The intensity measurement was performed with the FRAP setup using the attenuated, nonbleaching monitoring beam

The intensity measurement was performed with the FRAP setup using the attenuated, nonbleaching monitoring beam. clusters, advertising either enhancement or inhibition of signaling. Cholesterol and sphingolipid-enriched domains termed lipid rafts were shown in artificial lipid bilayers and proposed to exist in cell membranes (1, 4, 9, 10, 18, 26, 49, 50). In spite of a wealth of studies on the practical importance of Cl-C6-PEG4-O-CH2COOH relationships with raft-like domains for many cellular processes (examined in referrals 17, 18, 26, 49, 50, and 53), many questions Cl-C6-PEG4-O-CH2COOH remain concerning the size, lifetime, and even the living of lipid rafts in live cells (1, 8, 10, 17, 18, 23, 26, 27, Cl-C6-PEG4-O-CH2COOH 33, 45, 49, 51, 54). The original simplistic look at of lipid rafts was as preexisting liquid-ordered domains enriched in cholesterol and sphingolipids, into which specific proteins partition preferentially (4, 10, 49). More recent views Lox envision rafts as small and transient cholesterol-dependent assemblies complexed with proteins, where relationships among the specific proteins influence the formation, size, and stability of these constructions (1, 17, 44). The variations between these views involve primarily the nature of cholesterol-dependent assemblies in resting cell membranes. The studies presented here focus not within the resting state but rather on effects induced from the clustering of proteins associated with cholesterol-sensitive assemblies; consequently, we will refer to such assemblies throughout as rafts, without implications to a specific model. Several reports provide evidence in support of such domains in both the outer and inner plasma membrane leaflets (7, 18, 26, 44, 50, 53, 55). The coupling between raft-like domains in different membrane leaflets has an intriguing potential for modulating transbilayer signaling; however, this problem offers remained mainly unexplored. Related studies were carried out primarily in T cells, where external clustering of raft-associated molecules was reported to induce intracellular signaling, interpreted to indicate a role for raft stabilization/growth in transmission transduction (9, 20, 21, 37, 45, 53). However, even in these cells, which are characterized by high spatial corporation in the immunological synapse, the involvement of lipid rafts in clustering-induced transbilayer signaling was recently questioned (8, 15, 29, 54). Here, we used fluorescence recovery after photobleaching (FRAP) to study the effects of clustering outer-leaflet and transmembrane influenza hemagglutinin (HA) mutants that differ in raft association within the relationships of Ras isoforms with inner-leaflet raft domains and on Ras signaling. Ras proteins are small GTPases which operate as molecular switches in the inner leaflet and regulate proliferation, differentiation, and cell survival (18, 46). They may be highly suitable for these studies, since they provide a series of closely related proteins that are targeted to cholesterol-sensitive domains to different extents, depending on their lipid anchor, hypervariable C-terminal areas, and GTP/GDP loading state (18). The membrane anchors of H-, N-, and K-Ras all have a CAAX S-farnesylation motif, supplemented by one (N-Ras) or two (H-Ras) adjacent value is given, as could not be identified. Clustered HA(wt) and HA(2A520) were similarly immobile (not demonstrated). (C) Lateral diffusion of GFP-H-Ras(wt) coexpressed with un-cross-linked BHA-PI. (D) Clustering BHA-PI reduces of GFP-H-Ras(wt). (E and F) Quantification of the effects of clustering HA proteins on and of GFP-H-Ras(wt). Bars are means standard error of Cl-C6-PEG4-O-CH2COOH the means of 30 to 40 measurements. White colored bars, HA mutant coexpressed but not cross-linked (designated patched HA; ?); black bars, cross-linked HA. Asterisks show significant differences from your respective control, with comparisons between samples expressing the same HA protein with and without cross-linking (*, 0.01; ***, 10?10; Student’s two-tailed test). In the absence of coexpressed HA, the results were much like those of.