Apolipoprotein L3 Enhances CD8+ T Cell Antitumor Immunity of Colorectal Cancer by Promoting LDHA-mediated Ferroptosis

Aim: Colorectal cancer (CRC) is the leading cause of cancer associated death worldwide and immune checkpoint blockade therapy only benefit a small set of CRC patients. Tumor ferroptosis of CRC reflected immune-activation in our previous findings. Understanding the mechanisms underlying how to bolster CD8+ T cells function through ferroptosis in CRC tumor microenvironment (TME) will greatly benefit cancer immunotherapy. Methods: Genes between ferroptosis and CD8+ T cell function in CRC were screened through Cox, WGCNA and differential expression analysis. Immunohistochemistry and Immunofluorescence analysis were performed. Co-immunoprecipitation were performed to determine protein-protein interaction, mRNA level was determined by qRT-PCR. RSL3 was used to induce ferroptosis, and ferroptosis levels were evaluated by measuring Transmission Electron Microscope analysis, MDA, Fe2+level and cell viability. Results: We screened APOL3 as the significant modulator for ferroptosis-related CD8+ infiltration in CRC. Next, by in vitro and in vivo, we found that increased APOL3 expression was positively correlated with sensitivity to ferroptosis and antitumor ability of CD8+ T cells. Next, we demonstrated that APOL3 can binds LDHA and promote its ubiquitylation-related degradation. Then, based on in vivo analysis and tumor specimen, we discovered the APOL3-LDHA axis can facilitate the tumor ferroptosis and cytotoxic ability of CD8+ T cells through increased IFNγ and decreased lactic acid concentration. Conclusion: The present study demonstrated that APOL3 promotes ferroptosis and immunotherapy in colorectal cancer cells. The present work provides us with a novel target to overcome drug resistance to ferroptosis and immunotherapy.