|
||
Medical Research Council Group in Molecular Biology of Membranes, Department of Biochemistry, University of Alberta,
Edmonton, Alberta, Canada T6G 2S2
We have isolated and characterized a 12-kb
mouse genomic DNA fragment containing the entire
calreticulin gene and 2.14 kb of the promoter region.
The mouse calreticulin gene consists of nine exons and
eight introns, and it spans 4.2 kb of genomic DNA. A
1.8-kb fragment of the calreticulin promoter was subcloned into a reporter gene plasmid containing
chloramphenicol acetyltransferase. This construct was
then used in transient and stable transfection of NIH/
3T3 cells. Treatment of transfected cells either with the
Ca2+ ionophore A23187, or with the ER Ca2+-ATPase
inhibitor thapsigargin, resulted in a five- to sevenfold increase of the expression of chloramphenicol acetyltransferase protein. Transactivation of the calreticulin
promoter was also increased by fourfold in NIH/3T3
cells treated with bradykinin, a hormone that induces
Ca2+ release from the intracellular Ca2+ stores. Analysis of the promoter deletion constructs revealed that
A23187- and thapsigargin-responsive regions are confined to two regions (
115 to
260 and
685 to
1,763) in the calreticulin promoter that contain the
CCAAT nucleotide sequences. Northern blot analysis
of cells treated with A23187, or with thapsigargin, revealed a fivefold increase in calreticulin mRNA levels.
Thapsigargin also induced a fourfold increase in calreticulun protein levels. Importantly, we show by nuclear run-on transcription analysis that calreticulin gene
transcription is increased in NIH/3T3 cells treated with
A23187 and thapsigargin in vivo. This increase in gene
expression required over 4 h of continuous incubation
with the drugs and was also sensitive to treatment with
cycloheximide, suggesting that it is dependent on protein synthesis. Changes in the concentration of extracellular and cytoplasmic Ca2+ did not affect the increased
expression of the calreticulin gene. These studies suggest that stress response to the depletion of intracellular Ca2+ stores induces expression of the calreticulin
gene in vitro and in vivo.
This article has been cited by other articles:
|
|