Androgen formation and metabolism in the pulmonary epithelial cell line A549: expression of 17beta-hydroxysteroid dehydrogenase type 5 and 3alpha-hydroxysteroid dehydrogenase type 3.

Surfactant synthesis within developing fetal lung type II cells is affected by testosterone and 5alpha-dihydrotestosterone (5alpha-DHT). The pulmonary epithelial cell line A549, isolated from a human lung carcinoma, like normal lung type II cell, produces disaturated phosphatidylcholines and has been widely used for studying the regulation of surfactant production. Androgen receptor has been detected in A549 cells; however, the capacity of these cells for androgen synthesis and metabolism has not been investigated at molecular level. This study was undertaken to identify the steroidogenic enzymes involved in the formation and metabolism of androgens from adrenal C19 steroid precursors in A549 cells. When cultured in the presence of normal FCS, A549 intact cells converted DHEA to androstenediol, androstenedione principally to testosterone, and 5alpha-DHT to 5alpha-androstane 3alpha,17beta-diol. High levels of 17beta-hydroxysteroid dehydrogenase (HSD) and 3alpha-HSD activities were detected in both cytosol and microsomes isolated from homogenates. Analysis of A549 RNA indicated the presence of 17beta-HSD type 4 and type 5, and of 3alpha-HSD type 3 messenger RNAs. Very low levels of 3beta-HSD type 1 and 5alpha-reductase type 1 messenger RNAs and activities were detected. With regard to active androgen formation, there was little or no capacity for the conversion of DHEA to 5alpha-DHT. In contrast, androstenedione was rapidly transformed to testosterone. The pattern of steroid metabolism was not affected by the use of charcoal-stripped FCS or by the synthetic glucocorticoid dexamethasone. Together, our findings show that A549 cells express a pattern of steroid metabolism in which 17beta-HSD type 5 and 3alpha-HSD type 3 are the predominant enzymes. The level of androgens is regulated at the level of catalysis in intact cells such that the intracellular level of testosterone is stabilized, whereas 5alpha-DHT is rapidly inactivated by reduction to 3alpha,17beta-diol. This pattern of androgen metabolism has implications for the relative importance of testosterone and 5alpha-DHT in normal lung development and surfactant production.