Jj. Enyeart et al., ACTH AND AII DIFFERENTIALLY STIMULATE STEROID-HORMONE ORPHAN RECEPTORMESSENGER-RNAS IN ADRENAL-CORTICAL CELLS, Molecular and cellular endocrinology, 124(1-2), 1996, pp. 97-110
NGFI-B and Ad4BP are steroid hormone receptor-like transcription facto
rs that may control steroidogenesis, growth and differentiation in the
adrenal cortex. We have studied-the induction of NGFI-B and Ad4BP mRN
As by the peptide hormones, ACTH, AII, IGF, FGF, and by KCl depolariza
tion in cultured bovine adrenocortical cells. The mRNAs for these two
transcription factors were most effectively but differentially induced
by ACTH and AII. mRNA for NGFI-B was,typically undetectable in unstim
ulated cells, but rapidly (< 30 min) accumulated in response to ACTH a
nd AII. Peak increases occurred within 2-3 h after which mRNA levels d
eclined. At maximally effective concentrations, AII produced increases
in NGFI-B mRNA 2.7-fold larger than those triggered by ACTH (n = 7).
In contrast to NGFI-B, Ad4BP mRNA was readily detectable in unstimulat
ed cells. ACTH and AII induced smaller, slower and more sustained incr
eases in Ad4BP mRNA. peak values were obtained in 6-8 h and Ad4BP mRNA
remained elevated for at least 18 h. ACTH produced increases in Ad4BP
that were 2.6-fold larger than those stimulated by AII (n = 8). Antag
onists of major signaling pathways that couple ACTH and AII receptors
to cortisol secretion, including T-type Ca2+ antagonists Ni2+ and penf
luridol, the CaM kinase antagonist KN-62, the A-kinase antagonist H-89
and the non-selective kinase antagonist staurosporine, all failed to
suppress increases in NGFI-B and Ad4BP mRNAs triggered by these two pe
ptides. Each of these agents effectively inhibited cortisol production
stimulated by the peptides. Further, arguing against their proposed r
ole as transcription factors' for steroidogenic enzymes, ACTH- and AII
-stimulated increases in steroid orphan receptor mRNAs were not correl
ated with corresponding increases in cortisol production measured over
24 h. The results show that NGFI-B and Ad4BP mRNAs are differentially
regulated by ACTH and AII. Only NGFI-B is rapidly and transiently inc
reased with kinetics common to immediate early genes. The lack of corr
elation between peptide-stimulated increases in orphan receptor mRNAs
and cortisol production in combination with the apparent divergence in
the associated signaling pathways argue against a primary role for th
ese transcription factors in ACTH- and AII-stimulated steroidogenesis.
The dual function of these peptide hormones as mediators of developme
nt and corticosteroid synthesis could necessitate the presence of sepa
rate, parallel signaling pathways. Copyright (C) 1996 Elsevier Science
Ireland Ltd.