Heparin-binding EGF-like growth factor in the human prostate: synthesis predominantly by interstitial and vascular smooth muscle cells and action as a carcinoma cell mitogen

Stromal-derived MAOB promotes prostate cancer growth and progression

Prostate cancer (PC) develops in a microenvironment where the stromal cells modulate adjacent tumor growth and progression. Here, we demonstrated elevated levels of monoamine oxidase B (MAOB), a mitochondrial enzyme that degrades biogenic and dietary monoamines, in human PC stroma, which was associated with poor clinical outcomes of PC patients. Knockdown or overexpression of MAOB in human prostate stromal fibroblasts indicated that MAOB promotes cocultured PC cell proliferation, migration, and invasion and co-inoculated prostate tumor growth in mice. Mechanistically, MAOB induces a reactive stroma with activated marker expression, increased extracellular matrix remodeling, and acquisition of a protumorigenic phenotype through enhanced production of reactive oxygen species. Moreover, MAOB transcriptionally activates CXCL12 through Twist1 synergizing with TGFβ1-dependent Smads in prostate stroma, which stimulates tumor-expressed CXCR4-Src/JNK signaling in a paracrine manner. Pharmacological inhibition of stromal MAOB restricted PC xenograft growth in mice. Collectively, these findings characterize the contribution of MAOB to PC and suggest MAOB as a potential stroma-based therapeutic target.

Interplay between Prostate Cancer and Adipose Microenvironment: A Complex and Flexible Scenario

Adipose tissue is part of the prostate cancer (PCa) microenvironment not only in the periprostatic area, but also in the most frequent metastatic sites, such as bone marrow and pelvic lymph nodes. The involvement of periprostatic adipose tissue (PPAT) in the aggressiveness of PCa is strongly suggested by numerous studies. Many molecules play a role in the reciprocal interaction between adipocytes and PCa cells, including adipokines, hormones, lipids, and also lipophilic pollutants stored in adipocytes. The crosstalk has consequences not only on cancer cell growth and metastatic potential, but also on adipocytes. Although most of the molecules released by PPAT are likely to promote tumor growth and the migration of cancer cells, others, such as the adipokine adiponectin and the n-6 or n-3 polyunsaturated fatty acids (PUFAs), have been shown to have anti-tumor properties. The effects of PPAT on PCa cells might therefore depend on the balance between the pro- and anti-tumor components of PPAT. In addition, genetic and environmental factors involved in the risk and/or aggressiveness of PCa, including obesity and diet, are able to modulate the interactions between PPAT and cancer cells and their consequences on the growth and the metastatic potential of PCa.

Exogenous fatty acid binding protein 4 promotes human prostate cancer cell progression

Epidemiologic studies have found that obesity is associated with malignant grade and mortality in prostate cancer. Several adipokines have been implicated as putative mediating factors between obesity and prostate cancer. Fatty acid binding protein 4 (FABP4), a member of the cytoplasmic fatty acid binding protein multigene family, was recently identified as a novel adipokine. Although FABP4 is released from adipocytes and mean circulating concentrations of FABP4 are linked with obesity, effects of exogenous FABP4 on prostate cancer progression are unclear. In this study, we examined the effects of exogenous FABP4 on human prostate cancer cell progression. FABP4 treatment promoted serum-induced prostate cancer cell invasion in vitro. Furthermore, oleic acid promoted prostate cancer cell invasion only if FABP4 was present in the medium. These promoting effects were reduced by FABP4 inhibitor, which inhibits FABP4 binding to fatty acids. Immunostaining for FABP4 showed that exogenous FABP4 was taken up into DU145 cells in three-dimensional culture. In mice, treatment with FABP4 inhibitor reduced the subcutaneous growth and lung metastasis of prostate cancer cells. Immunohistochemical analysis showed that the number of apoptotic cells, positive for cleaved caspase-3 and cleaved PARP, was increased in subcutaneous tumors of FABP4 inhibitor-treated mice, as compared with control mice. These results suggest that exogenous FABP4 might promote human prostate cancer cell progression by binding with fatty acids. Additionally, exogenous FABP4 activated the PI3K/Akt pathway, independently of binding to fatty acids. Thus, FABP4 might be a key molecule to understand the mechanisms underlying the obesity-prostate cancer progression link.

Insidious changes in stromal matrix fuel cancer progression

Reciprocal interactions between tumor and stromal cells propel cancer progression and metastasis. A complete understanding of the complex contributions of the tumor stroma to cancer progression necessitates a careful examination of the extracellular matrix (ECM), which is largely synthesized and modulated by cancer-associated fibroblasts. This structurally supportive meshwork serves as a signaling scaffold for a myriad of biologic processes and responses favoring tumor progression. The ECM is a repository for growth factors and cytokines that promote tumor growth, proliferation, and metastasis through diverse interactions with soluble and insoluble ECM components. Growth factors activated by proteases are involved in the initiation of cell signaling pathways essential to invasion and survival. Various transmembrane proteins produced by the cancer stroma bind the collagen and fibronectin-rich matrix to induce proliferation, adhesion, and migration of cancer cells, as well as protease activation. Integrins are critical liaisons between tumor cells and the surrounding stroma, and with their mechano-sensing ability, induce cell signaling pathways associated with contractility and migration. Proteoglycans also bind and interact with various matrix proteins in the tumor microenvironment to promote cancer progression. Together, these components function to mediate cross-talk between tumor cells and fibroblasts ultimately to promote tumor survival and metastasis. These stromal factors, which may be expressed differentially according to cancer stage, have prognostic utility and potential. This review examines changes in the ECM of cancer-associated fibroblasts induced through carcinogenesis, and the impact of these changes on cancer progression. The implication is that cancer progression, even in epithelial cancers, may be based in large part on changes in signaling from cancer-associated stromal cells. These changes may provide early prognostic indicators to further stratify patients during treatment or alter the timing of their follow-up visits and observations.

Enhanced shedding of extracellular vesicles from amoeboid prostate cancer cells: potential effects on the tumor microenvironment

The gene encoding the cytoskeletal regulator DIAPH3 is lost at high frequency in metastatic prostate cancer, and DIAPH3 silencing evokes a transition to an amoeboid tumor phenotype in multiple cell backgrounds. This amoeboid transformation is accompanied by increased tumor cell migration, invasion, and metastasis. DIAPH3 silencing also promotes the formation of atypically large (> 1 μm) membrane blebs that can be shed as extracellular vesicles (EV) containing bioactive cargo. Whether loss of DIAPH3 also stimulates the release of nano-sized EV (e.g., exosomes) is not established. Here we examined the mechanism of release and potential biological functions of EV shed from DIAPH3-silenced and other prostate cancer cells. We observed that stimulation of LNCaP cells with the prostate stroma-derived growth factor heparin-binding EGF-like growth factor (HB-EGF), combined with p38MAPK inhibition caused EV shedding, a process mediated by ERK1/2 hyperactivation. DIAPH3 silencing in DU145 cells also increased rates of EV production. EV isolated from DIAPH3-silenced cells activated AKT1 and androgen signaling, increased proliferation of recipient tumor cells, and suppressed proliferation of human macrophages and peripheral blood mononuclear cells. DU145 EV contained miR-125a, which suppressed AKT1 expression and proliferation in recipient human peripheral blood mononuclear cells and macrophages. Our findings suggest that EV produced as a result of DIAPH3 loss or growth factor stimulation may condition the tumor microenvironment through multiple mechanisms, including the proliferation of cancer cells and suppression of tumor-infiltrating immune cells.

Heparin-binding epidermal growth factor-like growth factor/diphtheria toxin receptor in normal and neoplastic hematopoiesis

Heparin-binding EGF-like growth factor (HB-EGF) belongs to the EGF family of growth factors. It is biologically active either as a molecule anchored to the membrane or as a soluble form released by proteolytic cleavage of the extracellular domain. HB-EGF is involved in relevant physiological and pathological processes spanning from proliferation and apoptosis to morphogenesis. We outline here the main activities of HB-EGF in connection with normal or neoplastic differentiative or proliferative events taking place primitively in the hematopoietic microenvironment.

Heparin-binding EGF-like growth factor enhances the activity of invasion and metastasis in thyroid cancer cells

Thyroid cancer sometimes contains poorly differentiated components, which have the potential of invasion and metastasis. We evaluated the possible roles of heparin-binding EGF-like growth factor (HB-EGF), a member of the epidermal growth factor (EGF) family, in cell growth and invasion of thyroid cancer cells, and demonstrated that HB-EGF is not only a potent mitogen but also a chemotactic factor in the thyroid cancer cells 8305C and SW579. The HB-EGF-mediated chemotaxis was inhibited by neutralizing antibody against the EGF receptor (EGFR/HER1/ErbB1) or tyrphostin AG1478, a specific inhibitor of the EGFR tyrosine kinase. The HB-EGF mRNA and protein expression was also analyzed using RT-PCR and immunofluorescence methods, respectively. In addition, in clinical immunohistochemical study, increased expression of HB-EGF and its receptors, HER1 and EGFR4 (HER4/ErbB4), was observed in thyroid carcinoma cells. Our findings suggest that HB-EGF acts as a potent paracrine and/or autocrine chemotactic factor as well as a mitogen that mediates HER1 and/or HER4 in the invasion and metastasis of thyroid carcinoma cells, including poorly differentiated papillary carcinomas or undifferentiated/anaplastic carcinomas. These data may aid in the development of novel therapeutic strategies for thyroid cancer.

Essential roles of heparin-binding epidermal growth factor-like growth factor in the brain

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is a member of the EGF family of growth factors, which interacts with the EGF receptor to exert mitogenic activity for various types of cells. Through its interactions with various molecules, it is involved in diverse biological processes, including wound healing, blast implantation, and tumor formation. At the same time, HB-EGF is widely expressed in the central nervous system, including the hippocampus and cerebral cortex, and is considered to play pivotal roles in the developing and adult nervous system. Because HB-EGF protein levels in the brain are much higher than those of TGF-α and EGF, it is possible that HB-EGF serves as a major physiologic ligand for the EGF receptor (ErbB1) within the central nervous system. Recent studies indicate that HB-EGF contributes to the neuronal survival and proliferation of glial/stem cells. HB-EGF also promotes the survival of dopaminergic neurons, an action mediated by mitogen-activated protein kinase (MAPK) as well as by the Akt signaling pathway. In this review, we discuss recent findings on the implications of HB-EGF in higher brain functions of the central nervous system.

Recreating the tumor microenvironment in a bilayer, hyaluronic acid hydrogel construct for the growth of prostate cancer spheroids

Cancer cells cultured in physiologically relevant, three-dimensional (3D) matrices can recapture many essential features of native tumor tissues. In this study, a hyaluronic acid (HA)-based bilayer hydrogel system that not only supports the tumoroid formation from LNCaP prostate cancer (PCa) cells, but also simulates their reciprocal interactions with the tumor-associated stroma was developed and characterized. HA hydrogels were prepared by mixing solutions of HA precursors functionalized with acrylate groups (HA-AC) and reactive thiols (HA-SH) under physiological conditions. The resultant viscoelastic gels have an average elastic modulus of 234 ± 30 Pa and can be degraded readily by hyaluronidase. The orthogonal and cytocompatible nature of the crosslinking chemistry permits facile incorporation of cytokine-releasing particles and PCa cells. In our bilayer hydrogel construct, the top layer contains heparin (HP)-decorated, HA-based hydrogel particles (HGPs) capable of releasing heparin-binding epidermal growth factor-like growth factor (HB-EGF) in a sustained manner at a rate of 2.5 wt%/day cumulatively. LNCaP cells embedded in the bottom layer receive the growth factor signals from the top, and in response form enlarging tumoroids with an average diameter of 85 μm by day 7. Cells in 3D hydrogels assemble into spherical tumoroids, form close cellular contacts through E-cadherin, and show cortical organization of F-actin, whereas those plated as 2D monolayers adopt a spread-out morphology. Compared to cells cultured on 2D, the engineered tumoroids significantly increased the expression of two pro-angiogenic factors, vascular endothelial growth factor-165 (VEGF(165)) and interleukin-8 (IL-8), both at mRNA and protein levels. Overall, the HA model system provides a useful platform for the study of tumor cell responses to growth factors and for screening of anticancer drugs targeting these pathways.

Endothelial-derived PDGF-BB and HB-EGF coordinately regulate pericyte recruitment during vasculogenic tube assembly and stabilization

Recently, we reported a novel system whereby human pericytes are recruited to endothelial cell (EC)-lined tubes in 3-dimensional (3D) extracellular matrices to stimulate vascular maturation including basement membrane matrix assembly. Through the use of this serum-free, defined system, we demonstrate that pericyte motility within 3D collagen matrices is dependent on the copresence of ECs. Using either soluble receptor traps consisting of the extracellular ligand-binding domains of platelet-derived growth factor receptor β, epidermal growth factor receptor (EGFR), and ErbB4 receptors or blocking antibodies directed to platelet-derived growth factor (PDGF)-BB, or heparin-binding EGF-like growth factor (HB-EGF), we show that both of these EC-derived ligands are required to control pericyte motility, proliferation, and recruitment along the EC tube ablumenal surface. Blockade of pericyte recruitment causes a lack of basement membrane matrix deposition and, concomitantly, increased vessel widths. Combined inhibition of PDGF-BB and HB-EGF-induced signaling in quail embryos leads to reduced pericyte recruitment to EC tubes, decreased basement membrane matrix deposition, increased vessel widths, and vascular hemorrhage phenotypes in vivo, in support of our findings in vitro. In conclusion, we report a dual role for EC-derived PDGF-BB and HB-EGF in controlling pericyte recruitment to EC-lined tubes during developmental vascularization events.

Activin receptor signaling regulates prostatic epithelial cell adhesion and viability

Mutational changes coupled with endocrine, paracrine, and/or autocrine signals regulate cell division during carcinogenesis. The hormone signals remain undefined, although the absolute requirement in vitro for fetal serum indicates the necessity for a fetal serum factor(s) in cell proliferation. Using prostatic cancer cell (PCC) lines as a model of cancer cell proliferation, we have identified the fetal serum component activin A and its signaling through the activin receptor type II (ActRII), as necessary, although not sufficient, for PCC proliferation. Activin A induced Smad2 phosphorylation and PCC proliferation, but only in the presence of fetal bovine serum (FBS). Conversely, activin A antibodies and inhibin A suppressed FBS-induced PCC proliferation confirming activin A as one of multiple serum components required for PCC proliferation. Basic fibroblast growth factor was subsequently shown to synergize activin A-induced PCC proliferation. Inhibition of ActRII signaling using a blocking antibody or antisense-P decreased mature ActRII expression, Smad2 phosphorylation, and the apparent viability of PCCs and neuroblastoma cells grown in FBS. Suppression of ActRII signaling in PCC and neuroblastoma cells did not induce apoptosis as indicated by the ratio of active/inactive caspase 3 but did correlate with increased cell detachment and ADAM-15 expression, a disintegrin whose expression is strongly correlated with prostatic metastasis. These findings indicate that ActRII signaling is required for PCC and neuroblastoma cell viability, with ActRII mediating cell fate via the regulation of cell adhesion. That ActRII signaling governs both cell viability and cell adhesion has important implications for developing therapeutic strategies to regulate cancer growth and metastasis.

Isoliquiritigenin inhibits migration and invasion of prostate cancer cells: possible mediation by decreased JNK/AP-1 signaling

Isoliquiritigenin (ISL, 4,2',4'-trihydroxychalcone), which is found in licorice, shallot and bean sprouts, is a potent antioxidant with anti-inflammatory and anti-carcinogenic effects. The purpose of this study was to investigate the effects of ISL treatment on the migration, invasion and adhesion characteristics of DU145 human prostate cancer cells. DU145 cells were cultured in the presence of 0-20 micromol/L ISL with or without 10 microg/L epidermal growth factor (EGF). ISL inhibited basal and EGF-induced cell migration, invasion and adhesion dose dependently. ISL decreased EGF-induced secretion of urokinase-type plasminogen activator (uPA), matrix metalloproteinase (MMP)-9, tissue inhibitor of metalloproteinase-1 (TIMP-1), and vascular endothelial growth factor (VEGF), but increased TIMP-2 secretion in a concentration-dependent manner. In addition, ISL decreased the protein levels of integrin-alpha2, intercellular adhesion molecule (ICAM) and vascular cell adhesion molecule (VCAM), and mRNA levels of uPA, MMP-9, VEGF, ICAM and integrin-alpha2. Furthermore, basal and EGF-induced activator protein (AP)-1 binding activity and phosphorylation of Jun N-terminal kinase (JNK), c-Jun and Akt were decreased after ISL treatment. However, phosphorylation of extracellular signal-regulated kinase (ERK)1/2 and p38 mitogen-activated protein kinase was not altered. The JNK inhibitor SP600125 inhibited basal and EGF-induced secretion of uPA, VEGF, MMP-9 and TIMP-1, as well as AP-1 DNA binding activity and cell migration. These results provide evidence for the role of ISL as a potent antimetastatic agent, which can markedly inhibit the metastatic and invasive capacity of prostate cancer cells. The inhibition of JNK/AP-1 signaling may be one of the mechanisms by which ISL inhibits cancer cell invasion and migration.

(Make) stick and cut loose--disintegrin metalloproteases in development and disease

"A disintegrin and metalloprotease" (ADAM) proteases form a still growing family of about 40 type 1 transmembrane proteins. They are defined by a common modular ectodomain architecture that combines cell deadhesion/adhesion and fusion motifs (disintegrin and cysteine-rich domains), with a Zn-protease domain capped by a large prodomain. Their ectodomain thus strikingly resembles snake venom disintegrin proteases, which by combined integrin blocking and extracellular proteolysis, can cause extensive tissue damage after snake bites. A surprisingly large proportion (13 ADAMs) is exclusively expressed in the male gonads, and only a minority can be found throughout all tissues. As predicted by their amino acid sequence, a major proportion of this family has not maintained a functional protease domain, most probably rendering them into pure adhesion and/or fusion proteins. For most ADAMs, the respective key function has remained elusive. Despite their overall conserved ectodomain structure, ADAMs appear to be subdivided into those with a predominant role in direct adhesion (e.g., ADAMs 1, 2, and 3) and those mainly acting as proteases (e.g., ADAMs 10 and 17). Only for a few of them are functions of more than one domain documented (e.g., ADAM9 in cell fusion and proteolysis). Several ADAMs exist in both membrane-resident and secreted isoforms; the functional significance of this dichotomy is in most cases still unclear. Knockout phenotypes have been informative only in a few cases (ADAMs 1, 2, 10, 12, 15, 17, and 19) and are mainly related to their protease function. A common denominator of ADAM-mediated proteolysis is the ectodomain shedding of a broad spectrum of substrates, including paracrine growth factors like epidermal growth factor receptor (EGFR) ligands, cell adhesion molecules like CD44 or cadherins, and the initiation of regulated intramembrane proteolysis (RIP), whereby the transmembrane fragment of the respective substrate is further cleaved by an intramembrane cleaving protease to release an intracellular domain acting as a nuclear transcription regulator. Most ADAMs feature a significant overlap of substrate specificities, explaining why an inactivation of individual ADAMs only rarely causes major phenotypes.

ADAM12 is highly expressed in carcinoma-associated stroma and is required for mouse prostate tumor progression

The interaction between stromal cells and tumor cells is emerging as a critical aspect of tumor progression. Yet there is a paucity of molecular markers for cells participating in such interactions, and only few genes are known to play a critical role in this process. Here, we describe the identification of ADAM12 (a disintegrin and metalloprotease 12) as a novel marker for a subpopulation of stromal cells that are adjacent to epithelial tumor cells in three mouse carcinoma models (models for prostate, breast and colon cancer). Moreover, we show that ADAM12 is essential for tumor development and progression in the W10 mouse model for prostate cancer. These results suggest that ADAM12 might be a useful marker for stromal cells in mouse tumors that are likely to participate in stromal/tumor cell crosstalk, and that ADAM12 is a potential target for design of drugs that prevent carcinoma growth.

Emergence of metastatic hormone-refractory disease in prostate cancer after anti-androgen therapy

The anti-androgens used in prostate cancer therapy have been designed to interfere with the normal androgen receptor (AR)-mediated processes that ensure prostate cell survival, triggering tumor cells to undergo programmed cell death. While anti-androgens were originally designed to treat advanced disease, they have recently been used to debulk organ-confined prostate tumors, to improve positive margins prior to surgery, and for chemoprevention in patients at high risk for prostate cancer. However, tumors treated with anti-androgens frequently become hormone refractory and acquire a more aggressive phenotype. Progression toward metastatic hormone-refractory disease has often been regarded as the outgrowth of a small number of hormone-independent cells that emerge from a hormone-dependent tumor during anti-androgen treatment by natural selection. While a number of selective advantages have recently been identified, there is also considerable evidence suggesting that the progression toward metastatic hormone-refractory disease is an dynamic process which involves abrogation of programmed cell death as a result of the attenuation of DNA fragmentation and maintenance of mitochondrial membrane potential in tumor cells; the upregulation of stromal-mediated growth factor signaling pathways; and the upregulation of extracellular matrix (ECM) protease expression.

Transactivation of epidermal growth factor receptor after heparin-binding epidermal growth factor-like growth factor shedding in the migration of prostate cancer cells promoted by bombesin

BACKGROUND

A pathway consisting of bombesin, G-protein coupling receptors (GPCRs), metalloproteases, pro-heparin-binding epidermal growth factor (proHB-EGF), and epidermal growth factor receptor (EGFR) has been reported in prostate cancer cells. The occurrence of HB-EGF shedding from proHB-EGF in this pathway, however, has not been proven directly. In addition, it is still unclear how much this pathway contributes to the migration of prostate cancer cells. In this study, we tried to directly elucidate HB-EGF shedding in this pathway and to determine its contribution to the migration of prostate cancer cells.

METHODS

RT-PCR and indirect immunofluorescence staining for HB-EGF and its receptors, such as EGFR and HER4/erbB4, were performed on PC-3 cells. The influences of bombesin, anti-EGFR neutralizing monoclonal antibody, HB-EGF, and HB-EGF shedding inhibitor on the migration of PC-3 cells were studied by means of in vitro wound assays. The amount of HB-EGF shed from PC-3 cells with alkaline phosphatase-tagged HB-EGF in the presence of bombesin was determined by measuring AP activity. Immunoprecipitations and phosphotyrosine Western blotting were performed to detect EGFR transactivated by bombesin.

RESULTS

PC-3 expressed HB-EGF and EGFR, but not HER4/erbB4. PC-3 migrated in the presence of bombesin, but its migration was partly inhibited by the neutralizing antibody against EGFR. PC-3 also migrated in the presence of HB-EGF, but HB-EGF shedding inhibitor partly inhibited this phenomenon. HB-EGF was shed from PC-3 cells in the presence of bombesin, and this shedding was inhibited by HB-EGF shedding inhibitor. In addition, the EGFR on PC-3 was activated in the presence of bombesin and inactivated in the presence of HB-EGF shedding inhibitor.

CONCLUSIONS

These results indicated that HB-EGF shedding and the following transactivation of EGFR occurs in this pathway and that this pathway partly contributes to the migration of prostate cancer cells.

Transactivation of ErbB1 and ErbB2 receptors by angiotensin II in normal human prostate stromal cells

BACKGROUND

Heparin-binding epidermal growth factor-like growth factor (HB-EGF) is synthesized primarily in the stromal compartment of the human prostate and may regulate stromal as well as epithelial cell growth and survival. The primary cognate HB-EGF receptor, ErbB1, has been shown recently to be transactivated by G-protein coupled receptors (GPCRs) through regulated proteolytic cleavage of the membrane-bound, precursor form of HB-EGF. Previous studies have demonstrated that human prostate tissue, especially tissue from benign prostatic hyperplasia (BPH), has high angiotensin converting enzyme activity, and a high density of angiotensin (Ang) receptors in periurethral stromal cells. Because the pressor peptide Ang II signals through GPCRs, we tested the possibility that Ang II could transactivate ErbB1/ErbB2 in human prostate stromal (hPS) cells.

METHODS

Primary and early passage hPS cells were used as an in vitro model. Cells were stimulated by recombinant HB-EGF or Ang II and total cell lysates were harvested for immunoprecipitation and Western blot. Cell growth was measured by [(3)H]thymidine incorporation assay and 3-[4,5-dimethylthiazol-2-yl]-2,5-diphenyl-tetrazoliumbromide (MTT) assay.

RESULTS

Ang II receptors AT1 and AT2 were expressed in hPS cells. ErbB1 and ErbB2 receptors were activated by HB-EGF. Furthermore, Ang II was able to transactivate both ErbB1 and ErbB2, and this transactivation activity could be abolished by pretreatment with [Glu-52]-diphtheria toxin/CRM197, a specific inhibitor of HB-EGF bioactivity. Consistent with its transactivation activity, Ang II modestly promoted hPS cell growth and this effect was abolished by pretreatment with the ErbB1 antagonist AG1478.

CONCLUSION

These experiments suggest a regulatory role for Ang II in the prostate stroma and implicate the endogenous stromal growth factor HB-EGF as a mediator of Ang II signaling in the prostate.

Heparin-binding epidermal growth factor-like growth factor stimulates androgen-independent prostate tumor growth and antagonizes androgen receptor function

Peptide growth factors have been implicated in progression of prostate cancer (PCa) to the androgen-independent state; however, much of the evidence linking diffusible mitogens and survival factors to this process remains circumstantial. Heparin-binding epidermal growth factor-like growth factor (HB-EGF), a prostate stroma-derived factor, promotes survival, proliferation, and neuroendocrine differentiation of androgen-dependent LNCaP PCa cells in vitro. To test whether sustained exposure to HB-EGF can confer an androgen-independent phenotype, we generated stable populations of LNCaP cells that express constitutively a secreted form of HB-EGF (LNCaP/sHB). LNCaP/sHB cells proliferated more rapidly under androgen-depleted conditions in vitro and formed larger tumors with higher frequency in intact and castrated severe combined immunodeficient mice, in comparison to control cells. LNCaP/sHB tumors also expressed higher levels of the neuroendocrine marker, neuron-specific enolase, compared with control tumors. In castrates, increased neuron-specific enolase expression in LNCaP/sHB tumors was associated with reduced androgen receptor (AR) levels. In vitro, AR protein levels were reduced in LNCaP/sHB cells, and in transient transfection assays using an androgen-responsive promoter (mouse mammary tumor virus-long terminal repeat), LNCaP/sHB cells showed reduced sensitivity to dihydrotestosterone compared with controls. This is the first demonstration that continuous exposure of AR-positive PCa cells to a single growth factor can promote an androgen-independent phenotype in vivo. These findings also emphasize the potential role of pathways other than the AR axis in acquisition of androgen independence.

Chronic treatment with epidermal growth factor induces growth of the rat ventral prostate

OBJECTIVE

The epidermal growth factor (EGF) system is expressed in the rat prostate, and growth factors from this system induce proliferation in prostate epithelial and stromal cell cultures. The aim of the study was to investigate the possible growth-promoting effects of the system during the hyperplastic growth phase of the prostate in newborn rats.

MATERIAL AND METHODS

Newborn rats were treated for 8 weeks with EGF (150 microg/kg body weight per day), administered as daily subcutaneous injections. Sections of the prostate tissue were examined by a stereological technique to determine tissue composition.

RESULTS

Treatment with EGF increased the weight of the ventral prostate, relative to body weight, by 50% compared with placebo (p < 0.005). Neither the dorsolateral prostate, seminal vesicles nor coagulating glands were affected by EGF. Prostate tissue showed a significant increase in the volume of the prostate epithelium, the stroma and the lumen following EGF treatment, in a pattern resembling physiological growth of the ventral prostate. A significant correlation (r = 0.78, p < 0.0001) of the volume fraction of the lumen with the glandular weight of the ventral prostate was seen. Serum testosterone was not affected by chronic EGF administration.

CONCLUSIONS

EGF selectively induces growth of the ventral lobe of the prostate in newborn rats, in a pattern comparable to normal physiological growth. It may be hypothesized that the physiological growth of the prostate is directly correlated to endogenous activity of the EGF system in the rat prostate gland.

Effects and characterization of paracrine factors produced by human prostate stromal cells in bioassays using rat Sertoli cells, LNCaP tumor cells, and cultured prostate epithelial cells

BACKGROUND

Prostatic stroma affects both proliferation and differentiation of epithelial cells but the factors involved remain poorly understood. In order to identify and characterize potential paracrine mediators, we studied the effects of human prostate fibroblast-conditioned media (PFCM) in three bioassay systems.

METHODS

The first bioassay uses transferrin secretion by cultured rat Sertoli cells as an endpoint for differentiating activity. Factors active in this (heterologous) assay were compared to PModS, a mediator of mesenchymal-epithelial interactions in the testis, also produced by rat prostate stromal cells. The two other (homologous) bioassays use LNCaP tumor cells or subcultured human prostate epithelial cells (PEC) as targets. Differentiation is evaluated by prostate-specific antigen (PSA) secretion and reverse transcriptase-polymerase chain reaction (RT-PCR) for a number of markers of epithelial function. Proliferation is assayed by measurements of DNA and thymidine incorporation.

RESULTS

PFCM markedly stimulates transferrin production by Sertoli cells. The main factor(s) involved are acid stable and bind to heparin. However, both their size (approximately 37 kDa) and their behavior on reversed-phase chromatography differ from that of PModS. Although PFCM increases total RNA content of LNCaP, it does not increase or restore differentiated function of LNCaP or PEC. Proliferative effects are observed in LNCaP and these effects cannot be neutralized by an antiserum directed against basic fibroblast growth factor (bFGF). Antiproliferative effects are observed in PEC and these effects are largely due to transforming growth factor-beta (TGF-beta).

CONCLUSIONS

PFCM provokes differentiating effects in a Sertoli cell bioassay, but unlike with rat stromal cells, the factor(s) involved differ from PModS. In the two homologous systems studied, differentiating effects could not be demonstrated and discordant effects were noted on proliferation. Various bioassay systems will be required to identify the spectrum of mediators present in PFCM.

Heparin-binding epidermal growth factor-like growth factor is an autocrine mediator of human prostate stromal cell growth in vitro

PURPOSE

The physiological mechanisms by which soluble mediators of cell proliferation and survival alter expansion of the prostatic stroma in benign prostatic hyperplasia are poorly understood. We recently identified heparin-binding epidermal growth factor like growth factor (HB-EGF) as a product predominantly of the smooth muscle cell compartments of the adult human prostate. We assess the potential role of this growth factor as a stromal cell regulator.

MATERIALS AND METHODS

Primary cultures of desmin and alpha-actin positive human prostate stromal cells were shown to express several cell associated HB-EGF isoforms as well as the primary cognate HB-EGF receptor, ErbB1/HER1, suggesting the existence of an autocrine or juxtacrine regulatory loop. The related receptor tyrosine kinase, ErbB2/HER2, was also expressed as assessed by reverse transcriptase (RT) polymerase chain reaction (PCR). HB-EGF messenger RNA levels in human prostate stromal cells increased modestly (70%) in response to a repetitive mechanical stimulus, a lower response than has been reported for neonatal rat bladder smooth muscle cells, in which HB-EGF was originally identified as a mechanically responsive gene.

RESULTS

HB-EGF, epidermal growth factor and basic fibroblast growth factor stimulated human prostate stromal cell growth, while a specific antagonist of HB-EGF, [Glu52]-diphtheria toxin/CRM197, inhibited human prostate stromal growth in serum-free medium by a mechanism that did not involve increased apoptosis. A function blocking antibody against CD9/DRAP27/MRP-1, a cell surface binding partner of the membrane form of HB-EGF, also stimulated human prostate stromal cell proliferation.

CONCLUSIONS

HB-EGF is an endogenously produced human prostate stromal cell growth factor and, thus, may have a role as a physiologically relevant autocrine or juxtacrine mediator of stromal expansion in benign prostatic hyperplasia.

Cyclic stretch activates p38 SAPK2-, ErbB2-, and AT1-dependent signaling in bladder smooth muscle cells

Cyclic mechanical stretch of bladder smooth muscle cells (SMC) increases rates of DNA synthesis and stimulates transcription of the gene for heparin-binding epidermal growth factor-like growth factor (HB-EGF), an ErbB1/EGF receptor ligand that has been linked to hypertrophic bladder growth. In this study we sought to clarify the signaling pathways responsible for mechanotransduction of the stretch stimulus. HB-EGF mRNA levels, DNA synthesis, and AP-1/Ets DNA binding activities were induced by repetitive stretch of primary culture rat bladder SMC. Inhibitors of the p38 SAPK2 pathway, the angiotensin receptor type 1 (AT1), and the ErbB2 tyrosine kinase reduced each of these activities, while an inhibitor of the extracellular signal-regulated kinase mitogen-activated protein kinase (Erk-MAPK) pathway had no effect. Stretch rapidly activated stress-activated protein kinase 2 (p38 SAPK2) and Jun NH(2)-terminal kinase (JNK)/SAPK pathways but not the Erk-MAPK pathway and induced ErbB2 but not ErbB1 phosphorylation. Angiotensin II (ANG II) a bladder SMC mitogen previously linked to the stretch response, did not activate ErbB2, and ErbB2 activation occurred in response to stretch in the presence of an ANG receptor inhibitor, indicating that activation of the AT1-mediated pathway and the ErbB2-dependent pathway occurs by independent mechanisms. p38 SAPK2 and JNK/SAPK signaling also appeared to be independent of the ErbB2 and AT1 pathways. These findings indicate that stretch-stimulated DNA synthesis and gene expression in normal bladder SMC occur via multiple independent receptor systems (e.g., AT1 and ErbB2) and at least one MAPK pathway (p38 SAPK2). Further, we show that the Erk-MAPK pathway, which in most systems is linked to receptor-dependent cell growth responses, is not involved in progression to DNA synthesis or in the response of the HB-EGF gene to mechanical forces.

Quantitation of the mRNA expression of the epidermal growth factor system: selective induction of heparin-binding epidermal growth factor-like growth factor and amphiregulin expression by growth factor stimulation of prostate stromal cells

The epidermal growth factor (EGF) system is a rapidly expanding system of growth factors involved in many aspects of normal and cancerous growth. We have developed a method for the quantitation of mRNA coding for all six growth factors activating the human EGF receptor (HER-1) and for the quantitation of mRNA for the receptors HER-1 and its preferred dimerization partner, HER-2. The method is based on the generation of specific RNA standards, which are amplified by reverse transcriptase-polymerase chain reaction (RT-PCR) with the sample RNA and a set of calibrators. The resulting calibration curve is used to quantitate the unknown samples, which require only a single RT-PCR reaction. Our method has the advantage that quantitation is based on coamplification of an internal RNA standard, thereby controlling both the PCR and RT reactions. In addition, the RNA standards for all growth factors and receptors are combined in a single RT reaction, which minimizes variation and allows the quantitation of all eight mRNA species with only 0.1 microg RNA. This makes the method suitable for studies in which the supply of material is limited. The developed method has enabled us to demonstrate that prostate stromal cells in primary culture express EGF, heparin-binding EGF (HB-EGF), amphiregulin, betacellulin, and epiregulin as well as the HER-1 and HER-2 receptors, whereas no transforming growth factor-alpha mRNA is found. Furthermore, activation of the EGF system in these cells by stimulation with HB-EGF or EGF in mitogenic doses causes a selective increase in the expression of amphiregulin and HB-EGF mRNA (more than 15-fold and 25-fold, respectively), whereas there is no increase in the expression of mRNA for the other growth factors or receptors. In accord with the increase in amphiregulin mRNA, the amount of amphiregulin peptide released from the cells is also increased. The selective induction of amphiregulin and HB-EGF by growth factor stimulation may represent a mechanism to amplify the initial growth factor signal in prostate stromal cells.

Amphiregulin is coordinately expressed with heparin-binding epidermal growth factor-like growth factor in the interstitial smooth muscle of the human prostate

Peptide growth factors have been proposed as mediators of smooth muscle-epithelial cell interactions in the human prostate; however, the identity of these molecules has not been established. In this study, we compared expression levels of messenger RNAs (mRNAs) encoding the epidermal growth factor (EGF) receptor-related receptor tyrosine kinases (ErbB1 through 4), the six EGF receptor ligands, EGF, transforming growth factor (TGF)-alpha, amphiregulin (ARG), HB-EGF, betacellulin, and epiregulin, and the related molecule heregulin-alpha, in a series of 10 prostate tissue specimens. Only EGF showed a disease-specific association, with increased mRNA levels in four of five PCa specimens in comparison to matched normal tissue from the same subject. In contrast, ARG and HB-EGF mRNAs showed a coordinate pattern of expression in 7/10 specimens that was distinct from all other growth factor or receptor genes examined and from mRNAs for prostate specific antigen, the androgen receptor and GAPDH, a house-keeping enzyme. Analysis of an additional series of benign prostatic hyperplasia and prostate cancer specimens from 60 individuals confirmed that ARG and HB-EGF mRNA levels varied in a highly coordinate manner (r = 0.93; P < 0.0001) but showed no association with disease. ARG was immunolocalized largely to interstitial smooth muscle cells (SMC), previously identified as the site of synthesis of HB-EGF in the prostate, while the cognate ARG and HB-EGF receptor, ErbB1, was localized exclusively to ductal epithelial cells and carcinoma cells. Although ARG was a relatively poor mitogen for Balb/c3T3 cells in comparison to HB-EGF, it was similar in potency to HB-EGF in stimulating human prostate epithelial cell growth, suggesting that prostate epithelia may be a physiologic target for ARG in vivo. Expression of both ARG and HB-EGF mRNAs was induced in cultured prostate SMC by fibroblast growth factor-2, a human prostate SMC mitogen linked to prostate disease. These findings indicate that ARG and HB-EGF are likely to be key mediators of directional signaling between SMC and epithelial cells in the human prostate and appear to be coordinately regulated.

Isolation of mouse stromal cells associated with a human tumor using differential diphtheria toxin sensitivity

Tumor vascularization is accompanied by the migration of stromal cells, including endothelial cells, smooth muscle cells, and fibroblasts, into the tumor. The biological contributions of stromal cells to tumor vascularization have not been well-defined, partly due to the difficulty of culturing stromal cells in the presence of large numbers of fast-growing tumor cells. To address this problem, a strategy was devised to kill tumor cells but not stromal cells. Advantage was taken of the observation that diphtheria toxin (DT) kills human but not rodent cells. Human melanoma (MMAN) tumor cells were injected subcutaneously into nude mice. The tumors were excised, homogenized, and treated with 50 ng/ml DT for 24 hours. Elimination of melanoma cells by DT treatment was demonstrated by lack of detectable levels of microphthalmia, a transcription factor that is a marker for melanoma cells. The murine stromal cells were viable and found to be mostly smooth muscle cells. These cells constituted about 1.5% of the MMAN tumor. RNase protection assays using a specific murine vascular endothelial growth factor probe confirmed the murine origin of the stromal cells. This method allows rapid isolation of stromal cells and should facilitate biochemical and genetic analysis of tumor-stromal interactions.

Extracellular calcium influx stimulates metalloproteinase cleavage and secretion of heparin-binding EGF-like growth factor independently of protein kinase C

The phorbol ester, tetradecanoyl-phorbol 13-acetate (TPA), stimulates rapid proteolytic processing of the transmembrane, pro- form of heparin-binding epidermal growth factor-like growth factor (HB-EGF) at cell surfaces, suggesting the involvement of protein kinase C (PKC) isoforms in the HB-EGF secretion mechanism. To test this possibility, we expressed a chimeric protein, consisting of proHB-EGF fused to placental alkaline phosphatase (AP) near the amino terminus of processed HB-EGF, in NbMC-2 prostate epithelial cells. The proHB-EGF-AP chimera localized to plasma membranes and functioned as a diphtheria toxin receptor. Secreted HB-EGF-AP bound to heparin and exhibited potent growth factor activity. The presence of the AP moiety allowed highly quantitative measurements of cleavage-secretion responses of proHB-EGF to extracellular stimuli. As expected, rapid secretion of HB-EGF-AP was induced in a time- and dose-dependent manner by TPA. However, this was also observed with the Ca2+ ionophore, ionomycin, suggesting the involvement of extracellular Ca2+ ions in the secretion mechanism. Ionomycin-induced secretion was inhibited by extracellular calcium chelation but not by the PKC inhibitors, GF109203X, staurosporine, or chelerythrine. The TPA-mediated secretion effect was inhibited by staurosporine, GF109203X, and by pretreatment with TPA, but not by calcium chelation. A small secretion response was induced by thapsigargin, which releases Ca2+ from intracellular stores, but this was completely eliminated by extracellular calcium chelation. Ionomycin- and TPA-induced HB-EGF-AP secretion was not dependent on the presence of the proHB-EGF cytoplasmic domain and was specifically inhibited by the metalloproteinase inhibitors 1,10-phenanthroline and tissue inhibitor of metalloproteinase-1 (TIMP-1). These data demonstrate that extracellular Ca2+ influx activates a membrane-associated metalloproteinase to process proHB-EGF by a pathway that does not require PKC.