Androgen regulates MMTV RNA in the short-term in S115 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.

Antiandrogen action in the development of androgen insensitivity in S115 mouse mammary tumour cells

Endocrine therapy for steroid-sensitive tumours often involves administration of steroid antagonists which are designed to bind to the steroid receptor and block steroid action. However, the clinical problem remains the temporary nature of the tumour regression. Since in vitro models suggest that steroid ablation itself can result in loss of steroid sensitivity of tumour cells, these studies aimed to investigate the influence of the antiandrogen ICI 141,307 on this progression. This antiandrogen exhibits both agonist and antagonist actions on androgen-regulated cellular and molecular parameters of S115 mouse mammary tumour cells in culture. Its ability to regulate mouse mammary tumour virus (MMTV) RNA production in these cells confirms that the antiandrogen-receptor complex can not only bind to the steroid response element (SRE) in the MMTV DNA sequences but also activate gene transcription. Despite these molecular abilities of this antiandrogen, it was still unable to maintain androgen sensitivity in the long term. It was able to delay progression to insensitivity of the various steroid-regulated parameters, although the different parameters were delayed for different lengths of time, but ultimately the antiandrogen was unable to prevent loss of any parameters. It is thus concluded that the nature of the ligand is critical for maintenance of steroid sensitivity: only androgen and not antiandrogen will maintain long-term response. Previous molecular models for loss of steroid response suggest that it could result from inactivation of SRE in the genome when no receptor complex is bound. However, loss of response occurred in these experiments even in the presence of an activated receptor complex capable of binding to the SRE. Possible molecular mechanisms and the clinical implications are discussed.

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.

Androgen regulation of the mRNA encoding a major protein of the mouse vas deferens

A cDNA encoding the major mouse vas deferens protein (MVDP) has been cloned and characterized. Using in situ hybridization we have identified the epithelial cells of the vas deferens as the site of synthesis of MVDP mRNA. Northern blot analysis suggests that a high level of an mRNA corresponding to the MVDP gene is present in the mouse vas deferens whereas the amount of MVDP mRNA in vas deferens of other species studied, or in other mouse tissues, even if present, is undetectable. Steady-state levels of MVDP mRNA are decreased by approximately 42% 3 days after castration but a significant hybridization signal is still observed even 50 days after castration. Testosterone treatment for 2 weeks is necessary to completely reverse the effect of castration. In vitro transcription assays on isolated nuclei showed that the hormonal induction of the MVDP gene is achieved mainly at transcriptional level.

Antiandrogen ICI 176,334 does not prevent development of androgen insensitivity in S115 mouse mammary tumour cells

Many forms of endocrine therapy for steroid-sensitive tumours involve regimes of steroid agonist deprivation by administration of steroid antagonists. The partial or short-lived response to such therapy results from the inevitable progression of the tumour cells to a state of steroid insensitivity. Several cell culture systems have shown that steroid ablation results in loss of steroid sensitivity and we have used an in vitro model here to study the influence of steroid antagonists on this progression. Growth of androgen-responsive S115 mouse mammary tumour cells in the long-term absence of steroid results in a loss of androgen-sensitivity. We have studied here the effects of the pure antiandrogen ICI 176,334 on the growth of S115 cells and on their progression to steroid autonomy. Although a pure antiandrogen in its action on these cells with very low toxicity, it had no protective effect against loss of cellular or molecular androgen-responsive parameters. The clinical implications for endocrine therapy are discussed.

Temperature-sensitive mutants for steroid-sensitive growth of S115 mouse mammary tumor cells

We have generated temperature-sensitive (ts) mutants for steroid-regulated anchorage-independent cell growth. Androgen-responsive S115+A mouse mammary tumor cells were mutagenized with ethyl methane sulfonate and the variants which were growth-arrested in suspension at the nonpermissive temperature of 41 degrees C were selected by killing dividing wild-type cells with the DNA synthesis inhibitors 5-fluoro-2'-deoxyuridine or cytosine arabinoside. Fifteen clones were isolated and characterized for morphology and growth properties. Three (ts21, ts27, ts33) of the phenotypic variants were ts for androgen-maintained anchorage-independent growth, two of them (ts27 and ts33) also for growth in monolayer. Growth arrest at 41 degrees C was not due to a defect in androgen receptor function in any of the mutant cell lines as shown by steroid binding assays and by the androgen-stimulated expression of both endogenous MMTV RNA and the transiently transfected LTR-CAT gene at the nonpermissive temperature. It remains to be determined for clone ts33 whether the defect is in postreceptor events of steroid action or in genes affecting general mechanisms of cell growth. However, since in clones ts21 and ts27 general cell growth remains functional at 41 degrees C under serum stimulation, defects may be in postreceptor steroid-related pathways. It is hoped that these mutants will provide a useful tool for study of steroid regulation of cell growth and in particular of the property of anchorage-independent growth.

Acquired expression of hst-1 in an autonomous subline (Chiba subline 2) derived from androgen-responsive mouse mammary tumor (Shionogi carcinoma 115)

Since growth of Shionogi Carcinoma 115 (SC 115) and its autonomous subline (CS 2) were regulated by fibroblast growth factor-like peptide, expression of int-2 and hst-1 was examined in these cell lines. Hybridization of genomic DNA with long terminal repeat of mouse mammary tumor virus (MMTV) revealed the same pattern of restriction fragments, showing the same integration of MMTV. Although weak expression of int-2 was noticed in the two cells, clear expression of hst-1 was seen only in CS 2 cultured with/without testosterone. It is suggested that autonomous growth of androgen-unresponsive CS 2 is connected with expression of hst-1.

Binding of androgen-receptor complexes to alpha 2u-globulin genes and to the long terminal repeat of mouse mammary tumor virus

The binding of androgen-receptor complexes to fragments derived from two alpha 2u-globulin genes (RAP 01 and RAO 01) was studied using a DNA-cellulose competition assay. Rat prostate cytosol labelled with [3H]mibolerone was used as a source of the androgen receptor. Two controls were included in these studies: the long terminal repeat (LTR) of mouse mammary tumor virus which has previously been shown to act as an androgen response element and a fragment of the C3 gene of prostatic binding protein which has been demonstrated to bind androgen-receptor complexes. Our experiments indicate that androgen-receptor complexes bind specifically and with comparable affinity to the C3 gene fragment, the LTR and a fragment of RAP 01 located in the 5'-upstream region (bp -642 up to -584). No specific interaction was observed with fragments derived from RAO 01. The region of RAP 01 which binds androgen-receptor complexes has previously been shown to interact with glucocorticoid receptors and contains a 17 bp sequence homologous with the consensus sequence for glucocorticoid-receptor binding. A mutation in this sequence in RAO 01 may be responsible for the loss of glucocorticoid and androgen-receptor binding. It is concluded that at least one member of the alpha 2u-globulin gene family interacts directly with androgen-receptor complexes with an affinity comparable to that observed for other androgen-dependent genes. The binding is observed in a region displaying also affinity for the glucocorticoid receptor.

Control of spontaneous glucose intolerance, hyperinsulinemia, and islet hyperplasia in nonobese C3H.SW male mice by Y-linked locus and adrenal gland

An inbred strain predisposition to maturity-onset impairment of glucose tolerance was discovered in C3H.SW/SnJ inbred male mice. Males were group-caged from weaning and subjected to repetitive handling stress; deterioration of glucose tolerance developed between 5 and 8 months of age in association with extreme hyperinsulinemia. Some males developed transient chemical diabetes in which plasma glucose concentrations were inappropriately high in relation to the high levels of plasma insulin. By 12 months of age, males previously glucose intolerant had regained a normal glucose tolerance. At death, a massive hypertrophy and hyperplasia of the islet beta-cells was documented in these mice. The impaired glucose tolerance could be circumvented by adrenalectomy at weaning. Although these finding suggested the presence of an obesity gene, the C3H.SW group-caged males were not obese when compared with C3HeB/FeJ males which, although moderately hyperinsulinemic, did not develop the glucose intolerance syndrome. Transfer of the Y chromosome from the C3HeB/FeChp background into the C3H.SW inbred background led to a reduction in the hyperinsulinemic and hyperglycemic stress on the pancreatic islets. Thus the extrinsic environment (caging and handling stress), mediated in part via the adrenal gland, could interact with sex-linked genetic susceptibility modifiers to stimulate hyperplasia of the pancreatic islets and produce a transient insulin resistant state of impaired glucose tolerance in the absence of obesity.

Role of receptor occupancy in the transition from responsive to unresponsive states in cultured breast tumor cells

Progression from a steroid sensitive to insensitive state is characteristic of breast tumors, but little is known about the molecular mechanisms involved. Changes in steroid receptor can be associated with the progression. This paper reviews the cell culture data pertaining to loss of response and concludes that loss of receptor is a consequence rather than a cause of insensitivity. This view is based on evidence that loss of all response parameters occurs despite the presence of fully functional receptors as determined by transfection experiments. The postreceptor defect appears to be at the level of the hormone response element of the responsive genes and may involve DNA methylation. The implications of the model for human breast cancer biology are discussed.

Interaction of different steroid hormones during progression of tumour cells to steroid autonomy

Progression to steroid insensitivity poses a major problem in therapy of breast cancer, but studies of the origin of steroid-insensitive cells have been few and have concentrated in any one system on the loss of response to only one steroid. Since both normal and tumour mammary cells have complex endocrine requirements, we wondered how different steroids might interact during loss of steroid sensitivity. Cloned cells from the androgen-responsive Shionogi 115 mouse mammary carcinoma respond in vitro to both androgens and glucocorticoids in terms of both cellular and molecular parameters but, following prolonged absence of any steroid, these cells become unresponsive. We show here that 2 steroids can interact to prevent the progression to steroid insensitivity since the S115 cells can be protected against any loss of response to either androgen or glucocorticoid with either steroid alone. Androgen protects against loss of glucocorticoid sensitivity and glucocorticoid protects against loss of androgen sensitivity. The clinical implications are discussed.

Androgen regulated expression of a spermine binding protein gene in mouse ventral prostate

A full length cDNA (MP25) encoding the major mouse prostatic secretory glycoprotein (p25), whose expression is androgen dependent, has been cloned and characterised. Steady-state levels of mRNA are decreased approximately 100-fold after 3 days castration but are restored progressively over 4 days with testosterone treatment. The secreted glycoprotein appears to be a spermine binding protein since the nucleotide and predicted amino acid sequence of MP25 shares extensive homology with a spermine binding protein (SBP) found in rat ventral prostate. Genomic clones indicate that there is a single gene for SBP which consists of 4 exons, the first of which is only 11bp in length. The second exon encodes the signal peptide, the third contains a portion of the spermine binding protein unique to the mouse and the largest exon encodes the bulk of the secreted protein.

Androgen regulation by the long terminal repeat of mouse mammary tumor virus

Mouse mammary tumor virus (MMTV) has long been implicated in mouse mammary carcinogenesis, and it is now well established that the long terminal repeat (LTR) contains regulatory sequences responsible for glucocorticoid-mediated induction of viral RNA. However, we have demonstrated previously that androgens as well as glucocorticoids can regulate MMTV RNA in the S115 mouse mammary tumor cell line. To determine if androgens act directly on the LTR in these cells, plasmids were constructed with the MMTV LTR joined to the coding sequences of genes not normally expressed in the cells. Following transfection of these chimeric genes into S115 cells, we show that the expression of the genes is regulated by both androgens and glucocorticoids. Furthermore, hormonal regulation is also conferred by the LTR on the neighboring guanine phosphoribosyltransferase (gpt) gene. Thus, androgens can act on the LTR of MMTV when the appropriate receptors are present in the cells, and this interaction can influence the expression of additional adjacent genes.

Androgen regulation by the long terminal repeat of mouse mammary tumor virus

Mouse mammary tumor virus (MMTV) has long been implicated in mouse mammary carcinogenesis, and it is now well established that the long terminal repeat (LTR) contains regulatory sequences responsible for glucocorticoid-mediated induction of viral RNA. However, we have demonstrated previously that androgens as well as glucocorticoids can regulate MMTV RNA in the S115 mouse mammary tumor cell line. To determine if androgens act directly on the LTR in these cells, plasmids were constructed with the MMTV LTR joined to the coding sequences of genes not normally expressed in the cells. Following transfection of these chimeric genes into S115 cells, we show that the expression of the genes is regulated by both androgens and glucocorticoids. Furthermore, hormonal regulation is also conferred by the LTR on the neighboring guanine phosphoribosyltransferase (gpt) gene. Thus, androgens can act on the LTR of MMTV when the appropriate receptors are present in the cells, and this interaction can influence the expression of additional adjacent genes.

Steroid regulation of transfected genes in mouse mammary tumour cells

The regulation of mouse mammary tumour virus (MMTV) RNA by glucocorticoid hormones is well-established and has provided much information on how steroid hormones work. However, we have shown that androgens can also control MMTV RNA accumulation in S115 mouse mammary tumour cells. This novel androgen action could be explained on the basis that the MMTV long terminal repeat (LTR) can respond to several classes of steroid if appropriate receptors are present in the cells. We have used transfection experiments to demonstrate that androgens can act directly on the LTR in S115 cells. Hormonal regulation of transfected chimaeric genes into these cells was effected by androgen and glucocorticoid but not by oestrogen or progesterone, corresponding to the receptor status of the cells. Furthermore, hormonal control was also conferred by the LTR on expression of an independent cotransfected adjacent gene under its own separate promoter, suggesting that effects of an LTR can stretch to neighbouring genes in a type of hormone-enhancer insertion mechanism.