Steroid regulation of transfected genes in mouse mammary tumour cells

Steroid-involved transcriptional regulation of human genes encoding prostatic acid phosphatase, prostate-specific antigen, and prostate-specific glandular kallikrein

We have compared the steroid regulation of human genes encoding prostatic acid phosphatase (hPAP), prostate-specific antigen (hPSA), and prostate-specific glandular kallikrein (hK2) at the level of transcription. Reporter constructs of hPAP promoter covering the region -734/+467 were functional in both prostatic (LNCaP and PC-3) and nonprostatic (CV-1) cell lines in transient transfections. hPAP -231/+50 with eight identified transcription factor-binding sites showed the highest, and hPAP -734/+467 showed the lowest transcriptional activity in CV-1 cells. The hPAP promoter could not be induced with androgen, glucocorticoid, or progesterone, contrary to the hPSA (-620/+40) and hK2 (-493/+27) promoters in PC-3 cells cotransfected with the respective steroid receptor expression vector. Therefore, steroids cannot directly regulate hPAP gene expression via receptor binding to steroid response elements at -178 and +336, which have been shown to have androgen receptor-binding ability in vitro. Glucocorticoid was the most powerful activator of the hPSA construct at 10-nM steroid concentrations. On the contrary, glucocorticoid stimulation of the transcriptional activity of the hK2 construct was the weakest among the tested steroids. The results indicate that the steroid response elements in the proximal promoters of hPSA and hK2 genes are not androgen specific, offering the molecular basis for the expression of these genes outside the prostate in tissues containing steroid receptors.

Progression of androgen-sensitive mouse tumor (Shionogi carcinoma 115) to androgen-insensitive tumor after long-term removal of testosterone

Shionogi Carcinoma 115 (SC115) is an androgen-sensitive transplantable mouse tumor. To study the mode of progression from androgen-sensitive to -insensitive tumor, cloned SC115 cells were serially cultured without androgen. Shortly after withdrawal of androgen, SC115 cells showed markedly decreased growth, but growth resumed gradually with loss of response to androgen and the cells 60 weeks after androgen removal [A(-)60 cells] grew faster than SC115 cells cultured in the presence of androgen. A(-)60 cells showed malignant phenotype with morphological changes and tumorigenicity in male and female mice. Although mRNA and binding capacity of androgen receptor were maintained, the cells after removal of androgen rapidly lost expression of mouse mammary tumor virus-related gene and the loss was irreversible in A(-)60 cells. The stimulating effect of basic fibroblast growth factor (bFGF) temporarily decreased, then recovered to the initial level after long-term androgen removal. This fluctuation of response to bFGF was accompanied with changes in the number of bFGF receptors and amount of bFGF-like substance(s) secreted. The substance(s) seemed to be an FGF-like growth factor different from known factors. It was concluded that progression of SC115 cells to androgen-insensitive ones under an androgen-deprived condition proceeded with adaptation by means of increases in production of an FGF-like growth factor and in binding capacity to this factor.

Maintenance of androgen-, glucocorticoid- or estrogen-responsive growth in shionogi carcinoma 115 subline sustained in castrated mice with high dose of estrogen for 30 generations (3 years)

Shionogi carcinoma 115 (SC115), an androgen-dependent mouse mammary tumor, rapidly loses its androgen responsiveness after androgen withdrawal. The growth of this tumor can also be stimulated by high doses of estrogen or glucocorticoid. In the present study, the maintenance of hormone-responsive growth of SC115 tumors with a high dose of estrogen was examined in castrated male mice using an SC115 subline obtained by serial transplantations of SC115 tumors in estrogen-treated castrated mice for 3 years (30 generations) (subline E2). Seed tumors from both SC115 and subline E2 could rapidly grow in castrated mice given daily injections of testosterone propionate (TP), 17 beta-estradiol (E2), or dexamethasone (Dex) (100 micrograms/mouse/day) but not in those given vehicle alone. Although SC115 and subline-E2 tumors grown with TP or Dex showed temporary regression after steroid withdrawal, the tumors grown with E2 did not show such temporary regression. The TP-, E2-, or Dex-induced growth of subline-E2 tumors was almost the same as that of the original SC115 tumors. However, responsiveness to androgen, estrogen or glucocorticoid of both tumors disappeared within one passage in steroid-depleted castrated mice. The present findings demonstrate that the loss of responsiveness to androgen as well as to high doses of estrogen or glucocorticoid of SC115 tumors can be prevented in castrated mice not only with androgen but also with high doses of estrogen.

Non-classical androgenic actions of RU38486 in androgen-responsive Shionogi carcinoma 115 cells in serum-free culture

Antiglucocorticoid and antiprogestin RU38486 (RU486) stimulated the growth of highly androgen- and moderately glucocorticoid-sensitive SC-3 cells (a cloned cell line from Shionogi mouse mammary carcinoma 115) in a dose-dependent manner. A maximal 8-fold stimulation of growth by RU486 has been observed at 10(-7) M in a serum-free medium and its potency has been found to be almost the same as that of dexamethasone (Dex). The growth rate of SC-3 cells treated by triamcinolone acetonide (TA) or Dex combined with RU486 at 10(-9)-10(-7) M was enhanced compared to cells treated by TA or Dex alone, indicating that RU486 had additive rather than antagonistic effects. Our previous study revealed that RU486 could compete with the specific uptake of [3H]testosterone in intact SC-3 cells at relatively low affinity and the present study showed that the stimulatory effect of RU486 on the growth of SC-3 cells was significantly inhibited by pure antiandrogen flutamine and that half-maximal inhibition by flutamine was achieved at 10(-6) M. Moreover, we demonstrated that the conditioned medium from RU486-stimulated SC-3 cells contained growth-promoting activity which caused a 3.5-fold increase in DNA synthesis by SC-3 cells in the absence of RU486 and which was abolished by treatment with heparin-Sepharose. These results indicate that RU486-induced growth of SC-3 cells may be expressed as an androgenic activity through androgen receptor and mediated by a heparin-binding growth factor.

Characterization and expression of the prostatic arginine esterase gene, a canine glandular kallikrein

The prostatic arginine esterase gene was isolated from a genomic library prepared with dog liver DNA in lambda EMBL3. The selected clone contained an insert of approximately 17 kb which included the whole coding portion of arginine esterase mRNA (5 exons plus 4 introns), 2 kb upstream from the initiation site and 12 kb downstream from the polyadenylation site. The intron-exon boundaries were identical to all known mammalian kallikrein genes. The deduced amino acid sequence indicated a high degree of identity (51-61%) with other kallikreins expressed not only in the prostate but also in the pancreas of various animal species. The 5'-flanking sequences contained potential regulatory elements such as a variant TATA box (TTTAAA), a CCAAT box, a SP1 transcriptional factor binding site (GGGCGG), and two TGTCCT motifs resembling glucocorticoid response elements. Southern blot analysis with an amplified cDNA fragment of 487 bp corresponding to the 5' portion of the mRNA and with a DNA probe from a different portion of the arginine esterase gene indicated the presence of two to three homologous genes in the canine genome while in a previous study a single band was detected using a 400-bp arginine esterase cDNA corresponding to the 3' portion of the mRNA. These results suggest that the arginine esterase gene belongs to a small kallikrein gene family. Arginine esterase mRNA is expressed primarily in the prostate but also at an extremely low level (approximately a thousandfold less) in several other tissues including the liver, the gracilis thigh muscle, the kidney, and the pancreas.