EXPRESSION OF CAVEOLIN-1 AND CAVEOLIN-2 IN DIFFERENTIATING PC12 CELLSAND DORSAL-ROOT GANGLION NEURONS - CAVEOLIN-2 IS UP-REGULATED IN RESPONSE TO CELL INJURY

Caveolae are cholesterol/sphingolipid-rich microdomains of the plasma membrane that have been implicated in signal transduction and vesicula r trafficking. Caveolins are a family of caveolae-associated integral membrane proteins. Caveolin-1 and -2 show the widest range of expressi on, whereas caveolin-3 expression is restricted to muscle cell types. It has been previously reported that little or no caveolin mRNA specie s are detectable in the brain by Northern blot analyses or in neurobla stoma cell lines. However, it remains unknown whether caveolins are ex pressed within neuronal cells. Here we demonstrate the expression of c aveolin-1 and -2 in differentiating PC12 cells and dorsal root ganglio n (DRG) neurons by using mono-specific antibody probes. In PC12 cells, caveolin-1 expression is up-regulated on day 4 of nerve growth factor (NGF) treatment, whereas caveolin-2 expression is transiently up-regu lated early in the differentiation program and then rapidly down-regul ated. Interestingly, caveolin-2 is up-regulated in response to the mec hanical injury of differentiated PC12 cells; up-regulation of caveolin -2 under these conditions is strictly dependent on continued treatment with NGF. Robust expression of caveolin-1 and -2 is also observed alo ng the entire cell surface of DRG neurons, including high levels on gr owth cones. These findings demonstrate that neuronal cells express cav eolins.