Caveolin-1 and caveolin-2 expression in mouse macrophages - High density lipoprotein 3-stimulated secretion and a lack of significant subcellular co-localization

Evidence for caveolin expression in macrophages is scarce and conflicting. We therefore examined caveolin-1 and caveolin-2 expression in resident and thioglycollate-elicited mouse peritoneal macrophages (tg-MPM) and in the J7 74 mouse macrophage cell line by RT-PCR, ribonuclease protection assay, imm unoblotting, and immunofluorescence. We found that relative to 3T3 cells, r esident MPM and tg-MPM express low amounts of caveolin-1 (45 and 15% of tho se in 3T3 fibroblasts, respectively), while J774.A1 cells do not express an y. Caveolin-2, on the other hand, is expressed in all cells examined, with highest expression in tg-MPM and the lowest in J774 cells. The relative lev els of caveolin expression in the various cells correspond well with their respective mRNA levels, as measured by ribonuclease protection assay. Caveo lin-1, present primarily on the cell surface, does not co-localize signific antly with caveolin-2, which is present primarily in the Golgi compartment in all macrophages studied. Loading of tg-MPM with cholesterol or variation s in unesterified cholesterol content appear to have little effect on the l evel of caveolin-1 or -2 expression or their distribution. Stimulation of c holesterol efflux by HDL, leads to caveolin-1 and caveolin-2 secretion to t he cell culture medium, a process not detected in the absence of HDL,, The lack of significant co-localization of the two caveolin isoforms in primary macrophages and their secretion in the presence of HDL, provides an intere sting and physiologically relevant model system to study additional aspects of caveolin function.