RHOAY42C-driven cell lineage plasticity and immune remodeling of diffuse gastric cancer [CUT&Run]

Diffuse gastric adenocarcinoma (DGA) is an aggressive gastric cancer subtype with a poor prognosis. RHOAY42C is a recurrent mutation in DGA, yet its independent oncogenic role remains unclear. We used genetically engineered gastric organoid models to demonstrate that RHOAY42C, along with KrasG12D activation and Trp53 loss (RKP), is sufficient to drive DGA without loss of E-cadherin. Integrated single-cell RNA sequencing (scRNA-seq) and spatial transcriptomics (Xenium In Situ) revealed that RKP tumors exhibit mucinous histopathology and a unique lineage trajectory originating from Aqp5+ cells and differentiating into Muc1/Muc4+ cells via YAP1 signaling. RKP tumors establish a highly immunosuppressive tumor microenvironment in which AREG-mediated activation of EGFR promotes T cell exhaustion. Unlike E-cadherin loss-induced DGA, RKP tumors display strong susceptibility to PD-1 blockade. These findings redefine the oncogenic role of RHOAY42C, highlighting its sufficiency for DGA development and identifying PD-1 inhibition as a promising therapeutic strategy for patients with DGA harboring this mutation.