Evolution of human, chicken, alligator, frog, and zebrafish mineralocorticoid receptors: Allosteric influence on steroid specificity

Abstract

Although multiple steroid ligands of the glucocorticoid, mineralocorticoid, and progestin families bind to and regulate the activity of mineralocorticoid receptors (MRs), the responses to these ligands differ across species. To understand how the different domains of MRs contribute to the ligand-induced activation or inhibition of MR activity, we studied the response to eight steroids (aldosterone, 11-deoxycorticosterone, 11-deoxycortisol, cortisol, corticosterone, progesterone, 19-norprogesterone, and spironolactone) of human, chicken, alligator, frog, and zebrafish full-length MRs and truncated MRs, which lacked the N-terminal domain (NTD) and DNA binding domain (DBD). Compared to full-length MRs, some truncated MRs were not activated by the steroids, and others required higher steroid concentrations for activation. Progesterone, 19-norprogesterone, and spironolactone did not activate full-length or truncated human, alligator, or frog MRs. However, at 10 nM, these steroids activated full-length chicken and zebrafish MRs, whereas at 100 nM, these steroids had little activity for truncated chicken MRs, but they retained activity for truncated zebrafish MRs. This suggests that regulation of the activation of the chicken MR by progestin resides in the NTD-DBD and that of the zebrafish MR resides in the hinge-LBD. Zebrafish and chicken MRs contain a serine corresponding to Ser in human MR, which is required for the antagonist activity of progesterone for human MR, suggesting a previously uncharacterized mechanism of regulation of progestin activation of chicken and zebrafish MRs. These findings suggest that progesterone may be a physiological activator of chicken and zebrafish MRs.

Progesterone: An Enigmatic Ligand for the Mineralocorticoid Receptor

“…Because in vivo studies of binding and activation of the MR by corticosteroids and progesterone can be complicated by their binding to serum proteins [8], purified MR was needed for an accurate determination of the affinity of progesterone for human MR. Purified MR became available with the cloning of the human MR by Arriza et al, [6]. Using recombinant human MR, Arriza et al reported that aldosterone, cortisol, corticosterone, 11-deoxycorticosterone, and progesterone had a similar nM affinity for human MR. Further studies by Rupprecht et al [10], Geller et al [9] and Katsu et al [13] showed that progesterone was a human MR antagonist with sub nM affinity.…”

Transcriptional Activation of Elephant Shark Mineralocorticoid Receptor by Corticosteroids, Progesterone and Spironolactone

“…Thus, the identity of the physiological mineralocorticoid in cartilaginous fishes and ray-finned fishes is not established, although cortisol and 11-deoxycorticosterone have been proposed (39)(40)(41)(42)(43)(44)(45). Complicating the identity of the physiological mineralocorticoid in cartilaginous and rayfinned fishes is evidence that progesterone (Prog) and , along with spironolactone (Spiron) ( Figure 2), are transcriptional activators of several ray-finned fish MRs (24,36,44), including zebrafish MR (35,46), and of chicken MR (35). In contrast, these steroids are antagonists for human MR (25,27,47), alligator MR and Xenopus MR (35).…”

“…Complicating the identity of the physiological mineralocorticoid in cartilaginous and rayfinned fishes is evidence that progesterone (Prog) and , along with spironolactone (Spiron) ( Figure 2), are transcriptional activators of several ray-finned fish MRs (24,36,44), including zebrafish MR (35,46), and of chicken MR (35). In contrast, these steroids are antagonists for human MR (25,27,47), alligator MR and Xenopus MR (35). Ray-finned fish MRs and chicken MR differ in their response to Prog, 19norProg and Spiron, raising the question of whether the response to Prog and Spiron evolved in ray-finned fish before or after the divergence of ray-finned fish from the lobe-finned fish lineage that led to tetrapods.…”

“…This occurs in coelacanth MR, which contains Ser-816, corresponding to human MR Ser-810 (Figure 7) and to elephant shark MR Met-782. This mutation in coelacanth MR would be expected to eliminate the proposed van der Waals contact between helix 5 and helix 3, leading to antagonist activity of Prog in some terrestrial vertebrate MRs(35,47). However, a serine corresponding to Ser-810 in human MR also is present in chicken MR and ray-finned fish MRs(Figure 7), indicating another mechanism is involved in Prog activation of the MR in these vertebrates.Role for elephant shark MR in reproductive physiologyThe evidence from RNA-seq analysis of high MR expression in elephant shark ovary and testis (Figure 6A) suggests that a Prog-MR complex is important in reproductive responses in elephant shark.…”

“…summarizes the EC50s of corticosteroids for fulllength and truncated elephant shark MR.Table 1also contains, for comparison, previously determined EC50s of corticosteroids for full-length and truncated human, chicken, alligator, Xenopus and zebrafish MRs(35) and skate MR(61).…”