Letter to the Editor this criteria correspond to known functional groups of A Unified Nomenclature System for receptors. This procedure yields six subfamilies. All the the Nuclear Receptor Superfamily unusual receptors that contain only one of the two conserved domains (C or E) were grouped into a separate subfamily (subfamily 0) irrespective of their evolutionary Nuclear hormone receptors (NRs) are important tranorigin. Within subfamilies, groups of receptors are descriptional regulators involved in widely diverse physiofined as the most internal branches with bootstrap vallogical functions such as control of embryonic developues above 90%. In this nomenclature system, the numment, cell differentiation, and homeostasis (Gronemeyer ber of a given receptor inside a group does not carry and Laudet, 1995; Mangelsdorf et al., 1995). In addition, any specific information. In many cases these groups these molecules are extremely important in medical recontain arthropod and vertebrate members. The various search since a large number of them are implicated in homologs of the same gene in invertebrates (e.g., Drodiseases such as cancer, diabetes, or hormone resissophila and Caenorhabditis) have the same name. It is tance syndromes. Some of the NRs act as ligand-inducible transcription factors, while a large number of them have no defined ligand and are hence described as "orphan" receptors (Enmark and Gustafsson, 1996). Over the last decade, workers in the field have described more than 300 sequences of NRs using an increasingly complex and baroque nomenclature. The existence of several names for the same gene is an acute problem for the orphan receptors, which often cannot be described by their function, particularly at the moment of their discovery. As discussed during the Seventh International CBT Symposium on "Nuclear Orphan Receptors" in Huddinge, Sweden (September 9-12, 1995), this plethora of names has become more and more confusing and now constitutes a barrier for understanding of newly acquired knowledge to researchers outside as well as within the field. For that reason, four of us (V. L., J. A., J.-A. G., and W. W.) agreed to form a committee for the nomenclature of NRs. It is the purpose of this paper to recommend names for the subfamilies and groups of receptors based on a phylogenetic tree connecting all known NR sequences. This system, based on the evolution of the two well-conserved domains of NRs (the DNA-binding C domain and the ligand-binding E domain), offers a practical and significant framework to which subsequent genes can be easily added. The resulting nomenclature has now been endorsed by over 40 scientists 1 many of whom contributed to defining the nomenclature and to preparing this letter. This nomenclature has been discussed with the International Union of Pharmacology Committee on Receptor Nomenclature and Drug Classification (NC-IUPHAR). A subcommittee of NC-IUPHAR entitled "Nuclear Receptors" will be set up to further clarify receptor nomenclature to integrate structure and function.A summa...

In combination with androgens, estrogens can induce aberrant growth and malignancy of the prostate gland. Estrogen action is mediated through two receptor subtypes: estrogen receptors alpha (ERalpha) and beta (ERbeta). Wild-type (wt) and transgenic mice lacking a functional ERalpha (alphaERKO) or ERbeta (betaERKO) were treated with the synthetic estrogen diethylstilbestrol (DES). DES induced prostatic squamous metaplasia (SQM) in wt and betaERKO but not in alphaERKO mice, indicating an essential role for ERalpha, but not ERbeta, in the induction of SQM of prostatic epithelium. In order to determine the respective roles of epithelial and stromal ERalpha in this response, the following tissue recombinants were constructed with prostatic epithelia (E) and stroma (S) from wt and ERKO mice: wt-S+wt-E, alphaERKO-S+alphaERKO-E, wt-S+alphaERKO-E, and alphaERKO-S+wt-E. A metaplastic response to DES was observed in wt-S+wt-E tissue recombinants. This response to DES involved multilayering of basal epithelial cells, expression of cytokeratin 10, and up-regulation of the progesterone receptor. Tissue recombinants containing alphaERKO-E and/or -S (alphaERKO-S+alphaERKO-E, wt-S+alphaERKO-E, and alphaERKO-S+wt-E) failed to respond to DES. Therefore, full and uniform epithelial SQM requires ERalpha in the epithelium and stroma. These results provide a novel insight into the cell-cell interactions mediating estrogen action in the prostate via ERalpha.

The thermodynamics of sequence-specific DNA-protein interactions provide a complement to structural studies when trying to understand the molecular basis for sequence specificity. We have used fluorescence spectroscopy to study the chemical equilibrium between the wild-type and a triple mutant glucocorticoid receptor DNA-binding domain (GR DBD wt and GR DBDEGA, respectively) and four related DNA-binding sites (response elements). NMR spectroscopy was used to confirm that the structure of the two proteins is very similar in the uncomplexed state. Binding to DNA oligomers containing single half-sites and palindromic binding sites was studied to obtain separate determinations of association constants and cooperativity parameters involved in the dimeric DNA binding. Equilibrium parameters were determined at 10-35 degrees C in 85 mM NaCl, 100 mM KCl, 2 mM MgCl2, and 20 mM Tris-HCl at pH 7.4 (20 degrees C) and at low concentrations of an antioxidant and a nonionic detergent. GR DBDwt binds preferentially to a palindromic consensus glucocorticoid response element (GRE) with an association constant of (7.6 +/- 0.9) x 10(5) M-1 and a cooperativity parameter of 10 +/- 1 at 20 degrees C. GR DBDEGA has the highest affinity for an estrogen response element (ERE) with an association constant of (2.2 +/- 0.3) x 10(5) M-1 and a cooperativity parameter of 121 +/- 17 at 20 degrees C. The difference in cooperativity in the two binding processes, which indicates significant differences in binding modes, was confirmed using gel mobility assays. van't Hoff analysis shows that DNA binding in all cases in entropy driven within the investigated temperature range. We find that delta H0obs and delta S0obs for the formation of a GR DBDwt-GRE versus GR DBDEGA-ERE complex are significantly different despite very similar delta G0obs values. A comparison of GR DBDwt binding to two similar GREs reveals that the discrimination between these two (specific) sites is due to a favorable delta(delta S0obs) which overcompensates an unfavorable delta(delta H0obs), i.e., the sequence specificity is in this case entropy driven. Thus, entropic effects are of decisive importance for the affinity as well as the specificity in GR-DNA interactions. The molecular basis for measured equilibrium and thermodynamic parameters is discussed on the basis of published structures of GR DBD-GRE and ER DBD-ERE complexes.

Two protein fragments containing the DNA-binding domain (DBD) of the glucocorticoid receptor (GR) have been studied by two-dimensional 1H NMR spectroscopy. The two peptides (93 and 115 residues, respectively) contain a common segment corresponding to residues C440-I519 of the rat GR or residues C421-I500 of the human GR and include two Zn-binding "finger" domains. The structures of this segment are almost identical in the two protein fragments, as judged from chemical shifts and sequential NOE connectivities. More than 90% of all observable 1H resonances within a 71-residue segment encompassing C440-R510 (rat GR) could be sequentially assigned by standard techniques, and stereospecific assignments could be made for the methyl groups in four valine residues within this segment. Sequential NOE connectivities indicate several elements of secondary structure including two alpha-helical segments consisting of residues S459-E469 and P493-G504, a type I reverse turn between residues R479 and C482, a type II reverse turn between residues L475 and G478, and several regions of extended peptide conformation. No evidence for alpha-helical conformation was found within the two putative zinc-finger domains, indicating that the structures of these domains differ from that of TFIIIA-type zinc fingers. The observation of some very slowly exchanging amide protons in the N-terminal (CI) domain of the DBD in combination with slow rotation of the Y452 aromatic ring indicates that this domain has a restricted conformational flexibility compared to the C-terminal (CII) domain. We also observe several long-range NOE connectivities within C440-R510, suggesting that the sequential assignments presented here will provide a basis for a complete structure determination of this segment of the GR.

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