This artice is free to access.
Vascular endothelial surface-related activities may depend on the lateral mobility of specific cell surface macromolecules. Previous studies have shown that cytokines induce changes in the morphology and surface antigen composition of vascular endothelial cells in vitro and at sites of immune and inflammatory reactions in vivo. The effects of cytokines on membrane dynamic properties have not been examined. In the present study, we have used fluorescence photobleaching recovery (FPR) to quantify the effects of the cytokines tumor necrosis factor (TNF) and immune interferon (IFN-γ) on the lateral mobilities of class I major histocompatibility complex protein, of an abundant 96,000 M(r) mesenchymal cell surface glycoprotein (gp96), and of a phospholipid probe in cultured human endothelial cell (HEC) membranes. Class I protein and gp96 were directly labeled with fluorescein-conjugated monoclonal antibodies; plasma membrane lipid mobility was examined with the phospholipid analogue fluorescein phosphatidylethanolamine (F1-PE). In untreated, confluent HEC monolayers, diffusion coefficients were 30 x 10-10 cm2 s-1 for class I protein, 14 x 10-10 cm2 s-1 for gp96, and 80 x 10-10 cm2 s-1 for F1-PE. Fractional mobilities were >80% for each probe. Cultures treated at visual confluence for 3-4 d with either 100 U/ml TNF or 200 U/ml IFN-γ did not exhibit significant changes in protein or lipid mobilities despite significant changes in cell morphology and membrane antigen composition. In HEC cultures treated concomitantly with TNF and IFN-γ, however, diffusion coefficients decreased by 71-79% for class I protein, 29-55% for gp96, and 23-38% for F1-PE. Fractional mobilities were unchanged. By immunoperoxidase transmission electron microscopy, plasma membranes of untreated and cytokine-treated HEC were flat and stained uniformly for class I antigen. 'Line' FPR measurements on doubly treated HEC demonstrated isotropic diffusion of class I protein, gp96, and F1-PE. Finally, although TNF and IFN-γ retarded the growth of HEC cultures and disrupted the organization of cell monolayers, the slow diffusion rates of gp96 and F1-PE in confluent doubly treated monolayers were not reproduced in sparse or subconfluent untreated monolayers. We conclude that the slowing of protein and lipid diffusion induced by the combination of TNF and IFN-γ is not due to plasma membrane corrugations, to anisotropic diffusion barriers, or to decreased numbers of cell-cell contacts. We propose that cytokines act directly to regulate the mobility of membrane molecules in confluent HEC monolayers.
Stolpen, A. H., Golan, D. E., & Pober, J. S. (1988). Tumor necrosis factor and immune interferon act in concert to slow the lateral diffusion of proteins and lipids in human endothelial cell membranes. Journal of Cell Biology, 107(2), 781–789. https://doi.org/10.1083/jcb.107.2.781