Lipid rafts provide a platform for regulating cellular functions and participate in the pathogenesis of several diseases. However, the role of caveolin-1 in this process has not been elucidated definitely in neuron. Thus, this study was performed to examine whether caveolin-1 can regulate amyloid precursor protein (APP) processing in neuronal cells and to identify the molecular mechanisms involved in this regulation. Caveolin-1 is up-regulated in all parts of old rat brain, namely hippocampus, cerebral cortex and in elderly human cerebral cortex. Moreover, detergent-insoluble glycolipid (DIG) fractions indicated that caveolin-1 was co-localized with APP in caveolae-like structures. In DIG fractions, bAPP secretion was up-regulated by caveolin-1 over-expression, which was modulated via protein kinase C (PKC) in neuroblastoma cells. From these results we conclude that caveolin-1 is selectively expressed in senescent neurons and that it induces the processing of APP by beta-secretase via PKC downregulation.
Up-Regulation ; Receptors, Cell Surface/*metabolism ; Rats ; Protein Kinase C/metabolism ; Middle Aged ; Microscopy, Electron ; Humans ; Caveolin 1/*metabolism/physiology ; Caveolae/*metabolism/ultrastructure ; Brain/metabolism/pathology/ultrastructure ; Animals ; Amyloid beta-Protein Precursor/*metabolism ; Amyloid beta-Protein/*metabolism ; Alzheimer Disease/*metabolism ; Aging/metabolism ; Aged, 80 and over ; Aged

The purpose of this study was to demonstrate the cellular localization of cyclooxygenase-2 (COX-2) and caveolin-3 (Cav-3) in primarily cultured rat chondrocytes. In normal rat chondrocytes, we observed relatively high levels of Cav-3 and a very low level of COX-2 mRNA and protein. Upon treating the chondrocytes with 5 microM of CdCl2 (Cd) for 6 hr, the expressions of COX-2 mRNA and protein were increased with the decreased Cav-3 mRNA and protein expressions. The detergent insoluble caveolae-rich membranous fractions that were isolated from the rat chondrocytes and treated with Cd contained the both proteins of both COX-2 and Cav-3 in a same fraction. The immuno-precipitation experiments showed complex formation between the COX-2 and Cav-3 in the rat chondrocytes. Purified COX-2 with glutathione S-transferase-fused COX-2 also showed complex formation with Cav-3. Confocal and electron microscopy also demonstrated the co-localization of COX-2 and Cav-3 in the plasma membrane. The results from our current study show that COX-2 and Cav-3 are co-localized in the caveolae of the plasma membrane, and they form a protein-protein complex. The co-localization of COX-2 with Cav-3 in the caveolae suggests that the caveolins might play an important role for regulating the function of COX-2.
Animals ; Animals, Newborn ; Blotting, Western ; Cadmium Chloride/pharmacology ; Caveolae/drug effects/metabolism/ultrastructure ; Caveolin 3/*genetics/metabolism ; Cell Membrane/drug effects/metabolism ; Cells, Cultured ; Chondrocytes/cytology/drug effects/*metabolism ; Cyclooxygenase 2/*genetics/metabolism ; Gene Expression ; Immunoprecipitation ; Microscopy, Confocal ; Microscopy, Electron ; RNA, Messenger/genetics/metabolism ; Rats ; Reverse Transcriptase Polymerase Chain Reaction