Abstract. The ability of single subunit chimeric receptors containing various integrin fl intracellular domains to mimic and/or inhibit endogenous integrin function was examined. Chimeric receptors consisting of the extracellular and transmembrane domains of the small subunit of the human interleukin-2 receptor connected to either the fl~, f13, fl3B, or r5 intracellular domain were transiently expressed in normal human fibroblasts. When expressed at relatively low levels, the r3 and r5 chimeras mimicked endogenous ligandoccupied integrins and, like the fl~ chimera (LaFlamme, S. E., S. K. Akiyama, and K. M. Yamada. 1992. J. Cell Biol. 117:437), concentrated with endogenous integrins in focal adhesions and sites of fibronectin fibril formation. In contrast, the chimeric receptor containing the fl3s intracellular domain (a r3 intracellular domain modified by alternative splicing) was expressed diffusely on the cell surface, indicating that alternative splicing can regulate integrin receptor distribution by an intraceUular mechanism. Furthermore, when expressed at higher levels, the fl~ and r3 chimeric receptors functioned as dominant negative mutants and inhibited endogenous integrin function in localization to fibronectin fibrils, fibronectin matrix assembly, cell spreading, and cell migration. The r5 chimera was a less effective inhibitor, and the fl3B chimera and the reporter lacking an intracellular domain did not inhibit endogenous integrin function. Comparison of the relative levels of expression of the transfected fll chimera and the endogenous fl~ subunit indicated that in 10 to 15h assays, the fll chimera can inhibit cell spreading when expressed at levels approximately equal to to the endogenous/3~ subunit. Levels of chimeric receptor expression that inhibited cell spreading also inhibited cell migration, whereas lower levels were able to inhibit otsfl~ localization to fibrils and matrix assembly.Our results indicate that single subunit chimeric integrins can mimic and/or inhibit endogenous integrin receptor function, presumably by interacting with cytoplasmic components critical for endogenous integrin function. Our results also demonstrate that fl intracellular domains, expressed in this context, display specificity in their abilities to mimic and inhibit endogenous integrin function. Furthermore, the approach that we have used permits the analysis of intracellular domain function in the processes of cell spreading, migration and extracellular matrix assembly independent of effects due to the rest of integrin dimers. This approach should prove valuable in the further analysis of integrin intracellular domain function in these and other integrin-mediated processes requiring the interaction of integrins with cytoplasmic components.

The tube feet of Leptasterias hexactis adhere to and release from substrata by chemical interactions. In our laboratory these podia adhered to substrata coated with the ubiquetous anionic saccharide films produced by marine bacteria. Podia also attached to moderately anionic glass, but not to uncharged surfaces. The adhesive epithelia of tube feet labeled heavily with ruthenium red, indicating they were anionic. Tube feet secreted footprint films that bound crystal violet, a cationic dye. Trypsin removed the films. Adhesion to marine surfaces was prevented by 300 units/ml of heparin, a glycosaminoglycan (GAG) that may have competitively inhibited the glue from binding exosaccharide marine films. Lectins that bind bacterial exosaccharides did not inhibit attachment. We propose that tube-foot attachments are nonspecific ionic interactions established by secreted proteinaceous films and released when secreted GAG's compete with the tube-foot epithelium for sites on the film. This system agrees with the duo-gland model for adhesion and deadhesion.

We have examined the possibility that mouse bone marrow-derived cultured mast cells (BMCMC) have the capacity to attach to and migrate on extracellular matrix components in vitro through the use of time lapse videography. Unactivated mast cells did not display significant interaction with slide flasks coated with either 3% BSA or collagen IV, and Fc epsilon RI-mediated activation of BMCMC did not appreciably increase their attachment and migratory characteristics. Both activated and unactivated BMCMC adhered to surfaces coated with a synthetic IKVAV laminin polypeptide, but this association resulted in the immobilization of the cells to the substrate. BMCMC did not adhere to surfaces coated with laminin, fibronectin or matrigel until Fc epsilon RI-mediated activation, after which they displayed rapid, random movement on these surfaces. Cells continually interacted with laminin, fibronectin or matrigel by flattening, interspaced by periods of movement as rounded cells with small pseudopodia. The mean velocity of BMCMC on laminin, fibronectin or matrigel was similar and averaged approximately 180 microns/hr. The mean velocity of BMCMC on these three substrates was not significantly different from the mean velocity of monocytes on laminin. The movement of BMCMC on these substrates demonstrated a directional tendency. In summary, these results demonstrate that mast cells activated through Fc epsilon RI are capable of attachment to and motion on components of extracellular matrix, and demonstrate one mechanism by which mast cells may migrate to areas of inflammation and wound repair.

This pilot study found that, generally, HRQoL changes one week into a smoking cessation attempt. Smokers with higher addiction have lower HRQoL when they begin their cessation attempt, while smokers with lower addiction have greater change in HRQoL.