beta8 integrin critically contributes to pancreatic cancer cell radiochemoresistance and intracellular vesicle trafficking under stress conditions

Background: Pancreatic ductal adenocarcinoma (PDAC) is one of the five most lethal malignancies in the world and has a 5-year relative overall survival rate of less than 5%. Thus, there is a great need for functional targeting d 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 radiochemoresistance. Intriguingly, 8 integrin turned out to be one of the most potential novel targets in PDAC.
Material and methods: We performed a 3D 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, clonogenic survival assays were performed upon esiRNA-mediated knockdown, X-ray irradiation (6 Gy single dose) and gemcitabine. 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 pathway involved in changes of 8 integrin localization upon treatment.
Results: We identified a series of novel targets including 8 integrin. Without cytotoxicity, 8 integrin depletion elicited radiochemosensitization in PDAC, PDCs cell lines and reduced sphere formation and 3D invasion into collagen-I. Intriguingly, we found 8 integrin located in perinuclear area where it colocalized with the cis-Golgi matrix protein GM130. Upon irradiation and gemcitabine, 8 integrin dissociated from the perinuclear region and spread throughput the cytosol without enhanced localization to exosomes; a process abrogated by antimycin A or oligomycin pre-treatment.
Summary: Our findings, generated in 3D lrECM PDAC cell ccultures, suggest 8 integrin as a novel determinant of PDAC radiochemoresistance. Moreover, 8 integrin may, although not found in the cell membrane to facilitate cell adhesion, a critical role in intracellular vesicle trafficking under stress conditions. Ongoing work will unravel the underlying mechanisms how 8 integrin is controlling cytoplasmic and nuclear survival pathways.