Development and limitations of lentivirus vectors as tools for tracking differentiation in prostate epithelial cells

ETS transcription factor ELF3 (ESE-1) is a cell cycle regulator in benign and malignant prostate

This study aimed to elucidate the role of ELF3, an ETS family member in normal prostate growth and prostate cancer. Silencing ELF3 in both benign prostate (BPH-1) and prostate cancer (PC3) cell lines resulted in decreased colony forming ability, inhibition of cell migration and reduced cell viability due to cell cycle arrest, establishing ELF3 as a cell cycle regulator. Increased ELF3 expression in more advanced prostate tumours was shown by immunostaining of tissue microarrays and from analysis of gene expression and genetic alteration studies. This study indicates that ELF3 functions as part of normal prostate epithelial growth but also as a potential oncogene in advanced prostate cancers.

Cellular GFP Toxicity and Immunogenicity: Potential Confounders in in Vivo Cell Tracking Experiments

Green Fluorescent protein (GFP), used as a cellular tag, provides researchers with a valuable method of measuring gene expression and cell tracking. However, there is evidence to suggest that the immunogenicity and cytotoxicity of GFP potentially confounds the interpretation of in vivo experimental data. Studies have shown that GFP expression can deteriorate over time as GFP tagged cells are prone to death. Therefore, the cells that were originally marked with GFP do not survive and cannot be accurately traced over time. This review will present current evidence for the immunogenicity and cytotoxicity of GFP in in vivo studies by characterizing these responses.

Inhibition of the PI3K/AKT/mTOR pathway activates autophagy and compensatory Ras/Raf/MEK/ERK signalling in prostate cancer

The PI3K/AKT/mTOR pathway is frequently activated in advanced prostate cancer, due to loss of the tumour suppressor PTEN, and is an important axis for drug development. We have assessed the molecular and functional consequences of pathway blockade by inhibiting AKT and mTOR kinases either in combination or as individual drug treatments. In established prostate cancer cell lines, a decrease in cell viability and in phospho-biomarker expression was observed. Although apoptosis was not induced, a G1 growth arrest was observed in PTEN null LNCaP cells, but not in BPH1 or PC3 cells. In contrast, when the AKT inhibitor AZD7328 was applied to patient-derived prostate cultures that retained expression of PTEN, activation of a compensatory Ras/MEK/ERK pathway was observed. Moreover, whilst autophagy was induced following treatment with AZD7328, cell viability was less affected in the patient-derived cultures than in cell lines. Surprisingly, treatment with a combination of both AZD7328 and two separate MEK1/2 inhibitors further enhanced phosphorylation of ERK1/2 in primary prostate cultures. However, it also induced irreversible growth arrest and senescence.

Ex vivo treatment of a patient-derived xenograft (PDX) of prostate cancer with a combination of AZD7328 and the mTOR inhibitor KU-0063794, significantly reduced tumour frequency upon re-engraftment of tumour cells.

The results demonstrate that single agent targeting of the PI3K/AKT/mTOR pathway triggers activation of the Ras/MEK/ERK compensatory pathway in near-patient samples. Therefore, blockade of one pathway is insufficient to treat prostate cancer in man.

Stem cells and the role of ETS transcription factors in the differentiation hierarchy of normal and malignant prostate epithelium

Prostate cancer is the most common cancer of men in the UK and accounts for a quarter of all new cases. Although treatment of localised cancer can be successful, there is no cure for patients presenting with invasive prostate cancer and there are less treatment options. They are generally treated with androgen-ablation therapies but eventually the tumours become hormone resistant and patients develop castration-resistant prostate cancer (CRPC) for which there are no further successful or curative treatments. This highlights the need for new treatment strategies. In order to prevent prostate cancer recurrence and treatment resistance, all the cell populations in a heterogeneous prostate tumour must be targeted, including the rare cancer stem cell (CSC) population. The ETS transcription factor family members are now recognised as a common feature in multiple cancers including prostate cancer; with aberrant expression, loss of tumour suppressor function, inactivating mutations and the formation of fusion genes observed. Most notably, the TMPRSS2-ERG gene fusion is present in approximately 50% of prostate cancers and in prostate CSCs. However, the role of other ETS transcription factors in prostate cancer is less well understood. This review will describe the prostate epithelial cell hierarchy and discuss the evidence behind prostate CSCs and their inherent resistance to conventional cancer therapies. The known and proposed roles of the ETS family of transcription factors in prostate epithelial cell differentiation and regulation of the CSC phenotype will be discussed, as well as how they might be targeted for therapy.

Lent-On-Plus Lentiviral vectors for conditional expression in human stem cells

Conditional transgene expression in human stem cells has been difficult to achieve due to the low efficiency of existing delivery methods, the strong silencing of the transgenes and the toxicity of the regulators. Most of the existing technologies are based on stem cells clones expressing appropriate levels of tTA or rtTA transactivators (based on the TetR-VP16 chimeras). In the present study, we aim the generation of Tet-On all-in-one lentiviral vectors (LVs) that tightly regulate transgene expression in human stem cells using the original TetR repressor. By using appropriate promoter combinations and shielding the LVs with the Is2 insulator, we have constructed the Lent-On-Plus Tet-On system that achieved efficient transgene regulation in human multipotent and pluripotent stem cells. The generation of inducible stem cell lines with the Lent-ON-Plus LVs did not require selection or cloning, and transgene regulation was maintained after long-term cultured and upon differentiation toward different lineages. To our knowledge, Lent-On-Plus is the first all-in-one vector system that tightly regulates transgene expression in bulk populations of human pluripotent stem cells and its progeny.

An Endothelial Hsp70-TLR4 Axis Limits Nox3 Expression and Protects Against Oxidant Injury in Lungs

AIMS

Oxidants play a critical role in the pathogenesis of acute lung injury (ALI). Nox3 is a novel member of the NADPH oxidase (Nox) family of oxidant-generating enzymes, which our laboratory had previously identified to be induced in the lungs of TLR4(-/-) mice. However, the physiologic role of Nox3 induction in lungs and its precise relationship to TLR4 are unknown. Furthermore, the cell compartment involved and the signaling mechanisms of Nox3 induction are unknown.

RESULTS

We identified that Nox3 is regulated by heat shock protein 70 (Hsp70) signaling via a TLR4-Trif-signal transducer and activator of transcription 3 (Stat3) pathway and that Nox3 induction leads to increased oxidant injury and death in mice and lung endothelial cells. We generated Nox3(-/-)/TLR4(-/-) double knockout mice, endothelial-targeting lentiviral silencing constructs, and endothelial-targeted Stat3(-/-) mice to specifically demonstrate that Nox3 induction is responsible for the pro-oxidant, proapoptotic phenotype of TLR4(-/-) mice. We also show that an endothelial Hsp70-TLR4-Trif-Stat3 axis is required to suppress deleterious Nox3 induction.

INNOVATION

To date, a physiologic role for Nox3 in oxidant-induced ALI has not been identified. In addition, we generated unique double knockout mice and endothelial-targeted lentiviral silencing constructs to specifically demonstrate the role of a TLR4 signaling pathway in regulating pro-oxidant generation.

CONCLUSIONS

We identified an endothelial TLR4-Trif antioxidant pathway that leads to the inhibition of a novel NADPH oxidase, Nox3, in lungs and lung endothelial cells. We also identified the role of a TLR4 ligand, Hsp70, in suppressing Nox3 in basal and pro-oxidant conditions. These studies identify potentially new therapeutic targets in oxidant-induced ALI. Antioxid. Redox Signal. 24, 991-1012.

Harvesting Human Prostate Tissue Material and Culturing Primary Prostate Epithelial Cells

In order to fully explore the biology of a complex solid tumor such as prostate cancer, it is desirable to work with patient tissue. Only by working with cells from a tissue can we take into account patient variability and tumor heterogeneity. Cell lines have long been regarded as the workhorse of cancer research and it could be argued that they are of most use when considered within a panel of cell lines, thus taking into account specified mutations and variations in phenotype between different cell lines. However, often very different results are obtained when comparing cell lines to primary cells cultured from tissue. It stands to reason that cells cultured from patient tissue represents a close-to-patient model that should and does produce clinically relevant data. This chapter aims to illustrate the methods of processing, storing and culturing cells from prostate tissue, with a description of potential uses.

DNA hypermethylation in prostate cancer is a consequence of aberrant epithelial differentiation and hyperproliferation

Prostate cancer (CaP) is mostly composed of luminal-like differentiated cells, but contains a small subpopulation of basal cells (including stem-like cells), which can proliferate and differentiate into luminal-like cells. In cancers, CpG island hypermethylation has been associated with gene downregulation, but the causal relationship between the two phenomena is still debated. Here we clarify the origin and function of CpG island hypermethylation in CaP, in the context of a cancer cell hierarchy and epithelial differentiation, by analysis of separated basal and luminal cells from cancers. For a set of genes (including GSTP1) that are hypermethylated in CaP, gene downregulation is the result of cell differentiation and is not cancer specific. Hypermethylation is however seen in more differentiated cancer cells and is promoted by hyperproliferation. These genes are maintained as actively expressed and methylation-free in undifferentiated CaP cells, and their hypermethylation is not essential for either tumour development or expansion. We present evidence for the causes and the dynamics of CpG island hypermethylation in CaP, showing that, for a specific set of genes, promoter methylation is downstream of gene downregulation and is not a driver of gene repression, while gene repression is a result of tissue-specific differentiation.

Lentiviral delivery of RNAi for in vivo lineage-specific modulation of gene expression in mouse lung macrophages

Although RNA interference (RNAi) has become a ubiquitous laboratory tool since its discovery 12 years ago, in vivo delivery to selected cell types remains a major technical challenge. Here, we report the use of lentiviral vectors for long-term in vivo delivery of RNAi selectively to resident alveolar macrophages (AMs), key immune effector cells in the lung. We demonstrate the therapeutic potential of this approach by RNAi-based downregulation of p65 (RelA), a component of the pro-inflammatory transcriptional regulator, nuclear factor κB (NF-κB) and a key participant in lung disease pathogenesis. In vivo RNAi delivery results in decreased induction of NF-κB and downstream neutrophilic chemokines in transduced AMs as well as attenuated lung neutrophilia following stimulation with lipopolysaccharide (LPS). Through concurrent delivery of a novel lentiviral reporter vector (lenti-NF-κB-luc-GFP) we track in vivo expression of NF-κB target genes in real time, a critical step towards extending RNAi-based therapy to longstanding lung diseases. Application of this system reveals that resident AMs persist in the airspaces of mice following the resolution of LPS-induced inflammation, thus allowing these localized cells to be used as effective vehicles for prolonged RNAi delivery in disease settings.

Prominin-1 (CD133) Expression in the Prostate and Prostate Cancer: A Marker for Quiescent Stem Cells

The origin and phenotype of stem cells in human prostate cancer remains a subject of much conjecture. In this scenario, CD133 has been successfully used as a stem cell marker in both normal prostate and prostate cancer. However, cancer stem cells have been identified without the use of this marker, opening up the possibility of a CD133 negative cancer stem cell. In this chapter, we review the current literature regarding prostate cancer stem cells, with specific reference to the expression of CD133 as a stem cell marker to identify and purify stem cells in normal prostate epithelium and prostate cancer.

Prostate cancer stem cells: are they androgen-responsive?

The prostate gland is highly dependent on androgens for its development, growth and function. Consequently, the prostatic epithelium predominantly consists of androgen-dependent luminal cells, which express the androgen receptor at high levels. In contrast, androgens are not required for the survival of the androgen-responsive, but androgen-independent, basal compartment in which stem cells reside. Basal and luminal cells are linked in a hierarchical pathway, which most probably exists as a continuum with different stages of phenotypic change. Prostate cancer is also characterised by heterogeneity, which is reflected in its response to treatment. The putative androgen receptor negative cancer stem cell (CSC) is likely to form a resistant core after most androgen-based therapies, contributing to the evolution of castration-resistant disease. The development of CSC-targeted therapies is now of crucial importance and identifying the phenotypic differences between CSCs and both their progeny will be key in this process.

Prostate cancer stem cells: do they have a basal or luminal phenotype?

The prostate is a luminal secretory tissue whose function is regulated by male sex hormones. Castration produces involution of the prostate to a reversible basal state, and as the majority of prostate cancers also have a luminal phenotype, drug-induced castration is a front line therapy. It has therefore been assumed that the tumor arises from transformation of a luminal progenitor cell. Here, we demonstrate that a minority basal "cancer stem cell" (CSC) population persists in primary human prostate cancers, as in normal prostate, serving as a reservoir for tumor recurrence after castration therapy. While the CSCs exhibit a degree of phenotypic fluidity from different patients, the tumor-initiating cells in immunocompromised mice express basal markers (such as p63), but do not express androgen receptor (AR) or markers of luminal differentiation (PSA, PAP) when freshly fractionated from human tissues or following culture in vitro. Estrogen receptors α and β and AR are transcriptionally active in the transit amplifying (TA) cell (the progeny of SC). However, AR protein is consistently undetectable in TA cells. The prostate-specific TMPRSS2 gene, while upregulated by AR activity in luminal cells, is also transcribed in basal populations, confirming that AR acts as an expression modulator. Selected cells with basal phenotypes are tumor initiating, but the resultant tumors are phenotypically intermediate, with focal expression of AR, AMACR, and p63. In vitro differentiation experiments, employing lentivirally transduced SCs with a luminal (PSA-probasin) promoter regulating a fluorescent indicator gene, confirm that the basal SCs are the source of luminal progeny.

Cancer stem cells, models of study and implications of therapy resistance mechanisms

There is now compelling evidence for tumour initiating or cancer stem cells (CSCs) in human cancers. The current evidence of this CSC hypothesis, the CSC phenotype and methods of identification, culture and in vitro modelling will be presented, with an emphasis on prostate cancer. Inherent in the CSC hypothesis is their dual role, as a tumour-initiating cell, and as a source of treatment-resistant cells; the mechanisms behind therapeutic resistance will be discussed. Such resistance is a consequence of the unique CSC phenotype, which differs from the differentiated progeny, which make up the bulk of a tumour. It seems that to target the whole tumour, employing traditional therapies to target bulk populations alongside targeted CSC-specific drugs, provides the best hope of lasting treatment or even cure.