Directed movement of normal cells occurs when actin-related protein 2 and 3 complex (Arp2/3 complex) triggers the actin polymerization that forms lamellipodia immediately after binding to WAVE2. In order to determine whether the same mechanism correlates with liver metastasis from colorectal cancer, paired mirror sections of 154 cancer specimens (29 cases with liver metastasis and 125 cases without liver metastasis in which T factor, gender, primary tumor site, and age at operation were matched) were examined immunohistochemically for the localization of Arp2 and WAVE2.

Increased motility is one of the characteristics of cancer cells, and actin polymerization and disassembly are essential for cellular motility. Since actin-related protein (Arp) 2/3 complex acts as a nucleus for actin polymerization, in this study, we immunohistochemically investigated the expression of Arp2 and Arp3 in 175 colorectal tumors in various stages of neoplastic progression. Arp2 and Arp3 showed identical expression patterns, and both were expressed in the stromal cells around neoplastic tubules or glands and in the tumor cells themselves. The frequency of expression of Arp2 and Arp3 (Arp2&3) by the stromal cells increased with the atypia of the colorectal neoplasms, from 5.5% (3/55) in adenoma with mild or moderate atypia, to 11.8% (2/17) in adenoma with severe atypia, 53.3% (16/30) in intramucosal carcinoma, and 91.8% (67/73) in invasive carcinoma (Po0.0001). The frequency of expression of Arp2&3 in the tumor cells was similar and was 1.8% (1/55) in adenoma with mild or moderate atypia, 23.5% (4/17) in adenoma with severe atypia, 23.5% (7/30) in intramucosal carcinoma, and 32.9% (24/73) in invasive carcinoma. Expression of Arp2&3 by the stromal cells was significantly correlated with nuclear accumulation of p53 in the tumor cells and stromal expression of CD10. These results suggest that formation of Arp2/3 complex by both neoplastic and stromal cells contributes to the increased motility of both cell types and thus provides suitable conditions for invasion.

In acute inflammatory condition, little is known about the expression of the urokinase-type plasminogen activator (uPA) and its receptor (uPAR) in the gastric fibroblasts. To clarify the role of human gastric fibroblasts in acute inflammatory conditions such as gastric ulcer, the effects of interleukin (IL)-1beta and tumor necrosis factor (TNF)-alpha on the expression of uPA and uPAR, which were suggested to be associated with tissue remodeling, in gastric fibroblasts were investigated. The expression level of uPA mRNA and the amount of uPA antigen increased significantly on treatment with each concentration of IL-1beta (1 and 10 ng/ml) and 10 ng/ml TNF-alpha. On the other hand, the amounts of uPA antigen on cell surfaces were not affected significantly by IL-1beta and TNF-alpha stimulation. The expression level of uPAR mRNA increased in a dose-dependent manner on IL-1beta stimulation. The effect of indomethacin on uPA and uPAR expression in these cells was also examined. When gastric fibroblasts were treated with 50 microM indomethacin, the expression level of uPA mRNA decreased significantly, and the amount of uPA antigen in the culture medium and on cell surfaces decreased significantly with indomethacin in a dose-dependent manner. The increased uPAR mRNA expression caused by IL-1beta was reduced to the basal level by treatment with 50 microM indomethacin. Furthermore, we investigated the role of prostaglandin E2 (PGE2), which is suggested to play major roles in acute inflammation of the stomatch, on uPA and uPAR expression in gastric fibroblasts. The expression level of uPAR mRNA and the amount of uPA antigen on cell surfaces increased in a dose-dependent manner on treatment with PGE2 (10 and 50 ng/ml). These results suggest that uPA and uPAR expression in gastric fibroblasts is involved in the regulating system of PGE2 and that NSAIDs may delay healing of gastric mucosal injury in part through suppressing uPA production via inhibition of endogenous PG production.

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