Primary prostatic epithelial cell binding to human bone marrow stroma and the role of alpha2beta1 integrin

Integrin α2β1 decelerates proliferation, but promotes survival and invasion of prostate cancer cells

High expression level of integrin α2β1 is a hallmark of prostate cancer stem cell like cells. The role of this collagen receptor is controversial since it is down regulated in poorly differentiated carcinomas, but concomitantly proposed to promote metastasis. Here, we show that docetaxel resistant DU145 prostate cancer cells express high levels of α2β1 and that α2β1^High subpopulation of DU145 cells proliferates slower than the cells representing α2β1^Low subpopulation. To further study this initial observation we used Crispr/Cas9 technology to create an α2β1 negative DU145 cell line. Furthermore, we performed rescue experiment by transfecting α2 knockout cells with vector carrying α2 cDNA or with an empty vector for appropriate control. When these two cell lines were compared, α2β1 positive cells proliferated slower, were more resistant to docetaxel and also migrated more effectively on collagen and invaded faster through matrigel or collagen. Integrin α2β1 was demonstrated to be a positive regulator of p38 MAPK phosphorylation and a selective p38 inhibitor (SB203580) promoted proliferation and inhibited invasion. Effects of α2β1 integrin on the global gene expression pattern of DU145 cells in spheroid cultures were studied by RNA sequencing. Integrin α2β1 was shown to regulate several cancer progression related genes, most notably matrix metalloproteinase-1 (MMP-1), a recognized invasion promoting protein. To conclude, the fact that α2β1 decelerates cell proliferation may explain the dominance of α2β1 negative/low cells in primary sites of poorly differentiated carcinomas, while the critical role of α2β1 integrin in invasion stresses the importance of this adhesion receptor in cancer dissemination.

Functional Display of an α2 Integrin-Specific Motif (RKK) on the Surface of Baculovirus Particles

The use of baculovirus vectors shows promise as a tool for gene delivery into mammalian cells. These insect viruses have been shown to transduce a variety of mammalian cell lines, and gene transfer has also been demonstrated in vivo. In this study, we generated two recombinant baculovirus vectors displaying an integrin-specific motif, RKK, as a part of two different loops of the green fluorescent protein (GFP) fused with the major envelope protein gp64 of Autographa californica M nucleopolyhedrovirus. By enzyme linked immunosorbent assays, these viruses were shown to bind a peptide representing the receptor binding site of an α2 integrin, the α2I-domain. However, the interaction was not strong enough to overcome binding of wild type gp64 to the unknown cellular receptor(s) on the surface of α2 integrin-expressing cells (CHO-α2β1) or enhance the viral uptake. After treatment of these cells with phospholipase C, internalization of all viruses was blocked or decreased significantly. However, one of the RKK displaying viruses, AcGFP(K)gp64, was still able to internalize into CHO-α2β1 cells, although at a lower level as compared to non-treated cells. This may indicate the possible utilization of a PLC independent alternative route via, in this case, the α2β1 integrin.

Talin1 phosphorylation activates β1 integrins: a novel mechanism to promote prostate cancer bone metastasis

Talins are adaptor proteins that regulate focal adhesion signaling by conjugating integrins to the cytoskeleton. Talins directly bind integrins and are essential for integrin activation. We previously showed that β1 integrins are activated in metastatic prostate cancer (PCa) cells, increasing PCa metastasis to lymph nodes and bone. However, how β1 integrins are activated in PCa cells is unknown. In this study, we identified a novel mechanism of β1 integrin activation. Using knockdown experiments, we first demonstrated talin1, but not talin2, is important in β1 integrin activation. We next showed that talin1 S425 phosphorylation, but not total talin1 expression, correlates with metastatic potential of PCa cells. Expressing a non-phosphorylatable mutant, talin1^S425A, in talin1-silenced PC3-MM2 and C4-2B4 PCa cells, decreased activation of β1 integrins, integrin-mediated adhesion, motility, and increased the sensitivity of the cells to anoikis. In contrast, re-expression of the phosphorylation-mimicking mutant talin1^S425D led to increased β1 integrin activation and generated biologic effects opposite to talin1^S425A expression. In the highly metastatic PC3-MM2 cells, expression of a non-phosphorylatable mutant, talin1^S425A, in talin1-silenced PC3-MM2 cells, abolished their ability to colonize in the bone following intracardiac injection, while re-expression of phosphorylation-mimicking mutant talin1^S425D restored their ability to metastasize to bone. Immunohistochemical staining demonstrated that talin S425 phosphorylation is significantly increased in human bone metastases when compared to normal tissues, primary tumors, or lymph node metastases. We further showed that p35 expression, an activator of Cdk5, and Cdk5 activity were increased in metastatic tumor cells, and that Cdk5 kinase activity is responsible for talin1 phosphorylation and subsequent β1 integrin activation. Together, our study reveals Cdk5-mediated phosphorylation of talin1 leading to β1 integrin activation is a novel mechanism that increases metastatic potential of PCa cells.

Arachidonic acid induction of Rho-mediated transendothelial migration in prostate cancer

BACKGROUND

Bone metastases in prostate cancer (CaP) result in CaP-related morbidity/mortality. The omega-6 polyunsaturated fatty acid (PUFA) arachidonic acid (AA) and lipophilic statins affect metastasis-like behaviour in CaP cells, regulating the critical metastatic step of CaP migration to the bone marrow stroma.

METHODS

Microscopic analysis and measurement of adhesion and invasion of CaP cells through bone marrow endothelial cells (BMEC) was undertaken with AA stimulation and/or simvastatin (SIM) treatment. Amoeboid characteristics of PC-3, PC3-GFP and DU-145 were analysed by western blotting and Rho assays.

RESULTS

The CaP cell lines PC-3, PC3-GFP and DU-145 share the ability to migrate across a BMEC layer. Specific amoeboid inhibition decreased transendothelial migration (TEM). AA stimulates amoeboid characteristics, driven by Rho signalling. Selective knock-down of components of the Rho pathway (RhoA, RhoC, Rho-associated protein kinase 1 (ROCK1) and ROCK2) showed that Rho signalling is crucial to TEM. Functions of these components were analysed, regarding adhesion to BMEC, migration in 2D and the induction of the amoeboid phenotype by AA. TEM was reduced by SIM treatment of PC3-GFP and DU-145, which inhibited Rho pathway signalling.

CONCLUSIONS

AA-induced TEM is mediated by the induction of a Rho-driven amoeboid phenotype. Inhibition of this cell migratory process may be an important therapeutic target in high-risk CaP.

PCaAnalyser: a 2D-image analysis based module for effective determination of prostate cancer progression in 3D culture

Three-dimensional (3D) in vitro cell based assays for Prostate Cancer (PCa) research are rapidly becoming the preferred alternative to that of conventional 2D monolayer cultures. 3D assays more precisely mimic the microenvironment found in vivo, and thus are ideally suited to evaluate compounds and their suitability for progression in the drug discovery pipeline. To achieve the desired high throughput needed for most screening programs, automated quantification of 3D cultures is required. Towards this end, this paper reports on the development of a prototype analysis module for an automated high-content-analysis (HCA) system, which allows for accurate and fast investigation of in vitro 3D cell culture models for PCa. The Java based program, which we have named PCaAnalyser, uses novel algorithms that allow accurate and rapid quantitation of protein expression in 3D cell culture. As currently configured, the PCaAnalyser can quantify a range of biological parameters including: nuclei-count, nuclei-spheroid membership prediction, various function based classification of peripheral and non-peripheral areas to measure expression of biomarkers and protein constituents known to be associated with PCa progression, as well as defining segregate cellular-objects effectively for a range of signal-to-noise ratios. In addition, PCaAnalyser architecture is highly flexible, operating as a single independent analysis, as well as in batch mode; essential for High-Throughput-Screening (HTS). Utilising the PCaAnalyser, accurate and rapid analysis in an automated high throughput manner is provided, and reproducible analysis of the distribution and intensity of well-established markers associated with PCa progression in a range of metastatic PCa cell-lines (DU145 and PC3) in a 3D model demonstrated.

Bone-stromal cells up-regulate tumourigenic markers in a tumour-stromal 3D model of prostate cancer

Background

The cellular and molecular mechanisms that mediate interactions between tumour cells and the surrounding bone stroma are to date largely undetermined in prostate cancer (PCa) progression. The purpose of this study was to evaluate the role of alpha 6 and beta 1 integrin subunits in mediating tumour-stromal interactions.

Methods

Utilising 3D in vitro assays we evaluated and compared 1. Monocultures of prostate metastatic PC3, bone stromal derived HS5 and prostate epithelial RWPE-1 cells and 2. Tumour-stromal co-cultures (PC3 + HS5) to ascertain changes in cellular phenotype, function and expression of metastatic markers.

Results

In comparison to 3D monocultures of PC3 or HS5 cells, when cultured together, these cells displayed up-regulated invasive and proliferative qualities, along with altered expression of epithelial-to-mesenchymal and chemokine protein constituents implicated in metastatic dissemination. When co-cultured, HS5 cells were found to re-express N-Cadherin and chemokine receptor CXCR7. Alterations in N-Cadherin expression were found to be mediated by soluble factors secreted by PC3 tumour cells, while chemokine receptor re-expression was dependent on direct cell-cell interactions. We have also shown that integrins beta 1 and alpha 6 play an integral role in maintaining cell homeostasis and mediating expression of E-Cadherin, N-Cadherin and vimentin, in addition to chemokine receptor CXCR7.

Conclusions

Collectively our results suggest that both PC3 and HS5 cells provide a “protective” and reciprocal milieu that promotes tumour growth. As such 3D co-cultures may serve as a more complex and valid biological model in the drug discovery pipeline.

Conditional knockout of integrin α2β1 in murine megakaryocytes leads to reduced mean platelet volume

We have engineered a transgenic mouse on a C57BL/6 background that bears a floxed Itga2 gene. The crossing of this mouse strain to transgenic mice expressing Cre recombinase driven by the megakaryocyte (MK)-specific Pf4 promoter permits the conditional knockout of Itga2 in the MK/platelet lineage. Mice lacking MK α2β1 develop normally, are fertile, and like their systemic α2β1 knockout counterparts, exhibit defective adhesion to and aggregation induced by soluble type I collagen and a delayed onset to low dose fibrillar collagen-induced aggregation, results consistent with blockade or loss of platelet α2β1. At the same time, we observed a significant reduction in mean platelet volume, which is consistent with the reported role of α2β1 in MK maturation and proplatelet formation in vivo. This transgenic mouse strain bearing a floxed Itga2 gene will prove valuable to distinguish in vivo the temporal and spatial contributions of α2 integrin in selected cell types.

Definition of molecular determinants of prostate cancer cell bone extravasation

Advanced prostate cancer commonly metastasizes to bone, but transit of malignant cells across the bone marrow endothelium (BMEC) remains a poorly understood step in metastasis. Prostate cancer cells roll on E-selectin(+) BMEC through E-selectin ligand-binding interactions under shear flow, and prostate cancer cells exhibit firm adhesion to BMEC via β1, β4, and αVβ3 integrins in static assays. However, whether these discrete prostate cancer cell-BMEC adhesive contacts culminate in cooperative, step-wise transendothelial migration into bone is not known. Here, we describe how metastatic prostate cancer cells breach BMEC monolayers in a step-wise fashion under physiologic hemodynamic flow. Prostate cancer cells tethered and rolled on BMEC and then firmly adhered to and traversed BMEC via sequential dependence on E-selectin ligands and β1 and αVβ3 integrins. Expression analysis in human metastatic prostate cancer tissue revealed that β1 was markedly upregulated compared with expression of other β subunits. Prostate cancer cell breaching was regulated by Rac1 and Rap1 GTPases and, notably, did not require exogenous chemokines as β1, αVβ3, Rac1, and Rap1 were constitutively active. In homing studies, prostate cancer cell trafficking to murine femurs was dependent on E-selectin ligand, β1 integrin, and Rac1. Moreover, eliminating E-selectin ligand-synthesizing α1,3 fucosyltransferases in transgenic adenoma of mouse prostate mice dramatically reduced prostate cancer incidence. These results unify the requirement for E-selectin ligands, α1,3 fucosyltransferases, β1 and αVβ3 integrins, and Rac/Rap1 GTPases in mediating prostate cancer cell homing and entry into bone and offer new insight into the role of α1,3 fucosylation in prostate cancer development.

RGD-Binding Integrins in Prostate Cancer: Expression Patterns and Therapeutic Prospects against Bone Metastasis

Prostate cancer is the third leading cause of male cancer deaths in the developed world. The current lack of highly specific detection methods and efficient therapeutic agents for advanced disease have been identified as problems requiring further research. The integrins play a vital role in the cross-talk between the cell and extracellular matrix, enhancing the growth, migration, invasion and metastasis of cancer cells. Progression and metastasis of prostate adenocarcinoma is strongly associated with changes in integrin expression, notably abnormal expression and activation of the β₃ integrins in tumour cells, which promotes haematogenous spread and tumour growth in bone. As such, influencing integrin cell expression and function using targeted therapeutics represents a potential treatment for bone metastasis, the most common and debilitating complication of advanced prostate cancer. In this review, we highlight the multiple ways in which RGD-binding integrins contribute to prostate cancer progression and metastasis, and identify the rationale for development of multi-integrin antagonists targeting the RGD-binding subfamily as molecularly targeted agents for its treatment.

Emerging putative biomarkers: the role of alpha 2 and 6 integrins in susceptibility, treatment, and prognosis

The genetic architecture underpinning prostate cancer is complex, polygenic and despite recent significant advances many questions remain. Advances in genetic technologies have greatly improved our ability to identify genetic variants associated with complex disease including prostate cancer. Genome-wide association studies (GWASs) and microarray gene expression studies have identified genetic associations with prostate cancer susceptibility and tumour development. The integrins feature prominently in both studies examining the underlying genetic susceptibility and mechanisms driving prostate tumour development. Integrins are cell adhesion molecules involved in extracellular and intracellular signalling and are imperative for tumour development, migration, and angiogenesis. Although several integrins have been implicated in tumour development, the roles of integrin α(2) and integrin α(6) are the focus of this paper as evidence is now emerging that these integrins are implicit in prostate cancer susceptibility, cancer stem cell biology, angiogenesis, cell migration, and metastases to bone and represent potential biomarkers and therapeutic targets. There currently exists an urgent need to develop tools that differentiate indolent from aggressive prostate cancers and predict how patients will respond to treatment. This paper outlines the evidence supporting the use of α(2) and α(6) integrins in clinical applications for tailored patient treatment.

Enterolobium contortisiliquum trypsin inhibitor (EcTI), a plant proteinase inhibitor, decreases in vitro cell adhesion and invasion by inhibition of Src protein-focal adhesion kinase (FAK) signaling pathways

Tumor cell invasion is vital for cancer progression and metastasis. Adhesion, migration, and degradation of the extracellular matrix are important events involved in the establishment of cancer cells at a new site, and therefore molecular targets are sought to inhibit such processes. The effect of a plant proteinase inhibitor, Enterolobium contortisiliquum trypsin inhibitor (EcTI), on the adhesion, migration, and invasion of gastric cancer cells was the focus of this study. EcTI showed no effect on the proliferation of gastric cancer cells or fibroblasts but inhibited the adhesion, migration, and cell invasion of gastric cancer cells; however, EcTI had no effect upon the adhesion of fibroblasts. EcTI was shown to decrease the expression and disrupt the cellular organization of molecules involved in the formation and maturation of invadopodia, such as integrin β1, cortactin, neuronal Wiskott-Aldrich syndrome protein, membrane type 1 metalloprotease, and metalloproteinase-2. Moreover, gastric cancer cells treated with EcTI presented a significant decrease in intracellular phosphorylated Src and focal adhesion kinase, integrin-dependent cell signaling components. Together, these results indicate that EcTI inhibits the invasion of gastric cancer cells through alterations in integrin-dependent cell signaling pathways.

Individual rac GTPases mediate aspects of prostate cancer cell and bone marrow endothelial cell interactions

The Rho GTPases organize the actin cytoskeleton and are involved in cancer metastasis. Previously, we demonstrated that RhoC GTPase was required for PC-3 prostate cancer cell invasion. Targeted down-regulation of RhoC led to sustained activation of Rac1 GTPase and morphological, molecular and phenotypic changes reminiscent of epithelial to mesenchymal transition. We also reported that Rac1 is required for PC-3 cell diapedesis across a bone marrow endothelial cell layer. In the current study, we queried whether Rac3 and RhoG GTPases also have a role in prostate tumor cell diapedesis. Using specific siRNAs we demonstrate roles for each protein in PC-3 and C4-2 cell adhesion and diapedesis. We have shown that the chemokine CCL2 induces tumor cell diapedesis via Rac1 activation. Here we find that RhoG partially contributes to CCL2-induced tumor cell diapedesis. We also find that Rac1 GTPase mediates tight binding of prostate cancer cells to bone marrow endothelial cells and promotes retraction of endothelial cells required for tumor cell diapedesis. Finally, Rac1 leads to β1 integrin activation, suggesting a mechanism that Rac1 can mediate tight binding with endothelial cells. Together, our data suggest that Rac1 GTPase is key mediator of prostate cancer cell-bone marrow endothelial cell interactions.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Cancer to bone: a fatal attraction

When cancer metastasizes to bone, considerable pain and deregulated bone remodelling occurs, greatly diminishing the possibility of cure. Metastasizing tumour cells mobilize and sculpt the bone microenvironment to enhance tumour growth and to promote bone invasion. Understanding the crucial components of the bone microenvironment that influence tumour localization, along with the tumour-derived factors that modulate cellular and protein matrix components of bone to favour tumour expansion and invasion, is central to the pathophysiology of bone metastases. Basic findings of tumour-bone interactions have uncovered numerous therapeutic opportunities that focus on the bone microenvironment to prevent and treat bone metastases.

Design, synthesis and validation of integrin α2β1-targeted probe for microPET imaging of prostate cancer

PURPOSE

The ability of PET to aid in the diagnosis and management of recurrent and/or disseminated metastatic prostate cancer may be enhanced by the development of novel prognostic imaging probes. Accumulating experimental evidence indicates that overexpression of integrin α(2)β(1) may correlate with progression in human prostate cancer. In this study, (64)Cu-labeled integrin α(2)β(1)-targeted PET probes were designed and evaluated for the imaging of prostate cancer.

METHODS

DGEA peptides conjugated with a bifunctional chelator (BFC) were developed to image integrin α(2)β(1) expression with PET in a subcutaneous PC-3 xenograft model. The microPET images were reconstructed by a two-dimensional ordered subsets expectation maximum algorithm. The average radioactivity accumulation within a tumor or an organ was quantified from the multiple region of interest volumes.

RESULTS

The PET tracer demonstrated prominent tumor uptake in the PC-3 xenograft (integrin α(2)β(1)-positive). The receptor specificity was confirmed in a blocking experiment. Moreover, the low tracer uptake in a CWR-22 tumor model (negative control) further confirmed the receptor specificity.

CONCLUSION

The sarcophagine-conjugated DGEA peptide allows noninvasive imaging of tumor-associated α(2)β(1) expression, which may be a useful PET probe for evaluating the metastatic potential of prostate cancer.

Integrins and bone metastasis: integrating tumor cell and stromal cell interactions

Integrins on both tumor cells and the supporting host stromal cells in bone (osteoclasts, new blood vessels, inflammatory cells, platelets and bone marrow stromal cells) play key roles in enhancing bone metastasis. Tumor cells localize to specific tissues through integrin-mediated contacts with extracellular matrix and stromal cells. Integrin expression and signaling are perturbed in cancer cells, allowing them to "escape" from cell-cell and cell-matrix tethers, invade, migrate and colonize within new tissues and matrices. Integrin signaling through αvβ3 and VLA-4 on tumor cells can promote tumor metastasis to and proliferation in the bone microenvironment. Osteoclast (OC) mediated bone resorption is a critical component of bone metastasis and can promote tumor growth in bone and αvβ3 integrins are critical to OC function and development. Tumors in the bone microenvironment can recruit new blood vessel formation, platelets, pro-tumor immune cells and bone marrow stromal cells that promote tumor growth and invasion in bone. Integrins and their ligands play critical roles in platelet aggregation (αvβ3 and αIIbβ3), hematopoietic cell mobilization (VLA-4 and osteopontin), neoangiogenesis (αvβ3, αvβ5, α6β4, and β1 integrin) and stromal function (osteopontin and VLA-4). Integrins are involved in the pathogenesis of bone metastasis at many levels and further study to define integrin dysregulation by cancer will yield new therapeutic targets for the prevention and treatment of bone metastasis.

Cyclic RGD-targeting of reversibly stabilized DNA nanoparticles enhances cell uptake and transfection in vitro

Reversibly stabilized DNA nanoparticles (rSDN) were prepared by coating reducible polycation/DNA complexes with multivalent N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers. RGD-targeted rSDN were formulated by linking cyclic c(RGDyK) to the surface layer of rSDN. Cellular uptake in B16F10 mouse melanoma cells, human umbilical vein endothelial cells (HUVEC), and THLE immortalized hepatic cells was quantified by real-time PCR. RGD-targeted rSDN exhibited approximately twofold higher cell uptake in integrin-positive cells: B16F10 and HUVEC compared to THLE cells with low integrin content. RGD-targeting mediated increased transfection activity in B16F10 cells but not in THLE cells. Overall, the studies show that rSDN can be effectively targeted with RGD while exhibiting reduced nonspecific cell interactions and favorable stability. As such, these gene delivery vectors have the potential to permit targeting therapeutic genes to tumors by systemic delivery. In addition, the study shows that real-time PCR could be used effectively for the quantification of cellular uptake of gene delivery vectors.

Molecular mechanisms of metastasis in prostate cancer

Prostate cancer (PCa) preferentially metastasizes to the bone marrow stroma of the axial skeleton. This activity is the principal cause of PCa morbidity and mortality. The exact mechanism of PCa metastasis is currently unknown, although considerable progress has been made in determining the key players in this process. In this review, we present the current understanding of the molecular processes driving PCa metastasis to the bone.

Characterization of benign and malignant prostate epithelial Hoechst 33342 side populations

BACKGROUND

The prostate epithelial stem cell has been proposed as the primary origin of neoplastic change in prostate cancer. However, the isolation and characterization of unexpanded prostate epithelial stem cells have proven problematic.

METHODS

A prostate epithelial side population (SP) has been isolated utilizing a modified Hoechst 33342 dye efflux assay from both benign and malignant prostate tissue. CD45(-ve), integrin alpha2(+ve) Hoechst 33342 SP and NSP cells were isolated by FACS, immunophenotyped and functionally characterized in 3D culture.

RESULTS

FACS analysis revealed a verapamil sensitive SP accounting for 0.93 +/- 0.12% and 0.57 +/- 0.11% of the total epithelial population from both benign and malignant prostates. The benign SP phenotype revealed a heterogeneous cell population consisting predominantly of small basal cells containing minimal cytoplasm. Conversely, the malignant SP was of undetermined acinar origin and with a complete loss of expression of the CDK2 inhibitor p21(WAF1/Cip1). In vitro androgen-enhanced 3D culture of the benign and malignant SP cells led to the production of spheroids which had acinus like morphology and expressed primitive and basal cell markers. Incorporation of the CD133 marker isolated a further SP sub-fraction accounting for 0.037 +/- 0.01% of epithelial cells.

CONCLUSIONS

Our observations are consistent with the Hoechst 33342 dye efflux assay isolating a stem cell enriched population which can be further sub-fractionated by CD133 selection. Moreover, the loss of the CDK inhibitor in malignancy is consistent with the hypothesis that neoplastic change originates in the stem cell compartment.

Natural history of prostatic carcinoma: the pathologist's perspective

The stem (basal) cells of prostate acini are considered the origin of prostate cancer. Between these cells and the final secretory cells, different intermediate or transit cells can be observed, and every one of them can evolve into malignant cells, explaining the biological variability of prostatic cancer. The exact changes between normal gland and prostatic intraepithelial neoplasia (PIN) are not yet known, but a post-inflammatory atrophy lesion is being studied in this respect. The PIN lesion is considered the pre-invasive change of prostatic cancer and its presence in needle biopsy is clinically used for follow-up of the patient. The progressive knowledge of the stromal invasion in prostate cancer (loss of some cell-cell adhesion molecules and expression of others) can be correlated with the Gleason grading system, and the molecular changes in the progression to androgen-independent carcinoma can be used as a prognostic marker in conjunction with the classical pathological markers.

Human mesenchymal stem cells in contact with their environment: surface characteristics and the integrin system

The identification of mesenchymal stem cells (MSCs) in adult human tissues and the disclosure of their self-renew-al and multi-lineage differentiation capabilities have provided exciting prospects for cell-based regeneration and tis-sue engineering. Although a considerable amount of data is available describing MSCs, there is still lack of information regarding the molecular mechanisms that govern their adhesion and migration. In this work, we will review the current state of knowledge on integrins and other adhesion molecules found to be expressed on MSCs. The discussed topics include the characteristics of MSCs and their clinical applications, integrins and their central role in cell-matrix attachment and migration, and comments on mobilization, differentiation and contribution to tumour development. Finally, by understanding the complex and fundamental pathways by which MSCs attach and migrate, it might be possible to fine-tune the strategies for effective and safe use of MSCs in regenerative therapies.

Promotion of prostatic metastatic migration towards human bone marrow stoma by Omega 6 and its inhibition by Omega 3 PUFAs

Epidemiological studies have shown not only a relationship between the intake of dietary lipids and an increased risk of developing metastatic prostate cancer, but also the type of lipid intake that influences the risk of metastatic prostate cancer. The Omega-6 poly-unsaturated fatty acid, Arachidonic acid, has been shown to enhance the proliferation of malignant prostate epithelial cells and increase the risk of advanced prostate cancer. However, its role in potentiating the migration of cancer cells is unknown. Here we show that arachidonic acid at concentrations ⩽5 μM is a potent stimulator of malignant epithelial cellular invasion, which is able to restore invasion toward hydrocortisone-deprived adipocyte-free human bone marrow stroma completely. This observed invasion is mediated by the arachidonic acid metabolite prostaglandin E₂ and is inhibited by the Omega-3 poly-unsaturated fatty acids eicosapentaenoic acid and docosahexaenoic acid at a ratio of 1 : 2 Omega-3 : Omega-6, and by the COX-2 inhibitor NS-398. These results identify a mechanism by which arachidonic acid may potentiate the risk of metastatic migration and secondary implantation in vivo, a risk which can be reduced with the uptake of Omega-3 poly-unsaturated fatty acids.

Regulation of prostate cell collagen receptors by malignant transformation

Cell adhesion receptors, including the integrin-type collagen receptors (alpha1beta1, alpha2beta1, alpha10beta1 and alpha11beta1) participate in cancer progression and invasion. Quantitative RT-PCR indicated that all 4 receptors are abundantly expressed in sarcoma-derived cell lines, whereas most carcinoma-derived cells express alpha1beta1 and alpha2beta1 only. This was surprising because alpha11beta1 has been connected previously to the progression of lung adenocarcinomas. To test the hypothesis that alpha11 expression may not persist in cultured cancer cells we analyzed fresh tissue samples of 104 total prostatectomies, keeping in mind that prostate cancer cell lines showed negligible alpha11 mRNA levels. In prostate alpha2 expression was significantly lower in poorly differentiated carcinomas when compared to benign lesions (p = 0.0331). In immunohistochemistry the protein levels of alpha2 integrin decreased significantly (p = 0.0001) and the protein levels of alpha11 subunit increased significantly (p = 0.029) with the increasing grade of carcinoma. Thus alpha11beta1 may replace alpha2beta1 during tumor progression. Our observations support the idea that alpha11beta1 may be expressed in tumors but the corresponding cell lines may lose the expression of this integrin. Previous studies have shown that in cell culture androgen receptor (AR) controls alpha2beta1 expression. We measured AR mRNA levels and the number of AR positive nuclei in the prostate samples and the results showed a significant correlation between alpha2beta1 and AR. Androgen receptors may control the mechanisms regulating integrin expression in prostate.

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.

Molecular pathology of prostate cancer

The molecular pathology of prostate cancer is complex; not only are multiple genes involved in its pathogenesis, but additional environmental factors such as diet and inflammation are also involved. The exhaustive research into prostate cancer to date has demonstrated a complex interaction of multiple genes and environmental factors, some of which may be more important in individual prostate cancer cases. This is an exciting era, with the emergence of new investigative tools such as DNA microarray technology and the application of the field of proteomics to the study of human cancers. Knowledge of genetic changes underlying the initiation, development, and progression of prostate cancer is accumulating rapidly. With increasing knowledge, it may be possible to distinguish indolent from aggressive prostate tumours by molecular fingerprinting. This review discusses the most consistently reported molecular pathological findings in hereditary and sporadic prostate cancer, together with new concepts and technologies.

PTH-related protein enhances LoVo colon cancer cell proliferation, adhesion, and integrin expression

Parathyroid hormone-related protein (PTHrP) has been localized in human colon cancer tissue and cell lines. Tumor cell adhesion to extracellular matrix (ECM) proteins plays a major role in the invasion and metastasis of tumor cells, and is mediated via integrin subunits. The LoVo human colon cancer cell line was used as a model system to study the effects of PTHrP on cell proliferation and adhesion to ECM proteins found in normal liver. Clones of LoVo cells engineered to overexpress PTHrP by stable transfection with a PTHrP cDNA showed enhanced cell proliferation vs. control (empty vector-transfected) cells. PTHrP-overexpressing cells also showed significantly higher adhesion to collagen type I, fibronectin, and laminin, and enhanced expression of the [symbol: see text] integrin subunits. These results indicate that PTHrP may play a role in colon cancer invasion and metastasis by increasing cell proliferation and adhesion to the ECM via upregulation of proinvasive integrin expression.

Invasive characteristics of human prostatic epithelial cells: understanding the metastatic process

Prostate cancer has a predilection to metastasise to the bone marrow stroma (BMS) by an as yet uncharacterised mechanism. We have defined a series of coculture models of invasion, which simulate the blood/BMS boundary and allow the elucidation of the signalling and mechanics of trans-endothelial migration within the complex bone marrow environment. Confocal microscopy shows that prostate epithelial cells bind specifically to bone marrow endothelial-to-endothelial cell junctions and initiate endothelial cell retraction. Trans-endothelial migration proceeds via an epithelial cell pseudopodial process, with complete epithelial migration occurring after 232±43 min. Stromal-derived factor-1 (SDF-1)/CXCR4 signalling induced PC-3 to invade across a basement membrane although the level of invasion was 3.5-fold less than invasion towards BMS (P=0.0007) or bone marrow endothelial cells (P=0.004). Maximal SDF-1 signalling of invasion was completely inhibited by 10 μM of the SDF-1 inhibitor T140. However, 10 μM T140 only reduced invasion towards BMS and bone marrow endothelial cells by 59% (P=0.001) and 29% (P=0.011), respectively. This study highlights the need to examine the potential roles of signalling molecules and/or inhibitors, not just in single-cell models but in coculture models that mimic the complex environment of the bone marrow.

Prostate cancer and the met hepatocyte growth factor receptor

The hepatocyte growth factor/scatter factor (HGF/SF) and its receptor, the Met protein tyrosine kinase, form a classic ligand-receptor system for epithelial-mesenchymal communications in the normal and cancerous prostate. This review illustrates the expression and activities of HGF/SF and Met during prostate development, homeostasis, and carcinogenesis. The participation of HGF/SF in the morphogenetic program of rodent prostate development, the role of Met in normal human prostate epithelium, and underlying mechanisms of deregulated Met expression in localized and metastatic prostate cancer are discussed. On the basis of the commonly observed overexpression of Met in metastatic prostate cancer, HGF/SF-Met-targeted imaging and therapeutic agents can now be applied toward diagnosis and treatment.

Binding of α2 monoclonal antibody to human cervical tumor cell (SiHa) surface α2β1 integrin modulates MMP-2 activity

OBJECTIVE(S)

The purpose was to study the interrelationship between cell surface integrin receptor (alpha2beta1) and matrixmetalloproteinases.

METHODS

Immunoprecipitation and cell adhesion assay were done to assay alpha2beta1 and alpha3beta1 on SiHa cell surface. Zymogram was developed to assay secreted MMP activity of cells grown in presence of alpha2 monoclonal antibody. Immunoblot was developed to assay expression of MMP-2, FAK, and p-FAK. Plasma membrane-dependent activation of MMP2 was performed by incubating pure MMP-2 with membrane-enriched fraction isolated from SiHa cells.

RESULTS

Immunoprecipitation and cell adhesion assay results confirmed the presence of alpha2beta1 receptor on SiHa cells. Zymographic analysis of serum-free media collected at different time points from SiHa cells grown on alpha2 monoclonal antibody-coated culture dishes showed the expression and activation of MMP-2 within 2-4 h, confirmed by immunoblot. Western blot of cells grown on alpha2-coated dishes for 30 min-4 h showed increased phosphorylation of FAK. Membrane-enriched fraction isolated from SiHa cells was found to specifically activate proMMP-2 to its activated forms within 30 min.

CONCLUSION(S)

The experimental findings strongly indicate that SiHa cell surface alpha2beta1 regulates MMP-2 expression. Increased phosphorylation of focal adhesion kinase (FAK) strongly indicates the possible role of FAK in signaling cascade. Incubation of SiHa cell membrane fraction with pure MMP-2 strongly confirms the cell membrane-dependent activation of proMMP2.

Molecular pathway for cancer metastasis to bone

The molecular mechanism leading to the cancer metastasis to bone is poorly understood but yet determines prognosis and therapy. Here, we define a new molecular pathway that may account for the extraordinarily high osteotropism of prostate cancer. By using SPARC (secreted protein, acidic and rich in cysteine)-deficient mice and recombinant SPARC, we demonstrated that SPARC selectively supports the migration of highly metastatic relative to less metastatic prostate cancer cell lines to bone. Increased migration to SPARC can be traced to the activation of integrins alphaVbeta3 and alphaVbeta5 on tumor cells. Such activation is induced by an autocrine vascular endothelial growth factor (VEGF)/VEGF receptor (VEGFR)-2 loop on the tumor cells, which also supports the growth and proliferation of prostate cancer cells. A consequence of SPARC recognition by alphaVbeta5 is enhanced VEGF production. Thus, prostate cancer cells expressing VEGF/VEGFR-2 will activate alphaVbeta3 and alphaVbeta5 on their surface and use these integrins to migrate toward SPARC in bone. Within the bone environment, SPARC engagement of these integrins will stimulate growth of the tumor and further production of VEGF to support neoangiogenesis, thereby favoring the development of the metastatic tumor. Supporting this model, activated integrins were found to colocalize with VEGFR-2 in tissue samples of metastatic prostate tumors from patients.

Novel method for the isolation and characterisation of the putative prostatic stem cell

BACKGROUND

Prostate stem cells, responsible for the development, maturation, and function of the prostate, have been implicated in the aetiology of both benign prostate hyperplasia (BPH) and prostate cancer (CaP). However, research has been hampered by the lack of a definitive stem cell marker. We have adapted the protocol for differential Hoechst 33342 uptake by hemopoietic stem cells to enable isolation of putative stem cells from the prostate.

METHODS

Prostate epithelial cells isolated from prostate tissue obtained from patients with BPH after transurethral resection of the prostate were stained with Hoechst 33342. The Hoechst 33342 Red/Blue flow cytometry profile was then determined. Hoechst 33342 and Pyronin Y staining was used to determined the cell cycle status.

RESULTS

A verapamil-sensitive side population (SP) can be isolated from primary prostate tissue accounting for 1.38% +/- 0.07% of prostate epithelial cells. Cell cycle analysis of this SP population revealed that the majority of SP cells are in either G0 (12.38 +/- 0.31%) or G1 (63.19 +/- 2.13%).

CONCLUSIONS

The Hoechst 33342 dye efflux protocol can be adapted for the isolation of a SP from primary prostate tissue.

Parathyroid hormone-related protein upregulates integrin expression via an intracrine pathway in PC-3 prostate cancer cells

Parathyroid hormone-related protein (PTHrP) is expressed by human prostatic tissue and prostate cancer cell lines, and enhances prostate tumor cell growth both in vivo and in vitro. PTHrP expression also plays a role in the development of bone metastasis, which is a frequent complication in patients with prostate carcinoma. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. We previously showed that PTHrP overexpression increases adhesion of the human prostate cancer cell line PC-3 to the ECM molecules collagen type I, fibronectin, and laminin. Increased adhesion is accompanied by upregulation in the expression of alpha1, alpha5, alpha6, and beta4 integrin subunits. We used the same cell line to study the mechanism via which PTHrP upregulates integrin expression. Clonal PC-3 cells were established overexpressing wild-type PTHrP or PTHrP mutated in the nuclear localization sequence (NLS). Mutation of the NLS negated the effects of PTHrP on alpha1, alpha5, alpha6, and beta4 integrin expression, indicating that these effects are mediated via an intracrine pathway requiring nuclear localization. Expression of the alpha2, alpha3, alphav, and beta1 integrin subunits were comparable in wild-type and NLS-mutated PTHrP transfectants. These findings indicate that PTHrP may play a role in prostate tumor invasion and metastasis by upregulating the expression of specific integrin subunits via an intracrine pathway.

PTH-related protein modulates PC-3 prostate cancer cell adhesion and integrin subunit profile

Parathyroid hormone-related protein (PTHrP), which has been localized in prostate cancer tissue and cell lines, plays a role in the development of bone metastases, a frequent complication in prostate cancer patients. Tumor cell adhesion to extracellular matrix (ECM) components is mediated via integrin subunits, and plays a major role in the invasion and metastasis of tumor cells. The present experiments examined the ability of PTHrP to influence adhesion of the human prostate cancer cell line PC-3 to several ECM proteins found in normal tissues. Clonal PC-3 cells induced to overexpress PTHrP by stable transfection with PTHrP complementary DNA showed significantly higher adhesion to collagen type 1, fibronectin, and laminin than control (empty vector-transfected) cells. PTHrP-overexpressing cells also exhibited higher expression of the alpha1, alpha5, alpha6, and beta4 integrin subunits. These results suggest that PTHrP may play a role in prostate tumor invasion and metastasis by influencing cell adhesion to the ECM via upregulation of specific integrin subunits.

Specific residues within the alpha 2 integrin subunit cytoplasmic domain regulate migration and cell cycle progression via distinct MAPK pathways

The alpha(2) integrin subunit cytoplasmic domain is necessary for epidermal growth factor (EGF)-stimulated chemotactic migration and insulin-dependent entry into S-phase of mammary epithelial cells adherent to type I collagen. Truncation mutants revealed that the seven amino acids, KYEKMTK, in addition to the GFFKR motif were sufficient for these functions. Mutation of tyrosine 1134 to alanine inhibited the ability of the cells to phosphorylate p38 MAPK and to migrate in response to EGF but had only a modest effect on the ability of the cells to induce sustained phosphorylation of the ERK MAPK, to up-regulate cyclin E and cdk2 expression, and to enter S-phase when adherent to type I collagen. Conversely, mutation of the lysine 1136 inhibited the ability of the cells to increase cyclin E and cdk2 expression, to maintain long term phosphorylation of the ERK MAPK, and to enter S-phase but had no effect on the ability of the cells to phosphorylate the p38 MAPK or to migrate on type I collagen in response to EGF. Methionine 1137 was essential for both migration and entry into S-phase. Thus, distinctly different structural elements of the alpha(2) integrin cytoplasmic domain are required to engage the signaling pathways leading to cell migration or cell cycle progression.

Interactions of human prostatic epithelial cells with bone marrow endothelium: binding and invasion

Prostate cancer shows a propensity to form secondary tumours within the bone marrow. Such tumours are the major cause of mortality in this disease. We have developed an in vitro system to study the binding of prostate epithelial cells to bone marrow endothelium (BME) and stroma (BMS). The metastatic prostate cancer cell line, PC3 (derived from a bone metastasis), was seeded onto confluent layers of BME and its binding characteristics compared to human umbilical vein endothelial cells (HUVEC), lung endothelium (Hs888Lu) and BMS. The PC3 cell line showed significantly increased binding to BME (P< 0.05) compared to endothelium derived from HUVEC and lung or BMS with maximal binding occurring at 1 h. Following pre-incubation with a β1 integrin antibody PC3 binding to BME was inhibited by 64% (P< 0.001). Antibodies directed against the integrins β4, α2, α4, α5 and the cellular adhesion molecules P-selectin, CD31, VCAM-1 and sialy Lewis X showed no effect on blocking PC3 binding. Primary prostatic epithelial cells from both malignant (n = 11) and non-malignant tissue (n = 11) also demonstrated equivalent levels of increased adhesion to BME and BMS compared to HUVEC, peaking at 24 h. Further studies examined the invasive ability of prostate epithelial cells in response to bone marrow endothelium using Matrigel invasion chamber assays. In contrast to the previous results, malignant cells showed an increase (1000 fold) in invasive ability, whilst non-malignant prostate epithelia did not respond. We have shown that both malignant and non-malignant prostate epithelial cells can bind at equivalent levels and preferentially to primary human bone marrow endothelium in comparison to controls. However, only malignant prostate epithelia show increased invasive ability in response to BME. © 2001 Cancer Research Campaign www.bjcancer.com

Pathophysiologic interactions in skeletal metastasis

BACKGROUND

This review summarizes evidence that the formation of bone metastases is the result of multiple synergistic cellular and molecular interactions between metastatic cells and the unique microenvironment in bone.

METHODS

Molecular technologies have been used to detect cancer cells in bone and to define their genotypic and phenotypic properties. Bone organ cultures have been employed to analyze the ability of tumor cells to modulate bone resorption and to study the effects of resorption products on the phenotypic properties of cancer cells. Experimental models of bone metastasis provide the ability to examine the effects of modulating specific host or tumor properties in vivo by quantifying their effects on the formation of bone tumors.

RESULTS

By means of the blood stream, cells from many common neoplasms seed bone marrow as an early clinical event. The subsequent growth of these cells into clinically significant metastatic lesions is associated with their ability to stimulate bone resorption through osteoclasts and macrophages or through a direct action on bone. In turn, the products of bone resorption, which include matrix-derived growth factors, act on the tumor cells to stimulate the expression of properties that promote their metastatic competence. These include the induction of integrin adhesion molecules, the stimulation of cell motility and chemotaxis, the enhanced expression of matrix metalloproteinases, and the stimulation of tumor cell growth.

CONCLUSIONS

The interdependency of tumor cells and bone was recognized by Steven Paget over 100 years ago, and it provides a rational basis for the development of current therapeutic strategies against bone metastasis.

Scatter factor influences the formation of prostate epithelial cell colonies on bone marrow stroma in vitro

Prostate cancer metastases form selectively in the bone marrow. Previously we demonstrated motility was important for the formation of primary prostatic epithelial cell colonies in bone marrow stroma (BMS) co-culture. In this study we looked at the influence of motility factors on the colony formation of epithelial cells derived from benign (bPEC) or malignant (mPEC) prostate tissue. After 7 days co-culture we found that anti-scatter factor consistently inhibited prostate epithelial cell colony formation on BMS (7/7 mPEC and 4/7 bPEC samples showed significant inhibition). Antibodies against bFGF and 5T4 did not significantly affect colony formation. Addition of fibroblast conditioned media (derived from benign prostates) to co-cultures stimulated the colony formation of bPEC (170%) and mPEC (252%). This stimulation was eliminated by depletion of SF from the conditioned media. Immunohistochemical staining found c-Met expression in 5/6 bPEC cultures and 7/9 mPEC cultures. When grown in BMS co-culture expression of c-Met was positive in 3/6 bPEC and 2/7 mPEC samples. In conclusion, scatter factor influences the in vitro formation of prostate epithelial cell colonies on BMS co-culture.

RGD-recognizing integrins mediate interactions of human prostate carcinoma cells with endothelial cells in vitro

BACKGROUND

Interactions of cancer cells with endothelium are a crucial step in metastatic invasion. RGD-recognizing integrins play a definitive role in these interactions.

METHODS

Fluorescence-activated cell sorting (FACS) analysis of RGD-sensitive integrins in prostate epithelial cells was performed. Attachment inhibition assay was used to characterize functionality of particular integrins. Potential partners for RGD-binding integrins in human umbilical vein endothelial cells (HUVEC) were identified by Western blotting and attachment inhibition assay. To determine the RGD-flanking amino acids optimal for interactions with prostate cell integrins, these cells were biopanned with a phage library.

RESULTS

Different expressions of RGD-recognizing integrins and distinctions in RGD-dependent adhesion of nonmalignant and cancer cells were observed. Cancer but not control cells were detached from culture plastic by incubation with RGD peptide. Adhesion of carcinoma cells to HUVEC was RGD-sensitive, in contrast to nonmalignant cells. Antibodies against alpha3, alpha5, beta1, and alpha(v)beta3 inhibited interactions of carcinoma cells with HUVEC. Potential ligands for alpha5beta1, alpha3beta1, and alphaVbeta3 integrins, fibronectin, and vitronectin, were detected on the HUVEC surface. Several phages which preferentially bound to the surface of particular prostate cells were selected.

CONCLUSIONS

Interactions of prostate carcinoma with endothelium are mediated in part via alpha5beta1, alpha3beta1, and alpha(v)beta3 integrins. Because these interactions are RGD-sensitive, synthetic RGD peptides with optimized flanking amino acids can potentially be used as antimetastatic agents.