ABSTRACT
Previous studies suggest that NGAL (neutro phil gelatinase-associated lipocalin) is involved in the transformation and development of esophageal carcinoma. Alteration of NGAL expression can trigger the change of cellular morphology in esophageal carcinoma cells. However, the mechanisms remain unclear. To get a better understanding of NGAL function in esophageal carcinoma, NGAL protein was expressed in methylotrophic yeast, Pichia pastoris, and purified by chromatography. EC1.71 cells expressed high levels of NGALR (NGAL receptor) and EC109 cells expressed low levels of NGALR were used as cells model. The trafficking and the possible function of NGAL protein were then analyzed in the esophageal carcinoma cells. The results showed that 5-FAM-labeled recombinant NGAL protein could internalize into the EC1.71 and EC109 cells. Furthermore, the internalized NGAL protein could induce the alteration of cellular morphology, resulting in generation of autophagosome, transcriptional up-regulation of genes associated with autophagy and increase of phospho-ERK1/2 (p-ERK1/2). Interestingly, the treatment with the NGAL protein did not affect the intracellular iron level. These data indicate that induced autophagy by exogenous NGAL protein is a mechanism that internalized NGAL plays important roles in esophageal carcinoma cells, independent with NGAL-mediated iron transport process, while ERK1/2 signal pathway is involved in activation of autophagy by exogenous NGAL protein.