USE OF A BETA-1 INTEGRIN-DEFICIENT HUMAN T-CELL TO IDENTIFY BETA-1 INTEGRIN CYTOPLASMIC DOMAIN SEQUENCES CRITICAL FOR INTEGRIN FUNCTION

T cell activation rapidly and transiently regulates the functional act ivity of integrin receptors. Stimulation of CD3/T cell receptor, CD2 o r CD28, as well as activation with phorbol esters, can induce within m inutes an increase in beta 1 integrin-mediated adhesion of T cells to fibronectin. In this study, we have produced and utilized a mutant of the Jurkat T cell line, designated A1, that lacks protein and mRNA exp ression of the beta 1 integrin subunit but retains normal levels of CD 2, CD3, and CD28 on the cell surface. Activation-dependent adhesion of A1 cells to fibronectin could be restored upon transfection of a wild -type human beta 1 integrin cDNA. Adhesion induced by phorbol 12-myris tate 13-acetate-, CD3-, CD2-, and CD28 stimulation did not occur if th e carboxy-terminal five amino acids of the beta 1 tail were truncated or if either of two well-conserved NPXY motifs were deleted. Scanning alanine substitutions of the carboxy-terminal five amino acids demonst rated a critical role for the tyrosine residue at position 795. The ca rboxy-terminal truncation and the NPXY deletions also reduced adhesion induced by direct stimulation of the beta 1 integrin with the activat ing beta 1 integrin-specific mAb TS2/16, although the effects were not as dramatic as observed with the other integrin-activating signals. T hese results demonstrate a vital role for the amino-terminal NPXY moti f and the carboxy-terminal end of the beta 1 integrin cytoplasmic doma in in activation-dependent regulation of integrin-mediated adhesion in T cells. Furthermore, the A1 cell line represents a valuable new cell ular reagent for the analysis of beta 1 integrin structure and functio n in human T cells.