Salmon gonadotropin II beta subunit promoter contains multiple DNA elements responsible for stimulation by gonadotropin-releasing hormone through protein kinase C-dependent and -independent pathways

Gonadotropin-releasing hormone (GnRH) stimulates gonadotropin (GTH) product ion by activating GTH subunit gene transcription. In salmonid fish, the exp ression of the beta subunit gene of GTH II (sGTH II beta) is stimulated by GnRH at the final stages of reproduction. DNA elements required for the GnR H stimulation were examined by analyzing sGTH II beta promoter activity by transfection studies in a gonadotrope-derived cell line, alpha T3-1. A GnRH analog (GnRHa) specifically stimulated the sGTH II beta promoter (3358 bp) expression 3.6-fold, while phorbol myristate acid (PMA) stimulated it 6.2- 9-fold. Analysis of a series of 5'-deletion mutants has revealed that a pro ximal region (-258 to -199) was important in GnRHa stimulation through prot ein kinase C (PKC)-independent signal transduction pathways, because an int ernal deletion mutant (Delta(246-217)/3358) showed a significant decrease i n the level of GnRHa stimulation, but showed no change in stimulation by PM A. A large upstream region (-3358 to -1260) showed an enhancing activity of the GnRHa stimulation, and a far upstream 530 bp segment in this region (- 3358 to -2829) may be responsible for this activity. The present results su ggest that sGTH II beta gene may be controlled by GnRH through multiple DNA elements including those responsive to PKC-dependent and -independent sign al transduction pathways. (C) 1999 Elsevier Science Ireland Ltd. All rights reserved.