The negative regulation of the rat aldehyde dehydrogenase 3 gene by glucocorticoids: Involvement of a single imperfect palindromic glucocorticoid responsive element
Kc. Falkner et al., The negative regulation of the rat aldehyde dehydrogenase 3 gene by glucocorticoids: Involvement of a single imperfect palindromic glucocorticoid responsive element, MOLEC PHARM, 55(4), 1999, pp. 649-657
Glucocorticoids repressed the polycyclic aromatic hydrocarbon-dependent ind
uction of Class 3 aldehyde dehydrogenase (ALDH3) enzyme activity and mRNA l
evels in isolated rat hepatocytes by more than 50 to 80%, with a concentrat
ion-dependence consistent with the involvement of the glucocorticoid recept
or (GR). No consistent effect on the low basal transcription rate was obser
ved. This effect of glucocorticoids (GC) on polycyclic aromatic hydrocarbon
induction was effectively antagonized at the mRNA and protein level by the
GR antagonist RU38486. The response was cycloheximide-sensitive, because t
he protein synthesis inhibitor caused a GC-dependent superinduction of ALDH
3 mRNA levels. This suggests that the effects of GC on this gene are comple
x and both positive and negative gene regulation is possible. The CC-respon
se was recapitulated in HepG2 cells using transient transfection experiment
s with CAT reporter constructs containing 3.5 kb of 5'-flanking region from
ALDH3. This ligand-dependent response was also observed when a chimeric GR
(GR DNA-binding domain and peroxisome proliferator-activated receptor liga
nd-binding domain) was used in place of GR in the presence of the peroxisom
e proliferator, nafenopin. A putative palindromic glucocorticoid-responsive
element exists between -930 and -910 base pairs relative to the transcript
ion start site. If this element was either deleted or mutated, the negative
GC-response was completely lost, which suggests that this sequence is resp
onsible, in part, for the negative regulation of the gene. Electrophoretic
mobility shift analysis demonstrated that this palindromic glucocorticoid-r
esponsive element is capable of forming a specific DNA-protein complex with
human glucocorticoid receptor. in conclusion, the negative regulation of A
LDH3 in rat liver is probably mediated through direct GR binding to its can
onical responsive element.