Abstract
In the previous study, it has been found that the syntheses of the 78kDa glucose-regulated protein (GRP78) were vigorously induced by stresses, such as A23187, thapsigargin (TG) and geldanamycin (GA) in 9L rat brain tumor (RBT) cell line. In this study, we have found that an 8h treatment with either 2 μM A23187 or 300 nM TG caused the redistribution of GRP78 in 9L RBT cells. GRP78 exhibited the pattern outside the ER when respectively treated with A23187 and TG, but this phenomenon was less obvious after 5 μM GA treatment for 8h. Although GRP78 are primarily localized in the endoplasmic reticulum (ER), subcellular fractionation study showed that the stress-induced GRP78 was in the mitochondria-enriched fraction in from 9L RBT cells. Furthermore, confocal microscopic and immunogold electron microscopic studies confirmed that the stress-induced GRP78 was indeed localized in mitochondria. These results indicate that GRP78 is not present exclusively in the ER after stressed. This is the first report demonstrating that GRP78 is localized in mitochondria in 9L RBT cells after being exposed to GRP78-inducing stresses.