Familial adenomatous polyposis coli (FAP) is a disease characterized by the development of multiple colorectal adenomas, and affected individuals carry germline mutations in the APC gene. With the use of a conditional gene targeting system, a mouse model of FAP was created that circumvents the embryonic lethality of Apc deficiency and directs Apc inactivation specifically to the colorectal epithelium. loxP sites were inserted into the introns around Apc exon 14, and the resultant mutant allele (Apc580S) was introduced into the mouse germline. Mice homozygous for Apc580S were normal; however, upon infection of the colorectal region with an adenovirus encoding the Cre recombinase, the mice developed adenomas within 4 weeks. The adenomas showed deletion of Apc exon 14, indicating that the loss of Apc function was caused by Cre-loxP-mediated recombination.

Prion protein (PrP) is a glycoprotein constitutively expressed on the neuronal cell surface. A protease-resistant isoform of prion protein is implicated in the pathogenesis of a series of transmissible spongiform encephalopathies. We have developed a line of mice homozygous for a disrupted PrP gene in which the whole PrP-coding sequence is replaced by a drug-resistant gene. In keeping with previous results, we find that homozygous loss of the PrP gene has no deleterious effect on the development of these mice and renders them resistant to prion. The PrP-null mice grew normally after birth, but at about 70 weeks of age all began to show progressive symptoms of ataxia. Impaired motor coordination in these ataxic mice was evident in a rotorod test. Pathological examination revealed an extensive loss of Purkinje cells in the vast majority of cerebellar folia, suggesting that PrP plays a role in the long-term survival of Purkinje neurons.

Apc is a gene associated with familial adenomatous polyposis coli (FAP) and its inactivation is a critical step in colorectal tumor formation. The protein product, adenomatous polyposis coli (APC), acts to down-regulate intracellular levels of ␤-catenin, a key signal transducer in the Wnt signaling. Conditional targeting of Apc in the neural crest of mice caused massive apoptosis of cephalic and cardiac neural crest cells at about 11.5 days post coitum, resulting in craniofacial and cardiac anomalies at birth. Notably, the apoptotic cells localized in the regions where ␤-catenin had accumulated. In contrast to its role in colorectal epithelial cells, inactivation of APC leads to dysregulation of ␤-catenin͞Wnt signaling with resultant apoptosis in certain tissues including neural crest cells.T he Apc gene encoding a tumor suppressor protein, adenomatous polyposis coli (APC), is known to be responsible for familial adenomatous polyposis coli (FAP), an autosomaldominant inherited disorder characterized by multiple colorectal tumors (1, 2). Because Apc mutations are also frequently identified in sporadic colorectal tumors (3), the functional loss of APC is likely to be a key process in the colorectal tumorigenesis, especially during the early stages of tumor development. Indeed, conditional targeting of Apc in the colorectal epithelium initiated colorectal adenoma formation in mice (4).The biological function of APC is not fully understood, however it is thought to be a multifunctional protein and plays an important role in the regulation of growth, differentiation, and͞or migration of epithelial cells (5). Overexpression of APC can block cell cycle progression from G 0 ͞G 1 to S phase in NIH 3T3 cells (6). APC concentrates near the ends of microtubules that extend into actively migrating regions of epithelial cell membrane (7), and recently it was suggested that APC might regulate the actin cytoskeleton through Asef, a novel APCbinding protein (8). Moreover, the nuclear export function of APC has been reported by .Accumulating evidence has indicated that APC acts as a negative regulator of the Wnt signaling cascade through downregulation of ␤-catenin (10, 11). Functional loss of APC causes stabilization and accumulation of ␤-catenin (12), allowing it to form a complex with Tcf͞Lef transcription factors to activate Tcf target genes (13-15). Mutant mice lacking certain Wnt functions exhibited abnormal phenotypes involving embryonic induction, cell polarity, and cell fate determination in various tissues during development (16)(17)(18)(19)(20). In particular, injection of mRNA for ␤-catenin or that encoding a mutant form of Tcf-3 into zebrafish embryos affected the Wnt signaling and resulted in abnormal development of lateral and medial neural crest cells (21).To elucidate the function of APC in mammalian neural crest, in the present study we generated mutant mice harboring Apc disrupted specifically in the neural crest by using the Cre-loxP recombination system. We found that the mutant mice displayed severe craniofa...

Exposure to asbestos is a known etiological factor in malignant mesothelioma (MM). However, in vitro cell culture studies have provided paradoxical evidence that asbestos exposure to mesothelial cells causes cytotoxicity or apoptosis rather than malignant transformation. Although it has been shown that the iron associated with asbestos participates in the cell toxicity and probably MM pathogenesis via generation of reactive oxygen species (ROS), the molecular mechanisms largely remain unknown. Here, we demonstrate that ferritin heavy chain (FHC), a core subunit of iron-binding protein ferritin, works as an anti-apoptotic protein against toxic asbestos and oxidative stress in human mesothelial cells and MM cells. We found that FHC was induced in asbestos-exposed MeT-5A human mesothelial cells. The mesothelial cell line stably expressing FHC generated less amount of hydrogen peroxide (H2O2), one of the main ROS, after asbestos exposure and was more resistant to apoptosis induced by H2O2 compared with the cells transfected with the empty vector. Next, we investigated biological roles of FHC in human MM cell. We found that NCI-H2052, a human MM cell line, had a higher expression of endogenous FHC than MeT-5A and used the cell to address FHC function in MM. NCI-H2052 showed reduced H2O2 production and an apoptosis-resistant phenotype compared with MeT-5A. Suppression of the over-expressed FHC by using FHC small interfering RNA rendered the MM cells sensitive to apoptosis, suggesting the contribution of FHC to apoptosis resistance of the MM cells. Our findings highlight the potential role of FHC in the pathogenesis of asbestos-induced mesothelioma.