2.1 Identification of DEGs and annotation in PTC
A flowchart of this study is presented in Fig. 1. In total, 4,353 DEGs were screened in the PTC cell lines (CVPTC, BCPAP, and IHH4) relative to healthy thyroid cells (Fig. 2A). Additionally, 3,250 DEGs were screened in other PTC cells (TPC-1, BCPAP, and IHH4) relative to healthy thyroid cells (Fig. 2B). A total of 1,075 DEGs were screened in the PTC tissues (classic, RET/PTC mutation, and high cell variant) compared to adjacent normal tissues (Fig. 2C). However, there were no common DEGs between thyroid papillary carcinoma cell lines and thyroid papillary carcinoma tissues (Fig. 2D).
2.2 GSEA of PTC-specific DEGs
To determine the effects of PTC-specific DEGs, GO and KEGG analyses were conducted using the PTC cell lines and tissues for interpreting gene levels. The results showed 168 significantly enriched gene functions and 17 KEGG pathways compared to the PTC-derived cell lines (CVPTC, BCPAP, and IHH4) and 96 significantly enriched gene functions and eight KEGG pathways compared to other PTC-derived cell lines (TPC-1, BCPAP, and IHH4) (P < 0.0001). We also found 113 significantly enriched gene functions and 6 KEGG pathways compared to PTC tissues (classic, RET/PTC mutation, and high cell variant) (P < 0.0001).
The cell line genes were enriched mainly in extracellular matrix tissue, cell adhesion, angiogenesis, plasma membrane, and axon guidance. The genes in the PTC tissues (classic, RET/PTC mutation, and high cell variant) were mainly enriched in response to drugs, response to exogenous stimuli, signal transduction, angiogenesis, apoptosis, actin cytoskeleton, response to cytokines, and positive regulation of apoptosis. The cell component enrichment analysis indicated that two groups of PTC cell lines mainly correlated with the plasma membrane, extracellular matrix, cell surface, components of the plasma membrane, basement membrane, extracellular region, and receptor complex. The genes in the PTC tissues (classic, RET/PTC mutation, and high cell variant) were mainly enriched in extracellular bodies, cytoplasm, membrane, adhesion spots, cell surface, plasma membrane, glutamatergic synapses, cytoskeleton, and receptor complexes. Regarding molecular function, two groups of PTC cell line genes were mainly associated with protein binding, integrin binding, receptor binding, and transcription factor activity (Fig. 3A-B). The genes in the PTC tissues (classic, RET/PTC mutation, and high cell variant) were mostly associated with protein binding, protein homodimerization activity, actin binding, actin filament binding, cadherin binding, ligand-activated sequence-specific DNA binding, RNA polymerase II transcription factor activity, protein domain specific binding, and transcription factor binding (Fig. 3C).
The pathway analysis showed that the genes in the PTC-derived cell lines (CVPTC, BCPAP, and IHH4) were related to focal adhesion, the ECM receptor interaction signaling pathway, the MAPK pathway, the cancer pathway, the PI3K Akt pathway, the calcium pathway, hypertrophic cardiomyopathy, Cushing's syndrome, cell adhesion molecules, bladder cancer, human papillomavirus infection, amoebiasis, and the gastric acid secretion signaling pathway (Fig. 4A). The genes in the PTC-derived cell lines (TPC-1, BCPAP, and IHH4) were significantly enriched in pathways of cancer, dilated cardiomyopathy, axonal guidance, the MAPK signaling pathway, focal adhesion, hypertrophic cardiomyopathy, the Rap1 pathway, the cell adhesion molecule pathway, and ECM receptor interaction (Fig. 4B). The genes in the PTC tissues (classic, RET/PTC mutation, and high cell variant) were closely associated with tight junction, proteoglycans in cancer, the p53 pathway, transcriptional disorders in cancer, apoptosis, and the signaling pathways in cancer (Fig. 4C).
2.3 Construction of the PPI network
For establishing interactions among the selected DEGs in the PTC, the STRING database was used for constructing the PPI network. Then, the 10 most significant hub genes were selected in different groups in the whole network separately using the plug-in cytoHubba by the MCC method in Cytoscape (Figs. 5A, 5C, and 5E). They were TNF, IL6, EGFA, MMP9, EGF, TGFB1, CXCR4, PECAM1, IL1B, and FN1 in the PTC-derived cell lines (CVPTC, BCPAP, and IHH4). Also, VEGFA, EGFR, TNF, CXCL12, TGFB1, EGF, PECAM1, CXCR4, CD44, and SPP1 were the top 10 hub genes in the PTC-derived cell lines (TPC-1, BCPAP, and IHH4). The top 10 hub genes in the PTC tissues (classical PTC, RET/PTC mutated PTC, and high cell variant PTC) were JUN, VEGFA, CCND1, SRC, ESR1, HIF1A, BCL2L1, CD44, KIT, and FN1.
We also used the DEGs to perform a pathway analysis using the plug-in ClueGO in Cytoscape (Figs. 5B, 5D, and 5F). The significant vital MCC module showed functions, including proteoglycans in cancer, fluid shear stress, rheumatoid arthritis, AGE-RAGE pathway diabetes complications, leukocyte cross endothelial migration, atherosclerosis, and pathways in cancer in the PTC-derived cell lines. Additionally, the significant vital MCC module showed functions in PTC tissues, including proteoglycans in cancer, bladder cancer, breast cancer, Kaposi's sarcoma-associated herpesvirus infection, pathways in cancer, and mitotic phagocytosis.
2.4 Key transcription factors and network prediction
To elucidate the possible regulatory factors that target the genes in the critical MCC modules of our as-constructed PPI network, the plug-in iRegulon in Cytoscape was used for predicting targets and regulatory factors (Table 1). We identified 22 TFs to be the master regulators in the PTC-derived cell lines (CVPTC, BCPAP, and IHH4), including STAT6, CEBPB, EBF1, MYB, PDX1, CEBPA, CEBPE, CEBPG, CEBPD, KIAA0907, SPIC, SPIB, SPI1, EHF, ELF5, NFATC3, ELF3, ETV6, DAB2, STAT3, and AVEN (NES > 5.0) that targeted 30 genes. In total, 66 TFs were closely associated with the protein networks of the PTC-derived cell lines (TPC-1, BCPAP, and IHH4) with 48 targets. The top 22 transcription factors included TFAP2C, GTF2IRD1, PLAG1, AVEN, PARP1, E2F1, EGR1, EGR2, EGR3, EGR4, FOXD3, FOXC2, FOXC1, FOXD2, HLTF, FOXA1, FOXA2, FOXB1, FOXO4, FOXA3, SRF, and FOXL1 (NES > 5.0). Only one TF was estimated, and TCF12 was the most significant regulatory factor targeting seven genes in the PTC tissues (classic, RET/PTC mutation, and high cell variant).
Table 1
The prediction results of the major transcription factors in PTC-derived cell lines and PTC tissues
NES
|
Transcription factors
|
Target genes
|
CVPTC/BCPAP/IHH4 vs. normal thyroid cell
|
6.9256
|
STAT6, CEBPB, EBF1, MYB, PDX1, CEBPA, CEBPE, CEBPG, CEBPD
|
FN1, VEGFA, PECAM1, IL6, CXCR4, MMP9
|
5.41786
|
KIAA0907
|
FN1, CXCR4, VEGFA, PECAM1, EGF
|
5.31388
|
SPIC, SPIB, SPI1, EHF, ELF5, NFATC3, ELF3, ETV6
|
MMP9, VEGFA, FN1
|
5.25496
|
DAB2
|
FN1, CXCR4, EGF, PECAM1, VEGFA, MMP9
|
5.25149
|
STAT3
|
VEGFA, FN1, MMP9
|
5.05046
|
AVEN
|
CXCR4, PECAM1, VEGFA, FN1, MMP9, IL1B, IL6, EGF
|
4.95688
|
EXOSC3
|
FN1, MMP9, VEGFA, CXCR4, IL1B, PECAM1, EGF
|
TPC-1/BCPAP/IHH4 vs. normal thyroid cell
|
6.93086
|
TFAP2C, GTF2IRD1
|
CXCR4, CD44, EGF
|
6.44082
|
PLAG1
|
EGFR, CXCR4, CXCL12
|
6.41632
|
AVEN
|
CXCR4, PECAM1, CD44
|
6.38202
|
PARP1
|
CXCR4, CD44, EGF
|
5.78907
|
E2F1
|
TGFB1, CXCR4
|
5.73027
|
EGR1, EGR2, EGR3, EGR4
|
CXCR4, CXCL12, TGFB1
|
5.54405
|
FOXD3, FOXC2, FOXC1, FOXD2, HLTF, FOXA1, FOXA2, FOXB1, FOXO4, FOXA3, SRF
|
TNF, CXCL12
|
5.51955
|
|
CXCL12, CXCR4, EGFR, TNF
|
5.46565
|
|
CD44, CXCR4
|
5.44114
|
FOXC2, FOXL1, FOXD3, FOXD2, FOXO3, FOXC1, FOXJ2, FOXO1, SRF, FOXK1
|
CXCL12, TNF
|
5.43134
|
SALL4, SALL3, SALL1, SALL2, ZNF236
|
TGFB1, CD44
|
5.34314
|
LTF, IRF1, IRF8, IRF7, IRF6, IRF2, IRF4, IRF3, IRF5, PRDM1, MYB
|
CXCR4, EGF, SPP1
|
5.25493
|
|
CXCL12, SPP1, EGFR, PECAM1, EGF
|
5.22553
|
PRDM1, IRF1, ZNF683
|
CXCL12, CD44, CXCR4
|
5.21083
|
|
CXCR4, CXCL12
|
5.08832
|
TCF3, HAND1, HAND2, NOBOX
|
CXCR4, EGFR
|
5.07852
|
NR3C1,NR2F2,NR2F1,HSF1,MAF,CHURC1,IKZF2,RFX1,SPZ1,OLIG2,PGR, ZFP42, YY1, MYB
|
CXCL12, EGFR
|
5.00991
|
FOXL1, FOXC2, FOXD2, FOXJ2, FOXF1, FOXJ1, FOXF2, FOXO1, FOXO4, FOXP3, FOXA1, HLTF, FOXO6, FOXJ3, FOXL2
|
TNF, CXCL12
|
classic /RET_PTC mutation /tall cell variant vs. normal thyroid tissue
|
5.97176
|
TCF12
|
BCL2L1, ESR1, CCND1, VEGFA, ESR1, BCL2L1, CCND1
|
4.80603
|
RBBP9
|
BCL2L1, ESR1, CCND1, ESR1, BCL2L1, CCND1
|
4.28996
|
CEBPD
|
VEGFA, FN1, BCL2L1
|
4.25049
|
FOXD2
|
CCND1, BCL2L1, VEGFA
|
4.16853
|
ESR1
|
ESR1, VEGFA, BCL2L1, CCND1
|