Downregulation of OPCML is associated with activation of AKT signaling and aggressive phenotypes in glioblastoma cells.

Background: OPCML (opioid-binding protein/cell adhesion molecule-like), a glycosylphosphatidylinositol (GPI)-anchored IgLON adhesion molecule with brain-enriched expression, has tumor-suppressive roles in several epithelial cancers; however, its role in glioblastoma (GBM) biology is unclear. Methods: We integrated two bulk microarray cohorts to derive a reproducible GBM signature and reanalyzed single-cell RNA sequencing (scRNA-seq) data to localize OPCML at single-cell resolution. The tissue distribution and clinical associations were evaluated using the Human Protein Atlas (HPA) and The Cancer Genome Atlas (TCGA), with survival modeling and a nomogram. The co-expression, STRING-based protein interaction, and Gene Ontology (GO)/Kyoto Encyclopedia of Genes and Genomes (KEGG) enrichment analyses outlined the molecular context. Immune infiltration was profiled using single-sample gene set enrichment analysis (ssGSEA) and cross-checked on TIMER2. Functional validation used a single OPCML small interfering RNA (siRNA) with a non-targeting siRNA control (siNC) in U87 and U251 cells with Transwell invasion, wound healing, colony formation, CCK-8 proliferation, and Western blotting for p-AKT and p-mTOR, with LY294002 rescue. Results: OPCML was consistently downregulated in GBM and across multiple cancers. Within GBM, a lower expression was associated with higher grade, older age, isocitrate dehydrogenase (IDH) wild type, and poorer overall survival. At the single-cell level, the OPCML transcripts were largely confined to a neuron-glia hybrid population and were scarce in classical malignant clusters. Genome-wide correlations in GBM showed positive links to extracellular matrix/synaptic programs and negative links to cell cycle/DNA replication pathways. In vitro, OPCML knockdown increased the invasion, migration, clonogenic growth, and CCK-8 readouts and was associated with elevated p-AKT and p-mTOR. PI3K inhibition reversed the signaling changes. Pan-cancer, OPCML tracked with denser immune signatures, whereas in GBM it was inversely correlated with multiple effector populations and with cancer-associated fibroblast (CAF) estimates across deconvolution methods. Conclusions: OPCML marks a neuron-leaning, less aggressive state and is associated with the regulation of PI3K-AKT-mTOR signaling in GBM. Loss of OPCML aligns with proliferative programs and a GBM-specific immune pattern. These data nominate OPCML as a prognostic marker and a surface-level modulator that could be leveraged alongside RTK/PI3K axis inhibitors in GBM.