A MUC1-ALIX complex regulates extracellular vesicle cargo loading with activated SRC to enhance pancreatic cancer progression.

Extracellular vesicles (EVs) are critical mediators of intercellular communication in the tumor microenvironment and play an essential role in tumor growth and metastasis. MUC1 has been identified in tumor cell-derived EVs, but its function in that context has not been well investigated. We show that MUC1 is highly enriched in EVs derived from pancreatic cancer cell lines and patient tumors but not normal pancreas. Pretreatment of mice with tumor derived MUC1 positive EVs promoted tumor cell growth and metastasis in vivo. MUC1 positive EVs enhanced tumor cell growth, motility and invasion in vitro. Proteomic profiling revealed that MUC1-positive EVs contain protein cargo distinct from MUC1-negative EVs, which implicates MUC1 in selective EV cargo regulation. We demonstrate that the cytoplasmic tail of MUC1 expressed in pancreatic cancer cells interacts with programmed cell death 6-interacting protein (ALIX) and influences EV biogenesis and loading of specific oncogenic cargo (PhosphoTyr416-Src) that are known to associate with MUC1. EVs from SRC inhibitor Bosutinib treated cells showed reduced effects on cell viability, migration, and invasion of MUC1 knockout cells as compared to EVs from untreated cells. Thus, MUC1-positive EVs containing activated Src promoted tumor cell proliferation and in vivo tumor growth, migration, and metastasis of orthotopic pancreatic cancer cells. Collectively, our findings identify a previously unrecognized role for MUC1 in influencing EV composition and function: influencing loading of oncogenic protein cargoes into EVs. Our data highlight a novel mechanism controlling tumor-specific EV cargo loading and demonstrate that oncogenic cargo in MUC1-associated EVs contributes to pancreatic cancer progression.