How PD-L1 expression is regulated in cancer is poorly understood. Here, we report that the ATP-binding activity of ERBB3 pseudokinase regulates PD-L1 gene expression in colorectal cancers (CRCs). ERBB3 is one of the four members of the EGF receptor family, all with protein tyrosine kinase domains. ERBB3 is a pseudokinase with a high binding affinity to ATP. We showed that ERBB3 ATP-binding inactivation mutant reduces tumorigenicity in genetically engineered mouse models and impairs xenograft tumor growth of CRC cell lines. The ERBB3 ATP-binding mutant cells dramatically reduce IFN-γ-induced PD-L1 expression. Mechanistically, ERBB3 regulates IFN-γ-induced PD-L1 expression through the IRS1-PI3K-PDK1-RSK-CREB signaling axis. CREB is the transcription factor that regulates PD-L1 gene expression in CRC cells. Knockin of a tumor-derived ERBB3 mutation located in the kinase domain sensitizes mouse colon cancers to anti-PD1 antibody therapy, suggesting that ERBB3 mutations could be predictive biomarkers for tumors amenable to immune checkpoint therapy.

We recently reported that PIK3CA mutant colorectal cancers (CRCs) are addicted to glutamine through up-regulation of glutamate pyruvate transaminase 2 (GPT2). A GPT2 inhibitor suppresses in vivo growth of PIK3CA mutant, but not wild-type, CRCs. This study indicates that targeting glutamine may be an effective approach to treat CRCs with PIK3CA mutations.