Intestinal epithelial cells (IEC) present a barrier to the intestinal lumen and as such can act a sentries to alarm the underlying tissues of an infection or problem. This capacity is mediated by several pro- inflammatory cytokines secreted by the IEC. In addition, IEC are known to secrete pro-inflammatory cytokines important in inflammatory bowel disease. We have extensively studied the regulation of one such cytokine, interleukin-6 (IL-6) by IEC. IEC in the intestine normally adhere to an extracellular matrix (ECM) composed of collagen Type IV, laminin, fibronectin, and other glycoproteins. However, during infections, inflammations, or wound healing, the makeup of the ECM may change drastically. Recent studies have indicated that the adherence of monocytes and fibroblasts to ECM proteins by specific cell surface receptors, or integrins, may regulate the production of enzymes and cytokines. This suggests that the specific integrins are involved in the regulatory signal transduction mechanisms of the cell. Using the human colonic careinoma cell line Caco-2, we have recently found that culture of the cells on fibronectin resulted in a significant enhancement of IL- 1 stimulated IL-6 secretion as compared to cells grown on laminin. This suggests that the type of ECM, through the different cell surface integrins, may send an important co-stimulatory signal to the cell to co-regulate IL-6 secretion. Therefore, IEC may respond differently to inflammatory stimuli during infections, inflammations, or wound healing as the make-up of the ECM changes. In this proposal, we will study the regulatory effect of ECM proteins and integrins on pro-inflammatory cytokine production by 'BC using the Caco-2 cell line as a model. Also, specific experiments with isolated normal mouse IEC will be done to confirm our findings. Specifically we will (1) characterize the effect of ECM proteins on Caco-2 cell cytokine secretion and define the integrins involved in the effect, (2) elucidate the intracellular signaling mechanisms involved in the co-regulation of cytokine secretion by integrins, and (3) determine if inflammatory cytokine secretion by isolated normal mouse 'BC is regulated by integrin co-signals. These studies should define the involvement of integrins and ECM proteins in IEC cytokine secretion and may provide a basis for possible targets to regulate the initiation or progression of mucosal inflammations by targeting specific integrins or the intracellular signaling pathways in IEC.
