Wp. Long et al., Protein kinase C modulates aryl hydrocarbon receptor nuclear translocator protein-mediated transactivation potential in a dimer context, J BIOL CHEM, 274(18), 1999, pp. 12391-12400
Protein kinase C (PKC)- and protein kinase A (PKA)mediated modulation of th
e transactivation potential of human aryl hydrocarbon receptor nuclear tran
slocator (hARNT), a basic helix-loop-helix (bHLH)-PAS transcription factor,
and the bHLH-ZIP transcription factors USF-1 (for upstream regulatory fact
or 1) and c-Myc were examined, An 81 nM dose of the PKC activator phorbol-1
2-myristate-13-acetate (PMA), shown here to specifically activate PKC in CO
S-l cells, or a 1 nM dose of the PKA activator 8-bromoadenosine-3',5'-cycli
c monophosphate (8-Br-cAMP) results in 2.6- and 1.9-fold enhancements, resp
ectively, in hARNT-mediated transactivation of the class B, E-box-driven re
porter pMyc3E1bLuc relative to identically transfected, carrier solvent-tre
ated COS-l cells. In contrast, 81 nM PMA and 1 nM 8-Br-cAMP did not enhance
transactivation of pMyc3E1bLuc-driven by USF-1 and c-Myc expression relati
ve to identically transfected, carrier-treated COS-1 cells. Co-transfection
of pcDNA3/ARNT-474-Flag, expressing a hARNT carboxyl-terminal transactivat
ion domain deletion, and pMyc3E1bLuc does not result in induction of report
er activity, suggesting PMA's effects do not involve formation of unknown h
ARNT-protein heterodimers. Additionally, PMA had no effect on hARNT express
ion relative to Me2SO-treated cells. Metabolic P-32 labeling of hARNT in ce
lls treated with carrier solvent or 81 nM PMA demonstrates that PMA does no
t increase the overall phosphorylation level of hARNT. These results demons
trate, for the first time, that the transactivation potential of ARNT in a
dimer context can be specifically modulated by PKC or PKA stimulation and t
hat the bHLH-PAS and bHLH-ZIP transcription factors are differentially regu
lated by these pathways in COS-1 cells.