Missense mutations in the 695-amino acid form of the amyloid precursor protein (APP695) cosegregate with disease phenotype in families with dominantly inherited Alzheimer's disease. These mutations convert valine at position 642 to isoleucine, phenylalanine, or glycine. Expression of these mutant proteins, but not of normal APP695, was shown to induce nucleosomal DNA fragmentation in neuronal cells. Induction of DNA fragmentation required the cytoplasmic domain of the mutants and appeared to be mediated by heterotrimeric guanosine triphosphate-binding proteins (G proteins).

APP is a transmembrane precursor of beta‐amyloid. In dominantly inherited familial Alzheimer's disease (FAD), point mutations V6421, V642F and V642G have been discovered in APP695. Here we show that expression of these mutants (FAD‐APPs) causes a clone of COS cells to undergo apoptosis associated with DNA fragmentation. Apoptosis by the three FAD‐APPs was the highest among all possible V642 mutants; normal APP695 had no effect on apoptosis, suggesting that apoptosis by APP mutants in this system is phenotypically linked to the FAD trait. FAD‐APP‐induced apoptosis was sensitive to bcl‐2 and most probably mediated by heteromeric G proteins. This study presents a model system allowing analysis of the mechanism for FAD‐APP‐induced cytotoxicity.

The tumor suppressor gene p53 is a potent transcriptional regulator of genes which are involved in many cellular activities including cell cycle arrest, apoptosis, and angiogenesis. Recent studies have demonstrated that the activation of the transcriptional factor nuclear factor kB (NF-kB) plays an essential role in preventing apoptotic cell death. In this study, to better understand the mechanism reponsible for the p53-mediated apoptosis, the eect of wild-type p53 (wt-p53) gene transfer on nuclear expression of NF-kB was determined in human colon cancer cell lines. A Western blot analysis of nuclear extracts demonstrated that NF-kB protein levels in the nuclei were suppressed by the transient expression of the wt-p53 in a dose-dependent manner. Transduced wt-p53 expression increased the cytoplasmic expression of IkBa as well as its binding ability to NF-kB, thus markedly reducing the amount of NF-kB that translocated to the nucleus. The decrease in nuclear NF-kB protein correlated with the decreased NF-kB constitutive activity measured by electrophoretic mobility shift assay. Furthermore, parental cells transfected with NF-kB were better protected from cell death induced by the wt-p53 gene transfer. We also found that the wtp53 gene transfer was synergistic with aspirin (acetylsalicylic acid) in inhibiting NF-kB constitutive activity, resulting in enhanced apoptotic cell death. These results suggest that the inhibition of NF-kB activity is a plausible mechanism for apoptosis induced by the wt-p53 gene transfer in human colon cancer cells and that anti-NF-kB reagent aspirin could make these cells more susceptible to apoptosis. Oncogene (2000) 19, 726 ± 736.

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In this study, we examined the distribution of heparanase protein in 75 esophageal squamous cell carcinomas by immunohistochemistry and analyzed the relationship between heparanase expression and clinicopathological characteristics. In situ hybridization showed that the mRNA expression pattern of heparanase was similar to that of the protein, suggesting that increased expression of the heparanase protein at the invasive front was caused by an increase of heparanase mRNA in tumor cells. Heparanase expression correlated significantly with depth of tumor invasion, lymph node metastasis, tumor node metastasis (TNM) stage and lymphatic invasion. Overexpression of heparanase in esophageal cancers was also associated with poor survival. In addition to its localization in the cytoplasm and cell membrane, heparanase was also identified in the nuclei of normal epithelial and tumor cells by immunohistochemistry. Furthermore, nuclear heparanase was detected in nuclear extract of cancer cell lines by Western blot and immunohistochemistry. Examination of the role of nuclear heparanase in cell proliferation and differentiation by double immunostaining for proliferating cell nuclear antigen (PCNA) and cytokeratin 10 (CK10) showed significant relationship between nuclear heparanase expression and differentiation (heparanase vs CK10), but not for proliferative state of esophageal cancer cells (heparanase vs PCNA). Our results suggest that cytoplasmic heparanase appears to be a useful prognostic marker in patients with esophageal cancer and that nuclear heparanase protein may play a role in differentiation. Inhibition of heparanase activity may be effective in the control of esophageal tumor invasion and metastasis.