黏附型GPCR BAI3的一种新型短亚型源自替代启动子，可逆转EMT过程并在多形性胶质母细胞瘤（GBM）中带来生存获益

BAI3 (ADGRB3 gene), a member of the adhesion G-protein-coupled receptors, is predominantly expressed in the brain and regulates dendritic morphogenesis, synaptic plasticity, etc. Here, we report for the first time the existence, transcriptional origin, and functional significance of ADGRB3 transcripts in GBM.Immunoblotting revealed both Full-length (FL-) and short (S-) BAI3 isoforms in wild-type mice, whereas only S-BAI3 was detected in exon 10-targeted BAI3 knockout (KO) mice. In contrast, neither isoform is present in exon 2 and 18-targeted BAI3 KO mice. Long-read isoform sequencing independently confirmed the presence of short transcripts in mice cortex. H3K4me3 and H3K27ac ChIP-Seq identified transcriptionally active promoter regions near exons 1 and 18 in mice. Consistently, we found that the short transcript, originating from alternative promoter in intron 17, is the most abundant ADGRB3 transcript in the human brain. Unlike FL-BAI3, S-BAI3 is preferentially localized to intracellular compartments rather than the cell membraneEvaluation of the transcripts-specific expression of ADGRB3 in GTEx-Brain and TCGA-GBM dataset revealed significant downregulation of both FL- and S-BAI3 protein-encoding transcripts in primary and recurrent GBM tumors. Analysis of whole-genome bisulfite sequencing (GSE121721) revealed multiple GBM-specific hypermethylated regions, representing epigenetic remodeling of regulatory regions of ADGRB3. Functional evaluation demonstrated that S-BAI3 overexpression significantly reduced the proliferation of LN229 glioblastoma cell lines. Overexpression of either isoform resulted in significantly delayed wound closure, reduced cell migration and invasion, with the strongest effects observed for S-BAI3. To determine the molecular mechanism of the antitumor activity of BAI3 isoforms, we assessed the alteration of 450 protein biomarkers by using a reverse-phase protein array. Both isoforms suppress epithelial-to-mesenchymal transition (EMT) signature and promote mesenchymal-to-epithelial shift, S-BAI3 exerting the strongest effect. Comparative analysis of TCGA-GBM and GTEx-Brain demonstrated similar patterns, linking EMT to the expression of BAI3 isoforms. To illustrate the in vivo effect of BAI3 isoforms, nude mice were orthotopically inoculated with IRFP720-expressing empty vector control, FL- and S-BAI3 overexpressing LN229 cells. Longitudinal analysis of the normalized IRFP720 signal revealed that both isoforms significantly attenuated tumor growth compared to the control, consistent with 3D tumor imaging by light sheet microscopy. Survival analysis demonstrated a significant increase in the median survival in the S-BAI3 overexpressing group (72.5 days; HR=0.25, P=0.007), whereas the FL-BAI3 overexpression did not confer survival benefit.Taken together, our results suggest that BAI3 isoforms are epigenetically silenced in GBM, and alternative promoter-driven S-BAI3 is a mechanistically distinct tumor-suppressor with direct implications for isoform-specific epigenetic reactivation and therapeutic targeting in GBM.