A reciprocal feedback between the PDZ binding kinase and androgen receptor drives prostate cancer.

Elucidation of mechanisms underlying the increased androgen receptor (AR) activity and subsequent development of aggressive prostate cancer (PrCa) is pivotal in developing new therapies. Using a systems biology approach, we interrogated the AR-regulated proteome and identified PDZ binding kinase (PBK) as a novel AR-regulated protein that regulates full-length AR and AR variants (ARVs) activity in PrCa. PBK overexpression in aggressive PrCa is associated with early biochemical relapse and poor clinical outcome. In addition to its carboxy terminus ligand-binding domain, PBK directly interacts with the amino terminus transactivation domain of the AR to stabilise it thereby leading to increased AR protein expression observed in PrCa. Transcriptome sequencing revealed that PBK is a mediator of global AR signalling with key roles in regulating tumour invasion and metastasis. PBK inhibition decreased growth of PrCa cell lines and clinical specimen cultured ex vivo. We uncovered a novel interplay between AR and PBK that results in increased AR and ARVs expression that executes AR-mediated growth and progression of PrCa, with implications for the development of PBK inhibitors for the treatment of aggressive PrCa.

Synthetic lethality between androgen receptor signalling and the PARP pathway in prostate cancer.

Emerging data demonstrate homologous recombination (HR) defects in castration-resistant prostate cancers, rendering these tumours sensitive to PARP inhibition. Here we demonstrate a direct requirement for the androgen receptor (AR) to maintain HR gene expression and HR activity in prostate cancer. We show that PARP-mediated repair pathways are upregulated in prostate cancer following androgen-deprivation therapy (ADT). Furthermore, upregulation of PARP activity is essential for the survival of prostate cancer cells and we demonstrate a synthetic lethality between ADT and PARP inhibition in vivo. Our data suggest that ADT can functionally impair HR prior to the development of castration resistance and that, this potentially could be exploited therapeutically using PARP inhibitors in combination with androgen-deprivation therapy upfront in advanced or high-risk prostate cancer.Tumours with homologous recombination (HR) defects become sensitive to PARPi. Here, the authors show that androgen receptor (AR) regulates HR and AR inhibition activates the PARP pathway in vivo, thus inhibition of both AR and PARP is required for effective treatment of high risk prostate cancer.

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.

Activated Notch1 maintains the phenotype of radial glial cells and promotes their adhesion to laminin by upregulating nidogen.

Radial glia are neural stem cells that exist only transiently during central nervous system (CNS) development, where they serve as scaffolds for neuronal migration. Their instability makes them difficult to study, and therefore we have isolated stabilized radial glial clones from E14.5 cortical progenitors (e.g., L2.3) after expression of v-myc. Activated Notch1 intracellular region (actNotch1) promotes radial glia in the embryonic mouse forebrain (Gaiano et al., (2000), and when it was introduced into E14.5 cortical progenitors or radial glial clone L2.3, the cells exhibited enhanced radial morphology and increased expression of the radial glial marker BLBP. A representative clone of L2.3 cells expressing actNotch1 called NL2.3-4 migrated more extensively than L2.3 cells in culture and in white matter of the adult rat spinal cord. Microarray and RT-PCR comparisons of mRNAs expressed in these closely related clones showed extensive similarities, but differed significantly for certain mRNAs including several cell adhesion molecules. Cell adhesion assays demonstrated significantly enhanced adhesion to laminin of NL2.3-4 by comparison to L2.3 cells. The laminin binding protein nidogen was the most highly induced adhesion molecule in NL2.3-4, and immunological analyses indicated that radial glia synthesize and secrete nidogen. Adhesion of NL2.3-4 cells to laminin was inhibited by anti-nidogen antibodies and required the nidogen binding region in laminin, indicating that nidogen promotes cell adhesion to laminin. The combined results indicate that persistent expression of activated Notch1 maintains the phenotype of radial glial cells, inhibits their differentiation, and promotes their adhesion and migration on a laminin/nidogen complex.

The inhibitory CD200R is differentially expressed on human and mouse T and B lymphocytes.

To ensure an adequate response against pathogens and prevent unwanted self-reactivity, immune cells need to functionally express both activating and inhibitory receptors. CD200R is an inhibitory receptor mainly expressed on myeloid cells that down-modulates cellular activation both in vivo and in vitro. Although previously mainly studied as a regulator of myeloid function, we now show that CD200R is differentially expressed on human and mouse T-cell subsets. In both species, CD4+ T cells express higher amounts of CD200R than CD8+ T cells, and memory cells express higher amounts of CD200R than naïve or effector cells. CD200R expression is up-regulated on both CD4+ and CD8+ T cells after stimulation in vitro. Furthermore, we show CD200R expression on human and mouse B cells. In human tonsils, CD200R is differentially expressed on B cells, with high expression on memory cells and plasmablasts. Mice lacking the ligand for CD200R, CD200-/- mice, do not show abnormal composition of the lymphocyte compartment and have normal B cell responses to antigenic challenge. Although the functional implications remain to be elucidated, the expression of CD200R on lymphocytes suggests a much broader role for CD200R-mediated immune regulation than previously anticipated.