Appicans are secreted or cell-associated brain
chondroitin sulfate proteoglycans produced by glia cells and containing Alzheimer
amyloid precursor
protein (APP) as a core
protein. Here, we report that rat C6
glioma cells transfected with
appican displayed a dramatic change in their phenotypic appearance compared with untransfected cells or cells transfected with APP.
Appican-transfected cells lost the round appearance of the untransfected control C6 cells, acquired a flat morphology, and elaborated more processes than control cells. Untransfected, or APP-transfected C6, cells were completely dissociated from their substrate after 40 min of treatment with cell dissociation
solution. Under the same conditions, however, <20% of the
appican-transfected C6 cells were dissociated from their substrate, suggesting that the
appican-transfected glia cells attach more avidly to their substrate than do untransfected or APP transfected control cells. In contrast,
appican-transfected fibroblast cells showed no morphological changes and dissociated from their substrate similarly to untransfected fibroblast cells. Extracellular matrix (ECM) prepared from
appican-transfected C6 cell cultures contained high levels of
appican and was a significantly better substrate for the attachment of C6 cells than ECM from either untransfected or APP-transfected cultures. Furthermore, cell adhesion to ECM was independent of the level of
appican expression of the plated cells. ECM from
appican-transfected C6 cultures stimulated adhesion of other neural cells including primary astrocytes, Neuro2a
neuroblastoma, and PC12
pheochromocytoma, but not fibroblast cells.
Conditioned media from
appican-transfected C6 cultures failed to promote cell adhesion. Together, these data suggest that secreted
appican incorporates into ECM and promotes adhesion of neural cells. Furthermore, our data suggest that the
chondroitin sulfate chain engenders APP with novel
biological functions.