Brefeldin A as a regulator of grp78 gene expression in mammalian cells

We report here that brefeldin A (BFA), which specifically blocks protein transport from an endoplasmic reticulum to the Golgi apparatus and causes resorption of Golgi membrane to the endoplasmic reticulum, specifically induced the endoplasmic reticulum-resident protein GRP78. Treatment of a human hepatoma cell line Alex-PC with BFA at a concentration of 5 micrograms/ml increased the grp78 transcript level by 12-fold. Analyses of the transcriptional rate of grp78 and the transfection with grp78 promoter suggested that this cell line utilized a posttranscriptional mechanism to increase the expression of grp78 in response to BFA. The induction process was partially dependent on de novo protein synthesis. Interestingly, in a hamster lung fibroblast cell line, K12, the induction of grp78 by BFA could be mediated by a transcriptional control mechanism. We further demonstrated that in K12 cells the region of the grp78 promoter responsive to BFA was within a 40-base pair region between -169 and -130, containing the conserved grp core and a 10-base pair region between -99 to -90 that contained a proximal CCAAT element. A model of how BFA regulates grp78 expression at both the transcriptional and posttranscriptional level is presented.