulation of EGFR/RAF signaling

The RAS-MAPK signaling cascade serves as the central node in the transduction of signals starting from the binding of the epidermal growth factor (EGF) ligand to the membrane receptors (EGFR) through to the nucleus. Recent studies suggested that different defined thresholds of RAS-MAPK activity are required for maintaining homeostasis as opposed to facilitating malignant transformation, and that Ras-oncogenic toxicity is quantitatively dictated by MAPK function. We and others have demonstrated that somatic MAPK1(E322K) mutations in MAPK1 occur in 8% of cervical squamous cell carcinoma (CSCC) and 3% of head and neck squamous cell carcinoma (HNSCC), suggesting that mutant MAPK1 may play an important part in tumorigenesis. To investigate the molecular mechanism involved in the effects of the mutated MAPK1, we transduced MAPK1 wild type and MAPK1(E322K) mutant as lentiviral constructs into the untransformed human embryonic kidney cell line HA1E. We found that cells expressing MAPK1(E322K) exhibited higher rates of proliferation and cellular mobility compared to the cells transduced with wild type MAPK1. However, the cells expressing wild type MAPK1 presented poor cell proliferation compared to the cells transduced with the empty lentiviral vector. Western blot analyses showed approximately two-fold increase phosphorylation of ERK (T202/Y204) following EGF treatment in the cells harboring the mutation compared to the cells expressing the wild type MAPK1. A similar pattern was observed with phospho-EGFR (T669, Y1148, Y1068, Y1148) phospho-cRaf (S259, S338, S289/296/301), phosphor-RSK1, phospho-AKT (S473, T389), phosphor-GSK3β (S9/21) and phospho-STAT5 (Y694), suggesting that MAPK1(E322K) mutation might reinforce the positive/negative feedback loop on EGFR and cRaf. Our data contributes to the understanding of the roles of MAPK1 in the RAS/RAF-MEK-MAPK1 signaling pathway and might help identifying possible therapeutic targets for HNSCC and CSCC patients with tumors harboring somatic MAPK1(E322K) mutations. Citation Format: Jianqing Zhang, Dewey J. Brooke, Jessica P. Blair, Jaques Riby, Akinyemi I. Ojesina. MAPK1E322K somatic mutation promotes cell proliferation via positive feedback regulation of EGFR/RAF signaling [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2019; 2019 Mar 29-Apr 3; Atlanta, GA. Philadelphia (PA): AACR; Cancer Res 2019;79(13 Suppl):Abstract nr 4350.