NetrinG1 ⁺ Cancer-Associated Fibroblasts Generate Unique Extracellular Vesicles that Support the Survival of Pancreatic Cancer Cells Under Nutritional Stress

Abstract

It is projected that in 5 years, pancreatic cancer will become the second deadliest cancer in the United States. A unique aspect of pancreatic ductal adenocarcinoma (PDAC) is its stroma; rich in cancer-associated fibroblasts (CAFs) and a dense CAF-generated extracellular matrix (ECM). These pathogenic stroma CAF/ECM units cause the collapse of local blood vessels rendering the tumor microenvironment nutrient-poor. PDAC cells are able to survive this state of nutrient stress via support from CAF-secreted material, which includes small extracellular vesicles (sEV). The tumor-supportive CAFs possess a distinct phenotypic profile, compared with normal-like fibroblasts, expressing NetrinG1 (NetG1) at the plasma membrane, and active Integrin α ₅β ₁ localized to the multivesicular bodies; traits indicative of poor patient survival. We herein report that NetG1 ⁺ CAFs secrete sEVs that stimulate Akt-mediated survival in nutrient-deprived PDAC cells, protecting them from undergoing apoptosis. Furthermore, we show that NetG1 expression in CAFs is required for the prosurvival properties of sEVs. In addition, we report that the above-mentioned CAF markers are secreted in distinct subpopulations of EVs; with NetG1 being enriched in exomeres, and Integrin α ₅β ₁ being enriched in exosomes. Finally, we found that NetG1 and Integrin α ₅β ₁ were detected in sEVs collected from plasma of patients with PDAC, while their levels were significantly lower in plasma-derived sEVs of sex/age-matched healthy donors. The discovery of these tumor-supporting CAF-EVs elucidates novel avenues in tumor–stroma interactions and pathogenic stroma detection.

Significance:

Results from this study identified two unique types of tumor-supporting CAF EVs, with evidence of these being detected in patients. Thus, this study facilitates a novel avenue to further dissect the subtleties of the tumor–stroma interactions responsible for PDAC homeostasis and progression, as well as the possibility of establishing future means to detect and monitor dynamic stroma staging.