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

Surfactant synthesis within developing fetal lung type II cells is affected by testosterone and 5 alpha-dihydrotestosterone (5 alpha-DRT). The pulmona ry epithelial cell line A549, isolated from a human lung carcinoma, like no rmal lung type II cell, produces disaturated phosphatidylcholines and has b een widely used for studying the regulation of surfactant production. Andro gen receptor has been detected in A549 cells; however, the capacity of thes e cells for androgen synthesis and metabolism has not been investigated at molecular level. This study was undertaken to identify the steroidogenic en zymes involved in the formation and metabolism of androgens from adrenal C1 9 steroid precursors in A549 cells. When cultured in the presence of normal FCS, A549 intact cells converted DHEA to androstenediol, androstenedione p rincipally to testosterone, and 5 alpha-DHT to 5 alpha-androstane 3 alpha,1 7 beta-diol. High levels of 17 beta-hydroxysteroid dehydrogenase (HSD) and 3 alpha-HSD activities were detected in both cytosol and microsomes isolate d from homogenates. Analysis of A549 RNA indicated the presence of 17 beta- HSD type 4 and type 5, and of 3 alpha-HSD type 3 messenger RNAs. Very low l evels of 3 beta-HSD type 1 and 5 alpha-reductase type 1 messenger RNAs and activities were detected. With regard to active androgen formation, there w as little or no capacity for the conversion of DHEA to 5 alpha-DHT. In cont rast, 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 sh ow that A549 cells express a pattern of steroid metabolism in which 17 beta -HSD type 5 and 3 alpha-HSD type 3 are the predominant enzymes. The level o f androgens is regulated at the level of catalysis in intact cells such tha t the intracellular level of testosterone is stabilized, whereas 5 alpha-DH T is rapidly inactivated by reduction to 3 alpha,17 beta-diol. This pattern of androgen metabolism has implications for the relative importance of tes tosterone and 5 alpha-DHT in normal lung development and surfactant product ion.