Regulation and clinical significance of the hypoxia-induced expression of ANGPTL4 in gastric cancer

Solid tumors are often exposed to hypoxia. Hypoxia inducible factor (HIF)-1 alpha upregulates numerous target genes associated with the malignant behavior of hypoxic cancer cells. A member of the angiopoietin family, angiopoietin-like protein 4 (ANGPTL4) is a hypoxia-inducible gene. The present study aimed to clarify whether ANGPTL4 is regulated by HIF-1a in gastric cancer cells. The study also assessed whether ANGPTL4 expression is associated with clinicopathological factors or HIF-1 alpha expression in gastric cancer tissues. Hypoxia-induced ANGPTL4 expression was quantitatively analyzed using reverse transcription-quantitative polymerase chain reaction (RT-qPCR) in 10 gastric cancer cell lines. RT-qPCR was further employed to investigate the HIF-1 alpha dependency of ANGPTL4 expression using HIF-1 alpha-knockdown transfectant 58As9-KD and control 58As9-SC gastric cancer cells. The HIF-1 alpha and ANGPTL4 expression levels were immunohistochemically analyzed in 170 gastric cancer tissue specimens and were assessed for any correlations with the clinicopathological factors and/or patient survival. Subsequently, hypoxia-induced ANGPTL4 expression was observed in 7 out of 10 gastric cancer cell lines. The hypoxic induction of ANGPTL4 was almost preserved in the 58As9-KD cells compared with that observed in the 58As9-SC cells, while the induction of known HIF-1 alpha target gene, carbonic anhydrase 9, was completely suppressed in the 58As9-KD cells. In the gastric cancer tissues, ANGPTL4 expression was inversely correlated with the tumor depth, whereas HIF-1 alpha expression was positively correlated with venous invasion. A survival analysis revealed that the expression of ANGPTL4 was significantly correlated with a longer survival time, whereas that of HIF-1 alpha was correlated with a shorter survival time. In conclusion, the present findings indicate that hypoxia-induced ANGPTL4 expression is independent of HIF-1 alpha in hypoxic gastric cancer cells. ANGPTL4 may be a favorable marker for predicting a long survival time, whereas HIF-1 alpha predicts a poor prognosis, in gastric cancer patients. The hypoxic environment independently induces ANGPTL4 and HIF-1 alpha, which are believed to exhibit adverse effects on tumor progression.