CRMP5 depletion does not promote apoptosis.(A): Apoptosis is monitored in GL15 cells transfected with CRMP5-siRNA1 and control-siRNA using caspase 3 antibody (1/400, BD Pharmingen, 559565). 5-bromo-2'-deoxyuridine (BrdU) indicates proliferating cells in both conditions. (B): TUNEL staining (marker of apoptosis) (Promega, G3250) in CRMP5-siRNA1 transfected GL15 cells Scale bar=20µm. (C): TUNEL staining quantification in CRMP5-siRNA transfected GL15 cells after 4 days. The total number of cells counted is indicated by DAPI quantification; TUNEL-stained cells were counted for each condition. The results were obtained from 3 independent experiments.
ARTICLE ABSTRACTCollapsin response mediator protein 5 (CRMP5) belongs to a family of five cytosolic proteins that play a major role in nervous system development. This protein was first described in cancer-induced autoimmune processes, causing neurodegenerative disorders (paraneoplastic neurologic syndromes). CRMP5 expression has been reported to serve as a biomarker for high-grade lung neuroendocrine carcinomas; however, its functional roles have not been examined in any setting of cancer pathophysiology. In this study, we report two different CRMP5 expression patterns observed in human glioblastoma (GBM) biopsies that establish connections between CRMP5 expression, Notch receptor signaling, and GBM cell proliferation. We demonstrated that elevated CRMP5 promotes Notch receptor expression and Akt activation in human tumor cell lines, GBM stem cells, and primary tumor biopsies. We have shown that the high CRMP5 and Notch expression in GBM xenograft is related to stem cells. This suggests that high CRMP5 expression pattern in GBM biopsies encompasses a subset of stem cells. Mechanistically, CRMP5 functioned by hijacking Notch receptors from Itch-dependent lysosomal degradation. Our findings suggest that CRMP5 serves as a major mediator of Notch signaling and Akt activation by controlling the degradation of the Notch receptor, with implications for defining a biomarker signature in GBM that correlates with and may predict patient survival. Cancer Res; 75(17); 3519–28. ©2015 AACR.