CH25H expression level downregulated in LUAD and correlated with prognosis
We analyzed the differential expression of CH25H in lung tumor tissues and normal tissues using online databases (Fig. 1A and 1B). The CH25H expression levels showed significant differences (p < 0.01) during different disease stages (stage1 - 4) in LUAD (Fig. 1C), but not in LUSC (Fig. 1D). We observed that in LUAD, this negative expression was significantly associated with sex (Fig. S1B), and nodal metastasis status (Fig. S1F). Other factors such as age (Fig. S1A), race (Fig. S1C), smoking habits (Fig. S1D), and histological subtypes (Fig. S1E) showed poor correlation with CH25H expression. However, in patients with LUSC, no outstanding relationship between CH25H expression and these factors was observed (Fig. S2).
The survival difference was evaluated, and results showed that compared with the low expression cohort, patients in the high expression cohort showed a significantly enhanced OS (P < 0.01, N = 478), indicating a better prognosis (Fig. 1E). However, compared with the lower expression cohort, LUSC patients with high CH25H expression showed a reduced trend of survival time in both OS, although the difference was not statistically significant (P > 0.05, N = 481, Fig. 1F).
CH25H associated with immune regulation
Heat maps showed that the top 20 significant genes were positively and negatively related to CH25H in LUAD (Fig. 2A–2B) and LUSC (Fig. 2E-2F), respectively. Notably, 6/20 genes (CD1C, CD74, HLA-DPB1, NLRP3, ADRB2 and AMICA1) were positively related to CH25H in LUAD. They were therefore responsible for the positive regulation of the immune system (17-22). Pathway analysis revealed an enriched immune regulation, such as the regulation of leukocyte activation, positive regulation of immune response, and adaptive immune system (Fig. 2C and 2D). However, in LUSC, CH25H showed a weak association with the immune regulation, as analyzed by gene enrichment (Fig. 2E and 2F) and pathway analysis (Fig. 2G and 2H). These results could possibly explain the importance of CH25H as a prognostic biomarker in case of LUAD only. It was therefore hypothesized that CH25H controls the spread and infiltration of tumor cells via immune regulation in LUAD.
Some studies have found that biomarkers such as CLEC3B (26) and YTHDF1/YTHDF2 (27) affect the immune microenvironment, and metastasis and prognosis of lung cancer. Therefore, we studied the correlation between CH25H expression and immune cell infiltration.
CH25H expression level associated with immune infiltration level
We hypothesized that CH25H expression regulates the infiltration levels of immune cells. We also investigated the relationship between CH25H expression and the abundance of immune infiltrates. The results showed that CH25H expression level was less associated with the infiltration of immune cells (for instance, B cells, T cells, and macrophages) in the LUSC subtype. However, the expression of CH25H was significantly positively correlated with immune cell infiltration in LUAD (Fig. 3A). These results confirmed that CH25H expression potentially regulates the immune infiltration in patients with LUAD.
In addition, we observed that CH25H expression was significantly correlated with immune infiltration in LUAD (Fig. 3B -3D), better than in LUSC (Fig. 3E–3G), as evaluated by stromal, immune, and comprehensive ESTIMAT, respectively.
Immune infiltration level associated with prognosis in LUAD
We further investigated the relationship between immune score and OS of LC patients, and the results (Fig. 4A and 4B) were similar to the result of CH25H expressional level and OS (Fig. 1E and 1F). The survival difference results showed that, compared with the low immune score cohort, the high immune score cohort showed a significantly enhanced OS (P < 0.05) in LUAD (Fig. 4A). Similar analyses were performed for LUSC, but the opposite result was obtained (P > 0.05, Fig. 4B).
CH25H level associated with immunotherapy in LUAD
Immunotherapy molecular marker analysis revealed that both, CD274 (P < 0.001) and CTLA4 (P < 0.01) significantly correlated with CH25H expression in LUAD (Fig. 4C and 4D), this was not seen in the case of PDCD1 (Fig. S3 (left)). However, in LUSC, only CD274 was significantly related to CH25H expression (Fig. 4E) but not CTLA4 (Fig. 4F) or PDCD1 (Fig. S3 (right)). The results of this study indicate that CH25H can be a potential biomarker for predicting immunotherapy efficacy.
Leukocytes CH25H expression level related to the lung tumor metastasis
To confirm the role of CH25H in lung cancer, we conducted a preliminary clinical study using leukocyte samples from patients having lung cancer. This study employed 34 patients newly diagnosed with LC between 2019 and 2020. The average age at the time of diagnosis was 64 years and the median age of the cohort was 65 years (range, 38–88 years). Other characteristics of the study participants are listed in Table 1.
Based on the tumor metastasis status, the patients were divided into metastatic and non-metastatic groups. Blood samples were collected to detect CH25H mRNA expression levels in leukocytes. The results showed that, in LUAD patients, CH25H expression was significantly decreased in the metastatic group (P < 0.01, Fig. 5). However, no significant decrease in the CH25H expression was observed in LUSC patients with tumor metastasis (P > 0.05, Fig. 5), indicating that the CH25H expression level is a potential biomarker for LC metastasis prediction, especially in LUAD.