The mRNA and protein expression of CCR7 in normal tissues and single-cell types
Supplementary Fig. 1A showed that CCR7 mRNA was mainly expressed in the bone marrow and lymphoid tissues, and CCR7 protein was expressed in the respiratory system, skin, bone marrow, and lymphoid tissues. Supplementary Fig. 1B and Supplementary Fig. 1C further showed the specific localization in respective tissues and organs, including the lung, spleen, lymph node, tonsil, bone marrow, appendix, and thymus. Moreover, Supplementary Fig. 2A indicated that CCR7 was significantly expressed in Langerhans cells, syncytiotrophoblasts, B cells, cytotrophoblasts, and T cells. The expression of CCR7 in distinctive single-cell tissues was shown in Supplementary Fig. 2B, which revealed that CCR7 was mainly expressed in adipose tissues, bone marrow, breast, endometrium, liver, lung, lymph node, placenta, prostate, salivary gland, skeletal muscle, skin, spleen, stomach, testis, thymus, tongue, and vascular. Besides, in most of these tissues, CCR7 expression was involved in blood and immune cells, such as macrophages, T cells, B cells, and Langerhans cells. Specially, in the placenta and testis, the expression of CCR7 was mainly in trophoblast cells (syncytiotrophoblasts and cytotrophoblasts) and germ cells.
Differential expression of CCR7 between cancer and normal tissue samples
We utilized the GTEx database to analyze the expression level of CCR7 in normal tissues, which demonstrated that the expression of CCR7 in blood and spleen is higher than in other normal tissues and is highest in the blood (Fig. 1A). According to the data from TGCA, in Fig. 1B, it was shown that CCR7 can be expressed extensively in all 33 types of cancers, especially in lymphoid neoplasm diffuse large B-cell lymphoma (DLBC) with the highest expression level of CCR7. In paired normal tissues, Fig. 1C indicated that skin cutaneous melanoma (SKCM) and thymoma (THYM) have higher levels of CCR7 than other tissues.
Moreover, the comparison between cancers and corresponding paired normal tissues on CCR7 expression was also conducted. According to the TCGA data, excluding those cancers that had no or very few normal tissue samples and cannot provide credible information, the expression level of CCR7 in 10 types of cancer was significantly different from that in normal tissue, including breast invasive carcinoma (BRCA), colon adenocarcinoma (COAD), head and neck squamous cell carcinoma (HNSC), kidney chromophobe (KICH), kidney renal clear cell carcinoma (KIRC), kidney renal papillary cell carcinoma (KIRP), lung squamous cell carcinoma (LUSC), pheochromocytoma and paraganglioma (PCPG), rectum adenocarcinoma (READ), and uterine corpus endometrial carcinoma (UCEC) (Fig. 1D). Amongst the 10 types of cancers, the expression of CCR7 was upregulated in BRCA, HNSC, KIRC, KIRP, PCPG, and UCEC. By contrast, a lower level of CCR7 in cancers than in normal tissues was shown in COAD, KICH, LUSC, and READ. Conversely, there is no remarkable difference in CCR7 levels in bladder urothelial carcinoma (BLCA), cervical squamous cell carcinoma and endocervical adenocarcinoma (CESC), cholangiocarcinoma (CHOL), esophageal carcinoma (ESCA), glioblastoma multiforme (GBM), liver hepatocellular carcinoma (LIHC), lung adenocarcinoma (LUAD), pancreatic adenocarcinoma (PAAD), prostate adenocarcinoma (PRAD), sarcoma (SARC), SKCM, stomach adenocarcinoma (STAD), thyroid carcinoma (THCA), and THYM. Besides, the TIMER database revealed that BRCA, COAD, HNSC, KICH, KIRC, KIRP, LUSC, PCPG, PRAD, READ, and THCA showed a significant difference between tumor tissues and paired normal tissues (Fig. 1E). The expression of CCR7 was upregulated in BRCA, HNSC, KIRC, PCPG, and was downregulated in other 6 types of cancer. These results revealed that the differential expression of CCR7 in the corresponding cancers can be a potential biomarker in cancer diagnosis.
Additionally, we used the HPA database to acquire the immunohistochemical images and evaluate the expression of CCR7 at the protein level. It can be demonstrated that the protein expression of CCR7 is significantly higher in lymphoma and head and neck cancer. In contrast, the expression levels of CCR7 in cervical cancer and melanoma are moderate relatively (Supplementary Fig. 3A). The subcellular localization of CCR7 was shown in A-549, Rh30, U2OS cells, which was involved in nucleus, microtubules, and ER (Supplementary Fig. 3B). According to HPA database, CCR7 was primarily located at mitochondria.
Diagnostic value analysis of CCR7
To assess the relevance of CCR7 in different tumor stages, we analyzed the expression levels of CCR7 in all 33 types of cancers and the differential expression level of CCR7 can be found in 8 types of cancers including BRCA, COAD, HNSC, LIHC, LUAD, SKCM, testicular germ cell tumors (TGCT), and THCA (Fig. 2A), which indicated that CCR7 can be as a valuable clinical marker in the diagnosis and staging of cancers. Moreover, we estimated the diagnostic accuracy by gene signature performance. Through ROC curves, the cutoff of AUC has been utilized to demonstrate low diagnostic accuracy (AUC: 0.5–0.7), relative diagnostic accuracy (AUC: 0.7–0.9), or high diagnostic accuracy (AUC: 0.9–1.0). In Fig. 2B, at 1 year, the AUC of the ROC curve has high diagnostic accuracy in KICH, relative diagnostic accuracy in TGCT, and low diagnostic accuracy in 9 types of cancers including adrenocortical carcinoma (ACC), DLBC, GBM, KIRP, acute myeloid leukemia (LAML), brain lower grade glioma (LGG), ovarian serous cystadenocarcinoma (OV), STAD, uterine carcinosarcoma (UCS), and uveal melanoma (UVM). At 3 years, the AUC of the ROC curve has relative diagnostic accuracy in TGCT and UVM, and low diagnostic accuracy in 8 types of cancers including CHOL, DLBC, ESCA, GBM, KIRP, LAML, LGG, and PRAD. At 5 years, the AUC of the ROC curve has relative diagnostic accuracy in TGCT and low diagnostic accuracy in 13 types of cancers including CHOL, DLBC, ESCA, GBM, KICH, KIRC, KIRP, LAML, LGG, LUSC, PAAD, PRAD, and UVM. Furthermore, it is noteworthy that AUC at 1 year, 3 years, and 5 years has been all higher than 0.5 in DLBC, GBM, KIRP, LAML, LGG, and TGCT.
Prognostic value analysis of CCR7
We further investigated the prognostic significance of CCR7 expression level in different cancers by conducting the survival association analysis. The results of the Kaplan-Meier OS analysis demonstrated that the expression level of CCR7 is associated with OS in BRCA (p=0.001), CESC (p<0.001), GBM (p=0.003), HNSC (p<0.001), LGG (p=0.002), LIHC (p=0.018), LUAD (p=0.039), OV (p=0.008), SARC (p=0.009), and SKCM (p=0.008) (Fig. 3). Moreover, CCR7 can be a low-risk (protective) factor for patients with BRCA, CESC, HNSC, LIHC, LUAD, OV, SARC, and SKCM, which indicated that high expression of CCR7 is associated with better OS in patients (Fig. 3A, B, D, F-J). However, CCR7 can be a high-risk factor for patients with GBM and LGG, which indicated that high expression of CCR7 can decrease the survival time of patients (Fig. 3C, E).
Kaplan-Meier DSS analysis revealed that CCR7 expression is associated with DSS in CESC (p<0.001), GBM (p=0.002), HNSC (p<0.001), LGG (p=0.003), LIHC (p=0.035), LUAD (p=0.010), OV (p=0.010), and UCEC (p=0.026) (Fig. 4). Thereinto, high expression of CCR7 can be a low-risk (protective) factor for patients with CESC, HNSC, LIHC, LUAD, OV, SKCM, and UCEC (Fig. 4A, C, E-I). While it can also act as a high-risk factor for patients with GBM and LGG, indicating that high expression of CCR7 results in poor prognosis (Fig. 4B, D).
Furthermore, Kaplan-Meier PFS analysis presented the expression level of CCR7 is associated with ACC (p=0.033), BRCA (p=0.003), CESC (p<0.001), GBM (p=0.021), HNSC (p=0.001), LIHC (p=0.023), and UCEC ((p=0.045) (Fig. 5A-G). High expression of CCR7 acts as a low-risk (protective) factor for patients with ACC, BRCA, CESC, HNSC, LIHC, and UCEC, which is beneficial for better PFS (Fig. 5A-C, E-G). However, low expression of CCR7 has an association with good PFS in patients with GBM (Fig. 5D). Among the patients with CHOL (p=0.043) and LIHC (p=0.028), the association between CCR7 expression and DFS showed that high expression of CCR7 contributes to the better prognosis of patients (Fig. 5H, I).
According to the results of Cox regression analyses, the results of OS indicated that CCR7 can be a low-risk (protective) factor for patients with CESC, HNSC, LIHC, LUAD, OV, SARC, SKCM, and UCEC, while it can be a high-risk factor for patients with GBM, LGG, and UVM (Fig. 6A). The DSS results revealed that CCR7 can be a low-risk (protective) factor for patients with CESC, HNSC, LIHC, LUAD, OV, SARC, and SKCM, while it can be a high-risk factor for patients with LGG (Fig. 6B). The DFS analysis showed that CCR7 acts as a low-risk (protective) factor for patients with CESC, LIHC, and OV, while it can be a high-risk factor for patients with KIRP (Fig. 6C). Ultimately, the PFS analysis demonstrated that CCR7 acts as a low-risk (protective) factor for patients with BRCA, CESC, CHOL, HNSC, OV, and UCEC, while it can be a high-risk factor for patients with LGG and STAD (Fig. 6D).
Association between CCR7 expression level and TME
The TME has a vital role in cancer initiation and progression. In our pan-cancer study, we calculated the stromal and immune cell scores in 33 types of cancer and then analyzed the association between CCR7 expression and these two scores. The TME correlation analysis indicated that CCR7 expression was positively associated with immune scores in ACC, BRCA, CESC, CHOL, COAD, DLBC, ESCA, GBM, HNSC, KICH, KIRC, KIRP, LIHC, LUAD, LUSC, mesothelioma (MESO), OV, PAAD, PCPG, PRAD, READ, SARC, SKCM, STAD, TGCT, THCA, THYM, UCEC, UCS, and UVM (Fig. 7A). Additionally, it was revealed that CCR7 expression was positively associated with stromal scores in ACC, CHOL, COAD, GBM, KICH, KIRC, KIRP, LIHC, LUSC, PAAD, PCPG, PRAD, SKCM, STAD, THCA, UCEC, UVM (Fig. 7B). Through the TME correlation analysis, most types of cancer have a significant correlation between the expression of CCR7 and immune cells in the TME, especially in CHOL (R=0.81, p<1.6e−7), KICH (R=0.8, p<2.2e−16), PRAD (R=0.83, p<2.2e−16), SKCM (R=0.84, p<2.2e−16), THCA (R=0.86, p<2.2e−16), UVM (R=0.81, p<2.2e−16).
Association between CCR7 expression level and immune cell infiltration
In Fig. 8, it was shown that CCR7 expression level had a positive association with M1 macrophages in ACC, CD8+ T cells in ACC, naïve B cells in BLCA, M1 macrophages in LGG, naïve B cells in MESO, naïve B cells in PAAD, regulatory T (Treg) cells in PCPG, and naïve B cells in THYM. Moreover, the CCR7 expression level is negatively related to activated dendritic cells in ACC, eosinophils in ACC, monocytes in ACC, activated NK cells in CHOL, activated NK cells in KICH, M2 macrophages in SKCM, M2 macrophages in THCA, and M0 macrophages in UCS. Among them, the CCR7 expression level is significantly associated with activated dendritic cells in ACC (R =-0.87, p=2e−11) and activated NK cells in CHOL (R=-0.8, p=1.7e−8), and ACC showed a strong correlation with immune cells. Moreover, through the TIMER database, we obtained several immune cells that were significantly associated with CCR7 expression in Supplementary Fig. 4, including CD8+ T cells, CD4+ T cells, Treg cells, follicular helper T cells (Tfh), B cells, DCs, macrophages, monocytes, myeloid derived suppressor cells (MDSC), whichshowed that the expression of CCR7 was positively correlated with immune cells in most types of cancer, especially for CD8+ T cells; however, CCR7 expression was negatively correlated with MDSC in most types of cancer.
Co-expression and correlation analysis of immune-related gene
We utilized the TISIDB database to evaluate the association between CCR7 and immune-related genes, including genes encoding immunostimulator, immunoinhibitor, MHC molecule, chemokine, and CCR protein (Fig. 9). Fig. 9A indicated the correlation between CCR7 expression and immunostimulator. Most of the genes encoding immunostimulator showed a positive correlation with CCR7 expression, especially for CD27, CD28, CD40LG, CD48, CD80, CD86, and ICOS; CD276, PVR, and ULBP1 showed associations with CCR7 expression negatively. Particularly, Supplementary Fig. 5A revealed that the expression of CD48 in CHOL had a positive association with CCR7 expression significantly (R=0.902, p<2.2e−16). Fig. 9B revealed that except KLR2DL1/3, most of the genes encoding immunoinhibitor had a strong correlation with CCR7 expression positively, especially for BTLA, CD96, CSF1R, CTLA4, PDCD1, and TIGIT. Among them, the expression of BTLA in CHOL (R=0.901, p<2.2e−16) and PAAD (R=0.919, p<2.2e−16) showed a significant association with CCR7 expression (Supplementary Fig. 5B, C). In Fig. 9C, it was indicated that for most of the genes encoding MHC molecules, the association between CCR7 expression and the expression of MHC molecules was positive in different types of cancers, except in BLCA.
Fig. 9D showed the correlation between CCR7 expression and chemokine. Except for CCL1/16/24/25/26/27, most of the genes encoding chemokine were associated with CCR7 expression. Additionally, in Fig. 9E, genes encoding CCR protein had a significant relationship with CCR7 expression, especially for the expression of CXCR5 in SKCM (R=0.901, p< 2.2e−16) Supplementary Fig. 5D). In particular, within all types of CCR protein, only CXCR4 expression in ACC showed a negative correlation with CCR7 expression Supplementary Fig. 5E).
GSEA of CCR7
We investigated the pathways which are related to CCR7 by using KEGG gene sets from the GSEA database. In Supplementary Fig. 6, it was shown that except in DLBC, MESO, THYM, and UCEC, the activity degree of CCR7-mediated signaling pathways was significantly correlated to the high expression of CCR7. In addition, for most types of cancer, CCR7 had an association with the pathways that are involved in immune function, especially in the chemokine signaling pathway, cytokine-cytokine receptor interaction, and T cell receptor signaling pathway. Among them, CCR7 was related to the T cell receptor signaling pathway in ACC, BRCA, CESC, CHOL, HNSC, KIRP, LAML, LGG, LIHC, LUAD, OV, PAAD, PCPG, SARC, SKCM, THCA, UCEC, UCS, and UVM; associated with chemokine signaling pathway in BRCA, CHOL, GBM, KICH, KIRC, KIRP, LGG, LIHC, LUSC, MESO, OV, PAAD, PCPG, PRAD, READ, SKCM, THCA, UCEC, and UCS; and related to cytokine-cytokine receptor interaction in BRCA, CHOL, GBM, HNSC, KICH, KIRC, KIRP, LAML, LGG, LIHC, LUAD, OV, PCPG, PRAD, SKCM, STAD, THCA, UCEC, UCS, and UVM.
Gene interaction analysis of CCR7
GeneMANIA is a user-friendly platform for us to evaluate the gene-gene interaction for CCR7 and the correlated genes. In Fig. 10, the results indicated that 20 genes were closely related to CCR7, and among them, 10 genes, including CCL19, CCL21, CCR10, CXCR5, CCR2, CCR1, CCL18, CCL26, CCR6, and CCL20, exert the biological functions that are related to the chemokine family, especially for CCL19, which showed the most significant association with CCR7. Additionally, it was revealed that the functions of CCR7 and its related genes had a close correlation to the regulation of cytosolic calcium ion concentration and cellular calcium ion homeostasis; besides, CCR7 and the members of chemokine family and correlated receptors showed associations with many immune functions, including lymphocyte migration, leukocyte chemotaxis, cell chemotaxis, and leukocyte migration.
Single-cell functional analysis of CCR7
Through CancerSEA, we investigated the function of CCR7 at the single-cell level in different cancers. It was revealed that CCR7 was negatively associated with DNA repair and invasion in GBM. In ALL, CCR7 was positive with differentiation and inflammation, and negative with proliferation. In BRCA, CCR7 was positive with differentiation and inflammation. CCR7 was negative with apoptosis, DNA damage, DNA repair, invasion, metastasis, and quiescence (Fig. 11).
DNA methylation analysis of CCR7
We utilized the UALCAN database to explore promoter methylation levels of CCR7 among two groups: “Normal” and “Patients with primary tumor”. The Y axis “beta value” reveals the promoter methylation level ranging from 0 (unmethylated) to 1 (fully methylated) and the beta value cutoffs can demonstrate hypomethylation (beta-value: 0.3–0.25) and hypermethylation (beta-value: 0.7–0.5). It was indicated that the promoter methylation level of CCR7 was higher in CESC, CHOL, ESCA, KIRP, PCPG, PRAD, STAD, THCA, THYM, and UCEC than those in normal groups (Fig. 12A). In Fig. 12B, CCR7 had 11 methylation probes, including cg13504059, cg07388018, cg17067993, cg07248223, cg16047279, cg26960939, cg04571513, cg11729107, cg07479709, cg22994634, cg23663547. Furthermore, we used the MethSurv web tool to obtain the association between methylation probes and patients’ prognosis (Table 2).
Gene mutation analysis of CCR7
Thanks to the cBioPortal website, we assessed the mutation of the CCR7 gene through “TCGA PanCancer Atlas” which contains 10953 samples. Fig. 13A showed that amplification is the most common in all types of mutation, especially in esophageal adenocarcinoma, STAD, BRCA, and UCS, which have high occurrence rates of 9.89%, 7.73%, 3.87%, and 3.51%, respectively. Fig. 13B showed that Amplification, missense mutation, and deep deletion are the main types of genetic alteration of the CCR7 gene. Furthermore, the mutation types, numbers, and sites of the CCR7 gene were shown in Supplementary Fig. 7A,which indicated that missense mutation is the most common type of genetic alteration. Supplementary Fig. 7B revealedthat diploid and gain function were the most frequent putative copy-number alteration of the CCR7 gene. In addition, Supplementary Fig. 7C showedthat genetic alteration of ALOX12P1, TOP2A, TNS4, IGFBP4, RAR4, ERBB2, CDC6, WIPF2, IKZF3, and SMARCE1 had higher frequency in the altered group than in the unaltered group.
TMB and MSI correlation analysis
We further investigated the correlation between CCR7 expression and TMB and MSI. In Supplementary Fig. 8A, CCR7 expression was negatively associated with TMB in DLBC, ESCA, HNSC, KIRC, KIRP, LIHC, LUSC, OV, SKCM, STAD, and TGCT. In addition, CCR7 expression was positively related to MSI in LGG and UCEC. For ACC, BLCA, HNSC, KIRC, KIRP, LIHC, LUAD, LUSC, MESO, PAAD, PRAD, READ, STAD, TGCT, THCA, and THYM, the expression of CCR7 was negatively correlated with MSI (Supplementary Fig. 8B).