Specific Region in Hormone Binding Domain Is Essential for Hormone Binding and Trans-Activation by Human Androgen Receptor

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Abstract
Complementary DNA (cDNA) clones encoding human-androgen receptors (haR) were isolated using synthetic oligonucleotides homologous to the human glucocorticoid, estradiol, progesterone, and aldosterone receptors as probes to screen a human testis .lambda. gt11 cDNA library. One of the receptor proteins (hARa) produced in vitro bound the [3H]dehydrotestosterone ([3H]DHT) with high affinity and selectively similar to the human androgen receptor present in target tissues and cells. A second cDNA clone (hARb) encoding an identical amino terminal and DNA binding domains, but differing by four amino acids at the hormone binding domain, did not bind [3H]DHT with high affinity when incubated with protein expressed by in vitro transcription-translation. Cotransfection of hARa in an expression vector with mouse mammary tumor virus (MMTV)-bacterial chloramphenicol acetyltransferase chimeric plasmids, followed a hormone-dependent trans-activation, defining the binding affinity of hARa between 5 .times. 10-10 and 1 .times. 10-9 M for [3H]DHT. A similar cotransfection experiment with hARb indicated a KD of hARb for [3H]DHT to be above approximately 10-8 M. The deduced primary structures of hARa and hARb contain the viral erbA homologous region found in other steroid, thyroid, and vitamin receptors and is identical to the hAR sequences reported by others. The amino acid sequence differs at the Gly stretch (16 Gly instead of 27, 24 or 23) of the N-terminal domain and in hARb, the sequence reads, I.F.F.F.F.L.L (816-822) instead of K.F.F.D.E.-L (816-821) in the hARa and other reported hAR sequences. The difference of four amino acids in the steroid binding domain of hARb is associated with altered DHT binding and thus a lack of trans-activation by way of AR responsive elements in MMTV-long terminal repeat. The interaction of hARa and hARb with synthetic responsive elements by gel-retardation assay and their responsiveness in trans-activation by calcium phosphate coprecipitation demonstrates that hARb can inhibit trans-activation hARa in this system.