gamma-chain dependent recruitment of tyrosine kinases to membrane rafts bythe human IgA receptor Fc alpha R

We show that the human IgA receptor, Fc alpha R, redistributes to plasma me mbrane rafts after cross-linking and that tyrosine kinases are relocated to these sites following Fc alpha R capping, We demonstrate by confocal micro scopy that Fc alpha R caps in membrane rafts by a gamma-chain-independent m echanism but that gamma-chain expression is necessary for Lyn redistributio n. Immunoblotting of rafts isolated by sucrose density gradient centrifugat ion demonstrated recruitment of gamma-chain and phosphorylated tyrosine kin ases Lyn and Bruton's tyrosine kinase to membrane rafts after Fc alpha R cr oss-linking. Time-dependent differences in Lyn phosphorylation and Bruton's tyrosine kinase distribution were observed between cells expressing Fc alp ha R plus gamma-chain and cells expressing Fc alpha R only. This study defi nes early Fc alpha R-triggered membrane dynamics that take place before Fc alpha R internalization.