PGE2 promotes breast cancer-associated lymphangiogenesis by activation of EP4 receptor on lymphatic endothelial cells.

BACKGROUND: Lymphatic metastasis, facilitated by lymphangiogenesis is a common occurrence in breast cancer, the molecular mechanisms remaining incompletely understood. We had earlier shown that cyclooxygenase (COX)-2 expression by human or murine breast cancer cells promoted lymphangiogenesis and lymphatic metastasis by upregulating VEGF-C/D production by tumor cells or tumor-associated macrophages primarily due to activation of the prostaglandin receptor EP4 by endogenous PGE2. It is not clear whether tumor or host-derived PGE2 has any direct effect on lymphangiogenesis, and if so, whether EP4 receptors on lymphatic endothelial cells (LEC) play any role. METHODS: Here, we address these questions employing in vitro studies with a COX-2-expressing and VEGF-C/D-producing murine breast cancer cell line C3L5 and a rat mesenteric (RM) LEC line and in vivo studies in nude mice. RESULTS: RMLEC responded to PGE2, an EP4 agonist PGE1OH, or C3L5 cell-conditioned media (C3L5-CM) by increased proliferation, migration and accelerated tube formation on growth factor reduced Matrigel. Native tube formation by RMLEC on Matrigel was abrogated in the presence of a selective COX-2 inhibitor or an EP4 antagonist. Addition of PGE2 or EP4 agonist, or C3L5-CM individually in the presence of COX-2 inhibitor, or EP4 antagonist, restored tube formation, reinforcing the role of EP4 on RMLEC in tubulogenesis. These results were partially duplicated with a human dermal LEC (HMVEC-dLyAd) and a COX-2 expressing human breast cancer cell line MDA-MB-231. Knocking down EP4 with shRNA in RMLEC abrogated their tube forming capacity on Matrigel in the absence or presence of PGE2, EP4 agonist, or C3L5-CM. RMLEC tubulogenesis following EP4 activation by agonist treatment was dependent on PI3K/Akt and Erk signaling pathways and VEGFR-3 stimulation. Finally in a directed in vivo lymphangiogenesis assay (DIVLA) we demonstrated the lymphangiogenic as well as angiogenic capacity of PGE2 and EP4 agonist in vivo. DISCUSSION/CONCLUSIONS: These results demonstrate the roles of tumor as well as host-derived PGE2 in inducing lymphangiogenesis, at least in part, by activating EP4 and VEGFR-3 on LEC. EP4 being a common target on both tumor and host cells contributing to tumor-associated lymphangiogenesis reaffirms the therapeutic value of EP4 antagonists in the intervention of lymphatic metastasis in breast cancer.

Decorin over-expression by decidual cells in preeclampsia: a potential blood biomarker.

BACKGROUND: Decorin, a leucine-rich proteoglycan that is produced by decidual cells, limits invasion and endovascular differentiation of extravillous trophoblast cells during early placentation by binding to multiple tyrosine kinase receptors, in particular, vascular endothelial growth factor receptor-2. OBJECTIVE: Because many studies have reported an association between poor trophoblast invasion and endovascular differentiation with preeclampsia, the studies reported here tested (1) whether decorin over-expression in the chorionic villi and/or basal decidua is associated with preeclampsia and, if so, (2) whether this association results in a hypoinvasive placenta, and (3) whether elevated plasma decorin concentration in the second trimester is a predictive biomarker for preeclampsia. STUDY DESIGN: Decorin messenger RNA expression was measured with quantitative polymerase chain reaction at the tissue level and with in situ hybridization at the cellular level using (35)S-labeled antisense complimentary RNA probe in placentas from healthy control subjects and subjects with preeclampsia (14 each, 23-40 weeks of gestation). Tissue sections of the same placentas were also immunostained for decorin protein. A decorin over-expressing human endometrial stromal cell line was tested for invasion-regulatory effects on an invasive first-trimester extravillous trophoblast cell line HTR-8/SVneo plated in cocultures that were separated by a semipermeable membrane. Furthermore, we conducted retrospective measurements of plasma decorin levels during the second trimester (15-18 weeks of gestation) in a cohort of 28 body mass index-matched pairs of control subjects and subjects with preeclampsia before the onset of clinical disease. RESULTS: First, decorin messenger RNA expression at the cellular level measured with in situ hybridization exhibited profoundly higher expression levels in basal plate decidual cells within the placentas from preeclamptic subjects than those from control subjects at all gestational ages, whereas no difference between the 2 subject groups was noted in villus mesenchymal cells. Similarly decorin messenger RNA expression at the tissue level in chorionic villi (primarily resulting from fetally derived mesenchymal cells) did not differ significantly between control and preeclampsia placentas. These findings were validated with immunostaining for decorin protein. Second, knocking down decorin gene in a decorin over-expressing endometrial cell line (used as an in vitro surrogate of decorin over-expressing decidual cells) in cocultures with extravillous trophoblast cells abrogated its invasion-restraining actions on trophoblast cells, which indicated paracrine contribution of decorin over-expressing decidua to the poor trophoblast invasiveness in situ. Finally, retrospective measurement of plasma decorin levels during the second trimester in 28 body mass index-matched pairs of control subjects and subjects with preeclampsia revealed elevated plasma decorin levels in all subjects with preeclampsia in all body mass index groups. A receiver operating characteristic curve analysis revealed strong diagnostic performance of plasma decorin in the prediction of preeclampsia status. Although there was no significant gestational age-related change in decorin levels during the second trimester in control or subjects with preeclampsia, we found that plasma decorin had a significant inverse relationship with body mass index or bodyweight. CONCLUSION: We conclude that decorin over-expression by basal decidual cells is associated with hypoinvasive phenotype and poor endovascular differentiation of trophoblast cells in preeclampsia and that elevated plasma decorin concentration is a potential predictive biomarker for preeclampsia before the onset of clinical signs.

Prostaglandin E2 receptor EP4 as the common target on cancer cells and macrophages to abolish angiogenesis, lymphangiogenesis, metastasis, and stem-like cell functions.

We previously established that COX-2 overexpression promotes breast cancer progression and metastasis. As long-term use of COX-2 inhibitors (COX-2i) can promote thrombo-embolic events, we tested an alternative target, prostaglandin E2 receptor EP4 subtype (EP4), downstream of COX-2. Here we used the highly metastatic syngeneic murine C3L5 breast cancer model to test the role of EP4-expressing macrophages in vascular endothelial growth factor (VEGF)-C/D production, angiogenesis, and lymphangiogenesis in situ, the role of EP4 in stem-like cell (SLC) functions of tumor cells, and therapeutic effects of an EP4 antagonist RQ-15986 (EP4A). C3L5 cells expressed all EP receptors, produced VEGF-C/D, and showed high clonogenic tumorsphere forming ability in vitro, functions inhibited with COX-2i or EP4A. Treating murine macrophage RAW 264.7 cell line with COX-2i celecoxib and EP4A significantly reduced VEGF-A/C/D production in vitro, measured with quantitative PCR and Western blots. Orthotopic implants of C3L5 cells in C3H/HeJ mice showed rapid tumor growth, angiogenesis, lymphangiogenesis (CD31/LYVE-1 and CD31/PROX1 immunostaining), and metastasis to lymph nodes and lungs. Tumors revealed high incidence of EP4-expressing, VEGF-C/D producing macrophages identified with dual immunostaining of F4/80 and EP4 or VEGF-C/D. Celecoxib or EP4A therapy at non-toxic doses abrogated tumor growth, lymphangiogenesis, and metastasis to lymph nodes and lungs. Residual tumors in treated mice revealed markedly reduced VEGF-A/C/D and phosphorylated Akt/ERK proteins, VEGF-C/D positive macrophage infiltration, and proliferative/apoptotic cell ratios. Knocking down COX-2 or EP4 in C3L5 cells or treating cells in vitro with celecoxib or EP4A and treating tumor-bearing mice in vivo with the same drug reduced SLC properties of tumor cells including preferential co-expression of COX-2 and SLC markers ALDH1A, CD44, OCT-3/4, ß-catenin, and SOX-2. Thus, EP4 is an excellent therapeutic target to block stem-like properties, angiogenesis, and lymphangiogenesis induced by VEGF-A/C/D secreted by cancer cells and tumor infiltrating macrophages.

Targeting COX-2 and EP4 to control tumor growth, angiogenesis, lymphangiogenesis and metastasis to the lungs and lymph nodes in a breast cancer model.

We reported that cyclo-oxygenase (COX)-2 expression in human breast cancer stimulated cancer cell migration and invasiveness, production of vascular endothelial growth factor (VEGF)-C and lymphangiogenesis in situ, largely from endogenous PGE2-mediated stimulation of prostaglandin E (EP)1 and EP4 receptors, presenting them as candidate therapeutic targets against lymphatic metastasis. As human breast cancer xenografts in immuno-compromised mice have limitations for preclinical testing, we developed a syngeneic murine breast cancer model of spontaneous lymphatic metastasis mimicking human and applied it for mechanistic and therapeutic studies. We tested the roles of COX-2 and EP receptors in VEGF-C and -D production by a highly metastatic COX-2 expressing murine breast cancer cell line C3L5. These cells expressed all EP receptors and produced VEGF-C and -D, both inhibited with COX-2 inhibitors or EP4 (but not EP1, EP2 or EP3) antagonists. C3H/HeJ mice, when implanted SC in both inguinal regions with C3L5 cells suspended in growth factor-reduced Matrigel, exhibited rapid tumor growth, tumor-associated angiogenesis and lymphangiogenesis (respectively measured with CD31 and LYVE-1 immunostaining), metastasis to the inguinal and axillary lymph nodes and the lungs. Chronic oral administration of COX-1/COX-2 inhibitor indomethacin, COX-2 inhibitor celecoxib and an EP4 antagonist ONO-AE3-208, but not an EP1 antagonist ONO-8713 at nontoxic doses markedly reduced tumor growth, lymphangiogenesis, angiogenesis, and metastasis to lymph nodes and lungs. Residual tumors in responding mice revealed reduced VEGF-C and -D proteins, AkT phosphorylation and increased apoptotic/proliferative cell ratios consistent with blockade of EP4 signaling. We suggest that EP4 antagonists deserve clinical testing for chemo-intervention of lymphatic metastasis in human breast cancer.

Mechanisms in decorin regulation of vascular endothelial growth factor-induced human trophoblast migration and acquisition of endothelial phenotype.

Extravillous trophoblast (EVT) cells of the human placenta invade the uterine decidua and utero-placental arteries to establish an efficient exchange of key molecules between maternal and fetal blood. Trophoblast invasion is stringently regulated in situ both positively and negatively by a variety of factors at the fetal-maternal interface to maintain a healthy utero-placental homeostasis. One such factor, decorin, a transforming growth factor (TGF)-beta binding, leucine-rich proteoglycan produced by the decidua, negatively regulates EVT proliferation, migration, and invasiveness independent of TGF-beta. We reported that these decorin actions were mediated by its binding to multiple tyrosine kinase receptors, including vascular endothelial growth factor receptor (VEGFR)-2. The present study explores the mechanisms underlying decorin antagonism of VEGF (VEGF-A) stimulation of endovascular differentiation of EVT using our EVT cell line, HTR-8/SVneo. We observe that decorin inhibits VEGF-induced EVT cell migration and endothelial-like tube formation on matrigel. VEGF activates MAPKs (p38 MAPK, MEK3/6, and ERK1/2) in EVT cells, and the activation is blocked in both cases by decorin. Employing selective MAPK inhibitors, we show that both p38 and ERK pathways contribute independently to VEGF-induced EVT migration and capillary-like tube formation. VEGF upregulates the vascular endothelial (VE) markers VE-cadherin and beta-catenin in EVT and endothelial cells, and this upregulation is blocked by decorin and MAPK inhibitors. These results suggest that decorin inhibits VEGF-A stimulation of trophoblast migration and endovascular differentiation by interfering with p38 MAPK and ERK1/2 activation. Thus decorin-mediated dual impediment of endovascular differentiation of the EVT and angiogenesis may have implications for pathogenesis of preeclampsia, a hypoinvasive trophoblast disorder in pregnancy.

Acetyl salicylic acid (aspirin) improves synthesis of maspin and lowers incidence of metastasis in breast cancer patients [corrected].

Maspin, a 42 kDa protein produced in normal breast cells, has been shown to inhibit the invasion and metastasis of breast cancer in an animal model. Ingestion of acetylsalicylic acid (aspirin) by breast cancer patients has been reported to restore the systemic synthesis of maspin through the stimulation of systemic nitric oxide production. Studies were carried out to determine the effect of aspirin on the incidence of breast cancer metastasis, which is reported to occur in 50% of patients who have previously received chemotherapy, radiation, and/or surgery. Thirty-five female patients (aged 41-65 years) with breast cancer who had previously received these therapies took one 75 mg/70 kg body weight enteric-coated aspirin tablet every 24 h, after an adequate meal, for 3 years. Their plasma nitric oxide and maspin levels were measured. The occurrence of metastasis was ascertained monthly by a qualified oncologist, and confirmed, if necessary, by biopsy. Daily ingestion of aspirin by participants resulted in an increase in maspin levels from 0.95 ± 0.04 to 4.63 ± 0.05 nM after 24 h. These levels were maintained for 3 years. These studies suggest that daily ingestion of aspirin might significantly reduce the incidence of breast cancer metastasis in patients who have previously received anticancer therapies.

Decorin is a novel VEGFR-2-binding antagonist for the human extravillous trophoblast.

Extravillous trophoblasts (EVT) of the human placenta invade the uterine decidua and its arteries to ensure successful placentation. We previously identified two decidua-derived molecules, TGF-ß and a TGF-ß-binding proteoglycan decorin (DCN), as negative regulators of EVT proliferation, migration, and invasiveness and reported that DCN acts via multiple tyrosine kinase receptors [epidermal growth factor-receptor (EGF-R), IGF receptor-1 (IGFR1), and vascular endothelial growth factor 2 receptor (VEGFR-2)]. Because binding of DCN to VEGFR-2 has never been reported earlier, present study explored this binding, the approximate location of VEGFR-2-binding site in DCN, and its functional role in our human first trimester EVT cell line HTR-8/SVneo. Based on far-Western blotting and coimmunoprecipitation studies, we report that DCN binds both native (EVT expressed) and recombinant VEGFR-2 and that this binding is abrogated with a VEGFR-2 blocking antibody, indicating an overlap between the ligand-binding and the DCN-binding domains of VEGFR-2. We determined that (125)I-labeled VEGF-E (a VEGFR-2 specific ligand) binds EVT with a dissociation constant (K(d)) of 566 pM, and DCN displaced this binding with an inhibition constant (K(i)) of 3.93-5.78 nM, indicating a 7- to 10-fold lower affinity of DCN for VEGFR-2. DCN peptide fragments derived from the leucine rich repeat 5 domain that blocked DCN-VEGFR-2 interactions or VEGF-E binding in EVT cells also blocked VEGF-A- and VEGF-E-induced EVT cell proliferation and migration, indicative of functional VEGFR-2-binding sites of DCN. Finally, DCN inhibited VEGF-E-induced EVT migration by interfering with ERK1/2 activation. Our findings reveal a novel role of DCN as an antagonistic ligand for VEGFR-2, having implications for pathophysiology of preeclampsia, a trophoblast hypoinvasive disorder in pregnancy, and explain its antiangiogenic function.

Location and function of STIM1 in the activation of Ca2+ entry signals.

Store-operated channels (SOCs) mediate Ca(2+) entry signals in response to endoplasmic reticulum (ER) Ca(2+) depletion in most cells. STIM1 senses decreased ER luminal Ca(2+) through its EF-hand Ca(2+)-binding motif and aggregates in near-plasma membrane (PM) ER junctions to activate PM Orai1, the functional SOC. STIM1 is also present in the PM, although its role there is unknown. STIM1-mediated coupling was examined using the stable EF20 HEK293 cell line expressing the STIM1-D76A/E87A EF-hand mutant (STIM1(EF)) deficient in Ca(2+) binding. EF20 cells were viable despite constitutive Ca(2+) entry, allowing study of SOC activation without depleting ER Ca(2+). STIM1(EF) was exclusively in stable near-PM junctions, 3.5-fold larger than formed with STIM1(WT). STIM(EF)-expressing cells had normal ER Ca(2+) levels but substantially reduced ER Ca(2+) leak. Expression of antiapoptotic Bcl-2 proteins (BCl-2, MCL-1, BCL-XL) were increased 2-fold in EF20 cells, probably reflecting survival of EF20 cells but not accounting for decreased ER Ca(2+) leak. Surface biotinylation and streptavidin pull-down of cells expressing STIM1(WT) or STIM1(EF) revealed strong PM interactions of both proteins. Although surface expression of STIM1(WT) was clearly detectable, STIM1(EF) was undetectable at the cell surface. Thus, the Ca(2+) binding-defective STIM1(EF) mutant exists exclusively in aggregates within near-PM junctions but, unlike STIM1(WT), is not trafficked to the PM. Although not inserted in the PM, external application of a monoclonal anti-N-terminal STIM1 antibody blocked constitutive STIM(EF)-mediated Ca(2+) entry, but only in cells expressing endogenous STIM1(WT) and not in DT40 STIM1 knock-out cells devoid of STIM(WT). This suggests that PM-STIM1 may play a regulatory role in SOC activation.