In previous experiments, a novel tumor cell line, which was characterized by dominated F6 mutated from human mesenchymal stem cells (hMSCs), was developed. The mechanism and biological characteristics of this mutation are still unclear. In this study, the histological type of F6 cells was investigated by immunohistochemistry with specific markers: vimentin, CD117, desmin, NSE and vWF. The characteristics of proliferation and metastasis were shown by PCNA (proliferating cell nuclear antigen), and nm23 and cell cycle-related genes, such as p16, p21, p53 and pRb, were analyzed by RT-PCR and immunohistochemistry. The expression of hTRAP and BMI-1 were detected by real-time PCR and Western blotting. The activity of telomerase was analyzed by TRAP (telomerase repeat amplification protocol) assay. The results showed that multi-directional differentiation occurred in F6 cells, i.e., special markers of muscle, endothelial cell and nerve system were co-expressed in F6 cells, while hardly expressed in hMSCs. F6 cells maintained the same properties as of MSCs, such as negativity for both CD117 and vimentin. F6 cells exhibited strong positivity for PCNA and negativity for nm23. The cell cycle-related genes, such as p16, p21, p53 and pRb, were not detected in F6 cells, while the expression of hTRAP and BMI-1 was significantly higher. The activity of telomerase was also significantly higher in F6 cells than that in hMSCs. These findings indicated that multi-directional differentiation occurred during the transformation of hMSCs into F6 cells, and that the genes of cell cycle and cell senescence may also be associated with the neoplasia of adult stem cells.

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