COMPARTMENTALIZATION OF PHOSPHATIDYLINOSITOL 4,5-BISPHOSPHATE IN LOW-DENSITY MEMBRANE DOMAINS IN THE ABSENCE OF CAVEOLIN

In cells that exhibit caveolae, the hormone-sensitive pool of PtdIns 4 ,5-P-2 is localized in a low density, caveolin-enriched membrane fract ion (1). Neuro 2a cells do not express caveolin. Nonetheless, the PtdI ns 4,5-P-2 in these cells is compartmentalized in a low density, deter gent-insoluble domain that also contains other signaling-related molec ules. Compartmentalization of PtdIns 4,5-P-2 was observed regardless o f whether Triton X-100-containing or detergent-free methods were used to prepare the membranes. However, the partitioning of receptor tyrosi ne kinases and GPI-anchored proteins into the low density domains was dependent upon the method of membrane preparation. Treatment of Neuro 2a cells with cyclodextrin delocalized the PtdIns 4,5-P-2 and inhibite d hormone-stimulated PtdIns turnover. These results suggest that compa rtmentalization of PtdIns 4,5-P-2 does not require caveolin but is nec essary for the proper functioning of phosphoinositide-based signaling. (C) 1998 Academic Press.