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Biomedical subjects

Steven P Balk

Publications and source records attributed to Steven P Balk.

30 records · Page 2Linked to original sources
PubMed2003

CD1d-restricted T cells regulate dendritic cell function and antitumor immunity in a granulocyte-macrophage colony-stimulating factor-dependent fashion.

CD1d-restricted T cells contribute to tumor protection, but their precise roles remain unclear. Here we show that tumor cells engineered to secrete granulocyte-macrophage colony-stimulating factor induce the expansion of CD1d-restricted T cells through a mechanism that involves CD1d and macrophage inflammatory protein 2 expression by CD8 alpha-, CD11c+ dendritic cells (DCs). The antitumor immunity stimulated by vaccination with irradiated, granulocyte-macrophage colony-stimulating factor-secreting tumor cells was abrogated in CD1d- and J alpha 281-deficient mice, revealing a critical role for CD1d-restricted T cells in this response. The loss of antitumor immunity was associated with impaired tumor-induced T helper 2 cytokine production, although IFN-gamma secretion and cytotoxicity were preserved. DCs from immunized CD1d-deficient mice showed compromised maturation and function. Together, these results delineate a role for CD1d-restricted T cell-DC cross talk in the shaping of antitumor immunity.

Animals↗
PubMed2003

A direct beta-catenin-independent interaction between androgen receptor and T cell factor 4.

T cell factor (Tcf) proteins bind beta-catenin and are downstream effectors of Wnt/beta-catenin signals. A recently demonstrated interaction between beta-catenin and the androgen receptor (AR) ligand binding domain has suggested that AR may be a Tcf-independent Wnt/beta-catenin effector. This study demonstrates that there is a direct interaction between the AR DNA binding domain (DBD) and Tcf4. Tcf4 bound specifically to a glutathione S-transferase-ARDBD fusion protein and could be coimmunoprecipitated with beta-catenin and transfected AR or endogenous AR in prostate cancer cells. Transfected Tcf4 repressed the transcriptional activity of full-length AR and a VP16-ARDBD fusion protein, and this repression was only partially reversed by transfected beta-catenin. AR activation by cyproterone acetate, a partial agonist that did not support beta-catenin binding to the AR, was also repressed by Tcf4, further indicating that repression was not due to beta-catenin sequestration. Tcf4 could recruit beta-catenin to the AR DBD in vitro and to the cyproterone acetate-liganded AR in vivo. Chromatin immunoprecipitation experiments in LNCaP prostate cancer cells showed that endogenous AR was bound to a Tcf4-responsive element in the c-myc promoter. These findings indicate that AR and Tcf4 can interact directly and that this interaction may occur on the promoters or enhancers of particular genes. The direct AR-Tcf4 interaction, in conjunction AR- and Tcf4-beta-catenin binding, provides a mechanism for cooperative and selective gene regulation by AR and the Wnt/beta-catenin-Tcf pathway that may contribute to normal and neoplastic prostate growth.

Androgen Antagonists↗
PubMed2003

Biology of prostate-specific antigen.

Prostate-specific antigen (PSA) is an androgen-regulated serine protease produced by both prostate epithelial cells and prostate cancer (PCa) and is the most commonly used serum marker for cancer. It is a member of the tissue kallikrein family, some of the members of which are also prostate specific. PSA is a major protein in semen, where its function is to cleave semenogelins in the seminal coagulum. PSA is secreted into prostatic ducts as an inactive 244-amino acid proenzyme (proPSA) that is activated by cleavage of seven N-terminal amino acids. PSA that enters the circulation intact is rapidly bound by protease inhibitors, primarily alpha1-antichymotrypsin, although a fraction is inactivated in the lumen by proteolysis and circulates as free PSA. This proteolytic inactivation, as well as the cleavage of proPSA to PSA, is less efficient in PCa. Serum total PSA levels are increased in PCa, and PSA screening has dramatically altered PCa presentation and management. Unfortunately, although high PSA levels are predictive of advanced PCa, a large fraction of organ-confined cancers present with much lower total PSA values that overlap those levels found in men without PCa. Measurement of free versus total PSA can increase specificity for PCa, and tests under development to measure forms of proPSA may further enhance the ability to detect early-stage PCa. PSA is also widely used to monitor responses to therapy and is under investigation as a therapeutic target. Finally, recent data indicate that there may be additional roles for PSA in the pathogenesis of PCa.

Humans↗
PubMed2003

Steroid hormone receptor signaling in cancer.

SHRs function as hormone activated, sequence specific DNA binding transcription factors that recruit multiple coactivator and other proteins to specific genes and generally stimulate transcription of these genes. SHR may have further genomic actions, that do not involve direct DNA binding, through protein-protein interactions with other sequence specific transcription factors, although these may still involve weak binding to nonconsensus steroid responsive elements in vivo. SHRs also appear to have nongenomic effects mediated through interactions with cytoplasmic signaling proteins. The major functions of SHRs in normal adult tissues appear to involve stimulation of differentiation, rather than proliferation. In contrast, the ER alpha and AR directly stimulate the growth of breast and prostate cancers, respectively, indicating a critical change in their functions. The ER alpha and AR appear to undergo further adaptation in tumor cells in response to hormonal therapies, that render these therapies ineffective. Understanding the molecular basis for these changes in SHR function during cancer development and progression may provide new targets for the generation of drugs to prevent and treat steroid stimulated cancers.

Animals↗
PubMed2003

Innate immune response to encephalomyocarditis virus infection mediated by CD1d.

CD1d-reactive natural killer T (NKT) cells can rapidly produce T helper type 1 (Th1) and/or Th2 cytokines, can activate antigen-presenting cell (APC) interleukin-12 (IL-12) production, and are implicated in the regulation of adaptive immune responses. The role of the CD1d system was assessed during infection with encephalomyocarditis virus (EMCV-D), a picornavirus that causes acute diabetes, paralysis and myocarditis. EMCV-D resistance depends on IL-12-mediated interferon-gamma (IFN-gamma) production. CD1d-deficient mice, which also lack CD1d-reactive NKT cells, were substantially more sensitive to infection with EMCV-D. Infected CD1d knockout mice had decreased IL-12 levels in vitro and in vivo, and indeed were protected by treatment with exogenous IL-12. IFN-gamma production in CD1d knockout mice was decreased compared with that in wild-type (WT) mice in response to EMCV-D in vitro, although differences were not detected in vivo. Treatment with anti-asialo-GM1 antibody, to deplete NK cells, caused a marked increase in susceptibility of WT mice to EMCV-D infection, whereas CD1d knockout mice were little affected, suggesting that NK-cell-mediated protection is CD1d-dependent. Therefore, these data indicate that CD1d is essential for optimal responses to acute picornaviral infection. We propose that CD1d-reactive T cells respond to early immune signals and function in the innate immune response to a physiological viral infection by rapidly augmenting APC IL-12 production and activating NK cells.

Animals↗
PubMed2002

CD1d and invariant NKT cells at the human maternal-fetal interface.

Invariant CD1d-restricted natural killer T (iNKT) cells comprise a small, but significant, immunoregulatory T cell subset. Here, the presence of these cells and their CD1d ligand at the human maternal-fetal interface was investigated. Immunohistochemical staining of human decidua revealed the expression of CD1d on both villous and extravillous trophoblasts, the fetal cells that invade the maternal decidua. Decidual iNKT cells comprised 0.48% of the decidual CD3+ T cell population, a frequency 10 times greater than that seen in peripheral blood. Interestingly, decidual CD4+ iNKT cells exhibited a striking Th1-like bias (IFN-gamma production), whereas peripheral blood CD4+ iNKT clones exhibited a Th2-like bias (IL-4 production). Moreover, compared to their peripheral blood counterparts, decidual iNKT clones were strongly polarized toward granulocyte/macrophage colony-stimulating factor production. The demonstration of CD1d expression on fetal trophoblasts together with the differential pattern of cytokine expression by decidual iNKT cells suggests that maternal iNKT cell interactions with CD1d expressed on invading fetal cells may play an immunoregulatory role at the maternal-fetal interface.

Antigens, CD1↗
PubMed2002

Bicalutamide functions as an androgen receptor antagonist by assembly of a transcriptionally inactive receptor.

Prostate cancers (PCa) that relapse after androgen deprivation therapy invariably express high levels of androgen receptor (AR) and AR-regulated genes. Most do not respond to secondary hormonal therapies, including AR antagonists, and the mechanisms of AR activation in these clinically androgen-independent tumors are unclear. Bicalutamide, the most widely used AR antagonist, is a competitive antagonist shown previously to stabilize AR association with cytosolic heat shock protein complexes. This study found nuclear AR expression in bicalutamide-treated androgen-independent PCa and found that bicalutamide could stimulate AR nuclear translocation. Moreover, specific DNA binding by the bicalutamide-liganded AR was demonstrated in vivo using a VP16-AR fusion protein and was confirmed by chromatin immunoprecipitation showing binding to the prostate-specific antigen enhancer in LNCaP PCa cells. Nonetheless, bicalutamide could not stimulate interactions between the AR N and C termini or recruitment of steroid receptor coactivator proteins (SRC-1 or -2), although SRC transfection augmented AR activity in the presence of dihydrotestosterone and inhibitory concentrations of bicalutamide. These results demonstrate that bicalutamide stimulates the assembly of a transcriptionally inactive AR on DNA and support altered coactivator (or corepressor) expression as a mechanism of bicalutamide-resistant androgen-independent PCa.

Androgen Antagonists↗
PubMed2002

Cutting edge: Compartmentalization of Th1-like noninvariant CD1d-reactive T cells in hepatitis C virus-infected liver.

Murine intrahepatic lymphocytes (IHL) are dominated by invariant TCR alpha-chain expressing CD1d-reactive NKT cells, which can cause model hepatitis. Invariant NKT (CD56(+/-)CD161(+)) and recently identified noninvariant CD1d-reactive T cells rapidly produce large amounts of IL-4 and/or IFN-gamma and can regulate Th1/Th2 responses. Human liver contains large numbers of CD56(+) NKT cells but few invariant NKT. Compared with matched peripheral blood T cell lines, primary IHL lines from patients with chronic hepatitis C had high levels of CD161 and CD1d reactivity, but the invariant TCR was rare. CD1d-reactive IHL were strikingly Th1 biased. IHL also demonstrated CD1d-specific cytotoxic activity. Hepatocytes and other liver cells express CD1d. These results identify a novel population of human T cells that could contribute to destructive as well as protective immune responses in the liver. CD1d-reactive T cells may have distinct roles in different tissues.

Antigens, CD1↗
PubMed2002

Androgen receptor as a target in androgen-independent prostate cancer.

Prostate cancer is dependent on androgen stimulation mediated by the androgen receptor (AR), a member of the steroid hormone receptor family of ligand-dependent nuclear receptors. Most patients respond to standard androgen ablation therapies, but virtually all patients eventually relapse with disease that has been termed hormone-refractory or androgen-independent disease. Efforts to use AR antagonists, such as flutamide or bicalutamide, to enhance responses to primary androgen ablation therapy or to treat androgen-independent prostate cancer have been disappointing, which has diminished enthusiasm for more aggressive or alternative methods to block AR function. However, many lines of evidence indicate that AR function contributes to tumor cell survival after androgen ablation and to growth of androgen-independent prostate cancer. This article outlines a number of mechanisms that may contribute to AR activity in androgen-independent prostate cancer, including AR amplification, AR mutation, altered expression of AR coactivator and corepressor proteins, and activation of other pathways that can enhance AR function. Understanding the mechanisms responsible for AR function in androgen-independent prostate cancer should allow the more rational development of antagonists that can enhance the efficacy of androgen ablation therapies.

Androgen Antagonists↗
PubMed2002

AR and ER interaction with a p21-activated kinase (PAK6).

A human protein termed p21-activated kinase 6 (PAK6), based on homology to the PAK family of serine/threonine kinases, was cloned as an AR interacting protein. PAK6 was a 75-kDa protein with a predicted N-terminal Cdc42/Rac interactive binding domain and a C-terminal kinase domain. PAK6 bound strongly to GTP-Cdc42 and weakly to GTP-Rac. In contrast to most PAKs, kinase activity was not stimulated by Cdc42 or Rac, but could be stimulated by AR binding. PAK6 interacted with the intact AR in a mammalian one-hybrid assay and bound in vitro, without ligand, to the hinge region between the AR DNA- and ligand-binding domains. PAK6 also bound to the ERalpha, and binding was enhanced by 4-hydroxytamoxifen. AR and ERalpha transcriptional activities were inhibited by PAK6 in transient transfections with episomal and integrated reporter genes. AR inhibition was not reversed by transfection with an activated Cdc42 mutant, Cdc42V12, which by itself also inhibited AR transactivation. Epitope-tagged PAK6 was primarily cytoplasmic in the absence or presence of AR and hormone. PAK6 transcripts were expressed most highly in brain and testis, with lower levels in multiple tissues including prostate and breast. PAK6 interaction provides a mechanism for cross-talk between steroid hormone receptors and Cdc42-mediated signal transduction pathways and could contribute to the effects of tamoxifen in breast cancer and in other tissues.

Amino Acid Sequence↗
PubMed2002

Inhibition of the dihydrotestosterone-activated androgen receptor by nuclear receptor corepressor.

Nuclear receptor corepressor (NCoR) mediates transcriptional repression by unliganded nuclear receptors and certain steroid hormone receptors (SHRs) bound to nonphysiological antagonists, but has not been found to regulate SHRs bound to their natural ligands. This report demonstrates that NCoR interacts directly with the androgen receptor (AR) and represses dihydrotestosterone-stimulated AR transcriptional activity. The NCoR C terminus, containing the receptor interacting domains, was necessary for repression, which was ablated by mutations in the corepressor nuclear receptor (CoRNR) boxes. In contrast, the NCoR N terminus, containing domains that can recruit histone deacetylases, was not necessary for repression. Binding studies in vitro with a series of glutathione-S-transferase-NCoR and -AR fusion proteins demonstrated a direct interaction that was similarly dependent upon the NCoR corepressor nuclear receptor boxes and AR ligand binding domain and was independent of ligand and helix 12 in the AR ligand binding domain. This NCoR-AR interaction was further demonstrated in mammalian two-hybrid assays and by coimmunoprecipitation of the endogenous proteins from a prostate cancer cell line. Finally, AR transcriptional activity could be enhanced in vivo by sequestration of endogenous NCoR with unliganded thyroid hormone receptor. These results demonstrate that AR, in contrast to other SHRs, is regulated by NCoR and suggest the possibility of developing selective AR modulators that enhance this interaction.

Amino Acid Sequence↗