The molecular events that precede the development of osteosarcoma, the most common primary malignancy of bone, are unclear, and concurrent molecular and genetic alterations associated with its pathogenesis have yet to be identified. Recent studies suggest that activation of ␤-catenin signaling may play an important role in human tumorigenesis. To investigate the potential role of ␤-catenin deregulation in human osteosarcoma, we analyzed a panel of 47 osteosarcoma samples for ␤-catenin accumulation using immunohistochemistry. Potential activating mutations were investigated by sequencing exon 3 of the ␤-catenin gene in genomic DNA isolated from tumor samples. Our findings revealed cytoplasmic and/or nuclear accumulation of ␤-catenin in 33 of 47 samples (70.2%); however, mutation analysis failed to detect any genetic alterations within exon 3, suggesting that other regulatory mechanisms may play an important role in activating ␤-catenin signaling in osteosarcoma. In our survival analysis, ␤-catenin deregulation conferred a hazard ratio of 1.05, indicating that ␤-catenin accumulation does not appear to be of prognostic value for osteosarcoma patients. When analyzed against other clinicopathologic parameters, ␤-catenin accumulation correlated only with younger age at presentation (26.4 vs. 39.8 years). Nevertheless, our results demonstrate that the deregulation of ␤-catenin signaling is a common occurrence in osteosarcoma that is implicated in the pathogenesis of osteosarcoma. © 2002 Wiley-Liss, Inc. Key words: Wnt signal; ␤-catenin; osteosarcoma; tumorigenesis; bone tumorOsteosarcoma is the most common primary malignant tumor of bone, encompassing a class of osteoid-producing neoplasms that range in clinical behavior and responsiveness to therapeutic regimens. 1 Best known of these lesions, the classic high-grade osteosarcoma, primarily afflicts individuals in the second decade of life and is distinguished by its locally aggressive character and early metastatic potential. Despite advances in chemotherapy, 5-year survival has remained around 60%. 2 The molecular events that precede the development of osteosarcoma are poorly understood. Given its relatively early age at presentation and predilection for early metastasis, osteosarcoma is likely the result of underlying early somatic and/or germline mutations. Alterations in tumor-suppressor genes such as retinoblastoma (Rb1) and p53 have been identified in osteosarcoma and hypothesized to predispose individuals to this malignancy at an especially early age. [3][4][5][6] Although several putative chromosomal regions have been suggested to harbor potential tumor-suppressor genes, the molecular nature and identity of these genes have not been elucidated.␤-Catenin is a cellular protein with multiple functions. As an important component of the adherens junction complex, it helps to anchor E-cadherin to the intracellular actin cytoskeleton through interactions with ␣-catenin. 7,8 As an important Wnt signal transducer, ␤-catenin plays an important role in many developmental...

Human gene therapy promises to change the practice of medicine by treating the causes of disease rather than the symptoms. Since the first clinical trial made its debut ten years ago, there are over 400 approved protocols in the United States alone, most of which have failed to show convincing data of clinical efficacy. This setback is largely due to the lack of efficient and adequate gene transfer vehicles. With the recent progress in elucidating the molecular mechanisms of human diseases and the imminent arrival of the post genomic era, there are increasing numbers of therapeutic genes or targets that are available for gene therapy. Therefore, the urgency and need for efficacious gene therapies are greater than ever. Clearly, the current fundamental obstacle is to develop delivery vectors that exhibit high efficacy and specificity of gene transfer. Recombinant adenoviruses have provided a versatile system for gene expression studies and therapeutic applications. Of late, there has been a remarkable increase in adenoviral vector-based clinical trials. Recent endeavors in the development of recombinant adenoviral vectors have focused on modification of virus tropism, accommodation of larger genes, increase in stability and control of transgene expression, and down-modulation of host immune responses. These modifications and continued improvements in adenoviral vectors will provide a great opportunity for human gene therapy to live up to its enormous potential in the second decade.

Wnt/beta-catenin pathway plays an important role in regulating embryonic development. Hepatocytes differentiate from endoderm during development. Hepatic progenitor cells (HPCs) have been isolated from fetal liver and extrahepatic tissues. Most current studies in liver development and hepatic differentiation have been focused on Wnts, beta-catenin, and their receptors. Here, we sought to determine the role of Wnt antagonists in regulating hepatic differentiation of fetal liver-derived HPCs. Using mouse liver tissues derived from embryonic day E12.5 to postnatal day (PD) 28, we found that 13 of the 19 Wnt genes and almost all of Wnt receptors/co-receptors were expressed in most stages. However, Wnt antagonists SFRP2, SFRP3, and Dkk2 were only detected in the early stages. We established and characterized the reversible stable HPCs derived from E14.5 mouse fetal liver (HP14.5). HP14.5 cells were shown to express high levels of early liver progenitor cell markers, but low levels or none of late liver markers. HP14.5 cells were shown to differentiate into mature hepatocytes upon dexamethasone (Dex) stimulation. Dex-induced late marker expression and albumin promoter activity in HP14.5 cells were inhibited by exogenous expression of SFRP3. Furthermore, Dex-induced glycogen synthesis of PAS-positive HP14.5 cells was significantly inhibited by SFRP3. Therefore, our results have demonstrated that the expression of Wnt antagonists decreases as hepatic differentiation progresses, suggesting that a balanced Wnt signaling may be critical during mouse liver development and hepatic differentiation.

Our results strongly suggest that RA signalling may play an important role in regulating hepatic differentiation.

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