Upregulated expression of LOX is a novel independent prognostic marker of worse outcome in gastric cancer patients after curative surgery

Abstract

Lysyl oxidase (LOX) initiates the enzymatic stage of collagen and elastin cross-linking. It also has intracellular functions involved in the regulation of cell differentiation, motility/migration and gene transcription. Aberrant expression of the LOX gene has been reported in multiple tumors. However, the correlation of its expression with clinicopathological parameters and its prognostic significance in gastric cancer remains largely unknown. In order to address this problem, total RNA of paired tissue samples (n=10) and a tissue microarray containing 161 paired tissues from patients with gastric cancers at different stages were collected. Quantitative real-time PCR and immunochemistry assay were conducted to investigate the expression of LOX. Based on the results, LOX mRNA was increased in gastric cancer tissues compared with the adjacent normal mucosa. Immunohistochemical detection revealed that expression of LOX was associated with depth of tumor invasion (P<0.05), lymph node status (P<0.05), TNM stage (P<0.05) and survival (P<0.05). Cox regression analysis revealed that positive expression of LOX (P=0.026) was an independent prognostic marker for survival in patients with gastric cancer.

Keywords: LOX gene; gastric cancer; prognostic marker; tissue microarray.

Figure 1

LOX mRNA expression was significantly higher in the primary gastric carcinoma tissues (70 vs. 30%, P<0.05). Relative expression of LOX mRNA in fresh gastric cancer tissues compared with normal tissues on qRT-PCR. All data were normalized using GAPDH as a reference gene. The consistency of the qRT-PCR starting template requires that the Ct-value be within 1. A normalized ratio of >2 on the Y-axis was considered to indicate gene expression upregulation; X-axis shows the specimen number. The black line corresponds to a Y-value of 2, showing the expression upregulation of the HOXC6 gene in specimen nos. 2, 3, 4,5, 8, 9 and 10. qRT-PCR, real-time quantitative reverse transcription polymerase chain reaction; LOX, lysyl oxidase.

Figure 2

(A) Expression of LOX in primary gastric carcinoma poorly differentiated adenocarcinoma H&E staining: (a) magnification, ×100; (b) magnifcation, ×400; immunohistochemical staining: (c) magnification, ×100; (d) magnification, ×400. (B) Expression of HOXC6 in primary gastric carcinoma. Intermediate-differentiated adenocarcinoma H&E staining: (a) magnification, ×100; (b) magnification, ×400; immunohistochemical staining: (c) magnification, ×100; (d) magnification, ×400. LOX, lysyl oxidase; H&E, hematoxylin and eosin.

Figure 2

(A) Expression of LOX in primary gastric carcinoma poorly differentiated adenocarcinoma H&E staining: (a) magnification, ×100; (b) magnifcation, ×400; immunohistochemical staining: (c) magnification, ×100; (d) magnification, ×400. (B) Expression of HOXC6 in primary gastric carcinoma. Intermediate-differentiated adenocarcinoma H&E staining: (a) magnification, ×100; (b) magnification, ×400; immunohistochemical staining: (c) magnification, ×100; (d) magnification, ×400. LOX, lysyl oxidase; H&E, hematoxylin and eosin.

Figure 3

Univariate analysis of LOX protein expression with reference to overall survival (P<0.05). Survival curve of patients with gastric cancer with regard to LOX expression. Patients with positive LOX expression had a lower overall survival rate than patients with negative expression (P<0.05). LOX, lysyl oxidase.

Figure 4

Univariate analysis of (A) tumor diameter (P<0.001), (B) depth of tumor invasion (P<0.001), (C) lymph node status (P<0.001) and (D) TNM stage (P<0.05) with reference to survival.