DEVELOPMENT OF CELL REGULATION METHOD BY MANIPULATING CAVEOLAR FUNCTIONS

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Caveolae are plasmalemmal invaginations where receptors and signaling molecules are concentrated and may be important for signal transduction. We aimed to find out methods to regulate cellular functions by manipulating caveolae functions in living cells, and obtained the following results.1) A transmembrane segment plus a short extracellular portion of a membrane protein were fused to caveolin molecules, to make artificial transmembrane proteins. One of the fusion proteins showed colocalization with endogenous caveolin-1, and by crosslinking an extracellular epitope by antibodies, it showed local aggregation. This method may be used to manipulate caveolae distribution from the extracellular surface.2) By using interstitial cells of Cajal, we revealed that dihydropyridine-nonsensitive calcium oscillation is related to the pacemaker function, and that calcium influx through TRP4 in caveolae is involved in the oscillation. Caveolae also contains IP3 receptor and calcium pump, and thus TRP4 might be a target molecule for caveolae manipulation.3) Lipid droplets contain a large amount of cholesterol as ester, and could harbor caveolins under some circumstances. We found a Rab protein (LD-Rab) exists in lipid droplets. Overexpression of LD-Rab caused changes in the molecular composition of lipid droplets, and also induced structural changes. LD-Rab is likely to be involved in the intracellular cholesterol trafficking, and a change of its expression level may affect the membrane microdomain.