Gene/Protein Disease Symptom Drug Enzyme Compound
Pivot Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound   Target Concepts: Gene/Protein Disease Symptom Drug Enzyme Compound

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Query: EC:2.7.11.1 (protein kinase)
81,284 document(s) hit in 31,850,051 MEDLINE articles (0.00 seconds)

Growth of prostatic epithelial cells is androgen-dependent; however, the mechanism of androgen action on cell growth is not well defined. We investigated whether androgen-dependent prostatic epithelial cell growth is mediated by androgen regulation of expression of genes controlling cell cycle progression. For this purpose, we used an androgen-dependent prostatic cancer cell line, LNCaP-FGC, as an in vitro model. We found that expression of CDK2 and CDK4 genes were up-regulated within hours of androgen treatment as detected in Northern and Western blot analyses. Kinase assay also confirmed that there was increased CDK2 kinase activity upon androgen stimulation. Moreover, androgen down-regulated expression of the cyclin-dependent kinase inhibitor p16 (MTS1, CDKN2) gene. The overall effects of these androgen actions result in an increased cyclin-dependent kinase activity and stimulation of the cell to enter S phase of the cell cycle, thereby enhancing cell proliferation. In contrast, an androgen-independent PC-3 cell line lost its response to androgen stimulation, and higher basal levels of CDK2, CDK4, and p16 genes were constitutively expressed in PC-3 cells. Collectively, these data suggest a possible signaling pathway of androgen in stimulating cell growth. These results also imply that in androgen-dependent prostate cancer, increased androgen receptor (AR) activity, resulting from AR gain-of-function mutations, AR gene amplification, or AR gene overexpression, malignantly stimulates proliferation of prostatic epithelial cells and constitutes one possible mechanism of androgen-dependent tumorigenesis.
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PMID:Regulation of androgen-dependent prostatic cancer cell growth: androgen regulation of CDK2, CDK4, and CKI p16 genes. 937 62

Functional domains of the androgen receptor (AR) have been localized through a combination of studies on naturally occurring AR gene mutations, in vitro mutagenesis studies and comparison with the structure of other members of the steroid/nuclear receptor superfamily. Two activation domains exist within the amino-terminal domain, and a ligand-dependent activation domain is present in the ligand binding domain. The poly(Gln) stretch within the amino-terminal domain may inhibit the transactivation function of the receptor. Different ligands or binding to different promoters may recruit the use of different activation domains, which may provide promoter-specific effects of receptor action. Co-activator proteins that modulate or enhance AR action have been identified, many of which interact with the ligand binding domain of the AR. Tissue-specific expression of such co-activators, and promoter-specific protein interactions, may also help control the specificity of androgen action. Target Ser residues for phosphorylation have been identified, which may be the site of action for cross-talk from protein kinase signalling pathways. However, the role of phosphorylation in AR function in general is still unclear. It is now clear that interactions occur between receptor domains, modulating functions including ligand dissociation, dimerization and transactivation. By studying the functional domains of the AR, and how they control receptor function in response to different activation signals, we are beginning to understand the mechanisms controlling the specificity of receptor action.
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PMID:Localization of functional domains in the androgen receptor. 940 77

When androgen receptor containing cells are cultured in the presence of the PKA stimulator forskolin, a rapid dephosphorylation of the androgen receptor occurs resulting in a decrease in the amount of 112 kDa androgen receptor isoform and an increase in 110 kDa androgen receptor isoform on SDS-PAGE. To establish which amino acid residues in the androgen receptor were phosphorylated in control and forskolin-treated cells, trypsin-digested androgen receptors were subjected to RP-HPLC analysis and subsequently to Edman degradation. It was observed that serine residues 506, 641, and 653 were potentially phosphorylated in control cells, while after forskolin treatment strong evidence was obtained that phosphorylation of serines 641 and 653 was significantly reduced. When the dephosphorylated androgen receptor was analyzed for its transcription activation capacity, it was observed that androgen-induced transcriptional regulation of two endogenous genes (PSA) and beta 1-subunit of Na,K-ATPase), in cells cultured in the presence of forskolin, was inhibited as compared to the control situation. The observation that the dephosphorylated androgen receptor was transcriptionally less active was further strengthened by the finding that the dephosphorylated androgen receptor was markedly impaired in ligand binding (Bmax was found to be reduced by approximately 40%). The current investigations show for the first time a clear function for the rapid phosphorylation which occurs directly after synthesis of the androgen receptor, namely, effective ligand binding.
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PMID:Forskolin-induced dephosphorylation of the androgen receptor impairs ligand binding. 952 5

The molecular mechanism of androgen-independent growth of prostate cancer after androgen ablation was explored in LNCaP cells. An androgen-dependent clonal subline of the LNCaP human prostate carcinoma cell line, LNCaP 104-S, progressed to a slow growing stage (104-R1) and then to a faster growing stage (104-R2) during more than 2 yr of continuous culture in the absence of androgen. Androgen-induced proliferation of 104-S cells is inhibited by the antiandrogen Casodex, while proliferation of 104-R1 and 104-R2 cells is unaffected by Casodex. This indicates that proliferation of 104-R1 and 104-R2 cells is not supported by low levels of androgen in the culture medium. Compared with LNCaP 104-S cells, both 104-R1 and 104-R2 cells express higher basal levels of androgen receptor (AR), and proliferation of these two cell lines is paradoxically repressed by androgen. After continuous passage in androgen-containing medium, 104-R1 cells reverted back to an androgen-dependent phenotype. The mechanism of androgenic repression of 104-R1 and 104-R2 sublines was further evaluated by examining the role of critical regulatory factors involved in the control of cell cycle progression. At concentrations that repressed growth, androgen transiently induced the expression of the cyclin-dependent kinase (cdk) inhibitor p21waf1/cip1 in 104-R1 cells, while expression of the cdk inhibitor p27Kip1 was persistently induced by androgen in both 104-R1 and 104-R2 cells. Induced expression of murine p27Kip1 in 104-R2 cells resulted in G1 arrest. Specific immunoprecipitates of Cdk2 but not Cdk4 from androgen-treated 104-R1 cells contained both p21waf1/cip1 and p27Kip1. This observation was confirmed by in vitro assay of histone H1 and Rb (retinoblastoma protein) phosphorylation by the proteins associated with the immune complex. Furthermore, inhibition of Cdk2 activity correlated with the accumulation of p27Kip1 and not p21waf1/cip1. From these results we conclude that androgenic repression of LNCaP 104-R1 and 104-R2 cell proliferation is due to the induction of p27Kip1, which in turn inhibits Cdk2, a factor critical for cell cycle progression and proliferation.
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PMID:Progression of LNCaP prostate tumor cells during androgen deprivation: hormone-independent growth, repression of proliferation by androgen, and role for p27Kip1 in androgen-induced cell cycle arrest. 965 99

We have examined the human androgen receptor (hAR) for its ability to activate AR-dependent transcription of a transgene in a ligand-independent manner. The transcriptional activity was determined by analysis of chloramphenicol acetyltransferase (CAT) activity in T47D cells cotransfected with a plasmid expressing the hAR and a natural AR-regulated promoter (the MVDP androgen-dependent enhancer) ligated to the reporter CAT gene. In this study, the effects of the protein kinase C (PKC) activator 12-O-tetradecanoyphorbol-13 acetate (TPA) on AR activity were tested. We demonstrated that in the absence of androgen, TPA enhanced AR-mediated transactivation by 10-12-fold. This effect was specific of the PKC pathway since stimulation to the PKA pathway did not activate the unliganded AR. This ligand-independent pathway can function through another androgen-regulated promoter as shown by the use of the mouse mammary tumor virus MMTV-CAT reporter. The human glucocorticoid receptor (hGR) and the rabbit progesterone receptor (rPR) could not be activated by TPA, indicating that the effects are not universal for steroid receptors. A reporter plasmid containing the MVDP androgen response element (ARE) in front of the thymidine kinase promoter ligated to the CAT gene was activated by DHT but not by TPA, indicating that the context of the natural promoter is critical for ligand-independent activation of the AR. Exogenous c-jun enhanced transcriptional activation by the AR in a ligand-dependent manner, but had no effect in the absence of DHT. Base pair substitutions in both AR-binding (5'-TGTTCT-3' to 5'-TTTTTT-3') and NF1-binding (5'-GTGGCTG-3' to 5'-GTTTTTG-3') sites resulted in a loss of TPA responsiveness. Our results suggest that ligand-independent activation of the AR by TPA results from interaction of unliganded AR with other proteins in the transcription machinery.
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PMID:Phorbol ester causes ligand-independent activation of the androgen receptor. 978 Feb 30

Interleukin-6 (IL-6) levels are frequently elevated in sera of patients with metastatic prostate cancer. IL-6 receptors are expressed in prostate cancer cell lines, as well as in benign prostate hyperplasia and prostate cancer tissue specimens. The androgen receptor (AR) is a key transcription factor that is present in all stages of prostate carcinoma, even in therapy-refractory tumors. In an attempt to investigate possible cross-talk between IL-6 and androgen signal transduction cascades, we tested the effects of this cytokine on AR transcriptional activity. The regulation of AR activity by IL-6 was studied in DU-145 cells, which were cotransfected with the androgen-responsive reporter plasmid ARE2TATACAT and the AR expression vector pSG5AR. We show that IL-6 up-regulates AR activity in a ligand-independent manner, as well as synergistically, with very low doses of the synthetic androgen methyltrienolone (5-10 pM). Therefore, AR activation by IL-6 may be operative in prostate cancer patients who have decreased androgen levels because of androgen ablation therapy. The maximal induction of reporter gene activity by IL-6 alone (50 ng/ml) was 67% of that stimulated by 1 nM of methyltrienolone. The nonsteroidal antiandrogen bicalutamide (Casodex) nearly completely inhibited AR activation by IL-6. IL-6 effects on AR activity were also abolished or greatly reduced by inhibitors of protein kinase A and C and mitogen-activated protein kinase pathways. In concordance with the results obtained in DU-145 cells, IL-6 induced AR-regulated prostate-specific antigen mRNA and protein in LNCaP cells. Stimulation of prostate-specific antigen protein secretion by IL-6 was antagonized by bicalutamide and inhibitors of protein kinase A and mitogen-activated protein kinase signaling pathways. Taken together, our data show for the first time that IL-6 is a nonsteroidal activator of the AR and that this activation is implicated in the regulation of prostate-specific proteins. Keeping in mind that IL-6, its receptor, and the AR are expressed in prostate cancers, cross-talk between IL-6 and AR signaling pathways may have clinical significance.
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PMID:Interleukin-6 regulates prostate-specific protein expression in prostate carcinoma cells by activation of the androgen receptor. 978 16

The androgen receptor (AR) protein is an important transacting factor that is necessary for mediating gene expression of androgen-responsive genes. The expression of the AR gene is regulated by androgens and agents that utilize the calcium, protein kinase A, and protein kinase C pathways. Although the role of the calcium and protein kinase A pathways in the regulation of the AR gene has been investigated, the mechanism of regulation of AR through the protein kinase C pathway is not known. We have isolated the 5'-flanking region of the mouse AR gene and identified a consensus TPA (12-O-tetradecanoylphorbol 13-acetate)-response element (TRE). Transient transfection assays indicate that the TRE sequence is sufficient to confer TPA responsiveness to cells treated with TPA. Gel retardation assays and DNA footprint analysis demonstrated specific binding of the TRE and protection of the TRE sequence. Thus, these results describe a TRE in the 5'-flanking region of the AR gene and demonstrate that the TRE is responsive to TPA treatment.
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PMID:Characterization of a TPA-response element in the 5'-flanking region of the androgen receptor gene. 979 20

We have employed a yeast (Saccharomyces cerevisiae) based rat androgen receptor expression system to examine the cross-talk between different signalling pathways. We report here the synergistic modulation of androgen regulated transcriptional activation of beta-galactosidase reporter activity by the activators of protein kinase-A, like forskolin and 8-bromo-cyclic AMP. A similar ligand-dependent enhancement of reporter activity compared to a DHT treated control has been noticed with okadaic acid, which is a potent inhibitor of protein phosphatase. The activation could be blocked by protein kinase-A/C inhibitor, H7. Forskolin treatment neither altered levels of receptor mRNA nor [3H]R1881 binding to the receptor. Although it promotes binding of receptor to an androgen response element, forskolin was unable to activate subsequent interaction with the transcription machinery in the absence of androgen. Additionally, the synergistic actions of these activators were independent of the degree of androgen response element occupancy. Anti-androgens, cyproterone acetate and flutamide, which failed to exhibit antagonistic behaviour with yeast expressed receptor, were able to antagonize only the forskolin mediated augmentation of reporter activity. Finally, analyses of mutants established the role of DNA and steroid binding domains of receptor for this synergism.
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PMID:Synergistic activation of yeast-expressed rat androgen receptor by modulators of protein kinase-A. 1002 42

Metastatic prostate cancer is a leading cause of cancer-related death in men. Although most patients will respond to androgen ablation as initial systemic therapy, nearly all patients will develop androgen-independent prostate cancer (AI CaP) and will succumb to the disease. Advances in molecular biology have demonstrated mutations in and persistent expression of the human androgen receptor in metastatic disease. Furthermore, recent evidence indicates that an apoptotic block through p53 mutations or bcl-2 overexpression may have a potential role in the poor responses seen with standard chemotherapy. Presently, the six general treatment options available for AI CaP are best supportive care, radiation therapy, radioisotopes, secondline hormonal therapy, chemotherapy (single agent or combination), and investigational therapies such as monoclonal antibodies, cyclin-dependent kinase inhibitors, matrix metalloproteinase inhibitors, and antiangiogenesis agents, among others. None of these modalities have produced durable remissions, although some have demonstrated palliative benefit. The next generation of clinical trials should not consist of futile hormonal manipulations or repetitive chemotherapy. Therapeutic strategies aimed at circumventing molecular blocks to cell death or targeting unique cancer molecules and genes will be more likely to improve quality of life and longevity. Furthermore, the aggressive use of palliative care will ensure effective caring for patients and the healing of families in the absence of cure.
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PMID:Treatment options in androgen-independent prostate cancer. 1007 98

Transcription of the prostate-specific antigen (PSA) gene escapes regulation by androgens in advanced prostate cancer. To determine the molecular mechanism(s) of androgen-independent regulation of the PSA gene, the possibility that the androgen receptor (AR) is activated in the absence of androgen by stimulation of protein kinase A (PKA) was investigated. Activation of PKA by forskolin resulted in elevated expression of the PSA gene in androgen-depleted LNCaP cells, an effect that was blocked by the antiandrogen, bicalutamide. Further evidence that induction of PSA gene expression was dependent on AR was obtained from experiments using PC3 cells devoid of AR. Neither PSA, PB, nor ARR3 androgen-responsive reporters could be induced by activation of PKA in the absence of transfected AR. In addition, when nuclear AR from forskolin-treated LNCaP cells was incubated with oligonucleotides encoding an androgen response element of the PSA promoter and examined by electromobility shift assay, an increase in AR-androgen response element complex formation was observed. Lastly, cotransfection of an expression vector for a chimeric protein encoding the amino-terminal domain of the human AR linked to Gal4 and a 5xGal4UAS reporter gene construct resulted in activation of the amino-terminal domain of the AR by stimulation of PKA activity. These results demonstrate androgen-independent induction of PSA gene expression in prostate cancer cells by an AR-dependent pathway.
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PMID:Androgen-independent induction of prostate-specific antigen gene expression via cross-talk between the androgen receptor and protein kinase A signal transduction pathways. 1007 69


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