Overexpression of MAL2 Correlates with Immune Infiltration and Poor Prognosis in Breast Cancer

Abstract

Background: Myelin and lymphocyte, T cell differentiation protein 2 (MAL2) is highly expressed in various cancers and associated with the development and prognosis of cancer. However, the relationship between MAL2 and breast cancer requires further investigation. This study aimed to explore the prognostic significance of MAL2 in breast cancer.

Methods: MAL2 expression was initially assessed using the Oncomine database and The Cancer Genome Atlas (TCGA) database and verified by quantitative real-time polymerase chain reaction (RT-qPCR). The chi-square test or Fisher's exact test was used to explore the association between clinical characteristics and MAL2 expression. The prognostic value of MAL2 in breast cancer was assessed by the Kaplan-Meier method and Cox regression analysis. Gene set enrichment analysis (GSEA) was performed to identify the biological pathways correlated with MAL2 expression in breast cancer. Besides, a single-sample GSEA (ssGSEA) was used to assess the relationship between the level of immune infiltration and MAL2 in breast cancer.

Results: Both bioinformatics and RT-qPCR results showed that MAL2 was expressed at high levels in breast cancer tissues compared with the adjacent tissues. The chi-square test or Fisher's exact test indicated that MAL2 expression was related to stage, M classification, and vital status. Kaplan-Meier curves implicated that high MAL2 expression was significantly associated with the poor prognosis. Cox regression models showed that high MAL2 expression could be an independent risk factor for breast cancer. GSEA showed that 14 signaling pathways were enriched in the high-MAL2-expression group. Besides, the MAL2 expression level negatively correlated with infiltrating levels of eosinophils and plasmacytoid dendritic cells in breast cancer.

Conclusion: Overexpression of MAL2 correlates with poor prognosis and lower immune infiltrating levels of eosinophils and plasmacytoid dendritic cells in breast cancer and may become a biomarker for breast cancer prognosis.

Figure 1

MAL2 expression in different types of cancers. (a) Expression of MAL2 gene in various cancers compared with matched normal tissues by the Oncomine database. Red and blue represent the number of data sets of increasing and decreasing MAL2 gene levels, respectively. (b) A meta-analysis of MAL2 expression across 10 analyses from the Oncomine database. Curtis breast (1–3), Ma breast (4), Perou breast (5), Sorlie breast (6–7), and TCGA breast (8–10). The colored squares represent the median rank of these genes (tumor tissues vs. normal tissues) across the 10 data sets. The significance level for the median rank analysis was set at P < 0.05.

Figure 2

Different MAL2 mRNA expression in tumor tissues compared with adjacent tissues isolated from breast cancer patients. (a) MAL2 mRNA expression was significantly higher in tumor tissues than in adjacent tissues. (b) Paired breast cancer patient samples revealed that MAL2 expression was also higher in tumor tissues than in paired adjacent tissues. (c) RT-qPCR analysis of MAL2 mRNA expression in 32 pairs of breast cancer tissues and adjacent tissues.

Figure 3

Differential MAL2 expressions in the boxplot. The expression of MAL2 is grouped by age (a), stage (b), T classification (c), N classification (d), M classification (e), vital status (f), ER status (g), PR status (h), and HER2 status (i).

Figure 4

Survival analysis of MAL2 expression in terms of overall survival. Kaplan—Meier survival curve analysis of all tumors (a), subgroup analysis of old patients (b), clinical stage I/II and III/IV (c and d), subgroup analysis of T classification (T1/T2 and T3/T4) (e and f), patients with lymphatic invasion (g), patients with nondistant metastasis (h), and patients with ER-, PR-, and HER2-positive status (i—k, respectively).

Figure 5

Forest plot for Cox proportional hazards model of overall survival in breast cancer.

Figure 6

Enrichment plots of GSEA in breast cancer with a high-MAL2-expression phenotype. GSEA results showed that MYC targets V1 (a), mTORC1 signaling pathway (b), E2F targets (c), mitotic spindle (d), G2M checkpoint (e), UA response (f), peroxisome (g), oocyte meiosis (h), spliceosome (i), cell cycle (j), insulin signaling pathway (k), and ubiquitin-mediated proteolysis (l) were enriched in high MAL2 expression in breast cancer.

Figure 7

Association analysis of MAL2 gene expression and immune infiltration: (a) association analysis between MAL2 expression and immune cells; (b) association analysis of MAL2 expression with immune infiltration levels of eosinophils; (c) association analysis of MAL2 expression with immune infiltration levels of plasmacytoid dendritic cells; and (d) abundance of cell infiltration of eosinophils and plasmacytoid dendritic cells in breast cancer.