ITGB4/BNIP3 Activates Autophagy and Reduces MHC-I Expression to Mediate Tumour Immune Escape in Pancreatic Cancer Cell Lines.

Abstract

This study attempted to identify the relevant pathways involved in autophagy activation of pancreatic cancer and explore the mechanisms underlying immune evasion. Western blot (WB) was used to detect the expression of ITGB4, BNIP3, autophagy-related proteins and MHC-I. Co-immunoprecipitation (Co-IP) was used to verify the binding mode of ITGB4 and BNIP3. Flow cytometry was used to detect the expression of MHC-I on the cell membrane. Transmission electron microscope (TEM) was used to observe cell autophagy. Confocal microscopy was used to observe the co-localisation relationship between MHC-I and autophagosomes in cells. ELISA was used to detect the level of lactate dehydrogenase and granzyme B in a tumour cell-CD8⁺ T-cell co-culture system. Mouse syngeneic transplant tumour model and orthotopic tumour model were constructed and treated with PD-1 monoclonal antibody to observe tumour growth. Quantitative reverse transcription polymerase chain reaction (qRT-PCR) was used to detect the mRNA expression of ITGB4 and BNIP3 in tumour tissues. WB was used to determine the expression of autophagy-related proteins. Flow cytometry was used to detect the expression of MHC-I on cell membranes and the proportion of CD3⁺ and CD8⁺ cells. The results of Co-IP experiments showed that ITGB4 could bind to BNIP3. It was observed under confocal microscopy that activating ITGB4/BNIP3 could promote the phagocytosis of MHC-I by autophagosomes. Finally, the subcutaneous tumour transplantation and orthotopic tumour experiments in mice demonstrated the downregulation of ITGB4 significantly improved the therapeutic effect of PD-1 antibodies on pancreatic cancer. In pancreatic cancer cells, autophagy is positively correlated with the ITGB4-BNIP3 complex protein expression level. Autophagy diminishes the protein expression of MHC-I, thereby promoting immune escape in pancreatic cancer cells.