Sf. Amato et al., TRANSCRIPTIONAL REGULATION OF THE JUNB PROMOTER IN MATURE B-LYMPHOCYTES - ACTIVATION THROUGH A CYCLIC ADENOSINE 3',5'-MONOPHOSPHATE-LIKE BINDING-SITE, The Journal of immunology, 157(1), 1996, pp. 146-155
The experiments presented herein were designed to understand the molec
ular mechanism(s) by which membrane Ig (mIg)-dependent signals are int
egrated at the level of the junB promoter to induce gene transcription
. Functional studies using chloramphenicol acetyltransferase reporter
gene constructs that contained deleted 5' flanking region junB sequenc
es identified a region located between -194 and -87 that contains an E
ts binding site and a putative cAMP response element binding site (CRE
-like). Point mutagenesis of the CRE-like site blocked junB promoter a
ctivation in response to mIg cross-linking in mature Bal17 B cells. Nu
clear extract binding activity to a synthetic oligonucleotide containi
ng the junB CRE-like site was detected in unstimulated B cells and was
increased in response to mIg cross-linking. Binding activity was comp
eted with unlabeled oligonucleotides that contained the junB CRE-like
site or the somatostatin CRE consensus motif; the latter observation s
uggests that members of the activating transcription factor/CRE bindin
g protein (CREB) family may mediate mIg-dependent junB transcription.
Consistent with this interpretation, recombinant CREB and activating t
ranscription factor proteins bound the junB CRE-like site, but did not
interact with a mutant CRE-like site. Expression of a dominant negati
ve CREB protein blocked mIg-mediated transcription from a junB CRE-lik
e site-chloramphenicol acetyltransferase reporter gene. CRE-like nucle
oprotein complexes from Bal17 B cells contained constitutively bound C
REB-1, which was phosphorylated on serine 133 in response to mIg cross
-linking. Activating transcription factor-1 protein was also constitut
ively expressed in CRE-like nucleoprotein complexes. Collectively, the
se results suggest that components of the protein kinase A signaling p
athway are recruited by mIg to induce junB transcription.