A study of androgen-resistant subjects indicates that the 6.7 pI/56 kDa protein in genital skin fibroblasts is related to the androgen receptor.

Two-dimensional gel electrophoresis of cultured human skin fibroblast lysates reveals a silver-stained "spot" of molecular mass 56 kilodaltons (kDa) and isoelectric point (pI) 6.7, occasionally as part of a doublet with a minor pI 6.5 partner. Its presence in each of 23 genital skin fibroblast strains (6 labium majus, 17 prepuce) and its absence in 30 of 32 control non-genital skin fibroblast strains accords with the 3-fold greater concentration of androgen-receptor activity in the former. However, the size and intensity of the spot do not change when cells are preincubated for 48 hours with 3 nM methyltrienolone (MT, a non-metabolizable androgen), and it is pulse-labeled with [35S]methionine to an autoradiographically equal extent, with or without incubation in 3 nM MT for 2 or 16 hours. Furthermore, the protein identified by the spot is found in the labium majus skin fibroblast strains from 2 of 12 unrelated subjects with complete androgen resistance due to negligible androgen-receptor activity, but it is absent from those of 2 others who have the same phenotype despite a normal level of qualitatively abnormal androgen-receptor activity. Hence, it is very unlikely to be an androgen-induced protein, and it cannot be a functional version of the androgen receptor itself. Its absence in 12 of 14 labium majus strains of subjects with complete androgen resistance, regardless of 5 alpha-reductase activities, indicates that it is neither a constitutive cytotypic marker of genital skin fibroblast differentiation nor a reflection of that enzyme. When intact prepuce fibroblasts are covalently labeled by photolysis with 50 nM [3H]MT, the only specific labeling detectable after two-dimensional electrophoresis is in the 6.7 and 6.5 pI doublet of the 56 kDa protein. Considering the sensitivity of silver staining and the incomplete concordance between the androgen-receptor activity of a strain and the size/intensity of its 6.7 pI/56 kDa spot on the gels, we postulate the latter to be a comparatively abundant androgen-binding protein that is causally related to the androgen receptor. The precise nature of this relation remains to be elucidated by use of novel immunologic and/or nucleic acid probes for this protein and for the mature androgen receptor. In any event, the presence or absence of the 6.7 pI/56 kDa protein in genital skin fibroblast lysates is a new marker of genetic heterogeneity within the class of complete androgen resistance.