LNCaP tumor cells, derived from a metastatic lesion of a human prostatic carcinoma, are androgen-sensitive in cell culture. Although increase in growth rate is observed with low doses of progestagens or estradiol, these cells contain exclusively androgen receptors. In the present study the binding affinity of different ligands for both non-DNA- and DNA-binding (transformed) forms of the androgen receptor were analyzed. The cytosolic (non-transformed) form of the receptor displayed an abnormal high affinity for progestagens and estradiol when compared with the cytosolic androgen receptor from other sources. Subsequently the non-transformed forms of the androgen receptor obtained from LNCaP cell nuclei was studied. A high binding affinity was found not only for dihydrotestosterone, but also for progesterone and the synthetic progestagen R5020 (relative binding affinity 42% and 10% of dihydrotestosterone). The binding characteristics of the transformed androgen receptor were examined in intact cells at 37 degrees C. LNCaP cells were compared in this respect with COS cells containing the cloned human androgen receptor, normal human skin fibroblasts and PC3 (prostate) and NHIK (cervix) human tumor cell lines. The affinity of the transformed androgen receptors for the progestagen R5020 in LNCaP cells was significantly higher than in the other cell systems, although the differences were less pronounced than for the non-transformed receptor form.
In conclusion: the LNCaP tumor cells contain an androgen receptor with an abnormal binding site. This might be due to a mutation and/or a post-transcriptional effect.