Sf. Amato et al., TRANSCRIPTIONAL REGULATION OF THE JUNB GENE IN B-LYMPHOCYTES - ROLE OF PROTEIN-KINASE-A AND A MEMBRANE IG-REGULATED PROTEIN PHOSPHATASE, The Journal of immunology, 159(10), 1997, pp. 4676-4685
We have examined herein whether membrane Ig (mIg) stimulates junB tran
scription through a protein kinase A (PKA)-dependent or PKA-independen
t pathway, PKA phosphotransferase activity was not increased following
mIg cross-linking of Bal17 B cells, However, junB transcriptional act
ivation was dependent upon PKA activity, as evidenced by inhibition of
goat anti-mouse IgM-stimulated junB promoter-chloramphenicol acetyltr
ansferase reporter gene activity in transfected Bal17 B cells treated
with the PKA inhibitor H-89, mIg-stimulated junB promoter-chlorampheni
col acetyltransferase activity was also blocked in B cells expressing
a specific PKA inhibitor peptide, whereas in vivo expression of an ina
ctive PKA inhibitor peptide variant was not inhibitory, Expression of
a mutant cAMP response element binding protein (CREB) containing an in
activated kinase A phosphoacceptor site at Ser(133) reduced mIg-stimul
ated junB transcription, Okadaic acid increased CREB1 phosphorylation
at Ser(133) and junB transcriptional activation, suggesting the action
of protein phosphatase-1 (PP-1) or -2A (PP-2A). Extracts from unstimu
lated B cells exhibited phosphatase activity against an in vitro PKA-p
hosphorylated peptide containing the Ser(133) phosphoacceptor site, Th
e involvement of a phosphatase activity in regulating mIg-stimulated j
unB transcription is supported by our finding that extracts from goat
anti-mouse IgM-stimulated B cells exhibited a significantly reduced le
vel of Ser(133) phosphatase activity, Hence, the level of CREB1 phosph
orylation is governed by the balance between PKA and phosphatase activ
ities, junB transcriptional activation results in part from mIg signal
s that negatively regulate a CREB1-targeted PP-1 or PP-2A activity.