Cytoplasmic domain mutants of β1 integrin, expressed in β1-knockout lymphoma cells, have distinct effects on adhesion, invasion and metastasis

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Abstract
Structural requirements for beta 1 integrin cytoplasmic domain functions in adhesion, migration and signaling have been studied mainly for fibroblasts in vitro. The relevance for beta 1-dependent in vivo migration of lymphoid cells has not been assessed. To study this, we transfected beta 1 mutants into beta 1-deficient double knockout (DKO) ESb lymphoma cells, and tested the capacity of the cells to metastasize to liver and spleen. This was compared to alpha 4 beta 1-dependent invasion into cell monolayers in vitro and Mn2+-induced adhesion to fibronectin. Deletion of the five C-terminal residues or mutation of both threonines T788 and T789 to alanines blocked invasion and metastasis and greatly reduced adhesion, in line with known in vitro effects. However, mutations of the NPXY motif tyrosines had unexpected consequences. A Y783F mutation had no effect at all, but a Y783,795F double mutation strongly reduced Mn2+-induced adhesion, whereas it had limited effects on invasion and metastasis. Furthermore, cells expressing a beta 1 beta 2 chimeric subunit, which contains phenylalanines in the NPXY/F motifs, adhered poorly but invasion and metastasis was fully restored to the same levels as for cells expressing wild-type beta 1. We conclude that part of the functions of the beta 1 cytoplasmic domain that are required for adhesion are not essential for beta 1-dependent invasion and metastasi

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