Dominant-negative androgen receptor inhibition of intracrine androgen-dependent growth of castration-recurrent prostate cancer

Mutation of androgen receptor N-terminal phosphorylation site Tyr-267 leads to inhibition of nuclear translocation and DNA binding

Reactivation of androgen receptor (AR) may drive recurrent prostate cancer in castrate patients. Ack1 tyrosine kinase is overexpressed in prostate cancer and promotes castrate resistant xenograft tumor growth and enhances androgen target gene expression and AR recruitment to enhancers. Ack1 phosphorylates AR at Tyr-267 and possibly Tyr-363, both in the N-terminal transactivation domain. In this study, the role of these phosphorylation sites was investigated by characterizing the phosphorylation site mutants in the context of full length and truncated AR lacking the ligand-binding domain. Y267F and Y363F mutants showed decreased transactivation of reporters. Expression of wild type full length and truncated AR in LNCaP cells increased cell proliferation in androgen-depleted conditions and increased colony formation. However, the Y267F mutant of full length and truncated AR was defective in stimulating cell proliferation. The Y363F mutant was less severely affected than the Y267F mutant. The full length AR Y267F mutant was defective in nuclear translocation induced by androgen or Ack1 kinase. The truncated AR was constitutively localized to the nucleus. Chromatin immunoprecipitation analysis showed that it was recruited to the target enhancers without androgen. The truncated Y267F AR mutant did not exhibit constitutive nuclear localization and androgen enhancer binding activity. These results support the concept that phosphorylation of Tyr-267, and to a lesser extent Tyr-363, is required for AR nuclear translocation and recruitment and DNA binding and provide a rationale for development of novel approaches to inhibit AR activity.

Role of miRNA let-7 and its major targets in prostate cancer

Prostate cancer is worldwide the sixth leading cause of cancer related death in men thus early detection and successful treatment are still of major interest. The commonly performed screening of the prostate-specific antigen (PSA) is controversially discussed, as in many patients the prostate-specific antigen levels are chronically elevated in the absence of cancer. Due to the unsatisfying efficiency of available prostate cancer screening markers and the current treatment outcome of the aggressive hormone refractory prostate cancer, the evaluation of novel molecular markers and targets is considered an issue of high importance. MicroRNAs are relatively stable in body fluids orchestrating simultaneously the expression of many genes. These molecules are currently discussed to bear a greater diagnostic potential than protein-coding genes, being additionally promising therapeutic drugs and/or targets. Herein we review the potential impact of the microRNA let-7 family on prostate cancer and show how deregulation of several of its target genes could influence the cellular equilibrium in the prostate gland, promoting cancer development as they do in a variety of other human malignant neoplasias.

Negative regulation of the androgen receptor gene through a primate-specific androgen response element present in the 5' UTR

The androgen receptor (AR) is a widely expressed ligand-activated transcription factor which mediates androgen signalling by binding to androgen response elements (AREs) in normal tissue and prostate cancer (PCa). Within tumours, the amount of AR plays a crucial role in determining cell growth, resistance to therapy and progression to fatal castrate recurrent PCa in which prostate cells appear to become independent of androgenic steroids. Despite the pivotal role of the AR in male development and fertility and all stages of PCa development, the mechanisms governing AR expression remain poorly understood. In this work, we describe an active nonconsensus androgen response element (ARE) in the 5' UTR of the human AR gene. The ARE represses transcription upon binding of activated AR, and this downregulation is relieved by disruption of the regulatory element through mutation. Also, multiple species comparison of the genomic region reveals that this ARE is specific to primates, leading to the conclusion that care must be exercised when elucidating the operation of the human AR in PCa based upon rodent promoter studies.

High SPDEF may identify patients who will have a prolonged response to androgen deprivation therapy

BACKGROUND

Due to the indolent nature of prostate cancer, new prognostic measures are needed to identify patients with life threatening disease. SAM pointed domain-containing Ets transcription factor (SPDEF) has been associated with good prognosis and demonstrates an intimate relationship with the androgen receptor (AR), however its role in prostate cancer progression remains unclear.

METHODS

A tissue microarray constructed from cores of 713 consecutive radical prostatectomy specimens were immunohistochemically stained for SPDEF and correlated with progression free and metastatic free survival. In vitro studies assessed growth rate, migration, and sensitivity to bicalutamide to explore mechanisms behind the tissue microarray observations.

RESULTS

Patients with high SPDEF demonstrate longer metastases free survival after receiving the standard of care (HR = 9.80, P = 0.006). SPDEF expression corresponded with bicalutamide growth inhibition and apoptosis induction in all cell lines studied. In addition, a feedforward loop of AR-SPEF expression regulation is observed.

CONCLUSIONS

SPDEF may be clinically useful to identify patients who will have extended benefits from androgen deprivation therapy. In vitro observations suggest SPDEF mediates initial sensitivity to androgen deprivation therapy through both AR regulation and downstream events.

Insulin receptor isoform switching in intestinal stem cells, progenitors, differentiated lineages and tumors: evidence that IR-B limits proliferation

Despite evidence for the impact of insulin on intestinal epithelial physiology and pathophysiology, the expression patterns, roles, and regulation of insulin receptor (IR) and IR isoforms in the intestinal epithelium are not well characterized. IR-A is thought to mediate the proliferative effects of insulin or insulin growth factors (IGFs) in fetal or cancer cells. IR-B is considered to be the metabolic receptor for insulin in specialized tissues. This study used a novel Sox9-EGFP reporter mouse that permits isolation of intestinal epithelial stem cells (IESCs), progenitors, enteroendocrine cells and differentiated lineages, the Apc(Min/+) mouse model of precancerous adenoma and normal human intestinal and colorectal cancer (CRC) cell lines. We tested the hypothesis that there is differential expression of IR-A or IR-B in stem and tumor cells versus differentiated intestinal epithelial cells (IECs) and that IR-B impacts cell proliferation. Our findings provide evidence that IR-B expression is significantly lower in highly proliferative IESCs and progenitor cells versus post-mitotic, differentiated IECs and in subconfluent and undifferentiated versus differentiated Caco-2 cells. IR-B is also reduced in Apc(Min/+) tumors and highly tumorigenic CRC cells. These differences in IR-B were accompanied by altered levels of mRNAs encoding muscleblind-like 2 (MBNL2), a known regulator of IR alternative splicing. Forced IR-B expression in subconfluent and undifferentiated Caco-2 cells reduced proliferation and increased biomarkers of differentiation. Our findings indicate that the impact of insulin on different cell types in the intestinal epithelium might differ depending on relative IR-B IR-A expression levels and provide new evidence for the roles of IR-B to limit proliferation of CRC cells.

High efficiency gene transfer to airways of mice using influenza hemagglutinin pseudotyped lentiviral vectors

BACKGROUND

A limitation to efficient lentivirus-mediated airway gene transfer is the lack of receptors to commonly used viral envelopes on the luminal surface of airway epithelia. The use of viral envelopes with natural tropism to the airway could be useful for overcoming this limitation.

METHODS

We investigated influenza hemagglutinin (HA) pseudotyped equine infectious anemia virus-derived lentiviral vector-mediated gene transfer to the airway epithelium of adult and newborn mice. For these studies, high-titer vectors were delivered by intranasal administration. In addition, we tested the feasibility of vector re-dosing to the nasal airway.

RESULTS

Delivery of high-titer HA pseudotyped lentiviral vectors by nasal administration to newborn mouse pups or adult mice results in the efficient transduction of airway epithelial cells in the nose, trachea, and lungs. In the nose, vector expression was predominant in the respiratory epithelium and was not observed in the olfactory epithelium. In the trachea and large airways of the lung, approximately 46% and 40%, respectively, of surface epithelial cells could be transduced. The efficiency of re-dosing to the nasal airway of mice was found to be dependent of the age of the animal when the first dose is administered, as well as the length of time between doses.

CONCLUSIONS

A single intranasal dose of concentrated influenza HA-pseudotyped lentiviral vector is sufficient for efficient gene transfer to the airways of mice. This is a promising result that could lead to the development of effective gene transfer reagents for the treatment of cystic fibrosis and other human lung diseases.