Association of ECRG4 with PLK1, CDK4, PLOD1 and PLOD2 in esophageal squamous cell carcinoma.

Esophageal cancer-related gene 4 (ECRG4) is a tumor suppressor gene associated with the prognosis of esophageal squamous-cell carcinoma (ESCC). Studies have reported that ECRG4 effectively inhibits the proliferation, migration and invasion of ESCC cells. In the current study, ectopic expression of ECRG4 significantly induced ESCC cell apoptosis. To further understand the molecular profile of ECRG4 overexpression in ESCC cells, tandem mass tag (TMT) labeling followed by LC-MS/MS analysis was applied on samples from ECRG4 overexpressed cells and control cells. Among the identified differentially expressed proteins, four up-regulated proteins (PLK1, CDK4, PLOD1 and PLOD2) associated with cell apoptosis, cell cycle and metastasis were chosen for the further investigation. The effects of ECRG4 protein levels on the expression of these four proteins were validated by manipulating the expression of ECRG4 in ESCC cells followed by Western blotting analysis. The immunohistochemical staining results showed a significant decrease in ECRG4 levels and a notable increase in the four proteins in ESCC samples as compared to matched esophageal tissues (n=75). More importantly, the protein levels of ECRG4 had a negative association with those of PLK1, CDK4, PLOD1 and PLOD2. Thus, our data suggested that the tumor-repressor functions of ECRG4 may be associated with PLK1, CDK4, PLOD1 and PLOD2, providing important insights into the molecular mechanisms of esophageal carcinogenesis.