Repair of a wound is orchestrated by signals from numerous growth factor, chemokines, and matrix fragments which are presented in response to wounding. Thus, a major question concerns how the cells integrate the multitude of signals to respond with the location- and time-appropriate behavior. For instance, what controls the major decision point to change from fibroblast repopulation to fibroblast-mediated wound closure? We hypothesize that there are specific intracellular signaling elements that integrate diverse extracellular signals to determine the exact biophysical response. Our goals are to fully define the intracellular pathways which lead from EGFR signaling to enhanced cellular responses critical for repair, movement and contractility to close the wound, and to determine the sites at which regulatory chemokines modulate this signaling to dictate specific cell functions. During the first period of this grant we found that growth factors and ELR-CXC chemokines promoted or limited cell motility, respectively, by affecting cell-substratum adhesiveness, and that this was mediated by activation, or inhibition thereof, of calpain. These studies have uncovered a novel, central role for the intracellular protease calpain in regulating the cellular responses to EGFR activation. Thus, we hypothesize that calpain is such an integrator of extracellular signals controlling the specific biophysical aspects of adhesiveness to alter the overall cell response to its changing environment from one of motility to contraction. To understand the cellular mechanisms to rationally design interventions, we propose to test the following hypotheses that probe the molecular mechanisms by which EGFR signals fibroblast motility and contractility and the mechanism by which these signaling pathways are modulated by wound chemokines: I. That the intracellular protease calpain serves as a central switch between pro- (EGF) and counter-regulatory (IP-10) signals for motility. II. That EGFR-mediated de-adhesion is primarily signaled by plasma membrane-localized activation of erk MAP kinases and calpain. III. That IP-10, by negatively regulating calpain activation and de-adhesion, promotes enhanced EGFR-mediated cell contractility and promotes wound closure. Understanding the delicate balance of these molecular mechanisms is important for rationally designing interventions to achieve normal wound healing.
Showing the most recent 10 out of 13 publications
