beta8 integrin determines radiochemoresistance pancreatic cancer cells by regulating autophagy and intracellular vesicle trafficking

Background: Pancreatic ductal adenocarcinoma (PDAC) is notoriously resistant to radio/chemotherapy and carries the most dismal prognosis among solid tumors with a 5-year relative overall survival rate of approximately 6% and. Thus, there is a great need for molecular-targeting strategies. As cell-matrix adhesion is essential for the survival, invasion and therapy resistance, we sought to identify the function of 117 focal adhesion proteins (FAP) in PDAC cell radioresistance. Intriguingly 8 integrin turned out to be one of the most potential novel targets in PDAC.
Material and methods: We performed a 3D tumor organoid endoribonuclease-prepared siRNA (esiRNA)-based high throughput screening (3DHTesiS) in PDAC cell cultures (established and patient-derived (PDC)) grown in laminin-rich extracellular matrix (IrECM). In addition to characterizing 8 integrin expression, distribution and co-localization with other cellular organelles such as golgi apparatus, tumor organoid forming ability was measured upon 8 integrin knockdown in X-ray (6 Gy) and/or gemcitabine-treated cells. Fiji software was used to determine Peason’s correlation coefficient, vesicle distribution and expression patterns upon irradiation or gemcitabine. An inhibitor screen was conducted to identify pathways involved in the perinuclear-to-cytoplasmic shift of 8 integrin upon treatment. Immunoprecipitation–Mass Spectrometry (IP-MS) was performed to identify 8 integrin interactome upon irradiation.
Results: We identified a series of novel targets including 8 integrin. Without cytotoxicity, 8 integrin depletion elicited radiochemosensitization in PDAC. Intriguingly, we found 8 integrin located in perinuclearly where it colocalize with the cis-Golgi matrix protein GM130. Upon irradiation or gemcitabine, 8 integrin dissociated from the perinuclear region and spread throughout the cytosol by interact with motor proteins including dynein, kinesin, myosin; a process abrogated by microtubule-disturbing agent colchicine. Additionally, 8 integrin depletion reduced PDAC cells autophagy by LC3 turnover assay.
Summary: Our findings, generated in 3D lrECM PDAC organoid cell cultures, suggest 8 integrin as a novel determinant of PDAC radiochemoresistance. Moreover, 8 integrin may facilitate, although not found in the cell membrane to facilitate cell adhesion, a critical role in intracellular vesicle trafficking and co-regulation of autophagy upon irradiation.