Truncated APC impairs innate immune response by targeting MAVS on mitochondria in colorectal cancer

Background: Most mutant adenomatous polyposis coli (APC) gene produced truncated APC protein (Trunc-APC), which has been shown to function as an oncogene in colorectal Cancer (CRC) pathogenesis; however, its role in modulating innate immune responses within tumor cells remains unexplored.

Methods: We utilized CRISPR-Cas9 to knockout mutant APC and performed transcriptome Sequencing across multiple CRC cell lines to investigate the immunomodulatory function of Trunc-APC. Subcellular fractionation, proteinase K protection assays, and immunofluorescence were employed to determine Trunc-APC subcellular localization. Protein interaction studies, ubiquitination assays, and aggregation analyses were conducted to elucidate Trunc-APC binding to MAVS and its impact on MAVS ubiquitination and RIG-I association. The effects of Trunc-APC deletion, alone or in combination with 5-azacytidine and trichostatin A, were evaluated on type I interferon activation, Apoptosis, and tumor growth both in vitro and in vivo.

Results: We found that Trunc-APC partially localizes to the mitochondrial outer membrane and attenuates type I interferon signaling by binding to MAVS, suppressing its K63-linked polyubiquitination, and disrupting MAVS-RIG-I interactions. Deletion of Trunc-APC, particularly when combined with 5-azacytidine and trichostatin A, enhanced innate immune activation, promoted tumor cell Apoptosis, and significantly inhibited CRC tumor growth both in vitro and in vivo.

Conclusions: Our study reveals a previously unrecognized role of Trunc-APC in dampening tumor-intrinsic innate immunity and suggests that co-targeting Trunc-APC with epigenetic therapy may offer a promising strategy to enhance anti-tumor immune responses in CRC.