Although PGE2 is a potent inhibitor of fibroblast function, PGE2 levels are paradoxically elevated in murine lungs undergoing fibrotic responses. Pulmonary fibroblasts from untreated mice expressed all four E prostanoid (EP) receptors for PGE2. However, following challenge with the fibrogenic agent, bleomycin, fibroblasts showed loss of EP2 expression. Lack of EP2 expression correlated with an inability of fibroblasts from bleomycin-treated mice to be inhibited by PGE2 in assays of proliferation or collagen synthesis and blunted cAMP elevations in response to PGE2. PGE2 was similarly unable to suppress proliferation or collagen synthesis in fibroblasts from EP2−/− mice despite expression of the other EP receptors. EP2−/−, but not EP1−/− or EP3−/− mice, showed exaggerated fibrotic responses to bleomycin administration in vivo as compared with wild-type controls. EP2 loss on fibroblasts was verified in a second model of pulmonary fibrosis using FITC. Our results for the first time link EP2 receptor loss on fibroblasts following fibrotic lung injury to altered suppression by PGE2 and thus identify a novel fibrogenic mechanism.

Hepatic ischemia/reperfusion (I/R) results in a neutrophildependent lung and liver injury. The process of neutrophil recruitment and activation in this injury is at least partially dependent on the presence of the ELR؉ CXC chemokines. Other investigations have shown that ELR؊ CXC chemokines can block ELR؉ CXC chemokine neutrophil recruitment and activation in vitro. To begin to investigate the role of the balance between these 2 types of molecules in vivo in neutrophil recruitment and activation following hepatic I/R, we used our rat model of lobar hepatic I/R and pretreated animals with pharmacologic doses of gamma-interferon (␥-IFN). ␥-IFN is known to upregulate some of the ELR؊ CXC chemokines, including ␥-IFN-inducible protein (IP-10) and monokine-induced by ␥-IFN (MIG), as well as down-regulate ELR؉ CXC chemokine production. Following hepatic I/R or sham laparotomy, hepatic and pulmonary levels of the ELR؊ chemokines, IP-10 and MIG, and the ELR؉ chemokines, rat cytokine-induced neutrophil chemoattractant (KC), macrophage inflammatory protein-2 (MIP-2), and epithelial neutrophil activating protein (ENA-78) were determined by ELISA, and lung and liver injury were assessed. In response to ␥-IFN, hepatic and pulmonary levels of the ELR؊ chemokines were increased and the levels of the ELR؉ chemokines were decreased. Immunohistochemical staining confirmed the hepatocyte as the source of these molecules, as well as the changes in chemokine levels in response to ␥-IFN. There was an associated significant decrease in liver and lung injury, although there was no significant decrease in neutrophil influx in either tissue. This suggests that the alteration in the balance of ELR؉ to ELR؊ CXC chemokines results in a decrease in tissue injury through a mechanism other than through an alteration in tissue neutrophil levels. (HEPATOLOGY 2000;31: 435-445.)

Adenomatous polyposis coli (APC) inactivating mutations are present in most human colorectal cancers and some other cancers. The APC protein regulates the β-catenin protein pool that functions as a co-activator of T cell factor (TCF)-regulated transcription in Wnt pathway signaling. We studied effects of reduced dosage of the Ctnnb1 gene encoding β-catenin in Apc-mutation-induced colon and ovarian mouse tumorigenesis and cell culture models. Concurrent somatic inactivation of one Ctnnb1 allele, dramatically inhibited Apc mutation-induced colon polyposis and greatly extended Apc-mutant mouse survival. Ctnnb1 hemizygous dose markedly inhibited increases in β-catenin levels in the cytoplasm and nucleus following Apc inactivation in colon epithelium, with attenuated expression of key β-catenin/TCF-regulated target genes, including those encoding the EphB2/B3 receptors, the stem cell marker Lgr5, and Myc, leading to maintenance of crypt compartmentalization and restriction of stem and proliferating cells to the crypt base. A critical threshold for β-catenin levels in TCF-regulated transcription was uncovered for Apc mutation-induced effects in colon epithelium, along with evidence of a feed-forward role for β-catenin in Ctnnb1 gene expression and CTNNB1 transcription. The active β-catenin protein pool was highly sensitive to CTNNB1 transcript levels in colon cancer cells. In mouse ovarian endometrioid adenocarcinomas (OEAs) arising from Apc- and Pten-inactivation, while Ctnnb1 hemizygous dose affected β-catenin levels and some β-catenin/TCF target genes, Myc induction was retained and OEAs arose in a fashion akin to that seen with intact Ctnnb1 gene dose. Our findings indicate Ctnnb1 gene dose exerts tissue-specific differences in Apc mutation-instigated tumorigenesis. Differential expression of selected β-catenin/TCF-regulated genes, such as Myc, likely underlies context-dependent effects of Ctnnb1 gene dosage in tumorigenesis.