Application value of SHOX2 and RASSF1A gene promoter region methylation detection for screening and diagnosis of early-stage lung adenocarcinoma / 肿瘤研究与临床

ABSTRACT

Objective:To investigate the value of SHOX2 and RASSF1A gene promoter region methylation detection for screening and diagnosis of early-stage lung adenocarcinoma.Methods:The mRNA sequencing data of 471 lung adenocarcinoma patients and corresponding methylation data of 413 cases were downloaded from The Cancer Genome Atlas (TCGA) database, the methylation levels of SHOX2 and RASSF1A gene promoter regions were calculated, and the difference in methy lation level between normal lung tissues and tumor tissues was analyzed. The clinical data of 54 patients with early-stage lung adenocarcinoma and 31 patients with benign lung tumors who underwent surgery at Drum Tower Hospital Affiliated to Nanjing University Medical School from January 2018 to January 2019 were retrospectively analyzed. The methylation status of SHOX2 and RASSF1A in tumor tissues and normal lung tissues (>5 cm from the edge of the tumor foci) (called clinical samples) was detect, and a positive methylation in the promoter region of either gene was considered as a combination of two genes methylation positivity. Using pathological diagnosis as the gold standard, the efficacy of gene methylation positivity in diagnosing early-stage lung adenocarcinoma was analyzed by receiver operating characteristic (ROC) curve. Patients with >80% of tumor cells in paraffin samples were screened, and mRNA high-throughput sequencing was performed in their tumor tissues and normal lung tissues. The relationship between positive methylation of the two genes and clinicopathological features was analyzed, and the correlation between the promoter region methylation level of the two genes and mRNA expression levels in clinical samples and TCGA database samples was analyzed by Spearman method. Gene set variance analysis (GSVA) method was used to analyze the differences in Kyoto Encyclopedia of Genes and Genomes enrichment pathways between two-gene methylation-positive clinical lung adenocarcinoma samples and corresponding methylation-negative lung adenocarcinoma.Results:In TCGA database, the SHOX2 promoter region methylation island contained 6 sequenced methylation sites, of which sites cg04532033 and cg01557547 methylation levels were higher in lung adenocarcinoma tissues than in normal lung tissues (both P < 0.05); the RASSF1A gene promoter region methylation island contained 11 sequenced methylation sites, and the methylation levels of 6 of these sites in lung adenocarcinoma tissues were higher than those in normal lung tissues (all P < 0.05). Compared with normal lung tissues, the methylation level of SHOX2 promoter region was higher in stage Ⅰ and Ⅱ lung adenocarcinoma tissues (both P < 0.05); the methylation level of RASSF1A promoter region was higher in all stages of lung adenocarcinoma ( P < 0.001). Among 54 patients with early-stage lung adenocarcinoma, 28 were positive for SHOX2 promoter region methylation in tumor tissues, 21 were positive for RASSF1A promoter region methylation, and 40 were positive for combined methylation of both genes; 31 benign lung nodules were negative for SHOX2 and RASSF1A methylation. ROC curve analysis showed that the sensitivity of positive SHOX2 promoter region methylation for diagnosing early-stage lung adenocarcinoma was higher than that of RASSF1A promoter region methylation positivity (51.8% vs. 38.9%), and the area under the curve (AUC) for diagnosis by two-gene methylation positivity was larger than that for diagnosis by SHOX2 or RASSF1A gene methylation positivity alone (0.870 vs. 0.759 and 0.694). The circulating thresholds (Ct) of SHOX2 and RASSF1A methylation tested by real-time fluorescence quantitative polymerase chain reaction (qRT-PCR) in stage Ⅰ and Ⅱ lung adenocarcinoma were lower than those in normal lung tissues (all P < 0.05); patients with two-gene methylation positivity were characterized by older age, longer tumor longest diameter and more advanced pathological stage compared with patients with two-gene methylation negativity (all P < 0.05). In clinical stage Ⅰ-Ⅱ lung adenocarcinoma samples, the Ct of SHOX2 and RASSF1A promoter region methylation tested by qRT-PCR was negatively correlated with their mRNA relative expression levels ( r=-0.43, P = 0.003; r = -0.48, P = 0.001); in TCGA database stage Ⅰ-Ⅱ lung adenocarcinoma samples, the level of SHOX2 promoter region methylation was negatively correlated with its mRNA relative expression level ( r = -0.23, P < 0.001), and the level of RASSF1A promoter region methylation was also negatively correlated with its mRNA relative expression level, but without statistical difference ( r = -0.05, P = 0.310). In two-gene promoter methylation-positive lung adenocarcinoma samples, the pathways related to folate metabolism and DNA stability were upregulated, and the pathways related to vasoconstriction and cell growth and differentiation were downregulated. Conclusions:The combined detection of SHOX2 and RASSF1A promoter region methylation can be used as an indicator for screening and diagnosis of early-stage lung adenocarcinoma. Abnormal promoter region methylation of the two genes may affect multiple tumor-related pathways and promote the occurrence and progression of early-stage lung adenocarcinoma.