Evolution of corticosteroid specificity for human, chicken, alligator and frog glucocorticoid receptors

Abstract

Abstract. We investigated the evolution of the response of human, chicken, alligator 1 and frog glucocorticoid receptors (GRs) to dexamethasone, cortisol, cortisone, 2 corticosterone, 11-deoxycorticosterone, 11-deoxycortisol and aldosterone. We find 3 significant differences among these vertebrates in the transcriptional activation of their 4 full length GRs by these steroids, indicating that there were changes in the specificity of 5 the GR for steroids during the evolution of terrestrial vertebrates. To begin to study 6 the role of interactions between different domains on the GR in steroid sensitivity and 7 specificity for terrestrial GRs, we investigated transcriptional activation of truncated 8GRs containing their hinge domain and ligand binding domain (LBD) fused to a GAL4 9 DNA binding domain (GAL4-DBD). Compared to corresponding full length GRs, 10 transcriptional activation of GAL4-DBD_GR-hinge/LBD constructs required higher 11 steroid concentrations and displayed altered steroid specificity, indicating that 12 interactions between the hinge/LBD and other domains are important in glucocorticoid 13 activation of these terrestrial GRs. 14 15 Short Title: Evolution of steroid specificity for terrestrial GRs 16 17

N-terminal Domain Regulates Steroid Activation of Elephant Shark Glucocorticoid and Mineralocorticoid Receptors

“…Overall, we find that the response to corticosteroids and RU486 [44,48] by elephant shark GR has some similarities and some differences to human GR [15,19,21,27], as well as to elephant shark MR [41]. In comparison to corticosteroid activation of elephant shark MR, corticosteroids have higher EC50s for elephant shark GR, indicating reduced sensitivity to corticosteroids [ Tables 1 and 2].…”

“…As the sequences of the NTDs of elephant shark and human GRs are poorly conserved, with 25% sequence identity ( Figure 2), it was not evident that there would be strong AF1 activity in the NTD in elephant shark GR. We also investigated the evolution of GR specificity for glucocorticoids through a comparison of steroid activation of full-length elephant shark GR to elephant shark MR and human GR [16,[19][20][21]23,27].…”

“…Unexpectedly, aldosterone and 11deoxycorticosterone, two mineralocorticoids, also activated elephant shark GR. These two mineralocorticoids have little activity for human GR [15,16,27], which is selective for cortisol and corticosterone [16,20,27]. Elephant shark GR is not activated by either progesterone or 19norprogesterone, in contrast to elephant shark MR, which also is activated by cortisol and corticosterone [41].…”

“…To investigate the effect of the elephant shark DBD on activation of elephant shark GR and MR, we replaced the DBD with GAL4 DBD, which has been used for analysis of transcription of the GR and MR [27,28,42,43]. As shown in Figure 3E, there was only a low level of activation by 10 nM corticosterone and aldosterone of GAL4 DBD GR hinge-LBD, and no activation by 11-deoxycorticosterone and cortisol.…”

“…The GR NTD is noteworthy for containing an activation function domain (AF1) that interacts with the DBD to provide a human GR NTD-DBD protein with constitutive activity [23][24][25][26]. AF1 also strongly stimulates transcriptional activation by glucocorticoids of the GR in humans [19,24,25,27], other terrestrial vertebrates [21,[27][28][29][30][31] and ray-finned fish [21,32]. Interaction of the NTD with coactivators as well as post-transcriptional modification of the NTD also regulates transcriptional activation of the GR [5,22,30,33,34].…”