Immunocytochemical detection of the expression of CD147 and Lewis y in three groups of ovarian cancer cells with varying degrees of malignancy
Immunocytochemical analysis showed positive CD147 staining in RMG-I-H, HO8910/PM, and COC1/DDP cells, as indicated by the detection of buffy particles in the cytoplasm and cell membrane; the cumulative optical density values were 66.91 ± 6.45, 38.83 ± 1.43, and 31.92 ± 2.81, respectively. CD147 positive stainig in RMG-I, HO8910, and COC1 cells was detected as amber particles, with cumulative optical density values of 16.54 ± 1.31, 19.10 ± 3.02, and 4.49 ± 0.13, respectively. Clustering expression of CD147 in RMG-I-H, HO8910/PM, and COC1/DDP cells was higher than that in the parental cell lines, and positive staining was significantly enhanced (P < 0.05, Fig. 1A and Table 2). Lewis y localized to the cell membrane and cytoplasm, and positively stained particles were detected as buffy or brown in RMG-I-H, HO8910/PM, and COC1/DDP cells; they were widely distributed, and the cumulative optical density values were 53.90 ± 4.33, 37.31 ± 0.19, and 28.52 ± 1.45, respectively. Lewis y positive staining in RMG-I, HO8910, and COC1 cells was detected as amber dispersed particles, and the cumulative optical density values were 22.18 ± 0.64, 14.96 ± 0.61, and 16.26 ± 0.83, respectively (Fig. 1B and Table 2). The expression of Lewis y was similar to that of CD147 and was significantly lower than that in the corresponding RMG-I-H, HO8910/PM, and COC1/DDPP cells (P < 0.05).
Table 2
The accumulative optical density values for CD147\Lewis y antigen in three groups of ovarian cancer cells with varying degrees of malignancy that were measured by using immuocytochemical methods
Cell line | CD147 | Lewis y |
RMG-I RMG-I-H HO8910 HO8910/PM COC1 COC1/DDP | 16.54 ± 1.31 66.91 ± 6.45* 19.10 ± 3.02 38.83 ± 1.43* 4.49 ± 0.13 31.92 ± 2.81* | 22.18 ± 0.64 53.90 ± 4.33* 14.96 ± 0.61 37.31 ± 0.19* 16.26 ± 0.83 28.52 ± 1.45* |
* P < 0.05, RMG-I-H compared to RMG-I cells, HO8910/PM compared to HO8910 cells, and COC1/DDP compared to COC1 cells. |
Quantitative real-time PCR detection of the expression of CD147 and FUT1 in three groups of ovarian cancer cells with varying degrees of malignancy
Figure 2A shows that the expression level of CD147 mRNA was approximately 1.6- (P < 0.05) and 3.5- (P < 0.01) fold higher in COC1/DDP and HO8910/PM cells than in COC1 and HO8910 cells. The expression level of CD147 mRNA in RMG-I-H cells was approximately 0.62-fold lower than that in RMG-I cells (P > 0.05). The results of real-time PCR confirmed that the expression level of FUT1 mRNA was 3.07-fold higher in RMG-I-H cells than in RMG-I cells, 2.41-fold higher in HO8910/PM cells than in HO8910 cells, and 2.72-fold higher in COC1/DDP cells than in COC1 cells (P < 0.05, Fig. 2B).
Western blot analysis of CD147 expression in three groups of ovarian cancer cells with varying degrees of malignancy
Figure 3 shows that the expression levels of the CD147 protein were significantly higher in the transfected line RMG-I-H, the highly metastatic line HO8910/PM, and the drug tolerant line COC1/DDP than in the parental cell lines, and the expression levels of the highly glycosylated form of CD147 were 1.43, 1.75, and 1.81 fold higher than those in the original parent cells, respectively ( P < 0.05). Compared with the highly glycosylated form, the low glycosylated form of CD147 did not change significantly. The expression levels of the low glycosylated form in HO8910 and the highly metastatic line HO8910/PM were significantly higher than those in RMG-I, RMG-I-H, COC1, and COC1/DDP cells. This difference may be related to the different forms of MMPs induced by CD147 with different molecular weights [7]. We detected a protein band with a molecular weight of approximately 26 kDa in the total protein lysates of the six cell lines analyzed. Because the CD147 core protein is 27 kDa, we assumed that it might be a membrane-detached form of CD147[8] or a subtype of CD147 basigin-3[9].
Determination of the correlation between Lewis y and CD147 in the six cell lines by immunoprecipitation
Immunoprecipitation results (Fig. 4) showed that Lewis y antigen expression was detected in CD147 molecules from the six cell lines. Lewis y was mainly expressed in the highly glycosylated form and the unknown form of CD147. The expression levels of Lewis y in CD147 were 2.12, 1.82, and 2.33 fold higher in the transfected line RMG-I-H, the highly metastatic line HO8910/PM, and the drug tolerant line COC1/DDP, respectively, than in the parental cell lines when the same amounts of CD147 antibody were used for the total proteins and the precipitates (P < 0.05). Lewis y antigen at high expression levels was also detected in CD147 with a molecular weight of about 26 kDa in the six types of ovarian cancer cells.
Function and enrichment analysis of CD147 involved in the differentially expressed genes in response to Lewis y
Based on the Metascape database, the biological functions and pathways for the differentially expressed genes associated with CD147 from our previous chip described above were analyzed. A heatmap of enriched terms across input gene lists, colored by P-values, was generated. The results showed that genes were mainly enriched in cytokine-mediated signaling pathways, regulation of cell adhesion, regulation of T cell apoptotic process, and hexose metabolic process (Fig. 5). Subsequently, we selected a high degree of enrichment, grouped clustering according to the correlation of functional pathways, and constructed a network, with different colors representing different categories (Fig. 6).
Construction of a protein–protein interaction network and module screening
We also constructed a protein interaction network to determine how these genes interact with each other, as well as to find the central node of the PPI network. The PPI network is depicted in Fig. 7. The PPI network included 207 nodes and 369 edges. Each node represents a protein, and the edge between the nodes represents the interaction between the two proteins. The thickness of the line represents the strength of the relationship. A greater connectivity is represented by a larger node. As shown in the figure, the highly connected proteins in the network were encoded by the ALDOA, ENO1, STAT3, ACTG2, and IL1A genes. These genes are all related to glycolysis, suggesting that the malignant behavior of ovarian cancer enhanced by the glycosylation of CD147 may be related to glycolysis in cells.
Validation of the differentially expressed genes by quantitative real-time PCR
Four differentially expressed genes, ALDOA, ENO1, STAT3, and IL1A, were selected for quantitative real-time PCR analysis. The proteins encoded by these genes were highly connected in the PPI network. As shown in Fig. 8, the mRNA levels of the four genes were significantly higher in three ovarian cancer cell lines with high expression of Lewis y and CD147 (RMG-I-H, HO8910/PM, and COC1/DDP cells) than in cells with a lower malignancy grade (RMG-I, HO8910, and COC1). This was consistent with the results of gene chip analysis.
Validation of protein expression by immunohistochemical staining
To confirm the gene expression results at the protein level, immunohistochemical staining for IL-1α and Lewis y antigen was performed on all paraffin embedded samples. Similar to Lewis y, IL-1α localized mainly to the membrane and cytoplasm (Fig. 9). The positive expression rates of IL-1α in the malignant, borderline, benign, and normal groups were 80.81%, 66.67%, 43.75%, and 30.00%, respectively (Table 3). IL-1α positive expression rate was highest in the malignant group and was significantly higher than the rate in the benign and normal groups (P < 0.01). The expression rate was higher in the malignant group than in the borderline group, although the difference was not statistically significant (P > 0.05). The positive expression rate of Lewis y was highest in the malignant group (86.87%), which was significantly higher than that in the benign group (37.50%) (Table 3).
Table 3
Expression of IL-1α and Lewis y antigen in various ovarian tissues
Groups | n | IL-1α | | Lewis y |
- | + | ++ | +++ | Positive (%) | | - | + | ++ | +++ | Positive (%) |
Malignant | 99 | 19 | 21 | 32 | 27 | 80 (80.81)a | | 13 | 19 | 34 | 33 | 86 (86.87)a |
Borderline | 12 | 4 | 1 | 6 | 1 | 8 (66.67)c | | 4 | 2 | 5 | 1 | 8 (66.67)b |
Benign | 16 | 9 | 3 | 3 | 1 | 7 (43.75) | | 10 | 2 | 4 | 0 | 6 (37.50) |
Normal | 10 | 7 | 3 | 0 | 0 | 3 (30.00) | | 10 | 0 | 0 | 0 | 0 (0) |
a Compared with the benign and normal group, both P < 0.01. |
b Compared with the benign group, P < 0.05. |
c Compared with the malignant, benign and normal group, all P > 0.05. |
Among the 99 cases of ovarian cancer, 53 and 26 cases showed simultaneous high or low expression patterns of both IL-1α and Lewis y antigen (Table 4). Spearman’s correlation analysis revealed a positive correlation between the expression of IL-1α and Lewis y (r = 0.575, P = 0.00003).
Table 4
The relevance of IL-1α and Lewis y expression in ovarian cancer samples
IL-1α | Lewis y | Total |
High (++, +++) | Low (-, +) |
High (++, +++) | 53 | 6 | 59 |
Low (-, +) | 14 | 26 | 40 |
Total | 67 | 32 | 99 |
Spearman correlation, r = 0.575, P = 0.00003 |