CHRDL1 Regulates Stemness in Glioma Stem-Like Cells

Glioblastoma (GBM) still presents as one of the most aggressive tumors in the brain, which despite enormous research efforts remains incurable until today. As many theories evolve around the persistent recurrence of this malignancy the assumption of a small population of cells with a stem-like phenotype remains as a key driver of its infiltrative nature. In this article we research Chordin-like 1 (CHRDL1), a secreted protein, as a potential key regulator of the glioma stem-like cell (GSC) phenotype. It has been shown that CHRDL1 antagonizes the function of Bone Morphogenic Protein 4 (BMP4), which induces GSC differentiation and hence reduces tumorigenicity. We therefore employed two previously described GSCs spheroid cultures and depleted them of CHRDL1 using stable transduction of a CHRDL1-targeting shRNA. We show with in vitro cell based assays (MTT, limiting dilution and sphere formation assays), western blots, irradiation procedures and quantitative real-time PCR that depletion of the secreted BMP4 antagonist CHRDL1 prominently decreases functional and molecular stemness traits resulting in enhanced radiation sensitivity. As a result, we postulate CHRDL1 as an enforcer of stemness in GSCs and find additional evidence that high CHRDL1-expression might also serve as a marker protein to determine BMP4-susceptibility.