Identification of DEmRNAs in tumor tissues from bone metastatic sites compared with other metastatic sites of breast cancer
Compared with lung metastatic sites, a total of 1280 DEmRNAs (645 up- and 635 down-regulated mRNAs) were detected in tumor tissues from bone metastatic sites of breast cancer. Compared with liver metastatic sites, a total of 1482 DEmRNAs (851 up- and 631 down-regulated mRNAs) were detected in tumor tissues from bone metastatic sites of breast cancer. Hierarchical clustering analysis of top 100 up- and down-regulated DEmRNAs was exhibited in Figure 1A and Figure 1B, respectively. Top 10 up- and down-regulated DEmRNAs were displayed in Table 2. After overlapped these 1280 DEmRNAs and 1482 DEmRNAs, a total of 237 DEmRNAs (149 up- and 88 down-regulated mRNAs), which were differentially expressed in bone metastasis compared with both lung metastasis and liver metastasis, were obtained (Figure 1C-D, supplemental table 2 and table 3).
GO and KEGG pathway analysis of DEmRNAs
GO analysis indicated that DEmRNAs in group of bone metastasis vs lung metastasis were significantly enriched in negative regulation of cell proliferation (GO: 0008285; FDR = 5.43E-15), cytoplasm (GO: 0005737; FDR = 3.82E-65) and protein binding (GO: 0005515; FDR = 9.71E-76) (Figure 2A); DEmRNAs in bone metastasis vs liver metastasis group were significantly enriched in blood coagulation (GO: 0007596; FDR = 2.81E-26), extracellular region (GO: 0005576; FDR = 5.82E-104) and protein binding (GO: 0005515; FDR = 4.33E-51) (Figure 2B); the common DEmRNAs in two group mentioned above were significantly enriched in cell adhesion (GO: 0007155; FDR = 2.35E-07), extracellular region (GO: 0005576; FDR = 6.22E-22) and protein binding (GO: 0005515; FDR = 3.35E-08) (Figure 2C), respectively. All the top 10 GO list between these two groups were shown in supplemental table 4.
KEGG pathway enrichment analysis indicated that DEmRNAs in group of bone metastasis vs lung metastasis were significantly enriched in Focal adhesion (FDR = 3.08E-06), Pathways in cancer (FDR = 1.22E-05) and ECM-receptor interaction (FDR = 1.73E-05) (Figure 3A); DEmRNAs in bone metastasis vs liver metastasis group were significantly enriched in complement and coagulation cascades (FDR = 3.77E-41), Drug metabolism-cytochrome P450 (FDR = 2.63E-16) and Retinol metabolism (FDR = 1.07E-14) (Figure 3B); the common DEmRNAs in two group mentioned above were significantly enriched in Focal adhesion (FDR = 7.32E-06), ECM-receptor interaction (FDR = 1.39E-05) and Fatty acid metabolism (FDR = 3.61E-04) (Figure 3C), respectively.
PPI network construction
The PPI network constructed with DEmRNAs in group of bone metastasis vs lung metastasis included 147 nodes and 121 edges. TRIM24 (degree = 9), FGB (degree = 8) and FAM189A2 (degree = 7) were three hub proteins of the PPI network (Figure 4A). The PPI network constructed with DEmRNAs in group of bone metastasis vs liver metastasis included 231 nodes and 228 edges. TNFAIP6 (degree = 26), ACAN (degree = 21) and ADH1C (degree = 14) were three hub proteins of the PPI network (Figure 4B).
Identification of DElncRNAs in tumor tissues from bone metastatic sites compared with other metastatic sites of breast cancer
Compared with lung metastatic sites, a total of 71 DElncRNAs (38 up- and 33 down-regulated lncRNAs) were detected in tumor tissues from bone metastatic sites of breast cancer (Supplemental table 5). Compared with liver metastatic sites, a total of 91 DElncRNAs (40 up- and 51 down-regulated lncRNAs) were detected in tumor tissues from bone metastatic sites of breast cancer (Supplemental table 6). Hierarchical clustering analysis of DElncRNAs was exhibited in Figure 5A and Figure 5B, respectively. Top 10 up- and down-regulated DElncRNAs were displayed in Table 2. After overlapped these 71 DElncRNAs and 91 DElncRNAs, a total of 3 DElncRNAs (2 up- and 1 down-regulated lncRNAs), which were differentially expressed in bone metastasis compared with both lung metastasis and liver metastasis, were obtained (Figure 5C-D, table 3).
Correlation study of DElncRNAs and DEmRNAs
The correlation study between DELncRNA and DEmRNA expression was analyzed by Person’s test, the correlation coefficient and p-value were shown in table 4 (bone metastasis vs lung metastasis and bone metastasis vs liver metastasis), only pairs whose P value was less than 0.05 were shown.
Cis nearby-targeted DEmRNAs of the DElncRNAs
A total of 7 DElncRNA-nearby-targeted DEmRNA pairs in group of bone metastasis vs lung metastasis, involving in 7 DElncRNAs and 7 DEmRNAs, were detected (Table 5). A total of 15 DElncRNA-nearby-targeted DEmRNA pairs in group of bone metastasis vs liver metastasis, involving in 12 DElncRNAs and 15 DEmRNAs, were detected (Table 5). Combined with correlation study, total 8 pairs were selected with significant correlation, and four pairs had correlation coefficient higher than 0.7, which were LOC641518- LEF1, FLJ35024- VLDLR, LOC285972- RARRES2 and LOC254896- TNFRSF10C respectively.
qRT-PCR validation
These four pairs whose correlation coefficient was above 0.7 were selected for verification by qRT-PCR using clinical samples from our hospital. As shown in Fig.6A, results showed that the relative expression of LEF1, VLDLR, RARRES2 and TNFRSF10C were significantly up-regulated compared to adjacent non-tumor tissues and other metastatic sites (P <0.05). As shown in Fig.6B, RNA levels of LncRNA LOC641518 and FLJ35024 showed same trend with bioinformatics data. Although RNA levels of LOC285972 and LOC254896 in the bone metastasis were also higher than adjacent non-tumor tissues, they were not different compared with lung and liver metastasis. All the mRNA and LncRNA levels of tested genes from adjacent non-tumor breast cancer was significantly lower than metastasis tumor tissues (Fig. 6). After that, we used the RNA relative levels of each pair LncRNA-mRNA from metastatic bone tumor tissues to perform a correlation analysis, which was shown in Fig6.C. Results demonstrated all the four LncRNA pairs had significantly positive correlation, although the coefficient is not high as bioinformatics prediction. The validation test by qRCR proved that most of bioinformatics predictions were reliable.
LOC641518 Promotes breast cancer Metastasis via Activation LEF1
Due to LEF1 has been long considered as a metastasis mediator [11, 12], in the current study, the Loc641518-LEF1 axis was selected to investigate whether Loc641518 regulates LEF1 expression to promote breast cancer metastasis by in vitro study, which can help to confirm the speculation from bioinformatics data mining.
The RNA levels of LOC641518 and LEF1 in non-carcinoma human breast epithelial cell line MCF-10A and two breast cancer cell lines, MCF-7 and MDA-MB-231, were examined by qRT-PCR (Fig.7A and 7B), which could find that RNA levels of LOC641518 and LEF1 is higher in cancer cells than non-carcinoma cells, and highest in MDA-MB-231.
siRNA was used to knock down the expression of LOC641518 in both MCF7 and MDA-MB-231 cells. As shown in Fig.7C, the expression of LOC641518 was significantly reduced by siRNA compared with scramble siRNA control. Meanwhile, the LEF1 mRNA level was also reduced in siRNA-LOC641518 groups compared with scramble groups (Fig.7D). The wound healing assay and migration assay both demonstrated that knocking down LOC641518 significantly reduced capability of migration and invasion (Fig.7E and 7F), and exogenous overexpression of LEF1 could reverse these phenomena.