C1RL expression was upregulated in GBM, especially mesenchymal GBM, primary GBM and IDH1 wt GBM.
C1RL expression was analyzed according to the WHO classification, GBM subtypes, GBM status and IDH1 mutation status. First of all, the expression of C1RL was always the highest in GBM in 5 datasets according both grading system and histology system (Fig. 1.A-H). But the expression levels of C1RL in GBM samples vary a lot. Furthermore, the C1RL expressions among different subgroups of GBM were analyzed. Among four transcriptomic subgroups of GBM, C1RL expression was always the highest in mesenchymal GBM (Fig. 1.I-L). Secondary GBM was developed from the lower grade glioma and accompanied with lower C1RL than that in primary GBM (Fig. 1.M-N). IDH mutation status is a well-accepted marker for glioma classification. C1RL is higher in IDH1 wt GBM than that in IDH1 mt GBM (Fig. 1.O-Q). In addition, C1RL is higher in IDH1 wt LGG than that in IDH1 mt LGG (Fig. 1.P and Q). These results suggested that higher C1RL expression accompanies higher malignancy in glioma, especially in GBM.
C1RL associated genes enriched in the biological processes of immune response.
The biological function of C1RL, especially in tumor, has not been clarified thoroughly. Therefore, we aimed to speculate the possible biological function of C1RL through the biological function of C1RL associated genes. C1RL associated genes were the genes which have the similar expression trends as C1RL in glioma samples. All the C1RL genes from each dataset were introduced to the GO analysis. The biological processes were listed in reverse order of their p values. The GO analyses showed that C1RL associated genes mainly enriched in the biological processes of immune response, inflammatory response, IFN-γ mediated signaling pathway, and innate immune response (Fig. 2.A-D).
In order to determine whether C1RL plays a positive role in anti-glioma immune response or not, the expression relationship between C1RL and existing biomarkers were analyzed. CD86 protein is the receptor of CTLA4 and mainly expresses on dendritic cells and monocytes. Galectin-9, encoded by LGALS9, was identified as the ligand of Tim-3 and play a key role the apoptosis of T cells. TGFB1 encodes a secreted ligand of the TGF-beta (transforming growth factor-beta) superfamily of proteins. CD86, LGALS9, and TGFB1 play immunosuppressive roles in glioma. Our results showed that C1RL expression exhibited a positive relation to CD86, LGALS9, and TGFB1 (Fig. 3.A-L).
C1RL expression was correlated with less tumor purity and more M2 macrophage infiltration
Immune response is based on the migration of immune cells. Both tumor purity and the infiltration of 22 leukocytes were assessed for each sample from TCGA datasets. The samples were displayed in order of their C1RL expression levels. Both immune score and stromal score exhibited a positive correlation with C1RL expression trends (Fig. 4.A and B, top panels). In addition, the tumor purity showed an inverse correlation with C1RL expression trends (Fig. 4.A and B, middle panels). Moreover, C1RL expression is mostly related to M2 macrophage infiltration among 22 leukocytes (Fig. 4.A and B, bottom panels).
High expression of C1RL predicted unfavorable survival and therapeutic resistance in glioma
The median expression value of C1RL was used to separate samples into two groups. We evaluated the prognostic value of C1RL in four glioma datasets. Patients with glioma containing higher C1RL expression had a significantly shorter survival times than their counterparts in the GSE16011mic, TCGAseq, CGGAmic, and CGGAseq datasets (Fig. 5.A-D). However, histopathology may contribute to these significant differences. Next, we compared the survival times among GBM patients with different C1RL expressions in five datasets. All the survival curves exhibited significant differences (Fig. 5.E-I). Moreover, the effectiveness of well-accepted treatment was evaluated in different C1RL level groups. The primary GBM patients with less C1RL expression showed better response to resection, radio chemotherapy (temozolomide), and standard therapy (Fig. 5.J-L). These results indicate that C1RL may contribute to therapeutic resistance.