CD44 and hyaluronan promote invasive growth of B35 neuroblastoma cells into the brain

Hyaluronan and its receptor CD44 are known to contribute to the invasive growth of different tumors of the central nervous system. It is not known, however, if CD44 is sufficient to activate invasive growth into the brain tissue. This study examines how CD44 regulates the motility and invasive growth of B35 neuroblastoma cells into a hyaluronan-rich environment. A comprehensive experimental approach was used encompassing biochemical techniques, single molecule microscopy, correlative confocal and scanning electron microscopy, morphometry of cellular extensions, live-cell imaging and tracking, transplantation onto organotypic brain slices, two-photon imaging and invasion assays. We found that CD44-GFP fusion protein was localized in filopodia and in focal bleb-like protrusions where it provided binding sites for hyaluronan. Transient expression of CD44-GFP was sufficient to increase the length of filopodia, to enhance cell migration and to promote invasive growth into hyaluronan-rich brain tissue. Thus, CD44 controls molecular devices localized in filopodia and bleb-like specializations of the cell surface that enhance cell migration and invasive growth.