Effects of ascites derived exosomes on the stemness and invasion ability of ovarian cancer stem-like cell

Abstract

Objective: To investigate the effects of ovarian cancer ascites-derived exosomes on the stem cell properties and invasion ability of ovarian cancer stem-like cell (OCS-LC). Methods: (1) A2780 cells were induced into OCS-LC in serum-free medium, and authenticating their stem-like properties by sphere-forming test, differentiation test and CD133 marker detection. (2) Exosomes from ascites and A2780 cell were extracted by ultracentrifugation, then authenticating them. The morphology of exosomes was observed by the transmission electron microscope, exosome particle size was measured by nanoparticle tracking analysis (NTA). The expressions of heat shock protein 70 (HSP-70), CD63 and CD9 were detected by western blot. (3) The exosomes from ovarian cancer ascites and tumor cell supernate were co-cultured with OCS-LC. The groups were divided into control group, ascites-derived exosomes (ADE) group (ADE+OCS-LC group), and cells-derived exosomes (CDE) group (CDE+OCS-LC group). The sphere-forming ability was evaluated by sphere-forming cycle, maximum sphere diameter and sphere-forming rate of each group; the expression of CD133 was detected by immunofluorescence staining under microscope; quantitative real-time (qRT)-PCR was used to detected the expression levels of octamer-4 (Oct-4), Nanog mRNA of the signature genes in the stem cells of each group; the metastasis ability of each group was measured by transwell assay. Results: (1) Identification of OCS-LC: sphere-forming experiment showed that the suspension of OCSC single cells was grown in serum-free medium in secondary sphere-forming. Differentiation function experiment showed that OCS-LC were differentiated into adherent A2780 cells by changing the growth mode in serum containing medium. Flow cytometry showed that the proportion of CD133 positive (CD133+) cells in OCS-LC group was (18.9±0.9)%, significantly higher than that of control group (0.6±0.5)% (t=38.570, P<0.01). (2) Under transmission electron microscope, clear lipid bilayer structure was observed in ADE and CDE, and one side presented a concave hemispheric or cup like structure. NTA showed that the diameter of exosomes mainly ranged from 30 to 100 nm, with an average diameter of 67.2 nm. Western blot analysis showed that the specific protein molecules HSP-70, CD63 and CD9 were positive. (3) Three groups' OCS-LC could continue to grow into spheres, and the group of ADE+OCS-LC showed two growth modes, most of the cells continued to grow into spheres, while a small part of cells grew in adherent differentiation. The sphere-forming rate of OCS-LC in the control group, ADE+OCS-LC group, and CDE+OCS-LC group were (1.05±0.20)%, (4.15±0.10)%, and (10.45±0.25)%, the sphere-forming cycle of OCS-LC in the three groups were (15.3±1.5), (10.3±0.6), and (6.7±0.6) days, and the maximum diameters of OCS-LC were (100.3±3.2), (145.2±5.1) and (170.0±2.1) μm, respectively. And the differences were statistically significant (all P<0.05). After co-culture of exosomes with OCS-LC, the sphere-forming ability of cells in the group of CDE+OCS-LC was prior to ADE+OCS-LC group (all P<0.05). Immunofluorescence staining showed that the number of CD133 green fluorescent chromophore cells in OCS-LC groups [(46.2±2.1)%, (58.4±2.2)%] was significantly higher than that in the control group [(26.6±1.5)%] after the addition of exosomes in co-culture, the positive rate of CD133 was higher than that in the control group(F=187.588, P<0.05). The qRT-PCR results showed that the expression levels of Oct-4 mRNA in ADE+OCS-LC and CDE+OCS-LC groups were 3.46±0.24, 4.03±0.31, compared with that in control group (1.04±0.12), the differences were statistically significant (F=134.932, P<0.05). The mRNA expression levels of Nanog were 1.57±0.32, 2.66±0.15, which were significantly higher than that in the control group (1.00±0.07), and the differences were statistically significant (F=49.329, P<0.05). And the expression of both in CDE+OCS-LC group increased more significantly than ADE+OCS-LC group (all P<0.05). The number of invasive cells in the three groups of OCS-LC were: control group 30±5, ADE+OCS-LC group 102±4, CDE+OCS-LC group 210±7, and there were statistically significant differences among three groups (F=820.800, P<0.05). Compared with the control group, the number of invaded cells in the co-culture group were significantly increased (P<0.05), and the CDE+OCS-LC group had the higher cell invasion ability then the ADE+OCS-LC group (t=23.202, P<0.05). Conclusions: Exosomes derived from ovarian cancer ascites could enhance and maintain the stemness of OSC-LC, and promote the invasion of tumor cells. Moreover, CDE is superior to ADE.