Gamma-chain dependent recruitment of tyrosine kinases to membrane rafts by the human IgA receptor Fc alpha R.

We show that the human IgA receptor, Fc alpha R, redistributes to plasma membrane rafts after cross-linking and that tyrosine kinases are relocated to these sites following Fc alpha R capping. We demonstrate by confocal microscopy that Fc alpha R caps in membrane rafts by a gamma-chain-independent mechanism but that gamma-chain expression is necessary for Lyn redistribution. Immunoblotting of rafts isolated by sucrose density gradient centrifugation demonstrated recruitment of gamma-chain and phosphorylated tyrosine kinases Lyn and Bruton's tyrosine kinase to membrane rafts after Fc alpha R cross-linking. Time-dependent differences in Lyn phosphorylation and Bruton's tyrosine kinase distribution were observed between cells expressing Fc alpha R plus gamma-chain and cells expressing Fc alpha R only. This study defines early Fc alpha R-triggered membrane dynamics that take place before Fc alpha R internalization.