| Inflammatory bowel disease (IBD) is an autoimmune disorder which is often characterized by an aberrant inflammatory response of the intestine with elevated levels of numerous pro-inflammatory cytokines (IL-1 and TNF-alpha), chemokines (CXCL8 and CCL2) and high number of infiltrating leukocytes like neutrophils and macrophages. Interestingly, intestinal epithelial cells (IECs) isolated from the inflamed regions of IBD patients have been shown to produce IL-1, TNF-alpha CXCL8 and CCL2. Also, IL-1 or TNF-alpha stimulation of freshly isolated IECs or IEC lines can secrete copious amounts of CXCL8 and CCL2 in response to IL-1 or TNF-alpha stimulation. Therefore, IECs may play a role in IBD. A recent study has shown that inhibiting the Rho-associated kinase (ROCK) suppressed the secretion of CXCL8 from IL-1-stimulated IECs, which may be due to an effect of ROCK on JNK signaling without affecting signaling to NF-kappaB. This study shows that ROCK inhibition had no effect on the formation of the upstream IRAK1-TRAF6 signaling complex in IL-1-stimulated cells. Also, inhibiting ROCK had no effect on p38 MAPK phosphorylation or the stability of CXCL8 mRNA. Yet, inhibiting ROCK suppressed the IL-1-induced phosphorylation of MKK4, a known activator of JNK, but not MKK7. Further, inhibiting ROCK suppressed the association of JNK with the JIP3 scaffold protein. Hence, ROCK-JIP3-JNK interaction may be a crucial regulatory sequence during IL-1-induced chemokine responses by IEC.;Our studies also demonstrate that suppressing ROCK activity inhibited CXCL8 secretion from IL-1 and TNF-alpha co-stimulated IECs. However, inhibiting ROCK enhanced IL-1 or TNF-alpha stimulated production of CCL2, possibly by suppression of MEK1/ERK activity which may be a cell line specific response. Finally, we report that ROCK has a role in the IL-1-stimulated secretion of CXCL8 and CCL2 from non-confluent cells but not confluent cells. These studies indicate that ROCK may be a key molecule in the signaling events of IL-1-stimulated IEC. Therefore, specific signaling molecules affected by ROCK may provide future targets for the suppression of chemokine responses from IECs in IBD patients. |
