A TGACG MOTIF MEDIATES GROWTH-HORMONE-FACTOR-1 PITUITARY-TRANSCRIPTIONAL-ACTIVATOR-1-DEPENDENT CAMP REGULATION OF THE RAINBOW-TROUT GROWTH-HORMONE PROMOTER/
F. Argenton et al., A TGACG MOTIF MEDIATES GROWTH-HORMONE-FACTOR-1 PITUITARY-TRANSCRIPTIONAL-ACTIVATOR-1-DEPENDENT CAMP REGULATION OF THE RAINBOW-TROUT GROWTH-HORMONE PROMOTER/, European journal of biochemistry, 238(3), 1996, pp. 591-598
The mechanisms involved in the regulation of the rainbow trout growth
hormone (tGH) gene promoter by the pituitary-specific transcription fa
ctor GHF1 (growth hormone factor 1), also called Pit1 (pituitary trans
criptional activator 1), and cAMP have been investigated in mammalian
and fish cells. The -340 to +24 5'-flanking region of the tGH gene fus
ed to the luciferase gene was activated in rat pituitary GC cells and
in HeLa cells cotransfected with an effector plasmid encoding rat GHF1
. GC cell nuclear extracts produced four GHF1-specific footprints (sit
es F1 to F4) on the tGH promoter, each containing multiple W(4)NCAT (W
, A or T) or closely related motifs. Mutational analysis performed in
GC cells indicated that the proximal F1 site alone can direct transcri
ption, but that the region encompassing the F2 and F3 sites is necessa
ry for optimal activation and contains a TGACG motif (cAMP-response el
ement, CRE) confering cAMP responsiveness. The role of the TGACG motif
in mediating cAMP regulation of the tGH promoter was confirmed in pri
mary cultures of trout pituitary cells. Cotransfection studies in carp
EPC cells using an effector plasmid encoding trout GHF1 demonstrated
the GHF1 dependence of a cAMP stimulation. Gel shift and southwestern
experiments revealed nuclear proteins of 43 kDa and 30 kDa in GC and f
ish cells, respectively, that bind specifically to the tGH CRE, sugges
ting the involvement of CRE-binding protein/activating-transcription-f
actor-1-related peptides in cAMP response. Incidentally, and in contra
st with previous reports, we found the rat tGH promoter, that lacks TG
ACG motifs, unresponsive to cAMP. Thus, the cAMP stimulation of the tG
H gene is more similar to its human counterpart, that is also GHF1 dep
endent and mediated by TGACG motifs in the promoter. It is suggested t
hat control of GH gene expression has evolved modularly, through vario
us assortments of the same regulatory units, rather than molecularly,
through innovative units.