Mol. Hum. Reprod. Advance Access published online on November 1, 2009
Molecular Human Reproduction, doi:10.1093/molehr/gap097
CAG repeat number is not inversely associated with androgen receptor activity in vitro
1Dept. of Clinical Sciences, Molecular Genetic Reproductive Medicine, Lund University, Malmö, Sweden 2 Institute of Clinical Medicine, University of Tromsø, Tromsø, Norway 3Reproductive Medicine Centre, Molecular Reproductive Medicine Research Unit, Malmö University Hospital, Lund University, Malmö, Sweden 4Dept. of Laboratory Medicine, Division of Occupational and Environmental Medicine, Lund University, Lund, Sweden 5Section of Endocrinology, Division of Internal Medicine, University Hospital of North Norway, Tromsø, Norway
Correspondence and reprint requests: Hannah Nenonen, Lund University, CRC, Building 91, Plan 10, SE 205 02 Malmö, Sweden, E-mail: Hannah.Nenonen{at}med.lu.se
A negative linear association between androgen receptor (AR) function and the CAG repeat numbers is generally assumed. However, in vivo data concerning the association between CAG number and androgenic effects have been conflicting.
Since former in vitro studies mostly have been based on extreme CAG lengths and reporter-systems containing viral promoters, the objective of this study was to investigate ARs with CAG lengths within normal range (16, 22 and 28) in a reporter-assay with the human prostate specific antigen promoter as target. We also wished to elucidate whether the interpretation of the results was depending on the methods used for adjustment of transfection efficiency and protein content.
With ß-galactosidase as transfection control, 22CAG had the highest activity (set to 100%) compared to 16CAG (mean 78% [range 41- 132], p=0.005) and 28CAG (68% [26-162], p=0.006), whereas renilla-luciferase resulted in 16CAG behaving similar to 22CAG (104% [56- 165], p=0.7) and 28CAG having lower activity (59% [33-101], p=0.004). In these experiments, also the empty vector displayed considerable background activity.
When adjusting for AR protein, the 22CAG genotype had the highest activity; 16CAG and 28CAG displaying 20% (10-47, p<0.0001) and 12% (5-21, p<0.0001) thereof. Similar results were obtained with adjustment for total protein
Thus, by normalising for AR-content, contrary to various control vectors, the highest AR activity was confined to the 22CAG and not 16 CAG, which may at least partly explain the discrepancy in data aiming to link physiological conditions to CAG repeat length.
Key Words: androgen receptor/function/polymorphism
Submitted on September 14, 2009; resubmitted on October 26, 2009; accepted on October 29, 2009.