Assembly and localization of extracellular matrix protein fibronectin modulates Natural killer cell infiltration in tumor spheroids.

Abstract

Abstract Natural Killer cells (NK), the major innate effector cells, with their broad cytotoxicity against tumors are ideal candidates for immunotherapy. Once having entered the malignant site, NK cells encounter a complex environment composed of tumor cells, non-tumor cells along with the extra cellular matrix (ECM). As one of the integral components of the tumor microenvironment (TME), the normal regulation of the extra cellular matrix (ECM) is necessary to prevent tumor progression and metastasis. Nevertheless, the impact of the matrix architecture found in solid tumors on immune cells and especially NK cells is not well characterized. Here we investigated the role of Fibronectin, a fibrous ECM protein, and its assembly and localization on NK cell infiltration into clear cell renal cell carcinoma (ccRCC) spheroids. 3D tumor spheroids established from the ccRCC cell line 786-O (RCC-) that lacks the Von Hippel-Lindau (VHL) gene are incapable of fibronectin assembly in their ECM. However, addition of the VHL gene into the 786-O cells (RCC+) reversed this phenotype facilitating fibronectin assembly. Fibronectin in RCC-spheroids exhibited prominent peripheral localization in contrast to RCC+ spheroids where fibronectin was detected towards the center of the spheroid. Coincident with fibronectin localization, PKH26 labeled Natural killer cell line, NKL, showed significantly increased infiltration into RCC+ spheroids compared to RCC-spheroids that lacked the tumor suppressor VHL. Thus, assembly and localization of fibronectin modulates NK cell infiltration in RCC tumors. Supported by grants from NIH U54MD012388 (NR and AV) and NIH U54CA143925 (NACP-NAU) to NR.