Evidence for a Dithiol-Activated Signaling Pathway in Natural Killer Cell Avidity Regulation of Leukocyte Function Antigen-l: Structural Requirements and Relationship to Phorbol Ester- and CD16-Triggered Pathways

Dithiothreitol (Dm) activation of the adhesive function of several different integrins suggests the existence of a common DlT-sensitive integrin regulatory element. Uill/E3, a natural killer (NK) cell-resistant murine target cell line genetically engineered to constitutively express human intercellular adhesion molecule-l (ICAM-1; CD%) was used in a flow cytometric experimental model to evaluate D l T effects on the NK cell integrin adhesion molecule, leukocyte function antigen-l (LFA-1; aU2, CD1 la/CD18). D l T and several structurally related dithiol compounds elicited a dramatic elevation in conjugate formation that was dependent on target cell CAM-1 expression, was blocked by LFA-1 (YL or p2 chainspecific antibodies, and occurred in the absence of Ui11/E3 target cell exposure to D l l or quantitative changes in NK cell membrane LFA-1 expression. This avidity modulation of LFA-1 by DlT required actin polymerization, was abrogated by the protein kinase C inhibitor calphostin C, involved activities of calyculin Aand okadaic acid-sensitive serine/threonine protein phosphatases PP-l and/or PP-PA but not geldanamycin-sensitive tyrosine kinases, and iffered with respect t o kinetics and enzyme inhibitor sensitivity from LFA-1 activation promoted by cross-linking of NK cell CD16 or phorbol ester treatment. A key structural feature of D l T was the presence of two thiol groups, both reduced but not physically adjacent as in the nonstimulatory dithiol, 2,3-