MUC4 interacts and stabilize EGFR1 in a ligand‐dependent manner leading to sustained oncogenic signaling

Epidermal growth factor receptor 1 (EGFR1)‐mediated signaling is critical for the initiation and progression of K‐ras‐dependent malignancies. In pancreatic cancer (PC), activation of EGFR1 through ERK1/2 (pT202/pY204) pathway potentiate mechanisms downstream of oncogenic Kras early during PC initiation. In addition to ligand‐dependent activation of EGFR1, the expression of the EGF‐like domain containing molecules have been shown to facilitate EGFR1 signaling. Mucins, especially MUC4, contain the unique combination of three juxtamembrane EGF‐like domains (MUC4‐β) along with multiple extracellular matrix interacting domains (MUC4‐α). MUC4 is not expressed in normal pancreas and inflammatory pathologies of the pancreas. However, its expression appears early during PC initiation coinciding with the essential requirement of EGFR1‐mediated signaling. Our previous studies have demonstrated that MUC4 interacts with EGFR family members including EGFR2 (HER2); however, its interaction with the key EGFR family member, EGFR1, remains poorly characterized. Using multiple biochemical approaches and PC patient samples, we investigated MUC4 and EGFR1 interactions and its clinical relevance. Co‐immunoprecipitation experiments using PC cell lines, CD18/HPAF and Colo357, demonstrated a direct physical interaction of MUC4 with EGFR1, and its phosphorylated form pY1068‐EGFR1 in an EGF‐dependent manner. Immunofluorescence experiments demonstrated that EGFR1 co‐localize with MUC4 on the plasma membrane of PC cells. Silencing of MUC4 resulted in increased internalization and subsequent degradation of EGFR1 following ligand activation. These findings were further corroborated by sub‐cellular fractionation studies where MUC4 silencing led to significantly elevated levels of EGFR1 in the cytoplasmic fraction suggesting the membrane stabilization of EGFR1 by the MUC4 to potentiate its signaling. Using deletion constructs of MUC4, we further demonstrated that MUC4‐β domain is necessary and sufficient to interact with EGFR‐1. Further analysis using PC patient samples showed that MUC4 co‐localize with EGFR1 in PC cells, suggesting the potential role of MUC4 and EGFR1 interaction in PC progression and plausible targeting of MUC4 and EGFR1 interactions interface for the therapeutic purpose. Collectively, our studies demonstrated that MUC4 physically interacts with EGFR1 in a ligand‐dependent manner and prevents its internalization thereby enhancing its stability and potentiate downstream signaling to facilitate K‐ras‐mediated PC initiation and progression. Support or Funding Information Grant Support: This work was, in parts, supported by funding from the National Institute of Health (PO1 CA217798, R01 CA183459, RO1 CA195586, RO1 CA206444, R21 AA026428, and RO1 CA228524). This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal .