Mouse mesenchymal stem cells expressing PAX-FKHR form alveolar rhabdomyosarcomas by cooperating with secondary mutations.

Alveolar rhabdomyosarcomas (ARMS) are highly malignant soft-tissue sarcomas that arise in children, adolescents, and young adults. Although formation and expression of the PAX-FKHR fusion genes is thought to be the initiating event in this cancer, the role of PAX-FKHR in the neoplastic process remains largely unknown in a progenitor cell that is undefined. We hypothesize that PAX-FKHR determine the ARMS progenitor to the skeletal muscle lineage, which when coupled to the inactivation and/or activation of critical cell signaling pathways leads to the formation of ARMS. Because a number of studies have proposed that mesenchymal stem cells (MSC) are the progenitor for several of the sarcomas, we tested this hypothesis in MSCs. We show that PAX-FKHR induce skeletal myogenesis in MSCs by transactivating MyoD and myogenin. Despite exhibiting enhanced growth in vitro, the PAX-FKHR-expressing populations do not form colonies in soft agar or tumors in mice. Expression of dominant-negative p53, or the SV40 early region, elicits tumor formation in some of the PAX-FKHR-expressing populations. Additional activation of the Ras signaling pathway leads to highly malignant tumor formation for all of the populations. The PAX-FKHR-expressing tumors were shown to have histologic, immunohistochemical, and gene expression profiles similar to human ARMS. Our results show the critical role played by PAX-FKHR in determining the molecular, myogenic, and histologic phenotype of ARMS. More importantly, we identify MSCs as a progenitor that can give rise to ARMS.

Detection of point mutation in K-ras oncogene at codon 12 in pancreatic diseases.

AIM: To investigate frequency and clinical significance of K-ras mutations in pancreatic diseases and to identify its diagnostic values in pancreatic carcinoma. METHODS: 117 ductal lesions were identified in the available sections from pancreatic resection specimens of pancreatic ductal adenocarcinoma, comprising 24 pancreatic ductal adenocarcinoma, 19 peritumoral ductal atypical hyperplasia, 58 peritumoral ductal hyperplasia and 19 normal duct at the tumor free resection margin. 24 ductal lesions were got from 24 chronic pancreatitis. DNA was extracted. Codon 12 K-ras mutations were examined using the two-step polymerase chain reaction (PCR) combined with restriction enzyme digestion, followed by nonradioisotopic single-strand conformation polymorphism (SSCP) analysis and by means of automated DNA sequencing. RESULTS: K-ras mutation rate of the pancreatic carcinoma was 79%(19/24) which was significantly higher than that in the chronic pancreatitis 33%(8/24) (P<0.01). It was also found that K-ras mutation rate was progressively increased from normal duct at the tumor free resection margin, peritumoral ductal hyperplasia, peritumoral ductal atypical hyperplasia to pancreatic ductal adenocarcinoma. The mutation pattern of K-ras 12 codon of chronic pancreatitis was GGT-GAT, GGT and CGT, which is identical to that in pancreatic carcinoma. CONCLUSION: K-ras mutation may play a role in the malignant transformation of pancreatic ductal cell. K-ras mutation was not specific enough to diagnose pancreatic carcinoma.