ABSTRACT
Talin is a major cytosolic protein that links the intracellular domains of β1 and β3 integrins to the cytoskeleton. It is required for focal adhesion assembly. However, its downregulation not only slows down cell spreading and organization of focal adhesions but also impairs the maturation of some β1 integrins, including the fibronectin receptor α5β1. To investigate this, we characterized the β1 integrin synthesized in cells expressing talin anti-sense RNA (AT22 cells). We identified a large intracellular pool of β1 integrins that is abnormally accumulated in an earlier compartment of the secretory pathway. In this report, we show that in talin-deficient AT22 cells, the aberrant glycosylation of integrin receptors is accompanied by a delay in the export of the integrin α5β1. In normal cells, talin was found associated with β1 integrins in an enriched membrane fraction containing Golgi and endoplasmic reticulum. Finally, microinjection of anti-talin antibodies resulted in accumulation of the integrins within the cells. These data strongly suggest that talin plays a specific role in the export of newly synthesized integrins. We propose that talin binding to the integrin may disclose a diphenylalanine export signal, which is present in the membrane-proximal GFFKR motif conserved in all integrin α chains.
