Cell culture
The A2780 Ovarian cell line was purchased from the Biotechnology Research Center of Bouali Research Institute of Mashhad (Mashhad, Iran). STR Profiling analysis was performed to confirm the validity of this cell line. The A2780 cell line was cultured in RPMI-1640 culture medium containing 10% fetal bovine serum (FBS) (Gibco, UK), 100 units/ml penicillin and streptomycin (Gibco, UK) at 37°C, 95% humidity and 5% CO2.
CD133 expression analysis by FCM
Flow cytometry was performed to evaluate the expression level of CD133 surface marker in the A2780 cell line. For this purpose, after the cells reached 80% confluency, they were washed with PBS buffer and trypsinized to make single-cells. Single cells with a number of at least 105/100µl were dissolved in PBS buffer containing 5% serum mixed with 10ml of FITC dye (Miltenyi Biotec, Germany)-conjugated CD133 antibody according to the instructions and was incubated for 10-15 minutes at 4°C in the dark. The labeled cells were analyzed by FACS Calibur flow cytometer and the results were studied by the FlowJo 7.6.2 software (Tree Star, Ashland, OR).
Isolation of CD133+ cells by the MACS technique
After accurately calculating the expression level of CD133 marker in this cell line, cell culture was performed in high volume and isolation was done by the MACS technique using specific CD133 antibody-conjugated microbeads. For this purpose, 108 A2780 cells were cultured in several T75 flasks at 37°C and after reaching a suitable confluency, they were trypsinized and single-celled. The single cells were passed through a 30 µm filter to remove clamps and multicellular masses. The cells were then counted accurately by trypan blue staining. The cell pellet was dissolved in 600μl of a combined buffer kit (MACS BSA Stock Solution 1:20 autoMACS Rinsing Solution). 200μl of the FcR Blocking Reagent was added to the mixture and finally 200μl of CD133 microbeads (Miltenyi Biotec, Germany) was added and mixed well. The mixture was placed at 4°C for 15 minutes and shaken gently every 2 minutes for better bonding of the microbeads. The cells were then washed with 10-20 ml of buffer and after centrifugation at 300xg for 10 minutes, were dissolved in 5 ml of buffer and then the isolation process was performed by magnet and column according to the kit instructions. Then, in order to confirm the isolation accuracy of CD133+ cells, 105 of these cells were counted and dissolved in 100 μl of buffer. CD133 antibody (10 μl) was added to the buffer and placed at 4°C for 10 minutes. The cells were then washed with 1-2 ml of buffer, centrifuged at 300xg for 10 minutes, and the cell pellet was dissolved in 400 μl of buffer for flow cytometry analysis.
Evaluation test for sphere formation of CD133 positive cells
To evaluate the self-regenerative nature of CD133+ cells isolated from the A2780 ovarian cell line, these cells were cultured as 2×105 in number in Ultra low attachment 6-cell plates (Sigma-Aldrich, Corning) containing 2 ml of serum-free DMEM/F12 medium including 20 ng/mL h-EGF, 20 ng/mL h-bFGF (Sigma-Aldrich), 2% B27 supplement, 5 μg/ml Insulin and 1% penicillin/streptomycin. Cell growth was examined daily with an inverted microscope (OPTIKA, Italy) and the size and number of spheres formed in CD133+ and CD133- cells were compared and analyzed.
RNA extraction and cDNA synthesis from CD133+ and CD133- cells
RNA was obtained from 8×105 CD133+ and CD133- cells with the Pars Toos extraction kit according to the company's instructions. The amount of light absorption at 260, 280, 230 nm wavelengths and A260/A280, A260/A230 ratios were measured with the nanodrop device. RNA samples were treated with DNaseI (Thermo Fisher Scientific, US) and cDNA synthesis was performed with the Pars Toos kit.
Fundamental markers expression analysis in CD133 + and CD133- cells
Comparative real-time PCR analysis was performed in duplicate using Master Mix Cybergreen (AMPLIQON, Denmark) and real-time thermocycler (Light Cycler 96, Roche, Germany). The GAPDH gene was used as an interior control. Fold changes greater than 1 were considered as increased expression, less than -1 as decreased expression, and between 1 and -1 were considered as no change in expression. Nucleotide primers were designed for real-time PCR reaction for the internal control gene and stemness markers were designed by the Oligo 7 software and by the Primer Blast software, the specificity of the primers was confirmed (Table 1). Real-time PCR was performed by using 5μl of SYBR Green PCR Master Mix, 10 pM of Forward and Reverse primers of each gene and 100 ng/μl of the cDNA synthesized in the previous step for each reaction in the final volume of 10 μl under the conditions provided by the manufacturer.
Table 1. Specifications of the primers used in real-time PCR
Sequence
|
Length
(base pairs)
|
Melting point (ºC)
|
GC%
|
Product length (base pairs)
|
Primer
|
F:GGAAGGTGAAGGTCGGAGTCA R:GTCATTGATGGCAACAATATCCACT
|
21
25
|
60
60
|
57.14
40
|
101
|
GAPDH
|
F: AACAGCCCGGACCGCGTCAA
R: TCGCAGCCGCTTAGCCTCGT
|
20
20
|
65
65
|
65
65
|
189
|
SOX2
|
F: GCAATGGTGTGACGCAGAAGGC
R:GCTCCAGGTTGAATTGTTCCAGGTC
|
22
25
|
65
65
|
59.09
52
|
137
|
NANOG
|
F: CCTGAAGCAGAAGACGATCA
R: CCGCAGCTTACACATGTTCT
|
20
20
|
63
63
|
50
50
|
148
|
OCT4
|
F: TGAGGGTTTGGAACTGTGG
R: GATTCTGACGCACACCTGG
|
19
19
|
65
65
|
52.63
57.89
|
155
|
ABCG2
|
F: GATCCCCGTGGCGTACTATG
R: TGGATCTTGTCAGCCCAACC
|
20
20
|
62
62
|
60
55
|
202
|
ALDH1
|
F: CCTTCCAACCTCAGCGTCTT
R: AGGGATTGAAGGCTTCGCAA
|
20
20
|
60
60
|
55
50
|
248
|
LGR5
|
F: GAGACTGACGCGCCCCAGCC
R: CGCCTGGTCCATGAAAGTGACG
|
20
22
|
60
60
|
75
59.09
|
213
|
Msi1
|
Real-time PCR data analysis was performed by the ΔΔCT method. Statistical differences were calculated using the GraphPad Prism 8.0 software and One-way ANOVA (parametric) test; a P <0.05 was considered as statistically significant.