A multi-subunit autophagic capture complex facilitates degradation of ER-stalled MHC class I in pancreatic cancer.

Pancreatic ductal adenocarcinoma (PDAC) evades immune surveillance in part through autophagic capture and lysosomal degradation of major histocompatibility complex class I (MHC-I), though the basis for this vulnerability is unclear. Using synchronized endoplasmic reticulum (ER) exit assays, we show that PDAC cells retain MHC-I in the ER and inefficiently traffic it to the plasma membrane. We identify an autophagic capture complex composed of the ER-phagy receptor TEX264 and the cargo receptor NBR1 that targets MHC-I for degradation. Suppression of either receptor restores total and surface MHC-I levels. Capture is linked to antigen loading, as impaired peptide loading increases MHC-I binding to the TEX264-NBR1 complex, while high-affinity peptides reduce binding and promote increased surface localization. A genome-wide CRISPRi screen identified the ER-localized E3 ligase NFXL1 as a mediator of MHC-I ubiquitylation and capture. Elevated NFXL1 correlates with reduced MHC-I expression and poor prognosis, highlighting a targetable pathway regulating PDAC immunogenicity.