Pancreatic and colon cancer stem cells escape NK cell effector function via PCNA–NKp44 interaction

Abstract

Abstract Natural killer (NK) cells play an important role in the innate immune response against cancer. Unlike B or T lymphocytes, NK cells do not require prior sensitization and can immediately respond to target cells. NK cell function depends on a balance of signals transmitted from activating and inhibitory receptors interacting with ligands on the surface of cells. Cancer cells may escape NK-mediated responses by expressing inhibitory ligands. Proliferating cell nuclear antigen (PCNA), in association MHC I, forms the inhibitory ligand for NKp44. Cancer stem cells (CSC), a unique subset of tumor cells, possess a stem-cell-like phenotype and are thought to facilitate metastasis by escaping NK cell effector function. CSC can be identified by a variety of markers such as surface co-expression of CD44 and CD133. In both Panc-1 and HCT 116 cell lines, surface PCNA is associated with co-expression of CD44 and CD133. Triple positive (PCNA+CD44+CD133+) cells have increased CSC transcription factor (NANOG, SOX2, and Oct-4) expression compared to double positive (PCNA−CD44+CD133+) or negative cells. Additionally, blocking the PCNA–NKp44 interaction alters IFN-g secretion and increases specific lysis of cancer cells by NK cells. Taken together, these data suggest that surface co-expression of PCNA, CD44, and CD133 are markers of pancreatic and colon CSC and blocking the PCNA–NKp44 interaction may provide an immunotherapeutic approach to target pancreatic and colon CSC and prevent metastasis.