Defective activation of androgen-receptor complexes a marker of androgen insensitivity

Abstract

Partially-purified 5α-dihydrotestosterone-receptor (DHT-R) complexes, extracted from normal genital skin fibroblasts (GSF) previously labelled with [ 3H]DHT, dissociate with monophasic kinetics and dissociation rate constants ( k −2) of 10, 6, 3 and 2 × 10 −3 min −1 at 40, 37, 32 and 29°C, respectively. An Arrhenius plot yields an activation energy of 28 kcal/mole. We studied 2 subjects who have constitutional androgen insensitivity (AI) despite a normal level of specific DHT-R activity in their GSF. Subject 1 has complete AI and unambiguous female external genitalia; subject 2 has partial AI and had ambiguous external genitalia at birth. In contrast to normal, the DHT-R complexes extracted from the GSF of these 2 subjects dissociate with biphasic kinetics. At 37°C the k −1 of their early (‘fast’) component is 21 ± 0.4 (±SEM) × 10 −3min −1 ( n = 7), while that of their late (‘slow’) component ( k −2) is 7.8 ± 0.3 × 10 −3min −1 ( n = 7). The latter value is very similar to the single k −2 (6.1 ± 0.1 × 10 −3min −1, n = 9) of the DHT-R complexes extracted from normal fibroblasts. When dissociation of DHT-R complexes is studied within intact fibroblasts, monophasic kinetics are observed for both the normal and mutant subjects. A k −2 of 18 × 10 −3min −1 was previously observed for both mutant subjects at 37°C (normal: k −2, 5.9 ± 0.3 × 10 −3min −1, n = 15). At 40°C subject 1 has a rate constant of 25 while that of subject 2 is 50 × 10 −3 min −1 (normal: 10 × 10 −3 min −1). An Arrhenius plot of the results from subject 1 yields an activation energy of 18 kcal/mole. The 2 sets of data suggest that inability of DHT-R complexes to transform from a rapidly-dissociating to a slowly-dissociating form within intact target cells is a marker of genetic mutations that alter the androgen receptor and thereby cause certain types of partial or complete AI.