Cathepsin D acts as an essential mediator to promote malignancy of benign prostatic epithelium

BACKGROUND

Stromal-epithelial interactions are important in both development and prostate cancer. Stromal changes have been shown to be powerful prognostic indicators of prostate cancer progression and of patient death helping to define lethal versus indolent phenotypes. The specific molecular underpinnings of these interactions are incompletely understood. We investigated whether stromal cathepsin D (CathD) overexpression affects prostate tumorigenesis through a paracrine mechanism.

METHODS

Normal prostate fibroblasts (NPF) were retrovirally transduced to overexpress cyclin D1 (CD1) and were designated NPF(CD1) . Cathepsin D expression was knocked down using shRNA in cancer associated fibroblasts (CAF) and NPF(CD1) . We analyzed these stromal cell lines using immunohistochemistry, Western blot, and tissue recombination.

RESULTS

An examination of human prostate tissue revealed significantly increased stromal staining of CathD in malignant prostate tissue. Overexpression of CD1 in normal prostate fibroblasts (NPF(CD1) ) produced a phenotype similar to, but more moderate than, CAF in a tissue recombination model. Knockdown studies revealed that CathD is required for NPF(CD1) motility and invasive growth in vitro. BPH-1 cell proliferation was found to be induced when cultured with NPF(CD1) conditioned medium, this effect was inhibited when CathD was knocked down in NPF(CD1) cells. Overexpression of CathD in prostate stromal cells induced malignancy in adjacent epithelium, and this transformation was inhibited when stromal CathD expression was knocked down in CAF.

CONCLUSIONS

The study presented here demonstrates increased CathD expression is seen in human CAF. The upregulation of CD1 results in concomitant increases in CathD expression. Elevated CathD expression in the stroma contributes to tumor promotion.

Stromal mediation of radiation carcinogenesis

Ionizing radiation is a well-established carcinogen in human breast and rodent mammary gland. This review addresses evidence that radiation elicits the critical stromal context for cancer, affecting not only frequency but the type of cancer. Recent data from the breast tumors of women treated with radiation therapy and the cellular mechanisms evident in experimental models suggest that radiation effects on stromal-epithelial interactions and tissue composition are a major determinant of cancer development.

Androgen action via testicular peritubular myoid cells is essential for male fertility

Androgens are essential for normal spermatogenesis and male fertility, but how androgens exert this effect remains uncertain. Androgen receptors (ARs) are expressed in several testicular cell types, but continuing uncertainty exists over which cell type mediates androgen control of spermatogenesis. Androgen signaling via Sertoli cells (SCs) is essential for complete spermatogenesis, but the role for androgen signaling via peritubular myoid (PTM) cells is contentious. To address this controversy, we generated PTM-specific AR-knockout (PTM-ARKO) mice in which gross reproductive development was normal, but all PTM-ARKO males were azoospermic and infertile. Testis weight was reduced beyond puberty, and in adulthood there was an 86% reduction in germ cells, compared with wild-type littermates. These changes were not explained by any deficits in testosterone, luteinizing hormone, or follicle-stimulating hormone concentrations. SC function was impaired in PTM-ARKO males, indicated by reduced seminiferous tubule fluid production and reduced expression of some androgen-dependent SC genes. Androgen action via PTM cells is therefore essential for normal testis function, spermatogenesis, and fertility in males. This study also provides the first direct evidence for the importance of androgen-driven stromal-epithelial interactions underpinning the regulation of spermatogenesis; PTM-ARKO mice will enable identification of the new molecular pathways involved.

Radiation carcinogenesis in context: how do irradiated tissues become tumors?

It is clear from experimental studies that genotype is an important determinant of cancer susceptibility in general, and for radiation carcinogenesis specifically. It has become increasingly clear that genotype influences not only the ability to cope with DNA damage but also influences the cooperation of other tissues, like the vasculature and immune system, necessary for the establishment of cancer. Our experimental data and that of others suggest that the carcinogenic action of ionizing radiation (IR) can also be considered a two-compartment problem: while IR can alter genomic sequence as a result of DNA damage, it can also induce signals that alter multicellular interactions and phenotypes that underpin carcinogenesis. Rather than being accessory or secondary to genetic damage, we propose that such non-targeted radiation effects create the critical context that promotes cancer development. This review focuses on experimental studies that clearly define molecular mechanisms by which cell interactions contribute to cancer in different organs, and addresses how non-targeted radiation effects may similarly act though the microenvironment. The definition of non-targeted radiation effects and their dose dependence could modify the current paradigms for radiation risk assessment since radiation non-targeted effects, unlike DNA damage, are amenable to intervention. The implications of this perspective in terms of reducing cancer risk after exposure are discussed.

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.

The ADAM17-amphiregulin-EGFR axis in mammary development and cancer

In order to fulfill its function of producing and delivering sufficient milk to newborn mammalian offspring, the mammary gland first has to form an extensive ductal network. As in all phases of mammary development, hormonal cues elicit local intra- and inter-cellular signaling cascades that regulate ductal growth and differentiation. Among other things, ductal development requires the epidermal growth factor receptor (EGFR), its ligand amphiregulin (AREG), and the transmembrane metalloproteinase ADAM17, which can cleave and release AREG from the cell surface so that it may interact with its receptor. Tissue recombination and transplantation studies demonstrate that EGFR phosphorylation and ductal development proceed only when ADAM17 and AREG are expressed on mammary epithelial cells and EGFR is present on stromal cells, and that local administration of soluble AREG can rescue the development of ADAM17-deficient transplants. Thus proper mammary morphogenesis requires the ADAM17-mediated release of AREG from ductal epithelial cells, the subsequent activation of EGFR on stromal cells, and EGFR-dependent stromal responses that in return elicit a new set of epithelial responses, all culminating in the formation of a fully functional ductal tree. This, however, raises new issues concerning what may act upstream, downstream or in parallel with the ADAM17-AREG-EGFR axis, how it may become hijacked or corrupted during the onset and evolution of cancer, and how such ill effects may be confronted.

Isolation and characterization of an immortalized mouse urogenital sinus mesenchyme cell line

BACKGROUND

Stromal-epithelial signaling plays an important role in prostate development and cancer progression. Study of these interactions will be facilitated by the use of suitable prostate cell lines in appropriate model systems.

METHODS

We have isolated an immortalized prostate mesenchymal cell line from the mouse E16 urogenital sinus (UGS). We characterized its expression of stromal differentiation markers, response to androgen stimulation, ability to induce and participate in prostate morphogenesis, response to Shh stimulation, and interaction with prostate epithelial cells.

RESULTS

UGSM-2 cells express vimentin and smooth muscle actin, but not the mature smooth muscle markers myosin and desmin. This expression profile is consistent with a myofibroblast phenotype. Unlike other fibroblasts such as 3T3, UGSM-2 cells express androgen receptor mRNA and androgen stimulation increases proliferation. UGSM-2 cells are viable when grafted with embryonic UGS under the renal capsule and participate in glandular morphogenesis, but are not capable of inducing prostate morphogenesis of isolated UGS epithelium. Co-culture of UGSM-2 cells with human BPH-1 cells or co-grafting in vivo results in organized clusters of BPH-1 cells surrounded by a mantle of UGSM-2 cells. UGSM-2 cells are responsive to Sonic hedgehog (Shh), an important signaling factor in prostate development, and mimic the transcriptional response of the intact UGS mesenchyme. In co-cultures with BPH-1, UGSM-2 cells exhibit a robust transcriptional response to Shh secreted by BPH-1.

CONCLUSIONS

UGSM-2 is a urogenital sinus mesenchyme cell line that can be used to study stromal-epithelial interactions that are important in prostate biology.

Of extracellular matrix, scaffolds, and signaling: tissue architecture regulates development, homeostasis, and cancer

The microenvironment influences gene expression so that the behavior of a cell is largely determined by its interactions with the extracellular matrix, neighboring cells, and soluble local and systemic cues. We describe the essential roles of context and organ structure in directing mammary gland development and differentiated function and in determining the response to oncogenic insults, including mutations. We expand on the concept of "dynamic reciprocity" to present an integrated view of development, cancer, and aging and posit that genes are like the keys on a piano: Although they are essential, it is the context that makes the music.