A newly identified epithelial cell adhesion molecule (EpCAM) from grass carp (Ctenopharyngodon idellus): Cloning, tissue distribution and lipopolysaccharide-induced expression in head kidney leucocytes

Epithelial cell adhesion molecule (EpCAM) was initially identified as a tumor-associated antigen in human. Recent studies show that EpCAM is a transmembrane glycoprotein with diverse functions in cell adhesion and other processes such as cellular signaling, cell migration, proliferation and differentiation. In fish, the knowledge on the structure and function of EpCAM is limited as only zebrafish EpCAM has been characterized and shown to play a role in embryonic development. In the present study, we isolated a cDNA encoding a homologue of zebrafish EpCAM from grass carp. The deduced grass carp EpCAM (gcEpCAM) protein of 306 amino acids shared 59-85% of similarity with the EpCAMs in other vertebrates. Protein sequence analysis revealed a transmembrane domain and two epidermal growth factor (EGF)-like repeats in the extracellular region of gcEpCAM which were both conserved in EpCAM from fish to mammal. RT-PCR analysis showed that gcEpCAM transcript was expressed with high abundance in skin, pituitary, kidney, head kidney, gill, thymus and head kidney leucocyte (HKL). Furthermore, real time PCR assay was developed to assess gcEpCAM mRNA expression in HKLs stimulated by lipopolysaccharide (LPS). Results showed that LPS significantly increased gcEpCAM mRNA expression in a time- and dose-dependent manner and the peak response was observed at 12 h after treatment with 30 μg/ml of LPS. These results indicated that gcEpCAM may be a LPS-induced gene involved in the immune response in fish head kidney.