Overexpression of ELF1 combined with MMP9 is associated with prognosis and tumor microenvironment in gastric cancer.

Gastric cancer (GC) is a prevalent malignancy of the digestive system. E74-like factor 1 (ELF1) is a transcription factor that is specific to T cells and belongs to the Ets family. They are typically expressed in numerous tumor cells, such as pancreatic cancer, oral squamous cell, endometrial carcinoma, nasopharyngeal carcinoma and prostate and colorectal cancer, where they can promote cell invasion and migration. MMP9 is an important protease of the MMP family, since it serves a vital role in tumor progression and prognostic evaluation in colorectal cancer, uveal melanoma and clear cell renal cell carcinoma. The present study aimed to investigate the expression, correlation with MMP9 and clinical significance of ELF1 in GC. In addition, it aimed to explore the possible mechanisms. The ELF1 mRNA expression profile was first assessed using the GEPIA database and R4.2.1 software (Limma package). Reverse transcription-quantitative PCR (RT-qPCR) was used then to validate ELF1 mRNA expression levels in fresh GC samples from 40 patients. The clinical diagnostic value of ELF1 was also assessed using RT-qPCR. Tissue microarray immunohistochemistry (TMA-IHC) was utilized to examine the expression levels of ELF1 and MMP9 proteins in 355 paraffin-embedded GC samples. Subsequently, the present study further investigated the relationship between ELF1 and MMP9 and their possible effects on the clinicopathological features and prognosis of patients with GC. Gene correlation analysis was conducted using the GEPIA database and complemented with Tumor Immune Estimation Resource (TIMER) and CIBERSORT analyses to explore associations with immune infiltration. A significantly higher expression of ELF1 mRNA was found in GC tissues compared with that in adjacent normal tissues (P<0.05). High ELF1 expression in GC tumor cells was found to distinguish GC tissues from adjacent normal tissues with a sensitivity of 87.5% and specificity of 77.5%. ELF1 and MMP9 proteins also showed higher expression in 355 GC compared with adjacent normal tissues, where they were significantly positively correlated (P<0.001). The two were closely associated with various clinicopathological features, including infiltration depth, lymph node involvement, metastasis, TNM staging, microscopic venous invasion, lymphatic invasion and blood serum carcinoembryonic antigen levels in GC. Furthermore, ELF1 and MMP9 expression levels were negatively associated with the overall survival of patients with GC. Prognostic analysis using the Cox proportional hazards model identified high ELF1 expression [hazards ratio (HR), 2.555; 95% CI, 1.546-4.224; P=0.002], high MMP9 expression (HR, 3.813; 95% CI, 2.406-6.041; P<0.001), advanced TNM stage (P=0.001) and advanced N stage (P=0.011) to be independent prognostic factors for patients with GC. Correlation analysis results from the GEPIA database indicated significant associations of ELF1 expression with various GC-related genes, including MutL homolog 1, erythroblastic leukemia viral oncogene homolog 2, PI3K catalytic subunit α, and tumor suppressor protein 53, MMP-9, Cadherin 1, TIMP1, growth factor A and kinase insert domain receptor. In addition, immune infiltration correlation analysis on TIMER and CIBERSORT revealed ELF1 positive relationship with specific infiltrating immune cell types, including naive B, memory-activated CD4 and gamma delta T cells, and activated NK cells (P<0.05). This observation was further confirmed using immunohistochemistry, showing that ELF1 was associated with CD19 (B-cells) (P<0.001) and CD4 (CD4+ T cells, P=0.002). In conclusion, results from the present study suggest that ELF1 is overexpressed in GC. ELF1 combined with MMP9 can serve as a predictor of malignant biological behavior in GC and therefore a prognostic indicator for patients, due to its association with the tumor microenvironment.