GRP78 Drives NSCLC Stemness and EMT via a SIX1/β-Catenin Signaling Axis

Non-small cell lung cancer (NSCLC) exhibits stem-like characteristics that drive tumor aggressiveness and treatment resistance. The molecular chaperone Glucose-Regulated Protein 78 (GRP78) is substantially elevated in NSCLC compared to normal tissues and cell lines. In clinical samples, GRP78 protein levels correlated with advanced tumor stage and lymph node metastasis. Pharmacological inhibition of GRP78 using BAPTA-AM and GRP78-IN-3 significantly suppressed NSCLC cell viability while promoting apoptosis. The inhibitors effectively attenuated cell migration by downregulating matrix metalloproteinases and reversed epithelial-mesenchymal transition by modulating key cadherin expression profiles. Importantly, GRP78 inhibition substantially reduced cancer stem cell markers and impaired spheroid formation capability. Genetic knockdown of GRP78 in A549 and H1975 cells recapitulated the effects of pharmacological inhibition, reducing cell migration, reversing EMT, attenuating stemness, and suppressing β-catenin signaling. Conversely, GRP78 overexpression in A549 and H1975 cells induced opposite effects, promoting mesenchymal markers, enhancing stemness proteins, and increasing spheroid size. Mechanistic studies revealed that this anti-tumor activity operates through suppression of β-catenin signaling mediated by SIX1, as evidenced by SIX1-overexpression rescue experiments. These findings demonstrate that GRP78 acts as a key regulator of NSCLC stemness and metastatic potential by coordinating epithelial plasticity and stemness pathways, positioning it as a promising therapeutic target for NSCLC treatment.