alphaB-crystallin is elevated in highly infiltrative apoptosis-resistant glioblastoma cells.
- NORLUX Neuro-Oncology Laboratory
We have previously established two distinct glioma phenotypes by serial xenotransplantation of human glioblastoma (GBM) biopsies in nude rats. These tumors undergo a gradual transition from a highly invasive nonangiogenic to a less-invasive angiogenic phenotype. In a protein screen to identify molecular markers associated with the infiltrative phenotype, we identified alpha-basic-crystallin (alphaBc), a small heat-shock protein with cytoprotective properties. Its increased expression in the infiltrative phenotype was validated by immunohistochemistry and Western blots, confirming its identity to be tumor-derived and not from the host. Stereotactic human GBM biopsies taken from MRI-defined areas verified stronger alphaBc expression in the infiltrative edge compared to the tumor core. Cell migration assays and immunofluorescence staining showed alphaBc to be expressed by migrating cells in vitro. To determine alphaBc function, we altered its expression levels. alphaBc siRNA depletion caused a loss of migrating tumor cells from biopsy spheroids and delayed monolayer wound closure. In contrast, glioma cell migration in a Boyden chamber assay was unaffected by either alphaBc knockdown or overexpression, indicating that alphaBc is not functionally linked to the cell migration machinery. However, after siRNA alphaBc depletion, a significant sensitization of cells to various apoptotic inducers was observed (actinomycin, tumor necrosis factor alpha, and TNF-related apoptosis-inducing ligand [TRAIL]). In conclusion, alphaBc is overexpressed by highly migratory glioma cells where it plays a functional role in apoptosis resistance.