The multi-site docking protein Grb2-associated binder 1 (Gab1) enhances interleukin-6-induced MAPK-pathway activation in an SHP2-, Grb2-, and time-dependent manner.

BACKGROUND: Cytokine-dependent activation of signalling pathways is tightly orchestrated. The spatiotemporal activation of signalling pathways dictates the specific physiological responses to cytokines. Dysregulated signalling accounts for neoplastic, developmental, and inflammatory diseases. Grb2-associated binder (Gab) family proteins are multi-site docking proteins, which expand cytokine-induced signal transduction in a spatial- and time-dependent manner by coordinating the recruitment of proteins involved in mitogen activated protein kinase (MAPK)/extracellular-signal regulated kinase (ERK) and phosphatidyl-inositol-3-kinase (PI3K) signalling. Interaction of Gab family proteins with these signalling proteins determines strength, duration and localization of active signalling cascades. However, the underlying molecular mechanisms of signal orchestration by Gab family proteins in IL-6-induced signalling are only scarcely understood. METHODS: We performed kinetic analyses of interleukin-6 (IL-6)-induced MAPK activation and analysed downstream responses. We compared signalling in wild-type cells, Gab1 knock-out cells, those reconstituted to express Gab1 mutants, and cells expressing gp130 receptors or receptor mutants. RESULTS: Interleukin-6-induced MAPK pathway activation can be sub-divided into an early Gab1-independent and a subsequent Gab1-dependent phase. Early Gab1-independent MAPK activation is critical for the subsequent initiation of Gab1-dependent amplification of MAPK pathway activation and requires binding of SH2 domain-containing phosphatase 2 (SHP2) to the interleukin-6 receptor complex. Subsequent and coordinated recruitment of Grb2 and SHP2 to Gab1 is essential for Gab1-dependent amplification of IL-6-induced late MAPK pathway activation and subsequent gene expression. CONCLUSIONS: Overall, we elaborated the molecular requirements for Gab1-dependent, spatiotemporal orchestration of interleukin-6-dependent MAPK signalling. We discriminated IL-6-induced Gab1-independent, early activation of MAPK signalling and Gab1-dependent, sustained activation of MAPK signalling.

Halogen-substituted anthranilic acid derivatives provide a novel chemical platform for androgen receptor antagonists.

Androgen receptor (AR) antagonists are used for hormone therapy of prostate cancer (PCa). However resistance to the treatment occurs eventually. One possible reason is the occurrence of AR mutations that prevent inhibition of AR-mediated transactivation by antagonists. To offer in future more options to inhibit AR signaling, novel chemical lead structures for new AR antagonists would be beneficial. Here we analyzed structure-activity relationships of a battery of 36 non-steroidal structural variants of methyl anthranilate including 23 synthesized compounds. We identified structural requirements that lead to more potent AR antagonists. Specific compounds inhibit the transactivation of wild-type AR as well as AR mutants that render treatment resistance to hydroxyflutamide, bicalutamide and the second-generation AR antagonist enzalutamide. This suggests a distinct mode of inhibiting the AR compared to the clinically used compounds. Competition assays suggest binding of these compounds to the AR ligand binding domain and inhibit PCa cell proliferation. Moreover, active compounds induce cellular senescence despite inhibition of AR-mediated transactivation indicating a transactivation-independent AR-pathway. In line with this, fluorescence resonance after photobleaching (FRAP) - assays reveal higher mobility of the AR in the cell nuclei. Mechanistically, fluorescence resonance energy transfer (FRET) - assays indicate that the amino-carboxy (N/C)-interaction of the AR is not affected, which is in contrast to known AR-antagonists. This suggests a mechanistically novel mode of AR-antagonism. Together, these findings indicate the identification of a novel chemical platform as a new lead structure that extends the diversity of known AR antagonists and possesses a distinct mode of antagonizing AR-function.

Designing optimal experiments to discriminate interaction graph models.

Modern methods for the inference of cellular networks from experimental data often express nondeterminism through an ensemble of candidate models. To discriminate among these candidates new experiments need to be carried out. Theoretically, the number of possible experiments is exponential in the number of possible perturbations. In praxis, experiments are expensive and there exist several limiting constraints. Limiting factors exist on the combinations of perturbations that are technically possible, which components can be measured, and on the number of affordable experiments. Further, not all experiments are equally well suited to discriminate model candidates. The goal of optimal experiment design is to determine those experiments that discriminate most of the candidates while minimizing the costs. We present an approach for experiment planning with interaction graph models and sign consistency methods. This new approach can be used in combination with methods for network inference and consistency checking. We applied our method to study the Erythropoietin signal transduction in human kidney cells HEK293. We first used simulated experiment data from an ODE model to demonstrate in silico that our experimental design results in the inference of the gold standard model. Finally, we used the approach to plan in vivo experiments that discriminate model candidates for the Erythropoietin signal transduction in this cell line.

The multi-site docking protein Gab1 is constitutively phosphorylated independent from its recruitment to the plasma membrane in Jak2-V617F-positive cells and mediates proliferation of human erythroleukaemia cells.

The constitutively active Janus kinase 2 mutant Jak2-V617F is responsible for cytokine-independent growth of hematopoietic cells and the development of myeloproliferative neoplasms, such as polycythaemia vera and essential thrombocythaemia. Cells expressing Jak2-V617F exhibit constitutive STAT, MAPK, and PI3K signalling, and constitutive association of the multi-site docking protein Gab1 to PIP3 at the plasma membrane. Here, we demonstrate the crucial role of Gab1 for the proliferation of Jak2-V617F-positive human erythroleukaemia (HEL) cells. In Jak2-V617F-expressing cells Gab1 is constitutively phosphorylated by Erk1/2 on serine residue 552, which regulates binding to PIP3. Additionally, Gab1 is constitutively phosphorylated on tyrosine residue 627. Tyrosine 627 is a SHP2 binding site and required for Gab1-dependent Erk1/2 activation. As previously shown, Jak2-V617F-dependent Erk1/2 and PI3K activation act synergistically on the proliferation of Jak2-V617F-positive cells. Here, we examined whether constitutive membrane association of Gab1 explains cytokine-independent Gab1 phosphorylation in Jak2-V617F-expressing cells. Although we could demonstrate Jak2-V617F-dependent constitutive serine 552 and tyrosine 627 phosphorylation of Gab1, interestingly, both phosphorylations do not require binding of Gab1 to PIP3 at the plasma membrane. Instead, we observed a constitutive interaction of Gab1 with the erythropoietin receptor in Jak2-V617F-expressing cells, which depends on Janus kinase activity. Thus, constitutive Gab1-dependent signalling in Jak2-V617F-expressing cells does not occur due to the constitutive association of Gab1 with PIP3 at the plasma membrane.

Choline Kinase Alpha as an Androgen Receptor Chaperone and Prostate Cancer Therapeutic Target.

BACKGROUND: The androgen receptor (AR) is a major drug target in prostate cancer (PCa). We profiled the AR-regulated kinome to identify clinically relevant and druggable effectors of AR signaling. METHODS: Using genome-wide approaches, we interrogated all AR regulated kinases. Among these, choline kinase alpha (CHKA) expression was evaluated in benign (n = 195), prostatic intraepithelial neoplasia (PIN) (n = 153) and prostate cancer (PCa) lesions (n = 359). We interrogated how CHKA regulates AR signaling using biochemical assays and investigated androgen regulation of CHKA expression in men with PCa, both untreated (n = 20) and treated with an androgen biosynthesis inhibitor degarelix (n = 27). We studied the effect of CHKA inhibition on the PCa transcriptome using RNA sequencing and tested the effect of CHKA inhibition on cell growth, clonogenic survival and invasion. Tumor xenografts (n = 6 per group) were generated in mice using genetically engineered prostate cancer cells with inducible CHKA knockdown. Data were analyzed with χ(2) tests, Cox regression analysis, and Kaplan-Meier methods. All statistical tests were two-sided. RESULTS: CHKA expression was shown to be androgen regulated in cell lines, xenografts, and human tissue (log fold change from 6.75 to 6.59, P = .002) and was positively associated with tumor stage. CHKA binds directly to the ligand-binding domain (LBD) of AR, enhancing its stability. As such, CHKA is the first kinase identified as an AR chaperone. Inhibition of CHKA repressed the AR transcriptional program including pathways enriched for regulation of protein folding, decreased AR protein levels, and inhibited the growth of PCa cell lines, human PCa explants, and tumor xenografts. CONCLUSIONS: CHKA can act as an AR chaperone, providing, to our knowledge, the first evidence for kinases as molecular chaperones, making CHKA both a marker of tumor progression and a potential therapeutic target for PCa.

Systems biology of IL-6, IL-12 family cytokines.

Interleukin-6-type cytokines play important roles in the communication between cells of multicellular organisms. They are involved in the regulation of complex cellular processes such as proliferation and differentiation and act as key player during inflammation and immune response. A major challenge is to understand how these complex non-linear processes are connected and regulated. Systems biology approaches are used to tackle this challenge in an iterative process of quantitative experimental and mathematical analyses. Here we review quantitative experimental studies and systems biology approaches dealing with the function of Interleukin-6-type cytokines in physiological and pathophysiological conditions. These approaches cover the analyses of signal transduction on a cellular level up to pharmacokinetic and pharmacodynamic studies on a whole organism level.

MAPK-induced Gab1 translocation to the plasma membrane depends on a regulated intramolecular switch.

The timely orchestration of multiple signalling pathways is crucial for the integrity of an organism and therefore tightly controlled. Gab family proteins coordinate signal transduction at the plasma membrane (PM) by acting as docking platforms for signalling components involved in MAP kinase (MAPK), PI3 kinase (PI3K), phospholipase C (PLC) and Rho family GTPase signalling. The interaction with these components as well as the targeting of the docking platform to the PM underlies complex spatial and temporal regulatory mechanisms. Deregulated Gab1 activation and membrane binding have been observed in some haematopoietic malignancies and solid tumours, thereby contributing, for example, to the development of Philadelphia chromosome-negative myeloproliferative neoplasms and certain lung cancers. Previously, we could demonstrate that the presence of PIP3 in the PM, which is increased in many cancer cells, is not sufficient for constitutive Gab1 membrane recruitment. In addition, MAPK-dependent phosphorylation of Gab1 at serine 552 (Ser552) is vital for Gab1 membrane binding. Here, we confirm our hypothesis that in the absence of MAPK activity an intrinsic part of Gab1 prevents binding to PIP3 at the PM. This epitope of Gab1, which encompasses Ser552, interacts directly with the Gab1 PH domain. Two arginines located in positions +4 and +8 of Ser552 are essential for the interaction with the PH domain, as well as for the inhibition of membrane recruitment of unphosphorylated Gab1. Ser552 phosphorylation is dispensable in respective arginine to alanine mutants of Gab1. Gab1 recruitment to the PM is highly dynamic and continuous PI3K and MAPK activities are both essential for sustained Gab1 membrane localisation. Our data document the existence of a sophisticated and robust control mechanism that prevents Gab1 translocation and signalling complex assembly after the activation of either MAPK or PI3K alone.

Novel Nor-Homo- and Spiro-Oxetan- Steroids Target the Human Androgen Receptor and Act as Antiandrogens.

The prostate adenocarcinoma is the cancer with the highest incidence for men in Western countries. Targeting the androgen receptor (AR) by antagonists is used as hormone therapy for prostate cancer (PCa), however, eventually therapy resistance occurs in most patients. In most of these cancer the AR signaling is active and thus AR remains an important drug target. Since many years we are characterizing novel chemical structural platforms to provide a broader possibility for compounds that bind to and act as AR antagonists. Here, we describe the chemical synthesis of a battery of novel steroidal derivatives as nor-homo-, spiro-oxolan- and spiro-oxetan- steroids. They modulate the transcriptional activity of the human AR. As AR antagonists, the spiro-oxetan- steroid derivatives seem to be the most potent steroid derivatives. They inhibit the transcriptional activity of both wild-type AR as well as the AR mutant T877A. In line with this, these compounds bind to the human AR and inhibit the proliferation of the human androgen-dependent growing PCa cell line LNCaP. Interestingly, the castration-resistant AR expressing human PC3-AR cells are also growth inhibited. On mechanistic level, fluorescence resonance energy transfer (FRET) assays with living cells indicate that the androgen-induced N/C terminal interaction of the AR is inhibited by the investigated compounds. Using fluorescence recovery after photobleaching (FRAP) assays in living cells suggest a higher mobility of the AR in the cell nuclei in the presence of spiro-oxetan- steroidal antagonists. Together, these findings suggest that spiro-oxetan- steroids are very useful as a chemical platform for novel AR antagonists.

Supraphysiological androgen levels induce cellular senescence in human prostate cancer cells through the Src-Akt pathway.

BACKGROUND: Prostate cancer (PCa) is the second leading cause of cancer mortality of men in Western countries. The androgen receptor (AR) and AR-agonists (androgens) are required for the development and progression of the normal prostate as well as PCa. However, it is discussed that in addition to their tumor promoting activity, androgens may also exhibit tumor suppressive effects. A biphasic growth response to androgens a growth-promoting and -inhibition has been observed that suggests that administration of supraphysiological androgen levels mediates growth reduction in AR expressing PCa cells. METHODS: Detection of senescence markers, three dimensional interphase fluorescence in situ hybridization (3D-iFISH), qRT-PCR, Western blotting, detection of GFP fusions, prostatectomy, ex vivo culturing. RESULTS: Here, we describe that supraphysiological levels of androgens induce cell cycle arrest and markers of cellular senescence in human PCa cells, which may in part explain the growth inhibitory role of androgens. The expression of the senescence associated beta galactosidase is observed by treatment with the natural androgen DHT or the less metabolized synthetic androgen R1881. The induction of senescence marker was detected in human PCa cell lines as well as in human primary PCa tissue derived from prostatectomy treated ex vivo. Using interphase FISH (iFISH) suggests that the androgen-induced cellular senescence is associated with localizing the genomic E2F1 locus to senescence associated heterochromatic foci. Analysis of different signaling pathways in LNCaP cells suggest that the p16-Rb-E2F1 pathway is essential for the induction of cellular senescence since treatment with siRNA directed against p16 reduces the level of androgen-induced cellular senescence. Based on the rapid induction of androgen-mediated cellular senescence we identified the Src-PI3K-Akt-signaling pathway and autophagy being in part involved in androgen regulation. CONCLUSIONS: Taken together, our data suggest that AR-agonists at supraphysiological levels mediate induction of cellular senescence in human PCa cells, which may have a protective anti-cancer role. These results provide also new insights for understanding androgen-mediated regulation of PCa growth.

A natural androgen receptor antagonist induces cellular senescence in prostate cancer cells.

We have previously identified a natural occurring, androgen receptor-specific antagonist. Atraric acid (AA) inhibits the transactivation of the androgen receptor (AR) and androgen-mediated growth of AR-expressing human prostate cancer (PCa) cell lines. Here we show that AA treatment of living cells provokes molecular changes of AR signaling. In addition to a deceleration of nuclear translocation a block of the intramolecular amino/carboxy (N/C)-terminal interaction of the AR was observed. Furthermore, using high-resolution confocal fluorescence microscopy, a reduced speckle formation of the AR was observed in line with an increased intranuclear mobility of the receptor. This suggests decreased DNA binding of the AR, which is further indicated by an impaired chromatin recruitment of the AR to the prostate-specific antigen promoter and enhancer shown by chromatin immunoprecipitation experiments. Using inhibitors of the non-receptor tyrosine kinase Src or Akt, known interaction partners of AR, reduced the level of androgen-induced cellular senescence suggesting a partly non-genomic pathway to induce cellular senescence by AA. Using PP2 (4-Amino-5-(4-chlorophenyl)-7-(t-butyl)pyrazolo[3,4-d]pyrimidine) pyrimidine or Akt inhibitors, inhibitors of the nonreceptor tyrosine kinase Src or Akt, known interaction partners of AR, reduced the level of androgen-induced cellular senescence, suggesting a partly nongenomic pathway to induce cellular senescence by AA. Treatment of LNCaP cells with AA is associated with hypophosphorylation of the retinoblastoma tumor suppressor and an increase of p16 expression, whereas the p53-p21 signaling pathway seems not be affected by AA treatment. Analyzing human PCa tissue samples treated with AA ex vivo also indicates an induction of cellular senescence associated with an increase of p16 expression but not p21. Taken together, these data indicate that AA exhibits novel features to inhibit AR amino/carboxy-terminal interaction, the AR-mediated nuclear activities and growth of PCa cells.

Chaperones for proper androgen action - a plethora of assistance to androgen receptor function.

Abstract The androgen receptor (AR) plays a major role for normal prostate growth and also promotes the development and progression of prostate cancer (PCa). PCa, an important age-related disease, is one of the most commonly diagnosed cancers and the second leading cause of cancer mortality for men in Western countries. AR function and activity are regulated by molecular chaperones. The AR belongs to the steroid hormone receptor (SHR) family and can be activated by androgens such as dihydrotestosterone. SHRs are ligand-dependent transcription factors that are predominantly localized in the cytoplasm in the absence of their appropriate ligand. Upon hormone binding, translocation to the nucleus occurs as shown for glucocorticoid receptors, mineralocorticoid receptors, or the AR, while others, such as estrogen and progesterone receptors, are mainly nuclear. Importantly, the newly synthesized and unliganded receptors bind stepwise with chaperones then being associated in a dynamic chaperone heterocomplex, including heat shock proteins. It emerges that chaperones are very important, not only in the proper folding of the AR but they are also involved in receptor stability, intracellular localization and androgen-controlled transcription. Accordingly, chaperones may be interesting future targets for PCa treatment. In this review we will summarize the involvement of chaperones controlling AR activity.

Sodium butyrate induces cellular senescence in neuroblastoma and prostate cancer cells.

Cellular senescence leads to an irreversible block of cellular division capacity both in cell culture and in vivo. The induction of an irreversible cell cycle arrest is very useful for treatment of cancer. Histone deacetylases (HDACs) are considered as therapeutic targets to treat cancer patients. HDAC inhibitors repress cancer growth and are used in various clinical trials. Here, we analyzed whether sodium butyrate (NaBu), an inhibitor of class I and II HDACs, induces cellular senescence in neuroblastoma and prostate cancer (PCa) including an androgen-dependent as well as an androgen-independent human PCa cell line. We found that the HDAC inhibitors NaBu and valproic acid (VPA) induce cellular senescence in tumor cells. Interestingly, also an inhibitor of SIRT1, a class HDAC III, induces cellular senescence. Both neuroblastoma and human prostate cancer cell lines express senescence markers, such as the Senescence Associated-ß-galactosidase (SA-ß-Gal) and Senescence Associated Heterochromatin Foci (SAHF). Furthermore, NaBu down-regulates the proto-oncogenes c-Myc, Cyclin D1 and E2F1 mRNA levels. The mRNA level of the cell cycle inhibitor p16 remains unchanged whereas that of the tumor suppressor p21 is strongly up-regulated. Interestingly, NaBu treatment robustly increases reactive oxygen species (ROS) levels. These results indicate an epigenetic regulation and an association of HDAC inhibition and ROS production with cellular senescence. The data underline that tumor cells can be driven towards cellular senescence by HDAC inhibitors, which may further arise as a potent possibility for tumor suppression.