METTL7B (methyltransferase-like 7B) identification as a novel biomarker for lung adenocarcinoma

Abstract

Background: Lung adenocarcinoma (LUAD) is still one of the major causes of cancer-related mortality across the globe. Therefore, there is a dire need to identify early specific and sensitive biomarkers or drug targets of LUAD for developing improved diagnosis and clinical management. We aimed to investigate the role of methyltransferase-like 7B (METTL7B) on LUAD tumor development and progression in this study.

Methods: METTL7B's expression was confirmed in two independent clinical cohort samples, including LUAD tissues microarray (TMA) via immunohistochemistry (IHC) and serum samples via enzyme-linked immunosorbent assay (ELISA). The correlation between METTL7B expression with clinicopathological features and overall survival rate in LUAD patients was then further analyzed. Meanwhile, the messenger ribonucleic acid (mRNA) and protein levels of METTL7B were verified in cell lines and in vitro experiments, including cell proliferation assay, and migration. Invasion assays were conducted to explore the effects of METTL7B on LUAD by silencing the protein expression.

Results: METTL7B was remarkably overexpressed in clinical LUAD tumor tissues and serum compared to the normal control group and in LUAD cell lines. The expression level of METTL7B was significantly correlated with tumor size, advanced tumor node and metastases (TNM) stages, and lymph node metastasis. The Kaplan-Meier survival curves proved that high METTL7B expression was significantly associated with a reduced survival rate in LUAD patients (P<0.05), and univariate analysis showed that high METTL7B expression was significantly associated with poor overall survival [hazard ratio (HR) =2.220, 95% confidence interval (CI): 1.211-4.086; P=0.010]. In vitro assays showed that METTL7B overexpression augmented cell proliferation, migration, and the invasion in LUAD.

Conclusions: METTL7B was overexpressed in LUAD and significantly associated with the poor progression, showing that METTL7B may serve as a potential novel biomarker for the diagnosis and prognosis of LUAD. Moreover, METTL7B plays a role in promoting tumor proliferation, migration, and invasion in LUAD.

Keywords: Biomarkers; lung adenocarcinoma (LUAD); metastasis; methyltransferase-like 7B (METTL7B).

Figure 1

Expression of METTL7B in LUAD tissues compared with adjacent normal tissues and its prognostic significance. (A) Overexpression of METTL7B in IHC and HE stained images of LUAD tissues compared with adjacent non-tumor tissues at scale bars, 20 mm, and 200 mm. And representative IHC images with different expression intensities of METTL7B and different percentages of METTL7B stained cells at 20 mm scale bar. (B) Kaplan-Meier survival analysis by the TMA database revealed that LUAD patients with higher expression of METTL7B had a significantly reduced survival rate (P<0.05). (C) ELISA showed that the average METTL7B level of the LUAD group (n=30) was significantly higher than the healthy control group. **, P<0.01. METTL7B, methyltransferase-like 7B; LUAD, lung adenocarcinoma; IHC, immunohistochemistry; HE, hematoxylin and eosin; TMA, tissue microarray; HG, healthy control group; n, number of samples.

Figure 2

Expression of METTL7B in LUAD cell lines (A) qPCR showed significant overexpression of METTL7B mRNA in LUAD cell lines (H1299, H1975, A549, H827, PC9, and SPCA1) than in normal cell (BEAS2B). (B) Western blot showed the upregulation of METTL7B in all LUAD cell lines when compared with the normal control lung epithelial cell lines. METTL7B, methyltransferase-like 7B; LUAD, lung adenocarcinoma.

Figure 3

Effects of METTL7B silencing on LUAD cell proliferation. (A) Western blot shows both shRNAs effectively knocked down METTL7B resulting in decreased expression in the LUAD cell lines as compared to the control group. (B) Cell proliferation assay denotes cell proliferation was significantly decreased with METTL7B’s depletion compared to the control, CCK-8 was used to measure cell viability. METTL7B, methyltransferase-like 7B; LUAD, lung adenocarcinoma. **, P<0.01.

Figure 4

Role of METTL7B in migration and invasion of LUAD in vitro (A) Wound healing assay showed that METTL7B knockdown led to profound impairment in cell migration ability of A549 and H827 relative to the control. (B) Invasion assays showed that METTL7B depletion resulted in conspicuous suppression of LUAD cell invasion capability. Scale bar, 20 µm. METTL7B, methyltransferase-like 7B; LUAD, lung adenocarcinoma. **, P<0.01; ***, P<0.001.