Glypican‐3 Upregulated by YTHDF1 in an m6A ‐Dependent Manner Interacts With MUL1 to Repress HSF1 Ubiquitination Degradation, Boost CD276 Transcription, and Mediate Immune Escape in Gastric Cancer

CD8+ T cell-mediated immune escape is a key mechanism in tumor progression. GPC3 has an impact on the progression of various tumors. However, its potential function and regulatory mechanism in the immune escape of gastric cancer (GC) are still unclear. GC clinical samples were collected to assess the expression of GPC3. The impact of GPC3 on GC prognosis was analyzed by bioinformatics analysis. CCK-8, colony formation, flow cytometry, and Transwell were utilized to detect changes in GC cell viability, proliferation, antiapoptosis, migration, and invasion ability. According to bioinformatics analysis, the linkage between N6 m6A modification, protein interactions, ubiquitination, and transcriptional regulation was revealed. The m6A modification effect of YTHDF1 on GPC3 was verified through MeRIP, RIP, RNA-pull-down assays, and multiribosome experiments. CO-IP and immunofluorescence were undertaken to validate the interaction between GPC3 and MUL1. The effect of GPC3 and MUL1 on HSF1 ubiquitination was assessed by the in vitro ubiquitination assay. Moreover, the transcriptional activation effect of HSF1 on CD276 was examined through ChIP and dual luciferase experiments. We constructed a co-culture system of tumor cells and CD8+T cells, detected CD8+T cell proliferation using CFSE, assessed cell toxicity using LDH, and evaluated the cytotoxicity of CD8+T cells by detecting the secretion of killing factors using ELISA. Finally, an allograft mouse model was constructed to validate the therapeutic effect of targeting GPC3 and CD276 monoclonal antibodies. Combining bioinformatics analysis, clinical sample testing, and cell experiments, it was confirmed that GPC3 was highly upregulated in GC, boosting malignant progression such as GC cell viability, proliferation, and antiapoptosis, and affecting the poor prognosis of GC. Mechanistically, YTHDF1 mediated m6A methylation to reinforce GPC3 translation. GPC3 interacted with MUL1 to repress ubiquitination degradation of HSF1, and HSF1 enhanced transcriptional activation of the immune checkpoint CD276. GPC3 depressed the antitumor activity of CD8+T cells through the MUL1/HSF1/CD276 axis, mediating GC tumor immune escape. YTHDF1 upregulates the expression of GPC3 in GC in an m6A-dependent manner. GPC3 interacts with MUL1 to depress the ubiquitination degradation of HSF1, thereby upregulating the immune checkpoint CD276 and affecting GC immune escape.