Calcitonin receptor-stimulated migration of prostate cancer cells is mediated by urokinase receptor-integrin signaling

Proteomic analysis of zoledronic-acid resistant prostate cancer cells unveils novel pathways characterizing an invasive phenotype

Proteomic analysis identified differentially expressed proteins between zoledronic acid-resistant and aggressive DU145R80 prostate cancer (PCa) cells and their parental DU145 cells. Ingenuity Pathway Analysis (IPA) showed a strong relationship between the identified proteins within a network associated with cancer and with homogeneous cellular functions prevalently related with regulation of cell organization, movement and consistent with the smaller and reduced cell-cell contact morphology of DU145R80 cells. The identified proteins correlated in publically available human PCa genomic data with increased tumor expression and aggressiveness. DU145R80 exhibit also a clear increase of alpha-v-(αv) integrin, and of urokinase receptor (uPAR), both included within the same network of the identified proteins. Interestingly, the actin-rich structures localized at the cell periphery of DU145R80 cells are rich of Filamin A, one of the identified proteins and uPAR which, in turn, co-localizes with αv-integrin, in podosomes and/or invadopodia. Notably, the invasive feature of DU145R80 may be prevented by blocking anti-αv antibody. Overall, we unveil a signaling network that physically links the interior of the nucleus via the cytoskeleton to the extracellular matrix and that could dictate PCa aggressiveness suggesting novel potential prognostic markers and therapeutic targets for PCa patients.

A-kinase anchoring protein 2 is required for calcitonin-mediated invasion of cancer cells

Expression of neuropeptide calcitonin (CT) and its receptor (CTR) is frequently elevated in prostate cancers (PCs) and activation of CT-CTR axis in non-invasive PC cells induces an invasive phenotype. Specific, cell-permeable inhibitors of protein kinase A abolish CTR-stimulated invasion of PC cells. Since PKA is ubiquitously distributed in cells, the present study examined the mechanism(s) by which CTR-stimulated PKA activity is regulated in time and space. CT reduced cell adhesion but increased invasion of PC cells. Both these actions were abolished by st-Ht31 inhibitory peptide suggesting the involvement of an A-kinase anchoring protein (AKAP) in CT action. Next, we identified the AKAP associated with CT action by the subtraction of potential AKAP candidates using siRNAs. Knock-down of membrane-associated AKAP2, but not other AKAPs, abolished CT-stimulated invasion. Stable knock-down of AKAP2 in PC3-CTR cells remarkably decreased their cell proliferation, invasion, clonogenicity and ability to form orthotopic tumors and distant metastases in nude mice. Re-expression of AKAP2-wt restored these characteristics. Primary PC specimens displayed remarkable upregulation of CTR/AKAP2 expression as compared to benign prostates. Metastatic cancers displayed significantly higher CTR/AKAP2 expression than localized cancers. These results for the first time demonstrate that AKAP2 is expressed in human prostates, its expression is elevated in metastatic prostate cancer, and the knock-down of its expression remarkably decreased tumorigenicity and metastatic ability of prostate cancer cells. AKAP2 may serve as a critical component of CTR-mediated oncogenic actions.

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.

Administration of calcitonin promotes blastocyst implantation in mice by up-regulating integrin β3 expression in endometrial epithelial cells

STUDY QUESTION

Does exogenous calcitonin improve the efficiency of implantation in mice by increasing uterine receptivity?

SUMMARY ANSWER

The administration of calcitonin could improve the efficiency of implantation by increasing the expression of several receptivity-related genes in endometrial epithelial cells (EECs).

WHAT IS KNOWN ALREADY

Calcitonin is one of the biomarkers of uterine receptivity, which is transiently produced in the uterine epithelia during the period of implantation both in humans and mouse.

STUDY DESIGN, SIZE, DURATION

Hormone-replaced mice were used for in vivo experiments. To evaluate the effect of calcitonin on uterine receptivity, the expression of endometrial genes was analyzed 36 h after i.p. injection of 0.5 IU calcitonin in a treatment group versus saline in the control. To evaluate the effect of calcitonin on implantation efficiency in vivo, two groups received 0.5 IU or 2 IU calcitonin (i.p.) 24 h before embryo transfer, and a control group received saline (i.p.) (n = 18 mice per group). Implantation sites were counted 7 days after embryo transfer. The RL95-2 human endometrial carcinoma cell line was used to study the mechanisms underlying the effect of calcitonin on gene expression in the endometria. Using an in vitro model of endometrium-trophoblast interaction, established with RL95-2 cells and JAR (human choriocarcinoma cell line) trophoblast, endometrial receptivity was evaluated by comparing attachment and outgrowth of JAR spheroids in control and treatment groups.

PARTICIPANTS/MATERIALS, SETTING, METHODS

Uterine receptivity in ovariectomized mice was induced by injection of estradiol and progesterone. Expression of eight genes in murine endometrium and RL95-2 cells was analyzed by real-time RT-PCR, western blot, immunohistochemical analysis, flow cytometry and enzyme-linked immunosorbent assay. We tested the effects of a protein kinase C inhibitor, matrigel and an antibody against integrin αvβ3 using RL95-2 cells and performed attachment and outgrowth assays using the in vitro model of endometrium-trophoblast interaction. Implantation efficiency was evaluated by counting the implantation sites after embryo transfer.

MAIN RESULTS AND THE ROLE OF CHANCE

Calcitonin up-regulated αvβ3 in RL95 cells, which in turn resulted in increased levels of the leukemia inhibitory factor (LIF) and heparin binding-epidermal growth factor (HB-EGF) mRNA (both P < 0.01 versus control) and protein (both P < 0.05 versus control). The attachment and expansion of JAR spheroids was promoted by pretreatment of EECs with calcitonin (P < 0.05 versus control) together with significantly increased expression of αvβ3, LIF and HB-EGF. Moreover, the injection of calcitonin in the preimplantation phase increased the total number of implantation sites in treatment groups (55 in control versus 78 and 85 in 0.5 and 2 IU groups, respectively). Compared with the control group (3.11 ± 2.14), the average number of implantation sites in the 2 IU calcitonin treatment group increased (4.72 ± 1.87, P = 0.022).

LIMITATIONS, REASONS FOR CAUTION

Experiments were performed in mice and human cell lines but not in primary cultures of human endometrial cells.

WIDER IMPLICATIONS OF THE FINDINGS

The findings presented here have important implications, in that calcitonin administration (currently used for treatment of hypercalcemia or osteoporosis) may have clinical benefits in assisted reproduction programs, by facilitating endometrial receptivity and embryo implantation. However, further studies are required to confirm these findings.

STUDY FUNDING/COMPETING INTEREST(S)

This work was supported by National Science Foundation of China (No. 81170619). There are no financial or commercial conflicts in this study.

Urokinase-type plasminogen activator receptor (uPAR)-mediated regulation of WNT/β-catenin signaling is enhanced in irradiated medulloblastoma cells

Urokinase plasminogen activator receptor (uPAR) is known to promote invasion, migration, and metastasis in cancer cells. In this report, we showed that ionizing radiation (IR)-induced uPAR has a role in WNT-β-catenin signaling and mediates induction of cancer stem cell (CSC)-like properties in medulloblastoma cell lines UW228 and D283. We observed that IR induced the expression of uPAR and CSC markers, such as Musashi-1 and CD44, and activated WNT-7a-β-catenin signaling molecules. Overexpression of uPAR alone or with IR treatment led to increased WNT-7a-β-catenin-TCF/LEF-mediated transactivation, thereby promoting cancer stemness. In contrast, treatment with shRNA specific for uPAR (pU) suppressed WNT-7a-β-catenin-TCF/LEF-mediated transactivation both in vitro and in vivo. Quercetin, a potent WNT/β-catenin inhibitor, suppressed uPAR and uPAR-mediated WNT/β-catenin activation, and furthermore, addition of recombinant human WNT-7a protein induced uPAR, indicating the existence of a mutual regulatory relationship between uPAR and WNT/β-catenin signaling. We showed that uPAR was physically associated with the WNT effector molecule β-catenin on the membrane, cytoplasm, and nucleus of IR-treated cells and CSC. Most interestingly, we demonstrated for the first time that localization of uPAR in the nucleus was associated with transcription factors (TF) and their specific response elements. We observed from uPAR-ChIP, TF protein, and protein/DNA array analyses that uPAR associates with activating enhancer-binding protein 2α (AP2a) and mediates β-catenin gene transcription. Moreover, association of uPAR with the β-catenin·TCF/LEF complex and various other TF involved during embryonic development and cancer indicates that uPAR is a potent activator of stemness, and targeting of uPAR in combination with radiation has significant therapeutic implications.

Role of integrins in regulating proteases to mediate extracellular matrix remodeling

The extracellular matrix (ECM) is an extracellular scaffold composed of complex mixtures of proteins that plays a pivotal role in tumor progression. ECM remodeling is crucial for tumor migration and invasion during the process of metastasis. ECM can be remodeled by several processes including synthesis, contraction and proteolytic degradation. In order to cross through the ECM barriers, malignant cells produce a spectrum of extracellular proteinases including matrix metalloproteinases (MMPs), serine proteases (mainly the urokinase plasminogen activator (uPA) system) and cysteine proteases to degrade ECM components. As major adhesion molecules to support cell attachment to ECM, integrins play critical roles in tumor progression by enhancing tumor cell survival, migration and invasion. Previous studies have shown that integrins can regulate the expression and activity of these proteases through different pathways. This review summarizes the roles of MMPs and uPA system in ECM remodeling and discusses the regulatory functions of integrins on these proteases in invasive tumors.

Methods for evaluation of structural and biological properties of antiinvasive natural products

Prostate cancer is considered the most common cancer form among males in Western countries. Very limited options are available for the treatment of advanced metastatic prostate cancer. More than 50% of today's anticancer drugs are natural products or derived from a natural origin. To discover new entities with potential to treat prostate cancer at androgen-refractory stages, 36 structurally diverse natural products were screened using functional-based assays. The tested compounds were selected broadly from major secondary metabolites of plants, marine invertebrates, and fungi. These diverse entities were prescreened for their antiinvasive ability against prostate cancer cells, PC-3M, using spheroid disaggregation assay. Active representatives including three selected structural classes, a macrolide, a β-carboline alkaloid, and a phenylmethylene hydantoin (PMH), were then tested for their ability to stabilize junctional complexes and enhance cell-cell adhesion of androgen independent prostate cancer cells. Transepithelial resistance (TER) and paracellular permeability assays were used to elicit the aforementioned properties. These studies led to the emergence of PMHs as a small molecule class from the marine sponge Hemimycale arabica with a unique potential to attenuate CT-stimulated prostate cancer growth, metastasis, paracellular permeability, and enhance TER and cell-cell adhesion of prostate cancer cells. The unique activities of PMHs were validated using several in vitro assays followed by in vivo testing in two mice models. A 3D QSAR was established using SYBYL 8.1-Comparative Molecular Field Analysis (CoMFA) model. This chapter includes the methodology for evaluation of structural and biological properties of new antiinvasive molecules with an exceptional potential to stabilize junctional complexes from diverse natural product sources.

Identification of a small molecule class to enhance cell-cell adhesion and attenuate prostate tumor growth and metastasis

Expression of calcitonin (CT) and its receptor (CTR) is elevated in advanced prostate cancer, and activated CT-CTR autocrine axis plays a pivotal role in tumorigenicity and metastatic potential of multiple prostate cancer cell lines. Recent studies suggest that CT promotes prostate cancer metastasis by reducing cell-cell adhesion through the disassembly of tight and adherens junctions and activation of beta-catenin signaling. We attempted to identify a class of molecules that enhances cell-cell adhesion of prostate cells and reverses the disruptive actions of CT on tight and adherens junctions. Screening several compounds led to the emergence of phenyl-methylene hydantoin (PMH) as a lead candidate that can augment cell-cell adhesion and abolish disruptive actions of CT on junctional complexes. PMH reduced invasiveness of PC-3M cells and abolished proinvasive actions of CT. Importantly, PMH did not display significant cytotoxicity on PC-3M cells at the tested doses. I.p. administered PMH and its S-ethyl derivative remarkably decreased orthotopic tumor growth and inhibited the formation of tumor micrometastases in distant organs of nude mice. PMH treatment also reduced the growth of spontaneous tumors in LPB-Tag mice to a significant extent without any obvious cytotoxic effects. By virtue of its ability to stabilize cell junctions, PMH could reverse the effect of CT on junctional disruption and metastasis, which strengthens the possibility of using PMH as a potential drug candidate for CT-positive androgen-independent prostate cancers.

Latrunculin A and its C-17-O-carbamates inhibit prostate tumor cell invasion and HIF-1 activation in breast tumor cells

The marine-derived macrolides latrunculins A ( 1) and B, from the Red Sea sponge Negombata magnifica, have been found to reversibly bind actin monomers, forming a 1:1 complex with G-actin and disrupting its polymerization. The microfilament protein actin is responsible for several essential functions within the cell such as cytokinesis and cell migration. One of the main binding pharmacophores of 1 to G-actin was identified as the C-17 lactol hydroxyl moiety that binds arginine 210 NH. Latrunculin A-17- O-carbamates 2- 6 were prepared by reaction with the corresponding isocyanates. Latrunculin A ( 1) and carbamates 4- 6 displayed potent anti-invasive activity against the human highly metastatic human prostate cancer PC-3M cells in a Matrigel assay at a concentration range of 50 nM to 1 microM. Latrunculin A ( 1, 500 nM) decreased the disaggregation and cell migration of PC-3M-CT+ spheroids by 3-fold. Carbamates 4 and 5 were 2.5- and 5-fold more active than 1, respectively, in this assay with less actin binding affinity. Latrunculin A ( 1, IC 50 6.7 microM) and its 17- O-[ N-(benzyl)carbamate ( 6, IC 50 29 microM) suppress hypoxia-induced HIF-1 activation in T47D breast tumor cells.