LEUKOTRIENE D-4-INDUCED ACTIVATION AND TRANSLOCATION OF THE G-PROTEINALPHA(I3)-SUBUNIT IN HUMAN EPITHELIAL-CELLS

The present results show that stimulation of Intestine 407 epithelial cells with LTD(4) (Leukotriene D-4) triggers a rapid activation of the pertussis-toxin-sensitive G(i3)-protein and a simultaneous translocat ion of its alpha-subunits to a crude cytoskeletal fraction. The activa tion of G alpha(i3), which was measured as the GTP/GDP exchange ratio, peaked about 15 s after the addition of LTD(4). Western blot analyses of subcellular fractions showed that G alpha(i3)-subunits accumulated in the cytoskeletal fraction and decreased in the membrane fraction, and the decrease was most marked 15 s after the exposure to LTD(4). No ne of the other pertussis-toxin-sensitive G-proteins (G(i1-2) and G al pha(0)) were activated or translocated upon stimulation with LTD(4). T his agonist was also found to reduce the GTP/GDP exchange ratio of G(s )-proteins without affecting the subcellular distribution of its alpha -subunits. These findings imply that the G(i3)-protein is the pertussi s-toxin-sensitive G-protein previously found to mediate several downst ream LTD(4)-stimulated signalling events. Furthermore, the translocati on of G alpha(i3)-subunits to the cytoskeleton and the simultaneous in hibition of G(s)-proteins indicate that the cytoskeleton might partici pate in the signalling process of human epithelial cells. (C) 1996 Aca demic Press, Inc.