Lipid rafts and T cell receptor signaling: a critical re-evaluation.
The current model suggesting that raft integrity is required for T cell activation is mostly (but not exclusively) based on the use of drugs, such as methyl-beta-cyclodextrin (M beta CD), that disorganize rafts and inhibit T cell receptor (TCR)-induced Ca2+ influx. Here we show that conditions that disrupt lipid raft integrity do not inhibit TCR triggering in Jurkat cells and normal T lymphocytes. Indeed, we found that the reported inhibition of TCR-induced Ca2+ influx by M beta CD treatment is mainly due to (a) nonspecific depletion of intracellular Ca2+ stores and (b) plasma membrane depolarization of T cells. When these side-effects are taken into account, raft disorganization does not alter TCR-dependent Ca2+ signaling. In line with these results, also TCR-induced tyrosine phosphorylation is not inhibited by dispersion of lipid rafts. By contrast, in the same conditions, Ca2+ signaling via the glycosylphosphatidylinositol (GPI)-anchored protein CD59 is totally abolished. These results indicate that, while signaling through GPI-anchored proteins requires lipid raft integrity, CD3-dependent TCR activation occurs independently of cholesterol extraction.
Pizzo
Paola
P
Department of Biomedical Sciences, University of Padova, Padova, Italy.
Giurisato
Emanuele
E
Tassi
Maristella
M
Benedetti
Angelo
A
Pozzan
Tullio
T
Viola
Antonella
A
D018957:CD59 Antigens / Q000502:physiology; D020013:Calcium Signaling; D003505:Cyclodextrins / Q000494:pharmacology; D006801:Humans; D019169:Jurkat Cells; D021962:Membrane Microdomains / Q000502:physiology*; D010766:Phosphorylation; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D014443:Tyrosine / Q000378:metabolism; D047392:beta-Cyclodextrins
D018957:CD59 Antigens; D003505:Cyclodextrins; D011948:Receptors, Antigen, T-Cell; D047392:beta-Cyclodextrins; C108732:methyl-beta-cyclodextrin; D014443:Tyrosine