TRANSACTIVATION OF THE GRP78 PROMOTER BY CA2- A COMPARATIVE-ANALYSIS WITH A23187 AND THE ENDOPLASMIC-RETICULUM CA2+-ATPASE INHIBITOR THAPSIGARGIN( DEPLETION )

The calcium ionophore A23187 has been shown to induce the expression o f a set of glucose-regulated protein (GRP) genes through the depletion of Ca2+ from the intracellular Ca2+ stores. Here we demonstrate that thapsigargin, which inhibits specifically the endoplasmic reticulum Ca 2+-ATPase and causes a discharge of the intracellular Ca2+ store, is a ble to induce the transcription of two grp genes (grp78/BiP and grp94) with kinetics and magnitude similar to that of A23187. The induction of the grp genes by both reagents requires several hours of sustained treatment, in contrast to the rapid induction previously described for c-jun and c-fos. The transactivation of the rat grp78 promoter by A23 187 is mediated through sequences spanning -154 to -130 and -99 to -90 . Further, simultaneous mutation of two 10-base pair regions, spanning -139 to -130 and -99 to -90, severely reduced the A23187 response. Th e induction by thapsigargin is also partially mediated through these s ame promoter elements, without the involvement of the TRE and CRE-like elements of the grp78 promoter. The Ca2+ response elements are furthe r defined by their ability to confer Ca2+ stress inducibility to a het erologous promoter. We show that subdomains of the grp78 promoter are capable of conferring the Ca2+ stress response. In particular, two cop ies of a 50-base pair region spanning -159 to -110, when cloned in eit her orientation, can confer a 5- and 9-fold induction by A23187 and th apsigargin, respectively. Our results lend support to the hypothesis t hat the induction of grp78 by A23187 and thapsigargin following ER Ca2 + discharge acts through a novel pathway in which a Ca2+ signal is tra nsduced through redundant elements containing CCAAT box-like motifs fl anked by GC-rich regions.