Expression of ARNTL2 in pan-cancer
We first assessed the expression of ARNTL2 using TCGA and GTEx data. We revealed that ARNTL2 was over-expressed in 26 among 33 cancers types, including BLCA, BRCA, CESC, CHOL, COAD, DLBC, ESCA, GBM, HNSC, KIRC, KIRP, LAML, LGG, LIHC, LUAD, LUSC, OV, PAAD, PCPG, READ, STAD, TGCT, THCA, THYM, UCEC, and UCS. In addition, ARNTL2 was low-expressed in only three cancer type, including ACC, PRAD, and SKCM (Figure 1A). To compare the expression of ARNTL2 only in tumor tissues, we found that ARNTL2 was highest expressed in HNSC and lowest in UVM (Figure 1B). For normal tissues from the GTEx database, results revealed that the expression of ARNTL2 was highest in vagina tissues and lowest in muscle (Figure 1C).
Regarding the tumor and adjacent normal tissues in TCGA cohort, ARNTL2 was also observed to be over-expressed in 15 cancers, such as BLCA, CESC, CHOL, COAD, ESCA, HNSC, KIRC, KIRP, LIHC, LUAD, LUSC, PCPG, READ, STAD, and THCA. (Figure 2A-O), while lowly expressed in KICH (Figure 2P).
We further investigated ARNTL2 expression at various tumor stages. The results revealed that ARNTL2 expression was elevated in the relative worse tumor stages in ACC, BLCA, LUAD, PAAD, UCEC, and UVM (Figure 3A-F).
Gene alteration of ARNTL2
Gene mutation status, DNA methylation, and CNA are main factors that influence gene expression. Thus, we assessed the mutation status, DNA methylation, and CNA of ARNTL2. We found that the highest alteration frequency of ARNTL2 in NSCLC patients was “Amplification”. For the correlation between ARNTL2 and CNA, we revealed that ARNTL2 expression were positively correlated with CNA in most tumor types, including LUAD (r = 0.41) (Figure 4B). In addition, we also found that the promoter methylation level of ARNTL2 was negatively correlated with ARNTL2 expression in LUAD (r = -0.59), which may also induce high expression of ARNTL2 (Figure 4C).
Prognostic role of ARNTL2
To assess the prognostic role of ARNTL2, the univariate Cox regression analysis (UniCox) and Kaplan-Meier survival analysis was performed. Results of the UniCox indicated that ARNTL2 was a risk factor for overall survival (OS), disease-free interval (DFI), progression-free interval (PFI), and disease-specific survival (DSS) of LUAD and PAAD patients (Figure 5A-D). Kaplan-Meier OS analysis proved that an elevated ARNTL2 expression predicted worse OS of patients with LGG, LUAD, MESO, PAAD, UCEC, and UVM (Figure 6A-F).
GSEA and GSVA of ARNTL2
To explore the potential pathways ARNTL2 may involve in tumor progression, we further conducted GSEA of ARNTL2. The top 50 genes most positively and negatively correlated with ARNTL2 were showed (Figure 7A-B). For the results of GSEA-GO, we found that ARNTL2 was enriched in most cell cycle-related terms (Figure 7C). For GSEA results based on KEGG and Reactome, ARNTL2 was enriched in cell cycle, Focal adhesion, PI3K-Akt signaling, Adaptive immune system, and innate immune system pathways (Figure 7D-F). For the GSVA results, we found that ARNTL2 was positively correlated with most oncogenic pathways, such as PI3K AKT MTOR signaling, Glycolysis, Hypoxia, Inflammatory response, and Interferon gamma response pathways (Figure 8). As we have proved that ARNTL2 was highly expressed in LUAD, and high expression of ARNTL2 indicated bad survival of LUAD patients. These results indicated that ARNTL2-regulated cell cycle-related and immune-related pathways may contribute to the poor survival of patients with tumors.
Immune cell infiltration analysis
To understand the role of ARNTL2 in TIME of LUAD, we performed the correlation analysis between ARNTL2 expression and stromal and immune scores calculated by R package “ESTIMATE”. Results indicated that ARNTL2 was positively correlated with stromal score, ESTIMATE score, and immune score and negatively correlated with tumor purity in most tumor types (Figure 9A) and LUAD (Figure 9B-E).
By analyzing the association between ARNTL2 expression and immune cell infiltration using the ImmuCellAI database, we found that ARNTL2 expression was positively associated with tumor associated macrophages (TAMs) and Tregs infiltration in pan-cancer (Figure 10A) and LUAD (Figure 10B). According to the results of TIMER2, we observed that ARNTL2 was positively associated with TAMs and cancer associated fibroblasts (CAFs) infiltration (Figure 11).
We also conducted a correlation analysis between immunosuppressive genes and ARNTL2. We found that ARNTL2 expression was positively correlated with most immunosuppressive genes in LUAD (Figure 12A). In addition, we also found that ARNTL2 expression was positively associated with immune checkpoints in LUAD, such as CD274 (PD-L1), CTLA4, LAG3, PDCD1 (PD-1), and TIGIT (Figure 12B). We further proved that ARNTL2 was closely associated with immunomodulatory genes, including MHC genes (Figure 13A), chemokines (Figure 13B) and chemokine receptors (Figure 13C).
Drug resistance analysis
Additionally, we analyzed the correlation between ARNTL2 and IC50 of 192 drugs. Among the 192 anti-cancer drugs, ARNTL2 expression was positively correlated with IC50 of 114 anti-cancer drugs, such as SB505124, Doramapimod, Nutlin-3a (-), Sabutoclax, AZD5991, PF-4708671, Elephantin, PRIMA-1MET, Sorafenib, Vorinostat, and MK-2206 (Figure 14, Supplementary Table 1).