Molecular characterization of the glucose-regulated protein 78 (GRP78) gene in planarian Dugesia japonica.

GRP78 (78 kDa glucose-regulated protein) has ubiquitously existed in nearly all organisms from yeast to humans, reflecting the central roles it plays in cell survival. In this report, we isolated and sequenced the full-length cDNA of GRP78 (designated DjGRP78) from the planarian Dugesia japonica. The cDNA is 2121 bp, including an open reading frame (ORF) of 1983 bp encoding a polypeptide of 660 amino acids with three HSP70 family signatures. DjGRP78 contains signal peptides at the N-terminus and a KTEL peptide motif at the C-terminus, which suggests that it localizes in the endoplasmic reticulum (ER). Fluorescent real time RT-PCR was employed to detect the expression pattern of Djgrp78 in response to different stressors. Our results show that heat shock and heavy metals (Hg(2+) and Pb(2+)) induce Djgrp78 expression, but starvation does not. Interestingly, we found that Djgrp78 was up-regulated in planarians with septic tissues, and also verified that it was up-regulated in response to bacterial challenge. Our data indicate that Djgrp78 may be a multifunctional gene, and play important roles in physiological and pathological stress in planarians.