Tumor Edge-to-Core Transition Promotes Malignancy in Primary-to-Recurrent Glioblastoma Progression in a PLAGL1/CD109-mediated mechanism

Background: Glioblastoma remains highly lethal due to its inevitable recurrence. This recurrence is found locally in most cases, indicating that post-surgical tumor-initiating cells (TICs) accumulate at tumor edge. These edge TICs then generate recurrent tumors harboring new core lesions. Here, we investigated the clinical significance of the edge-to-core transition (ECT) signature causing glioblastoma recurrence and sought to identify central mediators for ECT. Methods: First, we examined the association of the ETC-related expression changes and patient outcome in matched primary and recurrent samples (n=37). Specifically, we tested whether the combined decrease of the edge TIC marker PROM1 (CD133) with the increase of the core TIC marker CD109 representing ECT during the primary-to-recurrence progression indicates poorer patient outcome. We then investigated the specific molecular mediators that trigger tumor recurrence driven by the ECT signature. Subsequently, the functional and translational significance of the identified molecule was validated within our patient-derived tumor edge-TIC models in vitro and in vivo. Results: Patients exhibiting a CD133down/CD109up signature during recurrence representing ECT displayed a strong association with poorer progression-free survival and overall survival among all tested patients. Differential gene expression identified that PLAGL1 was tightly correlated with the core TIC marker CD109 and was linked to a shorter survival of glioblastoma patients. Experimentally, forced PLAGL1 overexpression enhanced, while its knockdown reduced, the glioblastoma edge-derived tumor growth in vivo and subsequent mouse survival, suggesting its essential role in the ECT-mediated glioblastoma development. Conclusions: ECT is likely an ongoing lethal process in primary glioblastoma contributing to its recurrence partly in a PLAGL1/CD109-mediated mechanism.