Esistono due forme di recettori androgeni : uno a forma di A ed uno a forma di B. Il Dott. Sawaya e la Dottoressa Maria Hordinsky hanno scoperto che la forma dei recettori cambia con il trattamento con finasteride da A a B.

La forma B promuove la crescita normale ed predominante nella zona posteriore della testa, ove i capelli non vengono colpiti da calvizie androgenetica.

Functional activities of the A and B forms of the human androgen receptor in response to  androgen receptor agonists and antagonists.

Mol Endocrinol 1998 May;12(5):654-63 (ISSN: 0888-8809)
Gao T; McPhaul MJ  Department of Internal Medicine, The University of Texas Southwestern Medical Center, Dallas  75235, USA.

The androgen receptor (AR) is present in many cells in two forms. The B form migrates with an  apparent mass of 110 kDa and constitutes more than 80% of the immunoreactive receptor in most  cell types. The A form of the AR migrates with an apparent mass of 87 kDa, appears to derive from  internal translation initiation at methionine-188 in the AR open-reading frame, and usually constitutes  20% or less of the immunoreactive AR present. Previous experiments designed to examine the  functional capacity of the A and B forms of the AR have been hampered by marked differences in the  expression levels of the two isoforms, as the nucleotide sequence surrounding the codon encoding   methionine-188 causes it to be used inefficiently as a translation initiation site. To circumvent this,  we altered the nucleotide sequence surrounding methionine-188 to render it more similar to that  surrounding the codon encoding methionine-1. Transfection of a cDNA containing these changes  resulted in similar levels of expression of A and B forms of the AR as assessed by immunoblot
assays using antibodies directed at an epitope preserved in both. Functional activities of these  cDNAs were assessed using cotransfection assays that employed two model androgen-responsive  genes (MMTV-luciferase and PRE2-tk-luciferase) in response to mibolerone, a potent androgen  agonist, in three different cell lines. These studies demonstrated subtle differences in the activities of  the A and B isoforms, which depended on the promoter and cell context. Additional studies failed to  reveal any major differences in the responses of the AR-A and AR-B isoforms to a variety of androgen   agonists and antagonists, suggesting that the previously reported functional defect of the AR-A is  due principally to its level of expression. When assays of AR function are performed under conditions  in which levels of expression of the two isoforms are equivalent, the AR-A and AR-B possess similar  functional activities.

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