Role of p63 and basal cells in the prostate

Trop2 identifies a subpopulation of murine and human prostate basal cells with stem cell characteristics

The epithelium of the adult prostate contains 3 distinct cell types: basal, luminal, and neuroendocrine. Tissue-regenerative activity has been identified predominantly from the basal cells, isolated by expression of CD49f and stem cell antigen-1 (Sca-1). An important question for the field is whether all basal cells have stem cell characteristics. Prostate-specific microarray databases were interrogated to find candidate surface antigens that could subfractionate the basal cell population. Tumor-associated calcium signal transducer 2 (TACSTD2/Trop2/M1S1/GA733-1) was identified because it was enriched after castration, in prostate sphere cells and in the basal fraction. In the murine prostate, Trop2 shows progenitor characteristics such as localization to the region of the gland proximal to the urethra and enrichment for sphere-forming and colony-forming cells. Trop2 subfractionates the basal cells into 2 populations, both of which express characteristic basal cell markers by quantitative PCR. However, only the basal cells expressing high levels of Trop2 were able to efficiently form spheres in vitro. In the human prostate, where Sca-1 is not expressed, sphere-forming progenitor cells were also isolated based on high expression of Trop2 and CD49f. Trop2-expressing murine basal cells could regenerate prostatic tubules in vivo, whereas the remaining basal cells had minimal activity. Evidence was found for basal, luminal, and neuroendocrine cells in prostatic tubules regenerated from Trop2(hi) basal cells. In summary, functionally distinct populations of cells exist within the prostate basal compartment and an epithelial progenitor can give rise to neuroendocrine cells in vivo.

Generation of a prostate from a single adult stem cell

The existence of prostate stem cells (PSCs) was first postulated from the observation that normal prostate regeneration can occur after repeated cycles of androgen deprivation and replacement in rodents. Given the critical role of PSCs in maintaining prostate tissue integrity and their potential involvement in prostate tumorigenesis, it is important to define specific markers for normal PSCs. Several cell-surface markers have been reported to identify candidate PSCs, including stem cell antigen-1 (Sca-1, also known as Ly6a), CD133 (Prom1) and CD44 (refs 3-10). However, many non-PSCs in the mouse prostate also express these markers and thus identification of a more defined PSC population remains elusive. Here we identify CD117 (c-kit, stem cell factor receptor) as a new marker of a rare adult mouse PSC population, and demonstrate that a single stem cell defined by the phenotype Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) can generate a prostate after transplantation in vivo. CD117 expression is predominantly localized to the region of the mouse prostate proximal to the urethra and is upregulated after castration-induced prostate involution-two characteristics consistent with that of a PSC marker. CD117(+) PSCs can generate functional, secretion-producing prostates when transplanted in vivo. Moreover, CD117(+) PSCs have long-term self-renewal capacity, as evidenced by serial isolation and transplantation in vivo. Our data establish that single cells in the adult mouse prostate with multipotent, self-renewal capacity are defined by a Lin(-)Sca-1(+)CD133(+)CD44(+)CD117(+) phenotype.

Minireview: regulation of prostatic stem cells by stromal niche in health and disease

The isolation and characterization of prostatic stem cells has received significant attention in the last few years based on the belief that aberrant regulation of adult stem cells leads to prostate disease including cancer. The nature of the perturbations in stem cell regulation remains largely unknown. Although adult stem cells are can be governed by autonomous regulatory mechanisms, the stromal niche environment also provides essential cues to direct directing differentiation decisions and can lead to aberrant proliferation and/or differentiation. Elegant tissue recombination experiments, pioneered by Gerald Cunha and colleagues, provided evidence that quiescent epithelial tissues containing adult stem cells were capable of altered differentiation in response to inductive and instructive mesenchyme. In more recent times, it has been demonstrated that embryonic mesenchyme is sufficiently powerful to direct the differentiation of embryonic stem cells into mature prostate or bladder. In addition, prostatic tumor stroma provides another unique niche or microenvironment for stem cell differentiation that is distinct to normal stroma. This review highlights the importance of the appropriate selection of the stromal cell niche for tissue regeneration and implies plasticity of adult stem cells that is dictated by the tissue microenvironment.

Exploring the origins of the normal prostate and prostate cancer stem cell

Prostate epithelial stem cells (PSCs) are primed by the urogenital mesenchyme to initiate bud formation and branching morphogenesis, ultimately culminating in a glandular structure composed of luminal, basal and neuroendocrine cells. Identity of this cell has remained elusive however cell populations enriched for cells exhibiting stem cell characteristics express the stem cell markers CD133(+), alpha2beta1(hi), CD44 and Sca-1 along with embryonic stem cell factors including Oct-1, Nanog, Sox2 and nestin. Androgens are critical to prostate organogenesis and play a major role in normal prostate function and the development of prostate cancer. Cell lineage is another variable in the development of prostate cancer. This review discusses the embryonic prostate stem cell niche, normal prostate development, isolation and characterization of normal prostate and prostate cancer stem cells, and current concepts on the origin of prostate cancer.

Prostate tumor progression is mediated by a paracrine TGF-beta/Wnt3a signaling axis

Transforming growth factor (TGF)-beta is an important paracrine factor in tumorigenesis. Ligand binding of the type I and II TGF-beta receptors initiate downstream signaling. The role of stromal TGF-beta signaling in prostate cancer progression is unknown. In mice, the conditional stromal knockout of the TGF-beta type II receptor expression (Tgfbr2(fspKO)) resulted in the development of prostatic intraepithelial neoplasia and progression to adenocarcinoma within 7 months. Clinically, we observed a loss of TGF-beta receptor type II expression in 69% of human prostate cancer-associated stroma, compared to 15% of stroma associated with benign tissues (n=140, P-value <0.0001). To investigate the mechanism of paracrine TGF-beta signaling in prostate cancer progression, we compared the effect of the prostatic stromal cells from Tgfbr2(fspKO) and floxed TGF-beta type II receptor Tgfbr2(floxE2/floxE2) mice on LNCaP human prostate cancer cells in vitro and tissue recombination xenografts. Induction of LNCaP cell proliferation and tumorigenesis was observed by Tgfbr2(fspKO) prostate stroma as a result of elevated Wnt3a expression. Neutralizing antibodies to Wnt3a reversed LNCaP tumorigenesis. The TGF-beta inhibition of Wnt3a expression was in part through the suppression of Stat3 activity on the Wnt3a promoter. In conclusion, the frequent loss of stromal TGF-beta type II receptor expression in human prostate cancer can relieve the paracrine suppression of Wnt3a expression.

Bad seeds produce bad crops: a single stage-process of prostate tumor invasion

It is a commonly held belief that prostate carcinogenesis is a multi-stage process and that tumor invasion is triggered by the overproduction of proteolytic enzymes. This belief is consistent with data from cell cultures and animal models, whereas is hard to interpret several critical facts, including the presence of cancer in "healthy" young men and cancer DNA phenotype in morphologically normal prostate tissues. These facts argue that alternative pathways may exist for prostate tumor invasion in some cases. Since degradation of the basal cell layer is the most distinct sign of invasion, our recent studies have attempted to identify pre-invasive lesions with focal basal cell layer alterations. Our studies revealed that about 30% of prostate cancer patients harbored normal appearing duct or acinar clusters with a high frequency of focal basal cell layer disruptions. These focally disrupted basal cell layers had significantly reduced cell proliferation and tumor suppressor expression, whereas significantly elevated degeneration, apoptosis, and infiltration of immunoreactive cells. In sharp contrast, associated epithelial cell had significantly elevated proliferation, expression of malignancy-signature markers, and physical continuity with invasive lesions. Based on these and other findings, we have proposed that these normal appearing duct or acinar clusters are derived from monoclonal proliferation of genetically damaged stem cells and could progress directly to invasion through two pathways: 1) clonal in situ transformation (CIST) and 2) multi-potential progenitor mediated "budding" (MPMB). These pathways may contribute to early onset of prostate cancer at young ages, and to clinically more aggressive prostate tumors.

Prostate cancer and metastasis initiating stem cells

Androgen refractory prostate cancer metastasis is a major clinical challenge. Mechanism-based approaches to treating prostate cancer metastasis require an understanding of the developmental origin of the metastasis-initiating cell. Properties of prostate cancer metastases such as plasticity with respect to differentiated phenotype and androgen independence are consistent with the transformation of a prostate epithelial progenitor or stem cell leading to metastasis. This review focuses upon current evidence and concepts addressing the identification and properties of normal prostate stem or progenitor cells and their transformed counterparts.

Stem cells: The root of prostate cancer?

The cancer stem cell (CSC) model states that tumors contain a reservoir of self-renewing cells that maintain the heterogeneous cell population of the tumor. These cells appear to be resistant to therapy and can therefore survive to repopulate the tumor during progression to therapy resistant disease. The biology of CSCs is still not definitive since it is difficult to isolate them from solid tumors and analyze their characteristics in vitro. Another challenge is to correlate these characteristics with tumor development and progression in vivo. Using the prostate CSC as a model, this review presents the CSC hypothesis, reviews the origin, identification and functions of prostate CSCs, and discusses the clinical implications and therapeutic challenges CSCs have for cancer therapy.

p63 in prostate biology and pathology

The identification of stem cells and differentiation programs regulating the development and maintenance of the normal prostate epithelium is essential for the identification of the cell type(s) and molecular alterations involved in the development and propagation of prostate cancer (CaP). The p53-homologue p63 is highly expressed in normal prostate basal cells and is a clinically useful biomarker for the diagnosis of CaP. Importantly, p63 has been shown to play a critical role in prostate development. Recent experimental evidence also suggests that this gene is essential for normal stem cell function in the prostate as well as other epithelial organs. Future studies aimed at better defining the role of p63 in the renewal of the adult prostate epithelium are likely to shed new light on the mechanisms involved in prostate carcinogenesis.

Prostate cancer stem cells: a new target for therapy

The existence of prostate cancer stem cells offers a theoretical explanation for many of the enduring uncertainties surrounding the etiology and treatment of the most commonly diagnosed tumor in US males. The study of cancer stem cells in prostate, as in other complex tissues, is critically dependent on the availability of pure cell populations, a situation complicated by the heterogeneity of prostate tumors. However, selection of cells with a CD133(+)/alpha 2 beta 1 integrin/ CD44(+) phenotype enriches for a tumor-initiating population from human prostate cancers. Among the most pressing needs is for enduring therapy in patients who have experienced failure of hormonal treatments. Because the putative cancer stem cell does not express androgen receptor, it is likely to be immune from most androgen-based therapies, and an inherent genetic instability would enable the tumor to develop the new variants present in hormone-refractory disease. Prostate cancer stem cells have a unique gene expression signature that can also be related to Gleason grade and patient outcome. The scarcity of cancer stem cells in a prostate tumor will probably limit their usefulness in cancer diagnosis and prognosis. However, the emergence of new stem-cell therapeutic targets not only will require new assays for efficacy (because of their relatively quiescent nature), but also holds real promise of more lasting treatments to augment those currently directed against the remaining tumor cells, which comprise 99.9% of tumor mass, but paradoxically have a poor tumor-initiating capacity.

Prostate stem cells and benign prostatic hyperplasia

Pharmacological approaches are available to medically-managed patients with symptomatic BPH before surgical intervention is required. These include daily treatment with alpha-blockers and 5-alpha-reductase inhibitors alone or in combination. These medical approaches have two major problems. First, treatments are chronic and must be taken daily. Second, there are significant financial costs and quality of life issues for such chronic treatments. Is it possible to develop effective acute therapy for symptomatic BPH without the long-term androgen deprivation-induced side effects? Two seminal but rarely cited studies of Walsh [Peters, Walsh: N Engl J Med 317:599-604, 1987] and Coffey et al. [Sufrin et al.: Invest Urol 13:418-423, 1976], combined with the growing understanding of the stem cell organization of the prostate stromal (S) and epithelial (E) compartments and their reciprocal paracrine and autocrine interactions provides the rationale for an acute approach.The Walsh study documents that: (1) androgen deprivation disrupts the reciprocal interaction between the prostate S and E thereby decreasing the weight of both compartments and (2) once BPH develops, androgen deprivation does not decrease the number of stem cell units in either the S or E compartments since subsequent androgen restoration fully restores the enlarged gland. The Coffey study documents that acute androgen deprivation sensitizes S-E interactions to radiation induced disruptions so that following radiation, androgen restoration does not induce full gland regrowth. Therefore, effective therapy for symptomatic BPH should be achievable by acute treatment with reversible androgen deprivation for a limited period followed by a single dose of conformal external beam radiation before allowing the man to recovery his normal serum testosterone.

Prostate stem cells: the niche and cell markers

Prostate cancer and benign prostatic hyperplasia are common diseases in elderly men worldwide. Identifying the prostate stem cell is an important tool to investigate the mechanism of these prostatic diseases. Although the prostate stem cell has not yet been detected, progress has been made. The 'niche' or place in which the prostate stem cell resides is thought to be located in the proximal region of the murine prostate, near the urethra. Several candidate prostate stem cell markers are currently under investigation. In this review, we summarize the historical approaches and recent evidence regarding the niche and prostate-specific stem cell markers.

Prostate epithelial cell fate

Androgen receptor (AR) within prostatic mesenchymal cells, with the absence of AR in the epithelium, is still sufficient to induce prostate development. AR in the luminal epithelium is required to express the secretory markers associated with differentiation. Nkx3.1 is expressed in the epithelium in early prostatic embryonic development and expression is maintained in the adult. Induction of the mouse prostate gland by the embryonic mesenchymal cells results in the organization of a sparse basal layer below the luminal epithelium with rare neuroendocrine cells that are interdispersed within this basal layer. The human prostate shows similar glandular organization; however, the basal layer is continuous. The strong inductive nature of embryonic prostatic and bladder mesenchymal cells is demonstrated in grafts where embryonic stem (ES) cells are induced to differentiate and organize as a prostate and bladder, respectively. Further, the ES cells can be driven by the correct embryonic mesenchymal cells to form epithelium that differentiates into secretory prostate glands and differentiated bladders that produce uroplakin. This requires the ES cells to mature into endoderm that gives rise to differentiated epithelium. This process is control by transcription factors in both the inductive mesenchymal cells (AR) and the responding epithelium (FoxA1 and Nkx3.1) that allows for organ development and differentiation. In this review, we explore a molecular mechanism where the pattern of transcription factor expression controls cell determination, where the cell is assigned a developmental fate and subsequently cell differentiation, and where the assigned cell now emerges with it's own unique character.

Inhibition of monoamine oxidase A promotes secretory differentiation in basal prostatic epithelial cells

Monoamine oxidase A (MAO-A) expression is associated with high-grade prostate cancer. Immunohistochemistry showed that MAO-A is also expressed in the basal epithelial cells of normal prostate glands. Using cultured primary prostatic epithelial cells as a model, we showed that MAO-A prevents basal epithelial cells from differentiating into secretory cells. Under differentiation-promoting conditions, clorgyline, an irreversible MAO-A inhibitor, induced secretory cell-like morphology and repressed expression of cytokeratin 14, a basal cell marker. More importantly, clorgyline induced mRNA and protein expression of androgen receptor (AR), a hallmark of secretory epithelial cells. In clorgyline-treated cells, androgen induced luciferase activity controlled by the promoter of prostate-specific antigen, an AR target gene, in a dose-dependent manner. This activity was blocked by the AR antagonist Casodex, showing that AR is functional. In turn, androgen decreased MAO-A expression in clorgyline-treated, secretory-like cells. Our results demonstrated that cultured basal epithelial cells have the potential to differentiate into secretory cells, and that inhibition of MAO-A is a key factor in promoting this process. Increased expression of MAO-A in high-grade prostate cancer may be an important contributor to its de-differentiated phenotype, raising the possibility that MAO-A inhibition may restore differentiation and reverse the aggressive behavior of high-grade cancer.

Characterization of adult prostatic progenitor/stem cells exhibiting self-renewal and multilineage differentiation

Demonstration of the hallmarks of stem cells, self-renewal and multilineage differentiation, is a challenge that has not been met for numerous tissues postulated to possess adult stem cells, including prostate tissue. Using a defined medium, we reproducibly isolated and maintained adult mouse prostatic cells with characteristics of progenitor/stem cells. Clonal populations of cells demonstrated tissue-specific multilineage differentiation by their ability to generate organized prostatic ductal structures in vivo, with luminal and basal cell layers, when grafted under the renal capsules of mice in the presence of fetal rat urogenital mesenchyme. Complete differentiation was demonstrated by the expression and secretion of terminally differentiated prostatic secretory products into the lumens. Self-renewal was demonstrated by serial transplantation of clonal populations that generated fully differentiated ductal structures in vivo. In vitro, undifferentiated cells expressed markers associated with prostate stem cells, including Sca 1 and CD49f, as well as basal cell markers (p63 and cytokeratins 5 and 14) and, at a low level, luminal cell markers (androgen receptor and cytokeratins 8 and 18). When grafted and allowed to differentiate in the presence of fetal urogenital mesenchyme, the cells differentiated into luminal cells and basal cells with more restricted protein expression patterns. These studies are the first to report a reproducible system to assess adult prostatic progenitor/stem cells.

Low-calcium serum-free defined medium selects for growth of normal prostatic epithelial stem cells

Stage-specific differentiation markers were used to evaluate the cellular composition and the origin of nonimmortalized (PrEC) and immortalized (PZ-HPV7, CA-HPV10, RWPE-1, and 957E/hTERT) human prostate cell lines. These studies documented that immortalized and nonimmortalized prostate epithelial cells established and maintained in low (i.e., <300 micromol/L) Ca(2+) serum-free defined (SFD) medium were all derived from normal nonmalignant prostate tissues and contain CD133(+)/ABCG2(+)/alpha(2)beta(1)(Hi)/p63(-)/PSCA(-)/AR(-)/PSA(-) prostate stem cells. In these cultures, prostate stem cells are able to self-renew and generate two distinct cell lineages: the minor proliferatively quiescent neuroendocrine lineage and the major transit-amplifying cell lineage. Subsequently, CD133(-)/ABCG2(-)/alpha(2)beta(1)(Hi)/p63(+)/PSCA(-)/AR(-)/PSA(-) transit-amplifying cells proliferate frequently and eventually mature into proliferatively quiescent CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(+)/AR(-)/PSA(-) intermediate cells. Such proliferatively quiescent intermediate cells, however, do not complete their full maturation into CD133(-)/ABCG2(-)/alpha(2)beta(1)(Lo)/p63(-)/PSCA(-)/AR(+)/PSA(+) luminal-secretory cells in low Ca(2+) SFD medium. Addition of universal type I IFN and synthetic androgen (R1881) to culture medium resulted in up-regulation of androgen receptor protein expression. However, it failed to induce full differentiation of intermediate cells into AR(+)/PSA(+) luminal-secretory cells. Our results indicate that such inability of prostate epithelial cells to complete their differentiation is due to continuous expression of Notch-1 receptor and its downstream effector, Hey-1 protein, which actively suppresses differentiation via its ability to transcriptionally repress a series of genes, including the GATA family of transcription factors.

Prostatic basal cells in the peripheral and transitional zones: zonal variation in morphology and in immunophenotype

BACKGROUND

Benign prostatic hyperplasia and prostatic adenocarcinoma exhibit prominent zonal predilections. Basal cells from the transitional zone and from the peripheral zone are postulated to have different underlying biological properties. We studied basal cells in both prostatic zones.

METHODS

Tissue microarrays (TMA) were prepared from 65 whole-mounted prostatectomy specimens with prostatic adenocarcinoma. The transitional zone and peripheral zone were sampled from each prostate. TMA sections were stained with a basal cell cocktail (CK 34betaE12 + p63). The immunostaining pattern and the morphology of basal cells were recorded.

RESULTS

Triangular-shaped basal cells were highlighted by CK 34betaE12 cytoplasmic and p63 nuclear staining. These basal cells had their long axis oriented perpendicular to the basement membrane and their apex toward the lumen interdigited between secretory luminal cells. This morphology was seen in the majority of peripheral zone benign prostatic glands (92.0%) but only a minority of transitional zone benign prostatic glands (18.0%). Basal cells of the transitional zone showed weak or absent CK 34betaE12 staining in 65.9% of glands while maintaining p63. All glands with high-grade prostatic intraepithelial neoplasia (HGPIN) contained the triangular basal cells. In addition, basal cell clusters were identified in 8.7% of peripheral zone glands and 5.2% of HGPIN glands.

CONCLUSIONS

Our results indicate that the basal cell morphology and the basal cell immunophenotype have a zonal variation. The finding of a unique morphology of basal cells and the presence of basal cell clusters in the peripheral zone suggests that the peripheral zone might be the stem/progenitor cell-rich area in the human prostates.

Stem cells in prostate cancer initiation and progression

Peter Nowell and David Hungerford's discovery of the Philadelphia chromosome facilitated many critical studies that have led to a paradigm shift in our understanding of cancer as a disease of stem cells. This Review focuses on the application of these concepts to investigation of the role of stem cells in prostate cancer initiation and progression. Major strides in the development of in vitro and in vivo assays have enabled identification and characterization of prostate stem cells as well as functional evaluation of the tumorigenic effects of prostate cancer-related genetic alterations.

Bisphenol A induces permanent squamous change in mouse prostatic epithelium

Bisphenol A (BPA) is a monomer of plastic products widely used in daily life, and has weak estrogenic activity. In this study, male BALB/c mice were treated with BPA and diethylstilbestrol (DES) in adult and fetal periods to investigate whether BPA could affect prostatic epithelial differentiation. Eight-to 9-week-old mice treated for 3 weeks with subcutaneous implants of 0.2-200 mg BPA pellets induced the expression of cytokeratin 10 (CK10) in prostatic basal epithelial cells in a dose-dependent manner. Utilizing organ culture of adult prostate, 1 nM and 1 microM BPA also induced CK10 expression and squamous metaplasia with multilayering of basal epithelial cells, respectively. Fetal exposure to low-dose BPA (20 microg/kg/day) from gestation day (GD) 13 to GD18 induced permanent CK10 expression in basal cells of the adult prostate similar to DES (0.2 microg/kg/day). These results indicate that in mouse, BPA can directly elicit CK10 expression in prostatic epithelium, and that this change can be elicited by doses as low as 20 microg/kg/day. We speculate that low-dose BPA during fetal life may also induce permanent squamous change in human prostate.

Anchorage-independent culture maintains prostate stem cells

Freshly isolated mouse prostate epithelial cells regenerate fully differentiated prostate tissue when combined with embryonic urogenital sinus mesenchyme and grafted in vivo. We show here that this regenerative capacity, which has been attributed to a small population of pleuripotential progenitor epithelial cells, is rapidly lost when the cells are placed in monolayer culture but can be maintained by culture in anchorage-independent conditions. Epithelial cells placed in anchorage-independent culture formed proliferating spheres that could be serially passaged and exhibited increased expression of putative stem cell markers as compared to cells grown in monolayer culture. Epithelial cells isolated from the fetal urogenital sinus, the newborn, and adult prostate formed spheres with similar efficiency, while cells isolated from the post-castration prostate exhibited significantly higher sphere-forming abilities. When passaged spheres were recombined with E17 rat urogenital sinus mesenchyme and grafted in vivo, they generated fully differentiated mouse prostate glandular epithelium containing both p63+ basal cells and p63- luminal cells and expressing a variety of prostate-specific and terminal differentiation markers.

Focal degeneration of basal cells and the resultant auto-immunoreactions: a novel mechanism for prostate tumor progression and invasion

The development of human prostate cancer is believed to be a multistep process, progressing sequentially from normal, to hyperplasia, to prostatic intraepithelial neoplasia (PIN), and to invasive and metastatic lesions. High grade PIN has been generally considered as the direct precursor of invasive lesions, and the progression of PIN is believed to be triggered primarily, if not solely, by the overproduction of proteolytic enzymes predominately by cancer cells, which result in the degradation of the basement membrane. These theories, however, are hard to reconcile with two main facts: (1) only about 30% untreated PIN progress to invasive stage, while none of the current approaches could accurately identify the specific PIN or individuals at greater risk for progression, and (2) results from recent world-wide clinical trials with a wide variety of proteolytic enzyme inhibitors have been very disappointing, casting doubt on the validity of the proteolytic enzyme theory. Since over 90% of prostate cancer-related deaths result from invasion-related illness and the incidence of PIN could be up to 16.5-25% in routine or ultrasound guided prostate biopsy, there is an urgent need to uncover the intrinsic mechanism of prostate tumor invasion. Promoted by the facts that the basal cell population is the source of several tumor suppressors and the absence of the basal cell layer is the most distinct feature of invasive lesions, our recent studies have intended to identify the early alterations of basal cell layers and their impact on tumor invasion using multidisciplinary approaches. Our studies revealed that a subset of pre-invasive tumors contained focal disruptions (the absence of basal cells resulting in a gap greater than the combined size of at least three epithelial cells) in surrounding basal cell layers. Compared to their non-disrupted counterparts, focally disrupted basal cell layers had several unique features: (1) significantly lower proliferation; (2) significantly lower p63 expression; (3) significantly higher apoptosis; and (4) significantly higher leukocyte infiltration and stromal reactions. Compared to their counterparts distant from focal disruptions or overlying non-disrupted basal cell layers, epithelial cells overlying focal basal cell layer disruptions showed the following unique features: (1) significantly higher proliferation; (2) significantly higher expression of cell cycle control-, cell growth-, and stem cell-related genes; and (3) physical continuity with adjacent invasive lesions. Together, these findings suggest that focal basal cell layer disruptions could substantially impact the molecular profile and biological presentations of the overlying epithelial cells. Based on these and other findings, we have proposed that prostate tumor invasion is triggered by a localized degeneration of aged or injured basal cells and the resultant auto-immunoreactions. Our hypothesized steps for prostate tumor invasion include the following: (1) due to inherited or environmental factors, some patients contained cell cycle control- and renewal-related defects in the basal cell population that cause elevated basal cell degenerations; (2) the degradation products of degenerated basal cells or diffusible molecules of the overlying epithelial cells attract leukocyte infiltration; (3) leukocytes discharge their digestive enzymes upon the direct physical contact, resulting in a focal disruption in the basal cell layer, which leads to several focal alterations: (a) a focal loss of tumor suppressors and paracrine inhibitory function; (b) a focal increase of the permeability for growth-required nutrients and oxygen; (c) a focal increase of growth factors; (d) direct physical contact between epithelial and stromal cells; and (e) the exposure of the overlying epithelial cells directly to the stromal tissue fluid. These alterations individually or collectively stimulate or favor a clonal proliferation and stromal invasion of tumor progenitor or stem cells. Our hypothesis differs from the traditional theories in several aspects, including the triggering factor for the initiation of tumor invasion, the stage of tumor invasion, the cellular origin of invasive lesions, the significance of immunoreactive and stromal cells, and the potential approaches for early detection, treatment, and prevention of invasion. Our hypothesis represents a novel in vivo model as to the cellular mechanism leading to prostate tumor invasion. If confirmed, it could lead to a new direction to search for more effective approaches to combat prostate cancer. It could also have an immediate impact on patient care through improved pathologic evaluation of prostate tumor biopsies. More importantly, our hypothesis might be applicable, and significantly impact the detection, treatment, and prevention of other epithelium-derived tumors.

Self-renewal and multilineage differentiation in vitro from murine prostate stem cells

Murine prostate stem cells express integrin alpha 6, which modulates survival, proliferation, and differentiation signaling through its interaction with the extracellular protein laminin. When plated in vitro in laminin containing Matrigel medium, 1 of 500-1,000 murine prostate cells can grow and form clonogenic spheroid structures that we term prostate spheres. Prostate spheres can be serially passaged individually or in bulk to generate daughter spheres with similar composition, demonstrating that sphere-forming cells are capable of self-renewal. Spheres spontaneously undergo lineage specification for basal and transit-amplifying cell types. P63-expressing cells localized to the outer layers of prostate spheres possess higher self-renewal capacity, whereas cells toward the center display a more differentiated transit-amplifying phenotype, as demonstrated by the expression of the prostate stem cell antigen. When dihydrotestosterone is added to the medium, the androgen receptor is stabilized, is imported to the nucleus, and drives differentiation to a luminal cell-like phenotype. A fraction of sphere cells returned to an in vivo environment can undergo differentiation and morphogenesis to form prostate tubular structures with defined basal and luminal layers accompanied by prostatic secretions. This study demonstrates self-renewal and multilineage differentiation from single adult prostate stem/progenitor cells in a specific in vitro microenvironment.

Prostate Cancer Associated withp53andRbDeficiency Arises from the Stem/Progenitor Cell–Enriched Proximal Region of Prostatic Ducts

Recently, we have shown that prostate epithelium-specific deficiency for p53 and Rb tumor suppressors leads to metastatic cancer, exhibiting features of both luminal and neuroendocrine differentiation. Using stage-by-stage evaluation of carcinogenesis in this model, we report that all malignant neoplasms arise from the proximal region of the prostatic ducts, the compartment highly enriched for prostatic stem/progenitor cells. In close similarity to reported properties of prostatic stem cells, the cells of the earliest neoplastic lesions express stem cell marker stem cell antigen 1 and are not sensitive to androgen withdrawal. Like a subset of normal cells located in the proximal region of prostatic ducts, the early neoplastic cells coexpress luminal epithelium markers cytokeratin 8, androgen receptor, and neuroendocrine markers synaptophysin and chromogranin A. Inactivation of p53 and Rb also takes place in the lineage-committed transit-amplifying and/or differentiated cells of the distal region of the prostatic ducts. However, the resulting prostatic intraepithelial neoplasms never progress to carcinoma by the time of mouse death. Interestingly, in an ectopic transplantation assay, early mutant cells derived from either region of the prostatic ducts are capable of forming neoplasms within 3 months. These findings indicate that p53 and Rb are critically important for the regulation of the prostatic stem cell compartment, the transformation in which may lead to particularly aggressive cancers in the context of microenvironment.

Prostate cancer cells with stem cell characteristics reconstitute the original human tumor in vivo

Cancer may arise from a cancer stem/progenitor cell that shares characteristics with its normal counterpart. We report the reconstitution of the original human prostate cancer specimen from epithelial cell lines (termed HPET for human prostate epithelial/hTERT) derived from this sample. These tumors can be described in terms of Gleason score, a classification not applied to any of the transgenic mouse models currently developed to mimic human disease. Immunohistochemical and Western blot analyses indicate that they do not express androgen receptor or p63, similar to that reported for prostate stem cells. These cell lines also express embryonic stem markers (Oct4, Nanog, and Sox2) as well as early progenitor cell markers (CD44 and Nestin) in vitro. Clonally derived HPET cells reconstitute the original human tumor in vivo and differentiate into the three prostate epithelial cell lineages, indicating that they arise from a common stem/progenitor cell. Serial transplantation experiments reconstitute the tumors, suggesting that a fraction of parental or clonally derived HPET cells have self-renewal potential. Thus, this model may enhance our understanding of human tumor development and provide a mechanism for studying cancer stem/progenitor cells in differentiation, tumorigenesis, preclinical testing, and the development of drug resistance.

SOX9 Is Expressed in Normal Prostate Basal Cells and Regulates Androgen Receptor Expression in Prostate Cancer Cells

SOX9 is a member of the SOX [Sry-related high-mobility group (HMG) box] family of HMG DNA-binding domain transcription factors and is required for the development and differentiation of multiple cell lineages. This report shows that basal epithelial cells express SOX9 in normal prostate, with no detectable expression in luminal epithelial cells. In contrast, SOX9 is expressed in primary prostate cancers in vivo, at a higher frequency in recurrent prostate cancer and in prostate cancer cell lines (LNCaP, CWR22, PC3, and DU145). SOX9 message and protein levels in prostate cancer cells were increased by treatment with glycogen synthase kinase 3beta inhibitor (SB415286), and SOX9 was reduced when beta-catenin was down-regulated by small interfering RNA (siRNA), indicating that SOX9 expression in prostate cancer is regulated by Wnt/beta-catenin signaling. SOX9 bound specifically to androgen receptor (AR) DNA-binding domain glutathione S-transferase fusion proteins, and this interaction was dependent on a short peptide immediately COOH-terminal to the DNA-binding domain (the C-terminal extension), which is required for interactions between steroid hormone receptors and the architectural HMG proteins. Exogenous SOX9 expressed at high nonphysiologic levels decreased AR expression and activity; however, at lower levels, SOX9 increased AR protein expression. Significantly, down-regulation of SOX9 by siRNA in prostate cancer cells reduced endogenous AR protein levels, and cell growth indicating that SOX9 contributes to AR regulation and decreased cellular proliferation. These results indicate that SOX9 in prostate basal cells supports the development and maintenance of the luminal epithelium and that a subset of prostate cancer cells may escape basal cell requirements through SOX9 expression.

Fibroblast growth factor receptor 2 tyrosine kinase is required for prostatic morphogenesis and the acquisition of strict androgen dependency for adult tissue homeostasis

The fibroblast growth factor (FGF) family consists of 22 members and regulates a broad spectrum of biological activities by activating diverse isotypes of FGF receptor tyrosine kinases (FGFRs). Among the FGFs, FGF7 and FGF10 have been implicated in the regulation of prostate development and prostate tissue homeostasis by signaling through the FGFR2 isoform. Using conditional gene ablation with the Cre-LoxP system in mice, we demonstrate a tissue-specific requirement for FGFR2 in urogenital epithelial cells--the precursors of prostatic epithelial cells--for prostatic branching morphogenesis and prostatic growth. Most Fgfr2 conditional null (Fgfr2(cn)) embryos developed only two dorsal prostatic (dp) and two lateral prostatic (lp) lobes. This contrasts to wild-type prostate, which has two anterior prostatic (ap), two dp, two lp and two ventral prostatic (vp) lobes. Unlike wild-type prostates, which are composed of well developed epithelial ductal networks, the Fgfr2(cn) prostates, despite retaining a compartmented tissue structure, exhibited a primitive epithelial architecture. Moreover, although Fgfr2(cn) prostates continued to produce secretory proteins in an androgen-dependent manner, they responded poorly to androgen with respect to tissue homeostasis. The results demonstrate that FGFR2 is important for prostate organogenesis and for the prostate to develop into a strictly androgen-dependent organ with respect to tissue homeostasis but not to the secretory function, implying that androgens may regulate tissue homeostasis and tissue function differently. Therefore, Fgfr2(cn) prostates provide a useful animal model for scrutinizing molecular mechanisms by which androgens regulate prostate growth, homeostasis and function, and may yield clues as to how advanced-tumor prostate cells escape strict androgen regulations.

The role of Shh transcription activator Gli2 in chick cloacal development

Patterning and differentiation along the dorsal-ventral (D-V) axis lead to cloacal partitioning into ventral urinary and dorsal alimentary tracts in most mammals, but not birds and fish. We previously reported that the major activator of Sonic hedgehog (Shh) signaling transcription factor Gli2 plays an essential role in cloacal partitioning along the D-V axis in a mouse model. Here, we report that chick cloacal patterning and differentiation is along the anterior-posterior axis. During chick cloacal formation, Shh is expressed strongly in hindgut endoderm; Gli2 is very weakly detected in the surrounding hindgut mesoderm. In the mesoderm of the cloacal region, the over-expression of the constitutively active form of mouse Gli2 has been shown to: not induce cloacal partitioning along the D-V axis; induce expression of Ptch1, Gli2, bmp4, wnt5a, and hoxd-13, which have been previously shown to play a role in hindgut patterning; increase cell proliferation; and reduce apoptosis. Interestingly, p63 expression in the cloacal endoderm is also up-regulated, suggesting an interaction between the Shh and p63 pathways. In conclusion, Gli2 alone is insufficient to induce partitioning along the D-V axis in the chick embryo. However, Gli2 regulates both epithelial and mesenchymal cell proliferation and apoptosis during cloacal development.

Origin of the ultimobranchial body cyst: T/ebp/Nkx2.1 expression is required for development and fusion of the ultimobranchial body to the thyroid

The ultimobranchial body (UBB) is an outpocketing of the fourth pharyngeal pouch that fuses with the thyroid diverticulum, giving rise to calcitonin-producing C-cells. In this study, we demonstrate that the UBB is composed of two types of cells: one expressing T/ebp/Nkx2.1 and the other expressing p63. The former cell type, accounting for a majority of the UBB, requires T/ebp/Nkx2.1 for their survival. In contrast, the p63-positive cells, even in the absence of T/ebp/Nkx2.1 expression, can proliferate and give rise to a vesicular structure that is lined by a monolayer of p63-negative cells, surrounded by a cluster and/or single layer of p63-positive cells, displaying the basal/stem cell phenotype. T/ebp/Nkx2.1 haploinsufficiency causes abnormal fusion of the UBB with the thyroid diverticulum, which stays as a cluster of C-cells around the vesicular structure, similar to the one observed in mice null for T/ebp/Nkx2.1 expression. These results demonstrate that T/ebp/Nkx2.1 plays a role in the survival of UBB cells, their dissemination into the thyroid diverticulum, and the formation of UBB-derived vesicular structure.

DeltaNp63 plays an anti-apoptotic role in ventral bladder development

The bladder, the largest smooth-muscle organ in the human body, is responsible for urine storage and micturition. P63, a homolog of the p53 tumor-suppressor gene, is essential for the development of all stratified epithelia, including the bladder urothelium. The N-terminal truncated isoform of p63, DeltaNp63, is known to have anti-apoptotic characteristics. We have established that DeltaNp63 is not only the predominant isoform expressed throughout the bladder, but is also preferentially expressed in the ventral bladder urothelium during early development. We observed a host of ventral defects in p63-/- embryos, including the absence of the abdominal and ventral bladder walls. This number of ventral defects is identical to bladder exstrophy, a congenital anomaly exhibited in human neonates. In the absence of p63, the ventral urothelium was neither committed nor differentiated, whereas the dorsal urothelium was both committed and differentiated. Furthermore, in p63-/- bladders, apoptosis in the ventral urothelium was significantly increased. This was accompanied by the upregulation of mitochondrial apoptotic mediators Bax and Apaf1, and concurrent upregulation of p53. Overexpression of DeltaNp63gamma and DeltaNp63beta in p63-/- bladder primary cell cultures resulted in a rescue, evidenced by significantly reduced expressions of Bax and Apaf1. We conclude that DeltaNp63 plays a crucial anti-apoptotic role in normal bladder development.

Immunohistochemical characterization of neuroendocrine cells in prostate cancer

BACKGROUND

Neuroendocrine (NE) cells increase in high grade/stage prostate cancer (PC) and may contribute to androgen-independent cancer. Their immunohistochemical phenotype has not been studied in detail and conflicting results have been reported.

METHODS

PC tissue was stained immunohistochemically for luminal secretory cell-associated cytokeratin, basal cell markers, ki-67, androgen receptor (AR), PSA, prostate acid phosphatase (PAP), and alpha-methylacyl coenzyme A racemase (AMACR).

RESULTS

The NE cells are positive for AE1/AE3, Cam 5.2, and negative for basal cell markers. They are negative for AR, PSA, and Ki-67 but positive for PAP. The benign NE cells are negative for AMACR while the malignant NE cells are positive for AMACR.

CONCLUSIONS

NE cells of PC constitute a unique subset of cancer cells, which have a unique immunohistochemical profile. They do not express AR, consistent with their resistance to hormonal therapy. They are post-mitotic cells but are malignant and part of the tumor.

Epigenetics of prostate cancer: beyond DNA methylation

Epigenetic mechanisms permit the stable inheritance of cellular properties without changes in DNA sequence or amount. In prostate carcinoma, epigenetic mechanisms are essential for development and progression, complementing, amplifying and diversifying genetic alterations. DNA hypermethylation affects at least 30 individual genes, while repetitive sequences including retrotransposons and selected genes become hypomethylated. Hypermethylation of several genes occurs in a coordinate manner early in carcinogenesis and can be exploited for cancer detection, whereas hypomethylation and further hypermethylation events are associated with progression. DNA methylation alterations interact with changes in chromatin proteins. Prominent alterations at this level include altered patterns of histone modification, increased expression of the EZH2 polycomb histone methyltransferase, and changes in transcriptional corepressors and coactivators. These changes may make prostate carcinoma particularly susceptible to drugs targeting chromatin and DNA modifications. They relate to crucial alterations in a network of transcription factors comprising ETS family proteins, the androgen receptor, NKX3.1, KLF, and HOXB13 homeobox proteins. This network controls differentiation and proliferation of prostate epithelial cells integrating signals from hormones, growth factors and cell adhesion proteins that are likewise distorted in prostate cancer. As a consequence, prostate carcinoma cells appear to be locked into an aberrant state, characterized by continued proliferation of largely differentiated cells. Accordingly, stem cell characteristics of prostate cancer cells appear to be secondarily acquired. The aberrant differentiation state of prostate carcinoma cells also results in distorted mutual interactions between epithelial and stromal cells in the tumor that promote tumor growth, invasion, and metastasis.

Mechanisms leading to the development of hormone-resistant prostate cancer

Advanced and metastatic prostate cancers remain potentially lethal tumors. Although androgen deprivation therapy remains the most effective treatment, patients who progress to androgen independence die of their disease. This article focuses on the mechanisms by which hormone resistance develops, including the reactivation of androgen receptor during androgen deprivation therapy, the role of cancer stem cells, and the emergence of epithelial-mesenchymal transition cells, which have increased metastatic potential. It is through an enhanced understanding of these mechanisms that new therapies can be developed to combat this disease.

Derivation of the consensus DNA-binding sequence for p63 reveals unique requirements that are distinct from p53

p63 is a member of the p53 family of proteins and plays an important role in epithelial development and differentiation. Although some p63 binding sites in the regulatory elements of epithelial genes have been identified, the optimal DNA-binding sequence has not been ascertained for this transcription factor. Here, we identify the preferred DNA-binding site of p63 by performing in vitro DNA selection experiments. Our analysis shows that the optimal p63 DNA-binding consensus motif consists of a CA(T)TG core and an AT-rich 5' and 3' flanking sequence. Gel shift and competition experiments demonstrate that there are specific sequence requirements that confer high DNA-binding affinity for p63 and that significant deviation from the consensus sequences result in poor or no binding. This pattern of DNA-binding is similar for both recombinant p63 and the endogenous protein present in keratinocyte nuclear extracts. Furthermore, we show that the consensus sequence is distinctly different from that of p53, particularly in the flanking sequences. Identification of the p63 consensus DNA-binding sequence will facilitate the validation of in vivo p63-responsive elements that mediate transcriptional regulation of a wide variety of target genes.

A subset of prostate basal cells lacks the expression of corresponding phenotypic markers

Immunohistochemical staining for cytokeratin (CK) 34ssE12 has been routinely used to elucidate prostate basal cells for differentiation between non-invasive and invasive lesions. Our previous studies, however, revealed that some morphologically distinct basal cells observed on H&E-stained sections completely lacked CK34ssE12 expression. Our current study attempted to assess whether these basal cells would also lack the expression of other phenotypic markers, and whether basal cell alterations would affect the proliferation status of the associated tumor cells. Consecutive sections from prostate tumors with large basal cell clusters that were morphologically distinct in H&E sections but were completely negative for CK 34ssE12 were morphologically and immunohistochemically assessed with a panel of basal cell phenotypic and other markers. In addition to CK 34ssE12, these basal cells also completely lacked the expression of other phenotypic markers, including CK5, CK14, p63, and maspin, in contrast to adjacent basal cells, which were strongly positive for these markers. Tumors surrounded by basal cell layers that lack the expression of basal cell phenotypic markers showed a significantly higher rate of cell proliferation and mast cell infiltration than their counterparts. These findings suggest that basal cells might be targets of a variety of pathological alterations, which could significantly impact biological presentations of associated tumor cells.

Functional compensation in Hedgehog signaling during mouse prostate development

Studies of hedgehog signaling in prostate development using anti-Shh antibodies, chemical inhibitors of hedgehog signaling and Shh(-/-) mutant mice have yielded conflicting data regarding the requirements of hedgehog signaling for normal ductal budding and glandular morphogenesis. We used transgenic mouse models in combination with chemical inhibitors and renal grafting to clarify the role of Hh signaling in prostate development. These studies showed that genetic loss of Shh is accompanied by an up-regulation of Indian Hedgehog (Ihh) and maintenance of Hh pathway activity. We found that while neither Gli1 nor Gli3 are required for normal prostate ductal budding, the urogenital sinus (UGS) of the Gli2(-/-) mutant mouse displays aberrant ductal budding in utero. When grown as a subcapsular graft, the Gli2(-/-) UGS exhibited prostatic differentiation but also displayed areas of focal epithelial hyperplasia. Functional redundancy between the three Gli transcription factors appears to mitigate the effect of Gli2 LOF as evidenced by residual Hh pathway activity in the E14 Gli2(-/-) UGS that could be inhibited by cyclopamine treatment. Together, these studies reveal a surprising degree of functional redundancy operating both at the level of the ligand and at the level of transcriptional regulation that effectively mitigates phenotypes associated with Hh-signaling perturbations.

Epithelial stem cells of the lung: privileged few or opportunities for many?

Most reviews of adult stem cells focus on the relatively undifferentiated cells dedicated to the renewal of rapidly proliferating tissues, such as the skin, gut and blood. By contrast, there is mounting evidence that organs and tissues such as the liver and pancreatic islets, which turn over more slowly,use alternative strategies, including the self-renewal of differentiated cells. The response of these organs to injury may also reveal the potential of differentiated cells to act as stem cells. The lung shows both slow turnover and rapid repair. New experimental approaches, including those based on studies of embryonic development, are needed to identify putative lung stem cells and strategies of lung homeostasis and repair.

Down regulation of PSA by C/EBPalpha is associated with loss of AR expression and inhibition of PSA promoter activity in the LNCaP cell line

Background

C/EBPα is a transcription factor essential for terminal differentiation of several cell types. It has not known if C/EBPα protein is expressed and functions in the prostate gland.

Methods

The presence of C/EBPα in normal and cancerous prostate epithelium was examined by immunochemistry. Over expression of C/EBPα in LNCaP cells was conducted with retrovirus-mediated transduction. PSA expression was examined by RT-PCR and western blot and PSA promoter activity by luciferase reporter assay.

Results

In normal prostate C/EBPα was expressed in the basal layer of the epithelium. In prostate cancer C/EBPα was detected at low levels throughout the cancers and in advanced prostate cancer C/EBPα expression was associated with decreased expression of AR and PSA. Overexpression of C/EBPα inhibited epigenetically PSA expression and was accompanied by the loss of expression of AR. Transient increase of C/EBPα inhibited the PSA promoter/enhancer activity independently of expression of AR.

Conclusion

In LNCaP cells C/EBPα over expression inhibits expression of PSA by AR -dependent and independent mechanisms and by extinguishing AR expression provides a model for hormonal independent cell growth.

Regulation of cell proliferation in a stratified culture system of epithelial cells from prostate tissue

Mechanisms controlling epithelial proliferation and differentiation in the prostate have been primarily investigated in mouse models. The regulation of proliferation and differentiation is poorly understood in human prostate epithelial cells. In vivo, the glandular prostate epithelium consists of a p63-positive proliferating basal cell layer and a post-mitotic p27-positive secretory cell layer. We have established an organized stratified culture system of human primary prostate epithelial cells to gain insight into mechanisms regulating proliferation and differentiation. In this system, expression of p63 is observed in the bottom layer. In addition, BrdU incorporation persists even though cells are confluent. In contrast, in the upper layer, p63 expression is greatly diminished, p27 is expressed, and the cells are growth arrested. Overexpression of cyclin D1 or knockdown of p27 does not increase proliferation. After inactivation of the nuclear phosphoprotein Rb, the cell layers remain organized and cell proliferation increases only in the bottom layer. Furthermore, the expression of p63 remains confined to the bottom layer after Rb inactivation. Altogether, this in vitro model recapitulates certain aspects of in vivo growth regulation and differentiation and suggests that the loss of Rb family proteins in human cells trigger hyperplasia but is not sufficient for transformation.

Stem/progenitor and intermediate cell types and the origin of human prostate cancer

Theories of cell lineage in human prostatic epithelium, based on protein expression, propose that basal and luminal cells: 1) are either independently capable of self-renewal or 2) arise from stem cells expressing a full spectrum of proteins (p63, cytokeratins CK5/14, CK8/18, and glutathione-S-transferase-pi [GST-pi]) similar to cells of the embryonic urogenital sinus (UGS). Such embryonic-like stem cells are thought to give rise to mature basal cells and secretory luminal cells. By single cell cloning of an immortalized, normal human prostate-derived, non-tumorigenic RWPE-1 cell line, we isolated and characterized two epithelial cell types, WPE-stem and WPE-int. WPE-stem cells show: i) strong, sixfold greater nuclear expression of p63; ii) nearly twofold greater expression of CK14; iii) threefold less CK18, and iv) low androgen receptor (AR) expression as compared with WPE-int cells. WPE-stem cells are androgen-independent for growth and survival. WPE-int cells express very low p63 and CK5/14, and high CK18. WPE-int cells are androgen-independent for growth and survival but are highly responsive as shown by androgen induction of AR and prostate specific antigen (PSA). Compared with WPE-int cells, WPE-stem cells are smaller and show more rapid growth. WPE-stem cells can grow in an anchorage-independent manner in agar with 4.5-fold greater cloning efficiency and as free floating "prostaspheres" in liquid medium; and express over 40-fold higher matrix metalloproteinase-2 activity. These results indicate that WPE-stem cells express several features characteristic of stem/progenitor cells present in the UGS and in adult prostatic epithelium. In contrast, WPE-int cells have an intermediate, committed phenotype on the pathway to luminal cell differentiation. We propose that in normal prostatic epithelium, cells exist at many stages in a continuum of differentiation progressing from stem cells to definitive basal and luminal cells. Establishment and characterization of clones of human prostatic epithelial cells provide novel models for determining cell lineages, the origin of prostate cancer, and for developing new strategies for tumor prevention and treatment.

Notch signaling is required for normal prostatic epithelial cell proliferation and differentiation

Notch pathway is crucial for stem/progenitor cell maintenance, growth and differentiation in a variety of tissues. Using a transgenic cell ablation approach, we found in our previous study that cells expressing Notch1 are crucial for prostate early development and re-growth. Here, we further define the role of Notch signaling in regulating prostatic epithelial cell growth and differentiation using biochemical and genetic approaches in ex vivo or in vivo systems. Treatment of developing prostate grown in culture with inhibitors of gamma-secretase/presenilin, which is required for Notch cleavage and activation, caused a robust increase in proliferation of epithelial cells co-expressing cytokeratin 8 and 14, lack of luminal/basal layer segregation and dramatically reduced branching morphogenesis. Using conditional Notch1 gene deletion mouse models, we found that inactivation of Notch1 signaling resulted in profound prostatic alterations, including increased tufting, bridging and enhanced epithelial proliferation. Cells within these lesions co-expressed both luminal and basal cell markers, a feature of prostatic epithelial cells in predifferentiation developmental stages. Microarray analysis revealed that the gene expression in a number of genetic networks was altered following Notch1 gene deletion in prostate. Furthermore, expression of Notch1 and its effector Hey-1 gene in human prostate adenocarcinomas were found significantly down-regulated compared to normal control tissues. Taken together, these data suggest that Notch signaling is critical for normal cell proliferation and differentiation in the prostate, and deregulation of this pathway may facilitate prostatic tumorigenesis.

A tumour stem cell hypothesis for the origins of prostate cancer

Cancer stem cells undoubtedly exist in many tumour types, including the prostate. This hypothesis can explain both the heterogeneity of prostate tumours and their variable responses to several conventional therapies. In the longer term, therapies directed against tumour stem cells should offer a real possibility of long-term cure, rather than current palliative therapy. Identifying specific tumour stem-cell markers will enhance this process, but the scarcity of these cells within the mass of more differentiated amplifying progeny that comprise >99.9% of most cancers makes this a severe technical challenge. In addition, many tumour stem-cell markers are probably shared with normal stem cells, both in prostate and in stem cells from other tissues, but tumour-specific patterns of gene expression, probably designed to allow the tumour stem cell to survive outside its protective 'niche' in normal tissues, will be the best initial targets for new therapeutic agents.

Growth, morphogenesis, and differentiation during mouse prostate development in situ, in renal grafts, and in vitro

BACKGROUND

In vitro organ culture and renal grafting of the urogenital sinus (UGS) have both been used as models of prostate development. However, neither has been rigorously examined for its fidelity to replicate the canonical process of prostate differentiation in situ.

METHODS

We assessed size, morphology, histology, and the mRNA expression of differentiation marker genes of the E14 male mouse UGS grown for 0-28 days as sub-renal capsule allografts in nude mice or in culture containing androgen and compared these to UGS development in situ.

RESULTS

Development of grafted tissues was morphologically and histologically similar to development in situ but differentiation occurred more rapidly. UGS growth in organ culture resulted in bud formation, but did not trigger cellular differentiation. However, the potential for differentiation was maintained and could be rescued by grafting tissues into nude mice.

CONCLUSIONS

In vitro organ culture and renal grafting of UGS tissues may be appropriate models for studying prostatic bud formation, but only grafting is an appropriate model for prostatic differentiation.

Differential expression of p63 isoforms in female reproductive organs

p63 is the identity switch for uterine/vaginal epithelial cell fate, and disruption of p63 expression by diethylstilbestrol (DES) induces cervical/vaginal adenosis in mice. In this article, we report the expression patterns of p63 isoforms (TA, DeltaN, alpha, beta and gamma) in mice, focusing on the reproductive tract. We also present the reproductive tract phenotype of female p63-/- mice. Finally, to better evaluate the potential role of p63 in human development of DES-induced cervical/vaginal adenosis, we describe the ontogeny of p63 in human female fetuses. In adult mice, the DeltaN isoforms of p63 were expressed only in squamous/basal/myoepithelial cells of epithelial tissues, while TA isoforms of p63 were highly expressed in germ cells of the ovary and testis. In fetal mice, the DeltaN and alpha forms of p63 were expressed in the cloacal and urogenital sinus epithelia. In the female p63-/- mice, the sinus vagina developed, but p63-/- sinus vaginal epithelium failed to undergo squamous differentiation confirming an essential role of p63 in squamous epithelial differentiation. Although TAp63 was highly expressed in developing primordial germ cells/oocytes, p63-/- ovaries and oocytes developed normally. The ontogeny of p63 in female reproductive organs was essentially identical in mouse and human. In the human fetus at the susceptible stage for DES-induced cervical/vaginal adenosis, most cervical/vaginal epithelial cells were columnar and negative for p63. Therefore, inhibition of p63 expression by DES should change the cell fate of human Müllerian duct epithelial cells and cause cervical/vaginal adenosis as previously demonstrated in mouse.

P63 deficiency: a failure of lineage commitment or stem cell maintenance?

A critical role for p63 in the development of stratified epithelia, such as the epidermis, has been recognized since the generation of mice lacking p63 expression. The molecular role of p63 in epidermal morphogenesis, however, remained controversial. The epidermal phenotype of p63-/- mice, which are born with a single-layered surface epithelium instead of a fully stratified epidermis, suggested that p63 could have a role in stem cell maintenance or in the commitment to stratification. In this review, we discuss evidence suggesting that p63 is required for the commitment to stratification, making p63 the earliest known gene expressed in the developing epidermis that is specific for the keratinocyte lineage.

Breast cancer resistance protein-mediated efflux of androgen in putative benign and malignant prostate stem cells

Malignantly transformed stem cells represent a potential common nidus for the primary cancer and the recurrent cancer that arises after treatment failure. Putative prostate stem cells and prostate tumor stem cells in benign and malignant human prostate tissue, in primary human prostate xenografts, and in the transgenic adenocarcinoma of the mouse prostate (TRAMP) mouse model of prostate cancer, are defined by expression of breast cancer resistance protein (BCRP), a marker of pluripotent hematopoietic, muscle, and neural stem cells, and by an absence of androgen receptor (AR) protein. Inhibition of BCRP-mediated efflux of dihydrotestosterone by novobiocin or fumitremorgin C in a rat prostate progenitor cell line that expresses BCRP and AR mRNAs, but minimal AR protein, results in stabilization and nuclear translocation of AR protein, providing a mechanism for lack of AR protein in BCRP-expressing stem cells. In both benign and malignant human prostate tissue, the rare epithelial cells that express BCRP and lack AR protein are localized in the basal cell compartment, survive androgen deprivation, and maintain proliferative potential in the hypoxic, androgen-deprived prostate. Putative prostate tumor stem cells that express BCRP but not AR protein in TRAMP are the source of a BCRP-negative and AR-negative, Foxa2- and SV40Tag-expressing, transit amplifying compartment that progresses to the poorly differentiated carcinomas that arise rapidly after castration. Therefore, BCRP expression isolates prostate stem/tumor stem cells from the prostate tissue microenvironment through constitutive efflux of androgen, protecting the putative tumor stem cells from androgen deprivation, hypoxia, or adjuvant chemotherapy, and providing the nidus for recurrent prostate cancer.

Sex steroids have differential effects on growth and gene expression in primary human prostatic epithelial cell cultures derived from the peripheral versus transition zones

The majority of human prostate cancers arise from the peripheral zone (PZ). Prostate epithelial stem cells have been localized to the basal epithelial cell compartment. In addition, basal cells have been shown to maintain luminal epithelial cell differentiation and may mediate signals between the stromal and luminal cell compartments. Therefore, the study of adult prostate basal cells derived from different prostate zones may give insights into the mechanisms underlying normal and abnormal prostate growth. We herein compare the basal and sex steroid-stimulated expression and activity of several genes/proteins that are known to be critical in prostate cancer development in primary cultures of basal cells derived from the transition zone (TZ) and PZ of prostatectomy specimens. Our results demonstrate that prostate basal cells derived from the PZ versus TZ are more viable in culture, particularly in response to sex steroid addition. PZ cells exhibit higher telomerase activity and increased expression levels of androgen receptor, the anti-apoptotic protein bcl-2, and the dominant-negative splice variant of Kruppel-like Factor 6. PZ cells have lower basal expression levels of estrogen receptor-beta, the pro-apoptotic protein Bax, and cell-cycle inhibitor proteins (p53, p21(waf1/Cip1)). Finally, we demonstrate divergent responses to sex hormones in the two basal cell populations. The gene expression pattern in the PZ cells may partially explain the predominance of prostate cancer development in this region.

p63 regulates commitment to the prostate cell lineage

Molecular mechanisms underlying prostate and urothelial development remain unclear. This situation presents major limitations in identifying the cell type(s) and molecular events involved in the development of prostate and bladder cancer. It has been shown that mice lacking the basal cell marker p63 present several epithelial defects, including epidermis and prostate buds agenesis and urothelial abnormalities. Here, we use the p63-/- mouse as a tool to define cell lineages in the prostate epithelium and urothelium. By complementing p63-/- blastocysts with p63+/+ beta-galactosidase (beta-gal)-positive ES cells, we show that secretory cells of the prostate originate from p63-positive basal progenitor cells. Importantly, our urogenital sinus transplantation studies demonstrate that p63 prevents intestinal differentiation of the urogenital sinus endoderm and is therefore required to maintain commitment to the prostate cell lineage. Finally, in contrast with the prostate findings, analysis of the urothelium from rescued p63-/- chimeras shows that umbrella (superficial) cells can develop and be maintained independently from p63-positive basal and intermediate cells.

Neonatal treatment of rats with diethylstilboestrol (DES) induces stromal-epithelial abnormalities of the vas deferens and cauda epididymis in adulthood following delayed basal cell development

This study investigated whether transient, neonatal (days 2-12) treatment of rats with the potent oestrogen, diethylstilboestrol (DES), altered the structure of the cauda epididymis/vas deferens in adulthood, and if the changes observed related to altered development of basal cells in early puberty. Neonatal treatment with 10 microg DES resulted in the following during adulthood: (a) coiling of the normally straight initial vas deferens, (b) gross epithelial abnormalities, (c) 4-fold widening of the periductal non-muscle layer, (d) infiltration of immune cells across the epithelium into the lumen, and (e) reduction/absence of sperm from the vas deferens lumen. Amongst affected animals>75% exhibited reduced epithelial immunoexpression of androgen receptor and aberrant oestrogen receptor-alpha immunoexpression and 63% exhibited multi-layering of basal cells coincident with increased epithelial cell proliferation. None of the aforementioned changes occurred in rats treated neonatally with 0.1 microg DES. As basal cells play a key role in the development of epithelia such as that in the epididymis and vas deferens, we went on to investigate if neonatal DES treatment affected basal cell development. In controls, basal cells were first evident at day 10 (vas deferens) or day 18 (cauda). Rats treated with 10 microg, but not those treated with 0.1 microg, DES, showed approximately 90% reduction (P<0.001) in basal cell numbers at day 15 and day 18. This decrease coincided with gross suppression of testosterone levels; co-treatment of rats with 10 microg DES+testosterone maintained basal cell numbers at control levels at day 18. However, suppression of testosterone production (GnRH antagonist treatment) or action (flutamide treatment) did not alter basal cell numbers. It is concluded that neonatal exposure to high oestrogen levels coincident with reduced testosterone action results in abnormal changes in the adult cauda/vas deferens that are preceded by delayed differentiation of basal cells. These findings imply a role for androgens and oestrogens in basal cell development and suggest that this may be pivotal in determining normal epithelial (and stromal) development of the cauda/vas deferens.