Specificity of glucuronosyltransferase activity in the human cancer cell line LNCaP, evidence for the presence of at least two glucuronosyltransferase enzymes

Recent findings obtained by our group showed that incubation of LNCaP cells with labeled steroids leads to the formation of 3- and 17-hydroxysteroid glucuronides. In this study, the specificity and the kinetic properties of 3-hydroxy-C(19)steroid uridine diphospho-glucuronosyltransferase (3-OH-UGT) and 17-hydroxy-C-19 steroid UGT (17-OH-UGT) activities in LNCaP cells were investigated. Results indicate that the UGT has a high affinity for testosterone, dihydrotestosterone (DHT), androsterone (ADT) and androstane-3 alpha,17 beta-diol (3 alpha-DIOL), with K-m values ranging from 0.25 to 0.68 mu M. The K-m values are approx. 10-fold higher for androst-5-ene-3 beta,17 beta-diol (5-ene-DIOL) and androstane-3 beta,17 beta-diol (3 beta-DIOL). The relative specificities (V-max/K-m) also showed higher turnover rates for testosterone, DHT, ADT and 3 alpha-DIOL with values ranging from 2.93 to 5.71, than for 3 beta-DIOL and 5-ene-DIOL with ratios of 0.41 and 1.10, respectively. Dixon plot and Cornish-Bowden analysis demonstrate that testosterone, DHT, ADT, and 3 alpha-DIOL inhibit the glucuronidation of DHT and ADT in a competitive fashion. In contrast, when the studies are performed with 3 beta-diol and 5-ene-DIOL the inhibition of ADT glucuronidation is uncompetitive while the glucuronidation of DHT is inhibited competitively, suggesting the presence of two UGT enzymes, one for glucuronidation of the 17 beta-OH group and a second for the 3 alpha-OH group. Further evidence for the presence of two UGTs in LNCaP cells was obtained by incubation with a variety of 3 beta-OH-C-19 steroids which caused a marked inhibition of DHT-G formation but had no effect on the glucuronidation of ADT. In summary, our data demonstrate the presence of at least two UGTs in the human prostate cancer cell line LNCaP. The relative specificity of the 17-OH-UGT in LNCaP cells is 3 alpha-DIOL > DHT > testosterone, while ADT is glucuronidated by the 3-OH-UGT.