The characteristics of the adenomatous polyposis coli (APC) associated protein EB1 were examined in mammalian cells. By immunocytochemistry EB1 was shown to be closely associated with the microtubule cytoskeleton throughout the cell cycle. In interphase cells EB1 was associated with microtubules along their full length but was often particularly concentrated at their tips. During early mitosis, EB1 was localized to separating centrosomes and associated microtubules, while at metaphase it was associated with the spindle poles and associated microtubules. During cytokinesis EB1 was strongly associated with the midbody microtubules. Treatment with nocodazole caused a diffuse redistribution of EB1 immunoreactivity, whereas treatment with cytochalasin D had no effect. Interestingly, treatment with taxol abolished the EB1 association with microtubules. In nocodazole washout experiments EB1 rapidly became associated with the centrosome and repolymerizing microtubules. In taxol wash-out experiments EB1 rapidly re-associated with the microtubule cytoskeleton, resembling untreated control cells within 10 min. Immunostaining of SW480 cells, which contain truncated APC incapable of interaction with EB1, showed that the association of EB1 with microtubules throughout the cell cycle was not dependent upon an interaction with APC. These results suggest a role for EB1 in the control of microtubule dynamics in mammalian cells.

Summary Expression of cyclooxygenase 2 (COX-2) is believed to play an important role in adenoma formation in murine polyposis models, and inhibition of COX-2 activity may, at least, partly explain the chemopreventative activity of non-steroidal anti-inflammatory drugs against colorectal cancer in humans. However, the mechanism by which COX-2 acts in intestinal tumorigenesis remains unresolved because of conflicting data on the cellular localization of COX-2 in intestinal mucosa. Using immunohistochemistry with specific COX-2 antiserum, we have shown that COX-2 protein is localized to interstitial cells at the base of and within adenomas of the small and large intestine of multiple intestinal neoplasia (Min) mice. No COX-2 staining was observed in dysplastic epithelial cells within adenomas or in histologically normal epithelium. Moreover, COX-2 staining was observed in lamina propria cells of histologically normal intestine of Min mice. No staining was demonstrated in wild-type littermates. The rat monoclonal antibody F4/80 was used to show that COX-2-positive cells represented a subset of the macrophage population present in the intestine of Min mice. Localization of COX-2 to macrophages implies a paracrine effect of COX-2 function on epithelial cells in adenomas and also on histologically normal epithelium. Up-regulation of COX-2 expression in lamina propria macrophages may precede loss of the second functional Apc allele in epithelial cells before adenoma formation in the Min mouse model of intestinal tumorigenesis.

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Herpesvirus saimiri (HVS)