Focadhesin interacts with SALL4 to regulate EGFR signaling and oncogenesis in non-small cell lung cancer

Owing to drug resistance to therapeutic targets, there is an urgent demand to find and validate new potent targets for non-small cell lung cancer (NSCLC). Although high SALL4 expression significantly promotes lung cancer growth, its oncogenic mechanism remains unclear. In the current study, focal adhesion molecular focadhesin (FOCAD), a candidate that has interacted with oncofetal SALL4, was identified by SALL4 immunoprecipitation and mass spectrometry. Immunoprecipitation, immunofluorescence stains, cell component separation, and molecular docking demonstrated the interaction of SALL4 and FOCAD. Immunoblotting and/or TCGA dataset analysis showed high expression of SALL4 and FOCAD paralleled in lung adenocarcinoma but not in lung squamous cell carcinoma. FOCAD knockdown resulted in dramatic inhibition of cell viability, colony formation, xenograft growth, wound healing, and invasion; apoptotic induction; and G₂-phase blockade in NSCLC cell lines through suppression of the EGFR or IGF1R signaling pathways and expression of FAK and β-catenin. Conversely, SALL4 overexpression partially attenuated the inhibition of cell viability and colony formation of FOCAD silencing in these cells. The combination of FOCAD shRNA knockdown with osimertinib treatment showed additive anti-tumor activity in NSCLC cell lines. Furthermore, FOCAD silencing also showed markedly anti-proliferative effects in the osimertinib-resistant NSCLC cell line. These findings demonstrate that FOCAD in NSCLC is generally associated with SALL4 and EGFR expressions and activation. There are functional correlations between FOCAD and SALL4, and targeting FOCAD could be an effective therapeutic strategy in both osimertinib-sensitive and -resistant NSCLC.