1 Pan-Cancer and Normal Tissue Samples Expression Landscapes of OAS2
Expression patterns of OAS2 gene across diverse tissues of the human body were characterized by using the GTEx data set (Fig. 1a). The expression levels of OAS2 were highest in spleen and lung tissue. Next, OAS2 expression levels in various cancers were analyzed (Fig. 1b). The highest level of OAS2 expression was in HNSC, while the lowest level of OAS2 expression was in KICH. OAS2 expression levels between tumor and adjacent normal tissue were also compared, based on TCGA data (Fig. 1c). OAS2 was highly expressed in 28 types of cancer between tumors and normal tissues, including BLCA, BRCA, CESC, CHOL, COAD, ESCA, GBM, HNSC, KICH, KIRC, KIRP, LAML, LGG, LIHC, LUAD, LUSC, OV, PAAD, PRAD, READ, SKCM, STAD, TGCT, THCA, THYM, UCEC and UCS (the detail cancer names of the abbreviations are in Table 1). Notably the largest difference between expression of OAS2 in cancer and normal tissues occurred for LAML and PAAD; while there was no significant difference in OAS2 levels between ACC, PAPG, SARC and non-tumor tissues.
The analysis on CPTAC (Clinical Proteomic Tumor Analysis Consortium) with UALCAN (The University of ALabama at Birmingham CANcer) database were performed. The result showed that the protein level of OAS2 in BRCA, UCSE, CRCC were significantly higher than those in normal tissues (Fig. 1d).
2 Mutation and methylation analysis of OAS2 in pan-cancer.
According to the cBioPortal database, our analysis of multiple TCGA pan-cancer studies revealed a noteworthy prevalence of OAS2 mutations. Specifically, we observed OAS2 mutation with frequency exceeding 4% in UCEC, SKCM, and BLCA. These findings indicated OAS2 maybe a candidate target for further investigation in these cancer types (Figs. 2A). As Figs. 2B shown, OAS2 expression was negatived related to the promoter methylation in many types of cancers, except for OV, KICH, GBM.
3 Clinical Value of OAS2 Across Cancers
To study the association between OAS2 expression level and cancer prognosis, survival association analysis including OS (Overall Survival), DSS (Disease-specific survival), DFS (Disease Free Survival), and PFS (Progression Free Survival) were performed.
OS Cox proportional hazards model analysis showed that OAS2 was a high-risk gene in LAML (HR = 1.268, P = 0.002), LGG (HR = 1.560, P < 0.001), PAAD (HR = 1.368, P < 0.001), TGCT (HR = 2.171, P = 0.043) and UVM (HR = 1.258, P = 0.035), while OAS2 was a low-risk gene in other types of cancer such as OV (HR = 0.934, P = 0.044), SARC (HR = 0.851, P = 00.026) and SKCM (HR = 0.891, P = 0.002) (Fig. 3A).
Worse DSS is also significantly correlated with elevated expression of OAS2 (Fig. 3B) in KIRP (HR = 1.361, P = 0.022), LGG (HR = 1.532, P < 0.001), PAAD (HR = 1.356, P = 0.001), TGCT (HR = 2.231, P = 0.047), and decreased expression in OV (HR = 0.934, P = 0.044) and SKCM (HR = 0.891, P = 0.002).
Analysis of DFS data revealed associations between high OAS2 expression and poor prognosis in patients with PAAD (HR = 1.443, P = 0.017). However, in patients with OV (HR = 0.890, P = 0.020), OAS2 expression exhibited the opposite relationship with prognosis (Fig. 3C). Regarding associations between OAS2 expression and PFI, forest plots showed associations between high OAS2 expression and poor PFI in KIRP ((HR = 1.227, P = 0.031) and LGG (HR = 1.336, P < 0.001), PAAD (HR = 1.286, P < 0.001), THYM (HR = 1.687, P = 0.008) and UVM (HR = 1.211, P = 0.047), while low OAS2 expression was associated with poor PFI in patients with CESC (HR = 0.842, P = 0.029) and OV (HR = 0.925, P = 0.013) (Fig. 3D).
Further investigation revealed that in HNSC the expression of OAS2 was lower in stage III and IV than that in stage I. Compared to stage I in SKCM, the expression of OAS2 was lower in stage II and III. In contrast, in PAAD, the expression of OAS2 was higher in stage II than that in stage I (Fig. 4).
4 Immune characteristics of OAS2 in the tumor microenvironment
OAS2 plays a critical role in innate immune. To clarify the immune characteristics of OAS2 in the TME, EATIMAT (23), immune, stromal score as well as the tumor purity were summarized in Fig. 5A. Notably, OAS2 expression was positively associated with the immune scores in all cancer types except THYM. In terms of storm score, OAS2 was observed positively associated with 29 cancers, while it has no correlation with DLBC, MESO, ESCA and THYM.
In addition, we examined the effects of OAS2 expression on the levels of infiltration immune-related cells (Fig. 5B). Overall, it was positively correlated with immune infiltrating levels of multiple infiltrates including CD8+ T cells, DCs, macrophages, monocytes, neutrophils, T cell regulatory cells, and γδ T cells, while negatively with mast cells, Th1 cells, NK cells. The profile indicated that OAS2 participated in the immune infiltration process and played a vital role in the immuno-oncological interactions. In SKCM and COAD, OAS2 was only positively correlated with activated NK cells, while negatively with rest NK cells (Fig. 5C).
Furthermore, gene co-expression analyses were conducted to explore the relationships between OAS2 expression and immune-related genes in 33 tumors. The analyzed genes included MHC, chemokine, chemokine receptor proteins, immune-activation, and immune-suppressive. The resulting heatmap indicated that almost all immune-related genes were co-expressed with OAS2 (Fig. 6A-E), of which the majority were positively correlated with OAS2 in all types of cancers. (P < 0.05)
In diverse cancer types, significant relationships existed between OAS2 expression and expression levels of recognized immune checkpoints including CTLA4, LAG3, TIGHT, PDCD1, CD274. The robust correlations in COAD, SKCM and TGCT were showed in Fig. 7A. The correlations between OAS2 and novel dynamic biomarkers of the immune checkpoint blockade (TMB and MSI) were further explored. As presented in Fig. 7B. OAS2 expression is positively related to the TMB in COAD, whereas a negative association was observed in BLCA, KIRC, THCA, LUAD, PCPG, KIRP and TGCT. For MSI, a positive association in GBM and COAD, as well as a negative association in THCA, SKCM, PRAD, KIRP, MESO, TGCT, DLBC was identified.
5 Immunotherapeutic Response of OAS2 prediction
To systematically clarify the underlying value of OAS2 as an immunotherapy target in these cancers, the association between OAS2 gene expression and therapy outcome were examined in clinical studies of immune checkpoint blockade (ICB) immunotherapy, which was based on several published works summarized in Tumor Immune Dysfunction and Exclusion (TIDE, http://tide.dfci.harvard.edu)(24). It was found that melanoma patients with higher OAS2 gene score appeared longer OS and PFS under the ICB immunotherapy, according to the cohort Gide2019_PD1 and Liu2019_PD1 _Ipi_Prog(subtype of Ipilimumab treatment Progressed. Moreover, patients with higher OAS2 expression level might be sensitive to ICB immunotherapy (Fig. 8).
6 Anticancer drug response
OAS2 expression was negatively associated with 50% inhibitory concentration (IC50) values of Bortezomib, Crizotinib, Dabrafenib, Topotecan. Additionally, there is a positive connection between OAS2 expression and IC50 value of Daporinad (Fig. 9).
7 Function enrichment analysis of OAS2 in SKCM
Considering the robust correlation between OAS2 and SKCM, an integrated analysis of GO, KEGG and GSVA was conducted to unravel the biological significance of OAS2. The data indicate that OAS2 is involved in various important biological processes, including T cell activation, regulation of lymphocyte activation, regulation of innate immune response, positive regulation of cytokine production, and the type I interferon signaling pathway (Fig. 10A). The associated molecular functions mainly focus on immune response processes, including immune cytokine receptor binding, antigen binding, and MHC protein binding (Fig. 10B).
KEGG analysis indicates a positive correlation between OAS2 expression and cell adhesion molecules, cytokine-cytokine receptor interaction, antigen processing and presentation, phagosome, and chemokine signaling pathways (Fig. 10C). These findings provided valuable insights into the molecular mechanisms underlying the involvement of OAS2 in SKCM development.
GSVA analysis further reveals the biological function of OAS2 in SKCM, with the most significant positively and negatively associated pathways being presented in Fig. 10D. Our results demonstrate that OAS2 expression is associated with signaling pathways related to tumor genesis, development, and metastasis as well as immune regulation, highlighting potential roles of OAS2 in the progression of SKCM.