Biomedical subjects

N Bruchovsky

Publications and source records attributed to N Bruchovsky.

At least 37 records · Page 2Linked to original sources

PubMed1997

Evaluation and follow-up of patients with N1-3 M0 or NXM1 prostate cancer in phase III trials.

OBJECTIVES: The aim of this discussion is to review the design and conduct of phase III trials in metastatic prostate cancer, to seek ways of improving their study design, accuracy, relevance to clinical practice, acceptability to patients, and ease of participation by clinicians. We also aim to try to set uniform definitions for the evaluation of the different endpoints used in clinical trials on metastasized prostate cancer. METHODS: The work was started by correspondence between the participants in the group for the year before the consensus meeting. Two comprehensive questionnaires were circulated and the answers were distributed to all the members of the group. The statements were finalized during the consensus meeting. RESULTS: There were some differing opinions concerning the methods of evaluation of endpoints for follow-up, such as time to tumor progression and time to treatment failure. After the consensus conference, there were no major disagreements within the group. CONCLUSIONS: The aim of phase III trials is to influence clinical management. To obtain a credible result they require a sound statistical basis with appropriate power and encompassing patients from small urologic practices as well as large or academic institutions. However, deviation from routine practice may affect the accrual rate, and the trial procedure should therefore be as similar as possible to routine management. Trials inevitably involve extra work and cost. Both should be kept to a minimum to encourage participation and hasten a timely conclusion. It is mandatory to create uniform ways of designing and evaluating clinical trials in prostate cancer.

Clinical Trials, Phase III as Topic↗

PubMed1997

Increased cystine uptake capability associated with malignant progression of Nb2 lymphoma cells.

Analysis of rat, pre-T cell 'Nb2 lymphoma' sublines, manifesting different degrees of malignant progression, can indicate phenotypic changes potentially useful as therapeutic targets. In this study, the prolactin (cytokine)-dependent Nb2-11 and autonomous Nb2-SFJCD1 sublines were compared for in vitro thiol growth requirements. Whereas Nb2-11 culture growth depended on 2-mercaptoethanol (2-ME; 33-100 microM), Nb2-SFJCD1 cells were 2-ME-independent. This difference stemmed from differential uptake of exogenous L-cystine, critically required for proliferation. Uptake of 35S-L-cystine (10 microCi/ml; 40 microM) showed Nb2-11 cells had low cystine uptake capability; 2-ME enhanced cystine uptake to growth-sustaining levels. Nb2-SFJCD1 cells did not require 2-ME due to intrinsic, 11-fold higher cystine uptake via the x(c)- cystine/glutamate transport system. In absence of 2-ME, monosodium glutamate abrogated Nb2-SFJCD1 proliferation by specifically inhibiting cystine uptake (85% at 10 mM). Elevated glutathione (GSH) levels were not essential for growth of either line as shown with L-buthionine-(S,R)-sulfoximine (0.1-4 mM) treatment. The cyst(e)ine requirement therefore did not primarily involve maintenance of normal GSH levels, reported critical for T lymphocyte replication. These and other results suggest increased cystine uptake capability constitutes another potential step in progression of T cell cancers which is not coupled to cytokine autonomy or metastatic ability development. The x(c)- transport system apparently provides a novel target for T cell cancer therapy. Its inhibition would suppress cystine uptake by certain progressed cells, and also interfere with cystine uptake, and subsequent cysteine release, by eg macrophages, thought to have a role in cysteine delivery to lymphoid cells.

Animals↗

PubMed1997

Neoadjuvant androgen withdrawal therapy decreases local recurrence rates following tumor excision in the Shionogi tumor model.

PURPOSE: The role of neoadjuvant androgen withdrawal before radical prostatectomy continues to be defined and remains investigational. It is unknown whether decreases in positive margin rates will translate into lower biochemical and local recurrence rates until long-term followup is available. We determined whether local recurrence rates after tumor excision were less with neoadjuvant compared to adjuvant androgen ablation in the Shionogi tumor model. Androgen withdrawal in this model triggers apoptosis and complete tumor regression but rapidly growing androgen independent tumors inevitably recur after 1 month. Conceptually, the ideal time for excision is after maximal castration induced tumor involution but before outgrowth of androgen resistant clones. MATERIALS AND METHODS: Shionogi tumors were allowed to grow to 1 to 2 gm. before mice were randomly assigned to group 1-tumor excision with wide margins and castration at tumor recurrence and group 2-neoadjuvant castration for 10 days followed by wide excision of the regressed tumor. RESULTS: Tumors recurred locally in 87% of group 1 mice after a median of 17 days (range 6 to 24) and all regressed completely with adjuvant castration. However, androgen independent tumors recurred in 92% of mice after a median of 36 days. In group 2 androgen independent disease recurred in 44% of mice after a median of 40 days. Tumor-free survival was significantly greater in group 2 than in group 1 (56 versus 20%, respectively, p <0.05). Inked surgical resection margins were positive in two-thirds of group 1 and one-third of group 2 mice. CONCLUSIONS: Neoadjuvant androgen withdrawal decreases local recurrence and positive margin rates by 50% after tumor excision in the Shionogi tumor model. Although this model cannot address the issue of effect of neoadjuvant therapy on subclinical metastases, extrapolation of these results to the clinical disease suggests that neoadjuvant therapy may help to decrease not only the positive margin rates but also the subsequent risk of local recurrence following radical prostatectomy.

Animals↗

PubMed1996

Intermittent androgen suppression delays progression to androgen-independent regulation of prostate-specific antigen gene in the LNCaP prostate tumour model.

In most patients with prostate cancer, continuous androgen suppression (CAS) therapy causes tumour regression and an accompanying decrease in serum prostate specific antigen (PSA). However, with tumour progression, regulation of both tumour growth and PSA gene expression becomes androgen-independent. Because androgen resistance develops, in part, from adaptive cell survival mechanisms activated by androgen withdrawal, we hypothesize that intermittent re-exposure to androgens may prolong time to androgen-independent progression. The objective of this study was to determine whether intermittent androgen suppression (IAS) could delay the onset of androgen-independent PSA gene regulation in LNCaP prostate tumour model when compared to CAS. Five or six cycles of IAS were possible before progression developed. IAS prolonged time to androgen-independent PSA gene regulation from an average of 26 days in CAS to 77 days in IAS. Serum PSA increased above pre-castrate levels in all mice treated with CAS by 28 days post-castration, but remained below pre-castrate levels in 75% of IAS-treated mice by 60 days post-castration. By 15 weeks post-castration, serum PSA levels increased 7-fold above pre-castrate levels in CAS-treated mice compared to 1.9-fold increase in IAS-treated mice. PSA mRNA expression levels highly correlated with serum PSA levels in both groups. Maintenance of androgen dependency through IAS may be due to androgen-induced differentiation and/or down-regulation of androgen-suppressed gene expression.

Androgens↗

PubMed1996

Characterization of type I 5 alpha-reductase activity in DU145 human prostatic adenocarcinoma cells.

The conversion of testosterone (T) to dihydrotestosterone (DHT) has been demonstrated to be catalysed by at least two isoforms of human steroid 5 alpha-reductase, designated types I and II. Type II 5 alpha-reductase expression predominates in human accessory sex tissues, localized to the fibromuscular stromal compartment. The type I isoform predominates in skin, prostatic epithelia and, to a lesser extent, in prostatic fibromuscular stroma. The significance of the type I isoform to prostatic cellular growth and function remains undefined. In cultured DU145 cells, we evaluated the metabolism of [14C]-T and demonstrated the time-dependent formation of [14C]-DHT. Oxidative metabolism (conversion of [14C]-T to [14C]-androstenedione) and the formation of conjugated androgen metabolites occurred at a relatively low rate in the DU145 cells. Using human type I 5 alpha-reductase cDNA, Northern blot analysis of DU145 cell mRNA revealed high levels of type I isoform expression. Analogous probing of the DU145 cells with a human 5 alpha-reductase II cDNA failed to reveal expression of the type II isoform. The expression of functional type I activity has been confirmed pharmacologically using isoform-selective 5 alpha-reductase inhibitors. Reductive metabolism of [3H]-T in the DU145 cells was inhibited in a concentration-dependent manner by LY306089, a potent non-steroidal type I-selective inhibitor (IC50 = 10.0 nM). SKF105657, a steroidal type II-specific inhibitor was distinctly less active at inhibiting [3H]-DHT formation. LY306089 was a non-competitive inhibitor of type I 5 alpha-reductase in DU145 cellular homogenates with an apparent Ki value of 4.0 nM. These studies have identified and pharmacologically defined type I 5 alpha-reductase activity in an androgen-insensitive prostatic cancer cell line and provide the basis for additional investigations into the significance of type I 5 alpha-reductase to human prostatic pathophysiology.

3-Oxo-5-alpha-Steroid 4-Dehydrogenase↗

PubMed1996

Low-dose cyproterone acetate plus mini-dose diethylstilbestrol--a protocol for reversible medical castration.

OBJECTIVES: To determine whether a low dose of cyproterone acetate (CPA) (50 mg twice a day) with minidose diethylstilbesterol (DES) is efficacious in rapidly reducing and maintaining serum testosterone at less than 10% of pretreatment level and whether the effect is reversible upon cessation of therapy. METHODS: Data were collected prospectively on 62 subjects, aged 50 to 90 years (mean 69) with histologically confirmed prostate cancer and normal serum testosterone levels. Treatment was initiated with CPA 50 mg twice a day plus DES 0.11 mg once a day, both administered orally, and continued or 6 months unless discontinued for reasons unrelated to the study. Subsequent management was at the discretion of the investigator/managing physician. Treatment was discontinued with determination of at least one follow-up testosterone level in 28 patients. RESULTS: Mean pretreatment testosterone level was 13.8 nmol/L (range 4.5 to 46.6, median 14.0, 95% confidence interval [CI] 12.0 to 15.0). Testosterone dropped to a mean of 0.6 nmol/L (range 0.1 to 2.2, median 0.5, 95% CI 0.4 to 0.6) by first follow-up (usually 1 month) in all patients (P <0.001) and remained at this level as long as treatment continued. Testosterone normalized in all subjects whose treatment was discontinued. Side effects were minimal. CONCLUSIONS: An oral dosage of CPA of 50 mg twice a day in combination with a mini-dose of DES results in rapid and reversible reduction in serum testosterone to castrate levels. This regimen minimizes morbidity and monetary costs of therapy and allows the implementation of novel treatment approaches such as intermittent or neoadjuvant withdrawal therapy.

Aged↗

PubMed1996

Induction of cell-free, in vitro transcription by recombinant androgen receptor peptides.

An in vitro, cell-free transcription system, based on prostate-derived transcriptional machinery and very powerful androgen response elements (AREs), has been developed. Multiple (p(ARR3)LovTATA) AREs from the androgen-regulated probasin gene were linked to G-free cassettes and used in nuclear extracts prepared from prostate carcinoma cell lines (PC3 and LNCaP cells) to test specific induction of transcription by full-length AR and by glutathione-S-transferase (GST)-fusion peptides in which the androgen receptor (AR) DNA-binding domain alone (AR524-649), or together with the ligand-binding domain (AR524-902), or a portion of the NH2-terminal domain (AR232-649) were incorporated. In the presence of AR, nuclear extracts from PC3 cells had greater activity in supporting transcription than those from LNCaP cells; and lower background activity than those from HeLa cells. All of the AR forms correctly initiated in vitro transcription of ARE-templates in an androgen-independent manner. The amount of specific, inducible transcript was dependent on the concentration of AR peptide present. AR524-902 was the most potent transactivator tested, with the maximal level of specific transcript over 900-fold higher than the minimal level. At all concentrations this peptide was three to four times more active than either AR524-649 or AR232-649. In conclusion, we have developed a very specific and sensitive cell-free transcription system for delineating trans-activational regions of the AR.

Androgen-Binding Protein↗

PubMed1996

Characterization of 5alpha-reductase gene expression in stroma and epithelium of human prostate.

The expression of 5alpha-reductase type 1 and type 2 isoenzymes in hyperplastic human prostate tissue and several human prostate cell lines was investigated by Northern blot analyses, reverse transcription-polymerase chain reaction (RT-PCR), and enzyme activity. Separation of stroma and epithelium was confirmed histologically and only preparations with no apparent contamination were employed in the subsequent studies. Poly(A)+ RNA was isolated from stromal and epithelial fractions and analysed by Northern blot and RT-PCR. Inhibition of epithelial and stromal 5alpha-reductase activities by 17beta-N,N-diethylcarbamoyl-4-methyl-4-aza-5alpha-androstan- 3-one (4MA) was assessed using a range of concentrations between 10(-13) and 10(-5) M. Results from Northern blot analyses and RT-PCR showed that the prostate stroma expressed 5alpha-reductase type 1 and type 2 isoenzymes, whereas the prostate epithelium only expressed 5alpha-reductase type 1. This was consistent with biphasic inhibition of 5alpha-reductase activity by 4MA in stroma and monophasic inhibition in epithelium. Cultured epithelial cells derived from human prostate only expressed 5alpha-reductase type 1 and had Vmax and Km values that approximated the lower end of the range reported for surgically removed prostate epithelium. The foregoing data explains the disparate activities of 5alpha-reductase, previously reported, in stroma and epithelium. The differential localization of these isoenzymes in the prostate suggests that future therapy of androgen-sensitive disease may be more successful through the use of selective inhibitors of the different 5alpha-reductase isoenzymes.

Aged↗

PubMed1996

Effects of intermittent androgen suppression on the stem cell composition and the expression of the TRPM-2 (clusterin) gene in the Shionogi carcinoma.

The proportion of tumorigenic stem cells and the expression of the apoptosis-related gene, TRPM-2 (clusterin), were studied in populations of Shionogi carcinoma cells subjected to multiple cycles of androgen withdrawal and replacement (intermittent androgen suppression). The parent androgen-dependent cell line was initially transplanted into a male mouse which was castrated when the estimated weight of the resultant tumour became approximately 3 g. After the tumour had regressed to 40% or less of the original weight, it was transplanted into the next non-castrated male. This was repeated for four cycles of transplantation and castration-induced apoptosis before the tumour progressed to an androgen-independent state. The proportion of total stem cells in the tumour, as determined by in vivo limiting dilution assays in male mice, was constant during the first three cycles but increased 15-fold between the third and fourth cycles. In the parent androgen-dependent tumour before androgen ablation, the androgen-independent stem cell population formed 0.8% of the total stem cell compartment. After the fourth cycle this population increased to 47%; a population of similar size (33%, P = 0.8) was found in the androgen-independent recurrent form of the tumour induced by one-time castration. Whether androgen withdrawal therapy was intermittent or continuous, conversion to androgen independence thus occurred when one-third to one-half of the total stem cell compartment was populated by androgen-independent stem cells. The androgen-repressed TRPM-2 (clusterin) gene was actively expressed in regressing tumours after androgen ablation, and also became constitutively expressed in non-regressing tumours after the first and subsequent cycles of androgen withdrawal. Staining of cytoplasm and nuclei with anti-clusterin antibody was observed in androgen-dependent tumour cells after each cycle of intermittent androgen suppression; the nuclear staining was more intense in recurrent androgen-independent cells. The anomalous nuclear localization of clusterin, an anti-cytolytic TRPM-2 encoded protein, may serve to inhibit early events in the apoptotic process and thereby foster the generation and outgrowth of androgen-independent stem cells in an androgen-depleted environment.

Androgens↗

PubMed1996

Biochemical and pathological effects of 8 months of neoadjuvant androgen withdrawal therapy before radical prostatectomy in patients with clinically confined prostate cancer.

PURPOSE: A prospective, nonrandomized trial was initiated to determine the duration of neoadjuvant therapy required for prostate specific antigen (PSA) to reach its nadir, evaluate the ability of an ultrasensitive assay to measure decreases in PSA less than 0.2 microgram./l., and characterize the effects of 8 months of neoadjuvant therapy on pathological stage, positive margin rates, proliferation and tumor marker immuno-staining. MATERIALS AND METHODS: We evaluated 50 patients with clinically localized prostate cancer treated by 8 months of reversible androgen ablation before radical prostatectomy. Serum PSA and testosterone levels were measured monthly. RESULTS: Serum PSA decreased by 84% after 1 month and by a further 52% between 3 and 8 months. Using an ultrasensitive assay, serum PSA decreased to undetectable levels (less than 0.1 microgram./l.) or reached its nadir in 22% of the cases after 3 months, 42% after 5 months and 84% after 8 months. Overall, the positive margin rate was 4%. Of the cases 68% were organ-confined and 24% were specimen-confined. The positive margin rate was not increased after reevaluation with cytokeratin, PSA and prostatic acid phosphatase immuno-staining but of 4 cases initially staged as P0 on hematoxylin and eosin evaluation 2 had microscopic foci of cancer with prostatic acid phosphatase staining. Immuno-staining with the proliferation markers proliferation cell nuclear antigen and Ki-67 showed decreased staining in surgical specimens relative to pretreatment needle biopsy specimens, which suggests that outgrowth of androgen independent clones does not develop during prolonged neoadjuvant therapy. CONCLUSIONS: Eight months of neoadjuvant androgen withdrawal therapy results in low positive margin rates and PSA nadir levels. The initial rapid decrease in PSA results from cessation of androgen regulated PSA synthesis and apoptosis, while the ongoing slower decrease reflects decreasing tumor volume.

Androgen Antagonists↗

PubMed1996

Control of tumor progression by maintenance of apoptosis.

The ability to induce multiple apoptotic regressions of an androgen-dependent tumor cell population by repeated cycles of androgen withdrawal and replacement may be advantageous in therapeutic strategies aimed at delaying or preventing tumor progression. With greater insight into factors that either initiate or limit apoptosis, more efficient application of intermittent therapy might be achieved, especially if methods could be devised to increase the length or number of treatment cycles. Both calreticulin and clusterin represent proteins with a potential role in the regulation of apoptosis. Calreticulin may inhibit target gene transcription by interacting with steroid hormone receptors, thereby masking their DNA-binding sites and triggering the onset of the apoptotic process. Clusterin, on the other hand, is a membrane-stabilizing protein that appears to be involved in limiting the autophagic lysis of epithelial cells during apoptosis. Also, the increasing tendency for nuclear localization of clusterin after androgen withdrawal may preserve the nuclear environment, limiting the lethal effect of treatment. Thus, tumor progression, characterized by the loss of apoptotic potential, appears to be linked in part to the inappropriate activation of TRPM-2 gene, which accounts for the constitutive expression of clusterin.

Amino Acid Sequence↗

PubMed1996

Optimal duration of neoadjuvant androgen withdrawal therapy before radical prostatectomy in clinically confined prostate cancer.

Experimental studies have shown that neoadjuvant androgen therapy dramatically reduces the rate of local recurrence after tumor excision. In the clinical setting, a 3-month course of neoadjuvant therapy before radical prostatectomy has been shown to significantly reduce positive margin rates, but follow-up is too short to assess the impact of such therapy on biochemical and clinical recurrence rates. A phase II study using an ultrasensitive assay showed that 8 months of neoadjuvant therapy were required before prostate-specific antigen (PSA) levels to reach their nadir in 84% of study participants. The positive margin rate in this study was substantially lower than those reported in the literature. Importantly, restaging of specimens after prostatic acid phosphatase (PAP) immunostaining did not upstage or increase positive margin rates. In addition, prolonged neoadjuvant therapy did not appear to result in progression of androgen-independent clones. A randomized phase III trial has been initiated to determine whether an 8-month course of neoadjuvant hormonal therapy is superior to a 3-month course in reducing positive margin rates and biochemical recurrences in patients with clinically confined prostate cancer.

Adult↗

PubMed1996

[Hormone release and intermittent hormonal therapy in the LN CaP model of human prostate cancer].

Androgen-independent progression invariably occurs following castration of patients with prostate cancer. Animal model data suggest that androgen resistance may result from adaptive cell survival mechanisms activated by androgen withdrawal. If this is true, then re-exposure to, or low levels of, androgens may suppress or downregulate these mechanisms. The objective of this study is to determine whether intermittent androgen suppression (IAS) delays the onset of nonandrogen-regulated PSA production in the LNCaP prostate tumour model, when compared to continuous androgen suppression (CAS). Serum PSA levels correlate highly with LNCaP tumour volume and decrease rapidly following castration; beginning 3-4 weeks post-castration LN CaP tumours become androgen-independent with respect to PSA gene expression and produce PSA in amounts similar to precastrate state. In this study, IAS-treated mice were implanted with testosterone pellets beginning two weeks post-castration; cycles of testosterone replacement for 1 week and withdrawal for 2 weeks were repeated until serum PSA levels no longer returned to baseline. IAS therapy prolonged time to androgen-independent PSA production 3-fold, from an average of 26 days in the CAS group to 77 days in the IAS group. Serum and LNCaP tumour mRNA PSA levels remained below precastrate levels by 60 days post-castration in 75% of the IAS group, while serum PSA in all mice in the CAS group exceeded precastrate PSA by 28 days post-castration. Following castration, serum PSA levels increased 9-fold faster with CAS compared to IAS therapy. Observations using IAS in the LNCaP tumour model suggest that the onset of androgen-independent PSA gene regulation is prolonged 3-fold, perhaps due to androgen-induced differentiation and/or downregulation of androgen-suppressed gene expression.

Androgens↗

PubMed1995

Intermittent androgen suppression in the treatment of prostate cancer: a preliminary report.

OBJECTIVES: To test the feasibility of using intermittent androgen suppression in the treatment of prostate cancer by taking advantage of the reversible action of medical castration. METHODS: Observations were made on a group of 47 patients (clinical Stage D2, 14; D1, 10; C, 19; B2, 2; and A2, 2) with a mean follow-up time of 125 weeks. Treatment was initiated with combined androgen blockade and continued for at least 6 months until a serum prostate-specific antigen (PSA) nadir was observed. Medication was then withheld until the serum PSA increased to a mean value between 10 and 20 ng/mL. This cycle of treatment and no treatment was repeated until the regulation of serum PSA became androgen independent. RESULTS: The first two treatment cycles lasted 73 and 75 weeks, with a mean time off therapy of 30 and 33 weeks and an overall mean percentage time off therapy of 41% and 45%, respectively. The mean time to achieve a nadir level of serum PSA was 20 weeks in cycle 1 and 18 weeks in cycle 2. Serum testosterone returned to the normal range within 8 weeks (range, 1 to 26) of stopping treatment. The off-treatment period in both cycles was associated with an improvement in sense of well-being and the recovery of libido and potency in the men who reported normal or near-normal sexual function before the start of therapy. In 7 patients with Stage D2 disease, the cancer progressed to an androgen-independent state. The mean and median times to progression were 128 weeks and 108 weeks, respectively. Seven patients have died, 1 from a noncancer-related illness, with mean and median overall survival times of 210 weeks and 166 weeks, respectively. CONCLUSIONS: Prostate cancer is amenable to control by intermittent androgen suppression. This approach affords an improved quality of life when the patient is off therapy. It also results in reduced toxicity and cost of treatment and possibly delays tumor progression. Whether survival is affected in a beneficial or adverse way remains to be studied in a randomized, prospective study.

Aged↗

PubMed1995

[Theoretical considerations and initial clinical results of intermittent hormone treatment of patients with advanced prostatic carcinoma].

Androgen suppression is the routine approach to the treatment of advanced prostate cancer. Using intermittent androgen suppression by taking the advantage of the reversible action of medical castration results in the maintenance of apoptotic potential. The experiments in the androgen-dependent androgen-dependent Shionogi carcinoma tumor model as well as clinical experience in a group of men with prostate malignancy are presented in this report. These consecutive cycles of androgen withdrawal and replacement afford an improved quality of life when the patient is off therapy. It is possible to reduce toxicity, cost of treatment and to delay tumor progression. Whether survival is affected in a beneficial or adverse way still remains to be studied.

Androgen Antagonists↗

PubMed1994

Cooperative binding of androgen receptors to two DNA sequences is required for androgen induction of the probasin gene.

The functional and structural interactions of two androgen receptor-binding sites in the 5'-flanking DNA of the rat probasin gene were determined. Deletion mapping and DNase I footprinting analysis had previously identified two androgen receptor-binding sites (ARBS) necessary for androgen induction of the probasin gene: ARBS-1, which resembled a glucocorticoid-responsive element, and ARBS-2, which had a unique sequence. In this study, maximal androgen induction in transient transfection studies only occurred when both sites were present. Neither binding site functioned independently, and deletion of the DNA sequence between the sites resulted in a 60% loss of androgen inducibility. Moreover, point mutations in either ARBS-1 or ARBS-2 led to > 90% loss in activity. Scatchard analysis indicated that ARBS-1 and ARBS-2 bound a synthetic androgen receptor, AR2, with Kd values of 20.0 and 6.7 nM, respectively. Consistent with the higher affinity, ARBS-2 bound AR2 at half the threshold concentration (200 ng) of that required in reciprocal DNase I footprinting experiments with ARBS-1. By comparison, protection occurred at a much lower threshold concentration of AR2 (60 ng) and to the same extent over each site when both sites were present, suggesting a cooperative interaction between the two sites. The cooperative effect was further substantiated when a point mutation in ARBS-1 blocked AR2 binding not only to ARBS-1, but also to ARBS-2. Similarly, a point mutation in ARBS-2 also prevented receptor binding to both sites. Androgen-specific regulation of probasin gene transcription therefore required an androgen-responsive region (positions -286 and +28) containing two androgen receptor-binding sites, where the binding of the androgen receptor to both sites occurred in a cooperative, mutually dependent manner.

Androgen-Binding Protein↗

PubMed1994

Inhibition of nuclear hormone receptor activity by calreticulin.

We have shown that a polypeptide of M(r) 60,000 (60K) that shares N-terminal homology with a calcium-binding protein, calreticulin, can bind to an amino-acid sequence motif, KXGFFKR, found in the cytoplasmic domains of all integrin alpha-subunits. The homologous amino-acid sequence, KXFFKR (where X is either G, A or V), is also present in the DNA-binding domain of all known members of the steroid hormone receptor family; amino acids in this sequence make direct contact with nucleotides in their DNA-responsive elements and are crucial for DNA binding. Here we show that both the 60K protein (p60), purified on a KLGFFKR-Sepharose affinity matrix, and recombinant calreticulin can inhibit the binding of androgen receptor to its hormone-responsive DNA element in a KXFFKR-sequence-specific manner. Calreticulin can also inhibit androgen receptor and retinoic acid receptor transcriptional activities in vivo, as well as retinoic acid-induced neuronal differentiation. Our results indicate that calreticulin can act as an important modulator of the regulation of gene transcription by nuclear hormone receptors.

Amino Acid Sequence↗

PubMed1994

Effect of tumour progression on the androgenic regulation of the androgen receptor, TRPM-2 and YPT1 genes in the Shionogi carcinoma.

Progression of an androgen-dependent tumour to an androgen-independent state is characterized by the loss of apoptotic potential, a property of cells which have differentiated under the influence of androgens. In an attempt to relate progression to mechanisms of apoptotic failure, we compared the relative levels of expression of androgen receptor and TRPM-2 (clusterin) genes in androgen-dependent and -independent tumours derived from the Shionogi carcinoma. The amount of 10 kb androgen receptor mRNA in androgen-dependent and -independent cells was similar thus showing no relationship to progression. Owing to cross-hybridization of androgen receptor cDNA with non-receptor transcripts, two new androgen-repressed mRNAs (ADS31 and ADS39) were cloned. Each was found to have a 20/21 bp GC-rich region of sequence homology with the androgen receptor, implying selective conservation of a domain whose function is unknown. Sequencing results also revealed that ADS31 cDNA encodes a polypeptide identical to mouse YPT1, a ras-related GTP-binding protein. Expression of the ADS31/YPT1, ADS39 and TRPM-2 genes was sensitive to androgen withdrawal and replacement both in the parent androgen-dependent and the recurrent androgen-independent carcinomas. The uncoupling of TRPM-2 expression and apoptosis observed in androgen-independent tumour cells implies that the function of androgen receptor becomes more restricted with tumour progression. Furthermore, the fact that the expression of ADS31/YPT1 transcript becomes dominant in the advanced stages of androgen-independent growth, suggests that the mechanism of progression is subserved by duplication and possibly redundancy of alternative (signal transduction) pathways mediating tumour cell survival and growth.

Androgens↗