Zhu et al. Journal of Experimental & Clinical Cancer Research 2010, 29:124 http://www.jeccr.com/content/29/1/124 Page 6 of 8 Figure 3 The genes expression in SKOV-3, ES-2, ELs from cancer cells and HUVEC induced by hypoxia. The SKOV-3, ES-2 and HUVEC cells were cultured for 7 d in normoxia or hypoxia conditions before harvested for the expression of HIF-1a, VEGF, Flk-1, CyclinD1, p53 and V-src genes detected by Real-time PCR. A. The genes expression in SKOV-3 and relative cells by Real-time PCR. B. The genes expression in ES-2 and relative cells by Real-time PCR. SKOV-3 EL: the endothelial-like cells induced from SKOV-3 cells; SKOV-3+Si: the SKOV-3 cells treated by Sirolimus under hypoxia; ES-2 EL: the endothelial-like cells induced from ES-2 cells; ES-2+Si: the ES-2 cells treated by Sirolimus under hypoxia; *, ^, and & indicates that P < 0.05 vs.HUVEC, SKOV-3 (or ES-2) and SKOV-3+Si (or ES-2+Si); **, ^^, and && indicates that P < 0.01 vs.HUVEC, SKOV-3 (or ES-2) and SKOV-3+Si (or ES-2+Si). Cyclin D1 mRNA expression in both of the two tumors’ ELs was greatly lower than that in the cells under normoxia, while there was no difference in Cyclin D1 mRNA expression in the cells treated with Sirolimus and HUVEC cells. p53 mRNA expression in both of the two tumors’ ELs was significantly higher than that in the cells under nor- moxia and in HUVEC cells, however, there was no sig- nificant changes after treated with Sirolimus. V-src mRNA didn’t express in all kinds of cells under hypoxia or normoxia. Discussion In the present study, we induced two ovarian cancer cell lines, SKOV-3 and ES-2, to endothelial-like cells by Table 2 The activity of telomerase in different cells SKOV-3 EL: the endothelial-like cells induced from SKOV-3 cells; SKOV-3+Si: the SKOV-3 cells treated by Sirolimus under hypoxia; ES-2 EL: the endothelial- like cells induced from ES-2 cells; ES-2+Si: the ES-2 cells treated by Sirolimus under hypoxia. CELLS HUVEC SKOV-3 SKOV-3 EL SKOV-3+Si ES-2 ES-2 EL ES-2+Si RESULT - + + + + - - hypoxia and harvested the ELs by LCM. On the base of our previous study [11], the ELs have the specific char- acteristics of endothelial cells, such as expressing CD34, vWF and uptaking acLDL. Here, we detected the biolo- gical behaviors of the ELs and compared with the HUVEC endothelial cells and the original cancer cells. As shown in the results, under the condition of hypoxia, the cancer cells’ growth was inhibited in the short period (3 d), however, after the long-time hypoxia (7 d) incubation, the cells were recovered to grow. The results of the proliferation assay, cell cycle and apoptosis assay demonstrated these. HUVEC, on the other hand, could not endure hypoxia, which showed inhibited prolif- eration, reduced S-phase ratio, and increases in apoptosis under the condition of hypoxia. As indicated by previous studies [10,18], the more aggressive of the cancer, the more strongly the cells could resistant to hypoxia. Under the condition of hypoxia, the cancer cells could change some characteristics into ELs to form VM, and then the tumor could perfuse itself independent of angiogenesis. Tumors exhibiting in VM related to more aggressive tumor biology and increased tumor-related mortality [19,20]. Invasion through the basement membrane is one of the features of the aggressive tumor. Under the condi- tion of hypoxia, the SKOV-3 and ES-2 ovarian cancer cells reduced the ability to invasion at first and then recovered to normal level after long-time hypoxia. Telomerase, an enzyme complex that binds the chro- mosome ends (telomeres) and maintains telomere length