An oncostatin M receptor and chloride intracellular channel 1 crosstalk drives key oncogenic pathways in glioblastoma.

Oncostatin M receptor (OSMR) plays diverse roles in several human malignancies, including brain, breast, and pancreatic cancer. In glioblastoma (GB), OSMR orchestrates a feedforward signaling mechanism with the truncated active mutant of epidermal growth factor receptor (EGFR), the EGFRvIII, and signal transducer and activator of transcription 3 (STAT3) to drive GB progression. Beyond EGFRvIII, OSMR promotes brain tumor stem cell (BTSC) respiration and therapy resistance. The molecular mechanisms underlying OSMR's multifaceted roles remain largely unclear. Here, we systematically mapped the OSMR interactome using Mammalian Membrane Two-Hybrid High-Throughput Screening (MaMTH-HTS). We identified OSMR-specific and OSMR/EGFRvIII-specific high-confidence candidate binding proteins, highlighting OSMR context-dependent functions. Among a subset of common interactors, we uncovered chloride intracellular channel 1 (CLIC1) as a critical regulator of OSMR-STAT3 signaling and the OSMR/EGFRvIII complex. CLIC1 physically associates with OSMR and EGFRvIII and facilitates EGFRvIII packaging into extracellular vesicles (EVs). Genetic deletion of CLIC1 disrupts the OSMR/EGFRvIII interaction, impairs STAT3 activation, reduces EGFRvIII EV content, and slows GB progression. Using whole-cell patch-clamp recordings and a monoclonal antibody that selectively targets transmembrane CLIC1 (tmCLIC1omab), we establish a distinct pharmacologically and biophysically tmCLIC1-mediated current in GB indispensable for sustaining EGFRvIII/STAT3 signaling. Importantly, we show that OSMR is required for maintaining CLIC1-mediated ionic balance at the plasma membrane (PM). Our study uncovers a bidirectional crosstalk between OSMR and tmCLIC1 in GB, essential for fueling its malignant growth.