Mutations in the cytoplasmic domain of the integrin beta(1) chain indicate a role for endocytosis factors in bacterial internalization

Mutations that result in defective beta(1)-integrin focal adhesion formation were analyzed for effects on bacterial internalization. Mutations in the cytoplasmic domain of the beta(1) chain that disrupt the sequence NPIY resulted in integrins deficient in bacterial uptake, Other mutations in the beta(1) chain that reduced cytoskeletal association showed enhanced bacterial uptake, Replacement of the NPIY sequence of the beta(1) subunit by the endocytosis internalization sequence PPGY resulted in integrin receptors highly proficient in bacterial internalization, yet severely defective in focal contact localization, Electron microscopy indicated that coated structures associated specifically with bacteria-binding beta(1)-integrins, with an apparent recruitment of coated pits from ventral cell surfaces to apical surfaces corresponding to nascent bacterial phagosomes. Clathrin inhibition studies indicated a role for the adaptor molecule AP2 as well as clathrin in integrin-mediated bacterial internalization. These results indicate that association of beta(1)-integrins with the cytoskeleton at focal contacts interferes with integrin-mediated bacterial internalization. Also, although actin polymerization is required for bacterial uptake, clathrin is probably involved in bacterial uptake promoted by beta(1)-integrins.