Interaction of folate receptor with signaling molecules lyn and G(alpha)(i-3) in detergent-resistant complexes from the ovary carcinoma cell line IGROV1

Emerging roles for folate receptor FOLR1 in signaling and cancer

Folates are B vitamins that function in one-carbon metabolism. Folate receptors are one of three major types of folate transporters. The folate receptors FOLR1 and FOLR2 are overexpressed in multiple cancers. The overexpression of FOLR1 is often associated with increased cancer progression and poor patient prognosis. There is emerging evidence that FOLR1 is involved in signaling pathways that are independent of one-carbon metabolism. Recent publications implicate a direct role of FOLR1 in three signaling pathways: JAK-STAT3, ERK1/2, and as a transcription factor. Six other signaling pathways have been proposed to include FOLR1, but these currently lack sufficient data to infer a direct signaling role for FOLR1. We discuss the data that support noncanonical roles for FOLR1, and its limitations.

Anti-Folate Receptor Alpha-Directed Antibody Therapies Restrict the Growth of Triple-negative Breast Cancer

Purpose: Highly aggressive triple-negative breast cancers (TNBCs) lack validated therapeutic targets and have high risk of metastatic disease. Folate receptor alpha (FRα) is a central mediator of cell growth regulation that could serve as an important target for cancer therapy.Experimental Design: We evaluated FRα expression in breast cancers by genomic (n = 3,414) and IHC (n = 323) analyses and its association with clinical parameters and outcomes. We measured the functional contributions of FRα in TNBC biology by RNA interference and the antitumor functions of an antibody recognizing FRα (MOv18-IgG1), in vitro, and in human TNBC xenograft models.Results: FRα is overexpressed in significant proportions of aggressive basal like/TNBC tumors, and in postneoadjuvant chemotherapy-residual disease associated with a high risk of relapse. Expression is associated with worse overall survival. TNBCs show dysregulated expression of thymidylate synthase, folate hydrolase 1, and methylenetetrahydrofolate reductase, involved in folate metabolism. RNA interference to deplete FRα decreased Src and ERK signaling and resulted in reduction of cell growth. An anti-FRα antibody (MOv18-IgG1) conjugated with a Src inhibitor significantly restricted TNBC xenograft growth. Moreover, MOv18-IgG1 triggered immune-dependent cancer cell death in vitro by human volunteer and breast cancer patient immune cells, and significantly restricted orthotopic and patient-derived xenograft growth.Conclusions: FRα is overexpressed in high-grade TNBC and postchemotherapy residual tumors. It participates in cancer cell signaling and presents a promising target for therapeutic strategies such as ADCs, or passive immunotherapy priming Fc-mediated antitumor immune cell responses. Clin Cancer Res; 24(20); 5098-111. ©2018 AACR.

Hematopoietic lineage cell-specific protein 1 (HS1), a hidden player in migration, invasion, and tumor formation, is over-expressed in ovarian carcinoma cells

Hematopoietic lineage cell-specific protein 1 (HS1), which is the hematopoietic homolog of cortactin, is an actin-binding protein and Lyn substrate. It is upregulated in several cancers and its expression level is associated with increased cell migration, metastasis, and poor prognosis. Here we investigated the expression and roles of HS1 in ovarian carcinoma cells. We analyzed the expression of HS1 in 171 ovarian cancer specimens and determined the association between HS1 expression and clinicopathological characteristics, including patient outcomes. In patients with stage II-IV disease, positive HS1 expression was associated with significantly worse overall survival than negative expression (P < 0.05). HS1 was localized in invadopodia in some ovarian cancer cells and was required for invadopodia formation. Migration and invasion of ovarian cancer cells were suppressed by down-regulation of HS1, but increased in cells that over-expressed exogenous HS1. Furthermore, ovarian cancer cells that expressed HS1 shRNA exhibited reduced tumor formation in a mouse xenograft model. Finally, we found that tyrosine phosphorylation of HS1 was essential for cell migration and invasion. These findings show that HS1 is a useful biomarker for the prognosis of patients with ovarian carcinoma and is a critical regulator of cytoskeleton remodeling involved in cell migration and invasion.

Folate receptor-targeted 19 F MR molecular imaging and proliferation evaluation of lung cancer

BACKGROUND

Folate receptors (FRs) hold great potential as important diagnostic and prognostic biological marker for cancer.

PURPOSE

To assess the targeted capability of the FR-targeted perfluorocarbon (PFC) nanoparticles and to assess in vivo the relationship between FR expression and tumor proliferation with fluorine-19 (¹⁹ F) MR molecular imaging.

STUDY TYPE

Prospective animal cancer model.

ANIMAL MODEL

H460 (n = 14) and A549 (n = 14) nude mice subcutaneous tumor models.

FIELD STRENGTH

9.4T, ¹ H and ¹⁹ F RARE sequences.

ASSESSMENT

Intracellular uptake of the PFC nanoparticles was tested in H460 and A549 cell lines. ¹⁹ F MRI of H460 and A549 subcutaneous tumors was performed following intravenous injection of PFC nanoparticles. The concentration of PFC in tumors were compared. 3'-Deoxy-3'-¹⁸ F-fluorothymidine (¹⁸ F-FLT) positron emission tomography / computed tomography (PET/CT) imaging, Ki-67, and proliferating cell nuclear antigen (PCNA) staining were performed to confirm tumor proliferation.

STATISTICAL TESTS

One-way or two-way analysis of variance. P < 0.05 was considered a significant difference.

RESULTS

The diameter of the FR-targeted nanoparticles was 108.8 ± 0.56 nm, and the zeta potential was -58.4 ± 10.8 mV. H460 cells incubated with FR-targeted nanoparticles showed ∼59.87 ± 3.91% nanoparticles-labeled, which is significantly higher than the other groups (P < 0.001). The PFC concentration in H460 tumors after injection with FR-targeted nanoparticles was 4.64 ± 1.21, 8.04 ± 1.38, and 9.16 ± 2.56 mmol/L at 8 hours, 24 hours, and 48 hours, respectively (P < 0.05 compared to others). The ratio of ¹⁸ F-FLT uptake for H460 and A549 tumors was 3.32 ± 0.17 and 1.48 ± 0.09 (P < 0.05), and there was more Ki-67 and PCNA in H460 tumor than A549. DATA CONCLUSION: ¹⁹ F MRI with FR-targeted PFC nanoparticles can be used in differentiating of FR-positive and FR-negative tumors, and further, in evaluation of the two cancer models proliferation.

LEVEL OF EVIDENCE

1 Technical Efficacy: Stage 2 J. Magn. Reson. Imaging 2018;48:1617-1625.

Expression status of folate receptor alpha is a predictor of survival in pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) has one of the poorest prognosis among malignancies. Thus, the identification of markers useful in developing innovative diagnostic and therapeutic methods is an imperative need. Folate receptor alpha (FRα) has been associated with prognosis in several cancers and has served as a target of novel anti-tumor therapies. However, FRα expression in PDAC and its correlation with the clinical course of the disease has not been thoroughly investigated. In this study, we analyzed FRα expression in 140 PDAC specimens and 7 PDAC cell lines in order to define the significance of FRα expression in PDAC and its potential role as a target for immunotherapy. Immunohistochemical analysis demonstrated that FRα expression intensity was low, intermediate and high in 22(16%), 73(52%) and 45(32%) PDACs, respectively. The staining was located in both membrane and cytoplasm in most cases (123, 88%). Lower FRα expression was associated with cigarette smoking (p<0.001), alcohol consumption (p<0.001), and lymphovascular invasion (p=0.002). Additionally, lower FRα expression was associated with poor overall survival (5-year overall survival: low 13%, intermediate 31%, high 33%; p=0.006). FRα expression (HR=0.61; p=0.03) and Charlson Comorbidity Index (HR=1.16; p=0.01) emerged as independent predictors of survival. The analysis by flow cytometry of 7 PDAC cell lines (AsPC-1, Capan-2, MIA PaCa-2, PANC-1, PDAC2, PDAC3, and PDAC5) demonstrated the highest expression of FRα on the PDAC3 cell line (45%). Therefore, a higher FRα expression is predictive of a favorable prognosis in PDAC and FRα may represent a promising target for novel treatments, including immunotherapy.

Potent Therapeutic Activity Against Peritoneal Dissemination and Malignant Ascites by the Novel Anti-Folate Receptor Alpha Antibody KHK2805

Many ovarian cancer patients often show peritoneal metastasis with malignant ascites. However, unmet medical needs remain regarding controlling these symptoms after tumors become resistant to chemotherapies. We developed KHK2805, a novel anti-folate receptor α (FOLR1) humanized antibody with enhanced antibody-dependent cellular cytotoxicity (ADCC) and complement-dependent cytotoxicity (CDC). The primary aim of the present study was to evaluate whether the anti-tumor activity of KHK2805 was sufficient for therapeutic application against peritoneal dissemination and malignant ascites of platinum-resistant ovarian cancer in preclinical models. Here, both the ADCC and CDC of KHK2805 were evaluated in ovarian cancer cell lines and patient-derived samples. The anti-tumor activity of KHK2805 was evaluated in a SCID mouse model of platinum-resistant peritoneal dissemination. As results, KHK2805 showed specific binding to FOLR1 with high affinity at a novel epitope. KHK2805 exerted potent ADCC and CDC against ovarian cancer cell lines. Furthermore, primary platinum-resistant malignant ascites cells were susceptible to autologous ADCC with KHK2805. Patient-derived sera and malignant ascites induced CDC of KHK2805. KHK2805 significantly reduced the total tumor burden and amount of ascites in SCID mice with peritoneal dissemination and significantly prolonged their survival. In addition, the parental rat antibody strongly stained serous and clear cell-type ovarian tumors by immunohistochemistry. Overall, KHK2805 showed cytotoxicity against both ovarian cancer cell lines and patient-derived cells. These translational study findings suggest that KHK2805 may be promising as a novel therapeutic agent for platinum-resistant ovarian cancer with peritoneal dissemination and malignant ascites.

High folic acid diet enhances tumour growth in PyMT-induced breast cancer

Background:

The B-vitamin folate is among the most studied bioactive food compound, and a dietary intake meeting the daily requirements has been found to reduce the risk of cancer and cardiovascular diseases as well as preventing neural tube defects during fetal development. Several countries have therefore introduced dietary fortification with folic acid. However, clinical and animal studies suggest that folic acid has a dual role in cancer development.

Methods:

During the period of initial tumour progression, MMTV-PyMT (MMTV-polyoma virus middle T) transgenic mice were fed with normal diet and high folic acid diet.

Results:

We found that PyMT-induced breast tumours highly express the cancer-specific folate receptor (FR), a feature they share with several human epithelial cancers in which expression of FRα correlates with tumour grade. Mice receiving a high folic acid diet displayed a significantly increased tumour volume compared with mice receiving normal diet. In the largest tumours, only found in mice on high folic acid diet, STAT3 was activated. In primary cells from PyMT tumours, STAT3 was activated upon treatment with folic acid in culture.

Conclusions:

Our results offer a novel molecular explanation for folic acid-induced growth of existing tumours.

Lesser-Known Molecules in Ovarian Carcinogenesis

Currently, the deciphering of the signaling pathways brings about new advances in the understanding of the pathogenic mechanism of ovarian carcinogenesis, which is based on the interaction of several molecules with different biochemical structure that, consequently, intervene in cell metabolism, through their role as regulators in proliferation, differentiation, and cell death. Given that the ensemble of biomarkers in OC includes more than 50 molecules the interest of the researchers focuses on the possible validation of each one's potential as prognosis markers and/or therapeutic targets. Within this framework, this review presents three protein molecules: ALCAM, c-FLIP, and caveolin, motivated by the perspectives provided through the current limited knowledge on their role in ovarian carcinogenesis and on their potential as prognosis factors. Their structural stability, once altered, triggers the initiation of the sequences characteristic for ovarian carcinogenesis, through their role as modulators for several signaling pathways, contributing to the disruption of cellular junctions, disturbance of pro-/antiapoptotic equilibrium, and alteration of transmission of the signals specific for the molecular pathways. For each molecule, the text is built as follows: (i) general remarks, (ii) structural details, and (iii) particularities in expression, from different tumors to landmarks in ovarian carcinoma.

Novel insights in folate receptors and transporters: implications for disease and treatment of immune diseases and cancer

Folate receptors and transporters as well as folate enzymes play an essential role in human disease and form important targets for the treatment of immune diseases and cancer. To discuss new developments in this area, every 2 years a multidisciplinary meeting is held, which aims to be an informal forum for fundamental scientists and clinicians. During this meeting, the regulation of folate transporters and folate enzymes is discussed at the level of expression, transcription, translation, post-translational modification, and splicing and enzyme regulation. Importantly, this knowledge is applied and translated into exciting clinical applications by clinicians with various backgrounds, such as surgeons, nephrologists, rheumatologists and oncologists. Moreover, the meeting provides an excellent forum for a scientific interaction between academia and industry.

Evidence for a time-dependent association between FOLR1 expression and survival from ovarian carcinoma: implications for clinical testing. An Ovarian Tumour Tissue Analysis consortium study

BACKGROUND

Folate receptor 1 (FOLR1) is expressed in the majority of ovarian carcinomas (OvCa), making it an attractive target for therapy. However, clinical trials testing anti-FOLR1 therapies in OvCa show mixed results and require better understanding of the prognostic relevance of FOLR1 expression. We conducted a large study evaluating FOLR1 expression with survival in different histological types of OvCa.

METHODS

Tissue microarrays composed of tumour samples from 2801 patients in the Ovarian Tumour Tissue Analysis (OTTA) consortium were assessed for FOLR1 expression by centralised immunohistochemistry. We estimated associations for overall (OS) and progression-free (PFS) survival using adjusted Cox regression models. High-grade serous ovarian carcinomas (HGSC) from The Cancer Genome Atlas (TCGA) were evaluated independently for association between FOLR1 mRNA upregulation and survival.

RESULTS

FOLR1 expression ranged from 76% in HGSC to 11% in mucinous carcinomas in OTTA. For HGSC, the association between FOLR1 expression and OS changed significantly during the years following diagnosis in OTTA (Pinteraction=0.01, N=1422) and TCGA (Pinteraction=0.01, N=485). In OTTA, particularly for FIGO stage I/II tumours, patients with FOLR1-positive HGSC showed increased OS during the first 2 years only (hazard ratio=0.44, 95% confidence interval=0.20-0.96) and patients with FOLR1-positive clear cell carcinomas (CCC) showed decreased PFS independent of follow-up time (HR=1.89, 95% CI=1.10-3.25, N=259). In TCGA, FOLR1 mRNA upregulation in HGSC was also associated with increased OS during the first 2 years following diagnosis irrespective of tumour stage (HR: 0.48, 95% CI: 0.25-0.94).

CONCLUSIONS

FOLR1-positive HGSC tumours were associated with an increased OS in the first 2 years following diagnosis. Patients with FOLR1-negative, poor prognosis HGSC would be unlikely to benefit from anti-FOLR1 therapies. In contrast, a decreased PFS interval was observed for FOLR1-positive CCC. The clinical efficacy of FOLR1-targeted interventions should therefore be evaluated according to histology, stage and time following diagnosis.

Folate receptor α associated with triple-negative breast cancer and poor prognosis

CONTEXT

Folate receptor α (FRA) has been shown to be selectively expressed in several types of human cancer, including breast cancer. Currently, several FRA target therapies are under intensive study.

OBJECTIVE

To investigate the expression pattern of FRA in a large cohort of patients with breast cancer and analyze its relationship with different clinicopathologic features, with expression of several key biomarkers, and with clinical outcome.

DESIGN

Four hundred forty-seven cases of infiltrating ductal carcinoma diagnosed between 1997 and 2008 at the University of Rochester Medical Center were identified and reviewed, and 25 blocks of tissue microassays were constructed. The association between expression of FRA and clinicopathologic features; expression of estrogen receptor (ER), progesterone receptor (PR), HER2/neu, and Ki-67; and clinical outcome of these tumors were evaluated.

RESULTS

The expression of FRA was significantly associated with tumors with high histologic grade, higher nodal stages, ER/PR negativity, and high proliferative activity (Ki-67 ≥ 15%), and was independent of HER2/neu overexpression. In all, 74% of ER/PR-negative and 80% of triple-negative breast cancers expressed FRA. The expression of FRA was significantly associated with a worse disease-free survival.

CONCLUSIONS

Our data demonstrate that a significant subgroup of ER/PR-negative and triple-negative breast cancers express FRA, and its expression is associated with worse clinical outcome.

The antitumor activity of the human FOLR1-specific monoclonal antibody, farletuzumab, in an ovarian cancer mouse model is mediated by antibody-dependent cellular cytotoxicity

Because of its high mortality rate, ovarian cancer is a leading cause of death among women and a highly unmet medical need. New therapeutic agents that are effective and well tolerated are needed and cancer antigen-specific monoclonal antibodies that have direct pharmacologic effects or can stimulate immunological responses represent a promising class of agents for the treatment of this disease. The human folate receptor α (FOLR1), which is overexpressed in ovarian cancer but largely absent in normal tissues, appears to play a role in the transformed phenotype in ovarian cancer, cisplatin sensitivity, and growth in depleted folate conditions and therefore has potential as a target for passive immunotherapy. The anti-FOLR1 monoclonal antibody MORAb-003 (farletuzumab) was previously shown to elicit antibody dependent cellular cytotoxicity (ADCC) and inhibit tumor growth of human tumor xenografts in nude mice. Because of its promising preclinical profile, farletuzumab has been evaluated in clinical trials as a potential therapeutic agent for ovarian cancer. In this report, we demonstrated that farletuzumab's antitumor effect against an experimental model of ovarian cancer is mediated by its ADCC activity.

Folate and folate receptor alpha antagonists mechanism of action in ovarian cancer

OBJECTIVE

The goal of this report is to review the activity of promising antifolate and folate receptor agents being developed for ovarian cancer including thymidylate synthase inhibitors, antifolate receptor antibodies, and folate-chemotherapy conjugates.

METHODS

A literature search was performed over the last 5 years using the terms "folate receptor" and "ovarian cancer" and those that specifically addressed the MOA were included. Abstracts presented within the last 3 years were also searched and included in this review where appropriate.

RESULTS

Thymidylate synthase inhibitors are a promising avenue for ovarian cancer treatment. Phase II trials have shown pemetrexed to have activity in patients with platinum resistant ovarian cancer. Several other thymidylate synthase inhibitors are in the early phase of development including BGC 945 and ZD-9331. Monoclonal antibodies that target the folate receptor have also shown potential in the development of ovarian cancer therapies. Farletuzumab is one of these antibodies. A recent phase III trial found that farletuzumab in combination with carboplatin and taxane did not meet the study's primary endpoint of progression-free survival (PFS). The post hoc exploratory analysis showed, however, a trend toward improved PFS in some patient subsets and further analysis is ongoing. The folate receptor is also utilized through folate conjugates. Vintafolide is one such agent which is currently in phase III development. Encouraging data from phase II trials showed an improvement in PFS from 2.7 months to 5 months. Folate can also be conjugated to radioisotopes for both therapeutic and imaging purposes, and early studies have shown correlation with amount of disease to therapy response.

CONCLUSION

Folate targeted agents continue to show promising antitumor activity in ovarian malignancy and initial clinical experience has demonstrated favorable toxicity profiles. Further development and resources targeted toward these therapies appear to be warranted.

Early detection biomarkers for ovarian cancer

Despite the widespread use of conventional and contemporary methods to detect ovarian cancer development, ovarian cancer remains a common and commonly fatal gynecological malignancy. The identification and validation of early detection biomarkers highly specific to ovarian cancer, which would permit development of minimally invasive screening methods for detecting early onset of the disease, are urgently needed. Current practices for early detection of ovarian cancer include transvaginal ultrasonography, biomarker analysis, or a combination of both. In this paper we review recent research on novel and robust biomarkers for early detection of ovarian cancer and provide specific details on their contributions to tumorigenesis. Promising biomarkers for early detection of ovarian cancer include KLK6/7, GSTT1, PRSS8, FOLR1, ALDH1, and miRNAs.

Characterization of the human folate receptor alpha via novel antibody-based probes

Folate receptor alpha (FRA) is a cell surface protein whose aberrant expression in malignant cells has resulted in its pursuit as a therapeutic target and marker for diagnosis of cancer. The development of immune-based reagents that can reproducibly detect FRA from patient tissue processed by varying methods has been difficult due to the complex post-translational structure of the protein whereby most reagents developed to date are highly structure-sensitive and have resulted in equivocal expression results across independent studies. The aim of the present study was to generate novel monoclonal antibodies (mAbs) using modified full length FRA protein as immunogen in order to develop a panel of mAbs to various, non-overlapping epitopes that may serve as diagnostic reagents able to robustly detect FRA-positive disease. Here we report the development of a panel of FRA-specific mAbs that are able to specifically detect FRA using an array of diagnostic platforms and methods. In addition, the methods used to develop these mAbs and their diverse binding properties provide additional information on the three dimensional structure of FRA in its native cell surface configuration.

Serous ovarian carcinoma patients with high alpha-folate receptor had reducing survival and cytotoxic chemo-response

The alpha-folate receptor (α-FR) is highly-expressed in various non-mucinous tumors of epithelial origin, including ovarian carcinoma. The aim of this study was to investigate the relationship between alpha-folate receptor (α-FR) and the clinico-pathologic features and outcomes of serous ovarian carcinoma patients and the possible mechanism of α-FR to chemo-resistance. Therefore, semi-quantitative reverse-transcription polymerase chain reactions for α-FR expression were performed in the 91 specimens of serous ovarian carcinomas. The expression of α-FR in each ovarian cancer tissue specimen was defined as the ratio of density of α-FR to density of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In vitro apoptotic experiments were tested in the original OVCAR-3 tumor cells and various OVCAR-3 α-FR-transfectants. Patients with an increased α-FR expression level had poorer responses to chemotherapy (per α-FR expression level increase: odds ratio (OR): 8.97 (95% confidence interval (CI): 1.40-57.36), p = 0.021). An increased α-FR expression level was an independently poor prognostic factor for disease free interval (DFI) (per α-FR expression level increase: hazard ratio (HR): 2.45 (95% CI: 1.16-5.18), p = 0.02) and had a negative impact on overall survival (OS) of these serous ovarian cancer patients (per α-FR expression level increase: HR: 3.6 (95% CI: 0.93-13.29), p = 0.03) by multivariate analyses. α-FR inhibited cytotoxic drug-induced apoptosis in our in vitro apoptotic assays. α-FR could induce chemo-resistance via regulating the expression of apoptosis-related molecules, Bcl-2 and Bax. Therefore, α-FR can be a potential biomarker for the prediction of chemotherapeutic responses and clinical prognosis. It also could be the target of ovarian cancer treatment.

Serous ovarian carcinoma patients with high alpha-folate receptor had reducing survival and cytotoxic chemo-response

The alpha-folate receptor (α-FR) is highly-expressed in various non-mucinous tumors of epithelial origin, including ovarian carcinoma. The aim of this study was to investigate the relationship between alpha-folate receptor (α-FR) and the clinico-pathologic features and outcomes of serous ovarian carcinoma patients and the possible mechanism of α-FR to chemo-resistance. Therefore, semi-quantitative reverse-transcription polymerase chain reactions for α-FR expression were performed in the 91 specimens of serous ovarian carcinomas. The expression of α-FR in each ovarian cancer tissue specimen was defined as the ratio of density of α-FR to density of glyceraldehyde-3-phosphate dehydrogenase (GAPDH). In vitro apoptotic experiments were tested in the original OVCAR-3 tumor cells and various OVCAR-3 α-FR-transfectants. Patients with an increased α-FR expression level had poorer responses to chemotherapy (per α-FR expression level increase: odds ratio (OR): 8.97 (95% confidence interval (CI): 1.40-57.36), p = 0.021). An increased α-FR expression level was an independently poor prognostic factor for disease free interval (DFI) (per α-FR expression level increase: hazard ratio (HR): 2.45 (95% CI: 1.16-5.18), p = 0.02) and had a negative impact on overall survival (OS) of these serous ovarian cancer patients (per α-FR expression level increase: HR: 3.6 (95% CI: 0.93-13.29), p = 0.03) by multivariate analyses. α-FR inhibited cytotoxic drug-induced apoptosis in our in vitro apoptotic assays. α-FR could induce chemo-resistance via regulating the expression of apoptosis-related molecules, Bcl-2 and Bax. Therefore, α-FR can be a potential biomarker for the prediction of chemotherapeutic responses and clinical prognosis. It also could be the target of ovarian cancer treatment.

Maternal intake of folic acid and neural crest stem cells

Maternal folic acid (FA) intake has beneficial effects in preventing neural tube defects and may also play a role in the prevention of adult onset diseases such as Alzheimer's disease, dementia, neuropsychiatric disorders, cardiovascular diseases, and cerebral ischemia. This review will focus on the effects of maternal FA intake on neural crest stem cell proliferation and differentiation. Although FA is generally considered beneficial, it has the potential of promoting cell proliferation at the expense of differentiation. In some situations, this may lead to miscarriage or postnatal developmental abnormalities. Therefore, a blind approach such as "FA for everyone" is not necessarily the best course of action. Ultimately, the best approach for FA supplementation, and potentially other nutritional supplements, will include customized patient genomic profiles for determining dose and duration.

Farletuzumab, a humanized monoclonal antibody against folate receptor alpha, in epithelial ovarian cancer: a phase I study

PURPOSE

Folate receptor α expression is highly restricted in normal adult tissues but upregulated in a wide range of human cancer types, including epithelial ovarian cancer. Farletuzumab, a humanized monoclonal antibody against folate receptor α, has shown antitumor activity and favorable toxicity in preclinical evaluation. This phase I, dose-escalation study was conducted to determine the safety of weekly i.v. farletuzumab and establish the maximum tolerated dose (MTD).

EXPERIMENTAL DESIGN

Patients with platinum-refractory or platinum-resistant epithelial ovarian cancer received farletuzumab (12.5-400 mg/m(2)) on days 1, 8, 15, and 22 of a 5-week cycle. Intrapatient dose escalation was not permitted. Dose-limiting toxicity (DLT) was defined by treatment-related adverse event of grade 3 or higher, and the MTD was the highest dose at which one or none of six patients experienced a DLT. Disease progression was recorded using Response Evaluation Criteria in Solid Tumors criteria and serum CA-125.

RESULTS

Twenty-five heavily pretreated patients were included in the safety, efficacy, and pharmacokinetic analyses. No DLTs or MTDs were encountered, and dose escalation was continued to farletuzumab 400 mg/m(2). C(max) and AUC(0-24) (area under the serum concentration-time curve) increased in an approximately dose-proportional manner, and a nuclear imaging substudy confirmed tumor targeting. There were no objective responses. Stable disease by Response Evaluation Criteria in Solid Tumors was observed in nine (36%) patients and CA-125 reduction in four. Three patients received continued therapy and completed a total of up to three cycles.

CONCLUSIONS

In this phase I study, farletuzumab administered as an i.v. infusion at doses of 12.5 to 400 mg/m(2) was generally safe and well tolerated in the management of heavily pretreated patients with epithelial ovarian cancer.

Novel folate binding protein-1 interactions in embryonic orofacial tissue

AIM

To identify proteins with which FolBp1 may interact within lipid rafts in tissue derived from embryonic orofacial tissue.

METHODS

A yeast two-hybrid screen of a cDNA library, derived from orofacial tissue from gestational day 11 to 13 mouse embryos, was conducted.

KEY FINDINGS

Using the full-length FolBp1 protein as bait, two proteins that bind FolBp1 were identified, Bat2d, and a fibronectin type III-containing domain protein. Results were confirmed by glutathione S-transferase pull-down assays.

SIGNIFICANCE

As a component of membrane lipid raft protein complexes, these binding proteins may represent "helper" or chaperone proteins that associate with FolBp1 in order to facilitate the transport of folate across the plasma membrane. The protein-protein interactions detected, while limited in number, may be critical in mediating the role of FolBp1 in folate transport, particularly in the developing embryo.

Maternal fumonisin exposure as a risk factor for neural tube defects

Fumonisins are mycotoxins produced by the fungus F. verticillioides, a common contaminant of maize (corn) worldwide. Maternal consumption of fumonisin B(1)-contaminated maize during early pregnancy has recently been associated with increased risk for neural tube defects (NTDs) in human populations that rely heavily on maize as a dietary staple. Experimental administration of purified fumonisin to mice early in gestation also results in an increased incidence of NTDs in exposed offspring. Fumonisin inhibits the enzyme ceramide synthase in de novo sphingolipid biosynthesis, resulting in an elevation of free sphingoid bases and depletion of downstream glycosphingolipids. Increased sphingoid base metabolites (i.e., sphinganine-1-phosphate) may perturb signaling cascades involved in embryonic morphogenesis by functioning as ligands for sphingosine-1-P (S1P) receptors, a family of G-protein-coupled receptors that regulate key biological processes such as cell survival/proliferation, differentiation and migration. Fumonisin-induced depletion of glycosphingolipids impairs expression and function of the GPI-anchored folate receptor (Folr1), which may also contribute to adverse pregnancy outcomes. NTDs appear to be multifactorial in origin, involving complex gene-nutrient-environment interactions. Vitamin supplements containing folic acid have been shown to reduce the occurrence of NTDs, and may help protect the developing fetus from environmental teratogens. Fumonisins appear to be an environmental risk factor for birth defects, although other aspects of maternal nutrition and genetics play interactive roles in determining pregnancy outcome. Minimizing exposures to mycotoxins through enhanced agricultural practices, identifying biomarkers of exposure, characterizing mechanisms of toxicity, and improving maternal nutrition are all important strategies for reducing the NTD burden in susceptible human populations.

Folate receptor expression in pituitary adenomas cellular and molecular analysis

Clinically nonfunctional pituitary adenomas cause hypopituitarism or compression of regional structures. Unlike functional tumors, there is no available medical treatment or specific imaging technique for these tumors. We have recently discovered that both folate receptor (FR)alpha mRNA and protein are uniquely overexpressed in nonfunctional pituitary tumors, but not in functional adenomas. We hypothesized that FRalpha may hold significant promise for medical treatment by enabling novel molecular imaging and targeted therapy. Here, we used murine pituitary tumor cell line alphaT3-1 as a model to investigate the biological significance of FRalpha and its mutant FR67. We demonstrate that overexpression of FR facilitated tumor cell growth and anchorage-independent growth in soft agar. More colonies were observed in FR overexpressing cells than in mutant FR67 clones in soft agar. Cell proliferation rate was increased, the percentage of cells in S-phase was increased, and high PCNA staining was detected in cells overexpressing the receptor. In alphaT3-1 cells transfected with mutant FR67, cell proliferation rate was reduced, the percentage of cells residing in S-phase was slightly decreased, and low PCNA staining was observed. By real-time quantitative PCR, the genes involved in NOTCH3 pathway including NOTCH3, HES-1, and TLE2 were altered; the mRNA expression of FGFR1 was upregulated, and ERbeta mRNA was downregulated in FR overexpressing cells. Our findings suggest that FRalpha plays a role in pituitary tumor formation, and this effect may in part be due to its regulation of the NOTCH3 pathway.

GPI-anchored receptor clusters transiently recruit Lyn and G alpha for temporary cluster immobilization and Lyn activation: single-molecule tracking study 1

The signaling mechanisms for glycosylphosphatidylinositol-anchored receptors (GPI-ARs) have been investigated by tracking single molecules in living cells. Upon the engagement or colloidal gold–induced cross-linking of CD59 (and other GPI-ARs) at physiological levels, CD59 clusters containing three to nine CD59 molecules were formed, and single molecules of Gαi2 or Lyn (GFP conjugates) exhibited the frequent but transient (133 and 200 ms, respectively) recruitment to CD59 clusters, via both protein–protein and lipid–lipid (raft) interactions. Each CD59 cluster undergoes alternating periods of actin-dependent temporary immobilization (0.57-s lifetime; stimulation-induced temporary arrest of lateral diffusion [STALL], inducing IP₃ production) and slow diffusion (1.2 s). STALL of a CD59 cluster was induced right after the recruitment of Gαi2. Because both Gαi2 and Lyn are required for the STALL, and because Lyn is constitutively recruited to CD59 clusters, the STALL of CD59 clusters is likely induced by the Gαi2 binding to, and its subsequent activation of, Lyn within the same CD59 cluster.

Dynamic recruitment of phospholipase C gamma at transiently immobilized GPI-anchored receptor clusters induces IP3-Ca2+ signaling: single-molecule tracking study 2

Clusters of CD59, a glycosylphosphatidylinositol-anchored receptor (GPI-AR), with physiological sizes of approximately six CD59 molecules, recruit Gαi2 and Lyn via protein–protein and raft interactions. Lyn is activated probably by the Gαi2 binding in the same CD59 cluster, inducing the CD59 cluster's binding to F-actin, resulting in its immobilization, termed stimulation-induced temporary arrest of lateral diffusion (STALL; with a 0.57-s lifetime, occurring approximately every 2 s). Simultaneous single-molecule tracking of GFP-PLCγ2 and CD59 clusters revealed that PLCγ2 molecules are transiently (median = 0.25 s) recruited from the cytoplasm exclusively at the CD59 clusters undergoing STALL, producing the IP₃–Ca²⁺ signal. Therefore, we propose that the CD59 cluster in STALL may be a key, albeit transient, platform for transducing the extracellular GPI-AR signal to the intracellular IP₃–Ca²⁺ signal, via PLCγ2 recruitment. The prolonged, analogue, bulk IP₃–Ca²⁺ signal, which lasts for more than several minutes, is likely generated by the sum of the short-lived, digital-like IP₃ bursts, each created by the transient recruitment of PLCγ2 molecules to STALLed CD59.

Binding of nuclear caveolin-1 to promoter elements of growth-associated genes in ovarian carcinoma cells

Caveolin-1 (cav-1), a member of a protein family associated mainly with cell membrane microdomains in many cell types, acts as a tumor suppressor in ovarian carcinoma cells. Biochemical analyses demonstrated that cav-1 was also localized in the nuclei of ovarian carcinoma cells, endogenously (SKOV3) or ectopically (IGtC3) expressing cav-1. By confocal analyses, the same cell lines as well as IGROV1 and SKOV3 cells transiently transfected with green fluorescent protein-cav-1 fusion protein showed nuclear punctate speckled pattern. Subnuclear distribution analysis revealed cav-1 mainly associated with the nuclear matrix, but also slightly with chromatin. Cav-1 was found in nuclear high-molecular weight complexes and by confocal analysis was found to co-localized with the inner nuclear membrane protein emerin. Cyclin D1 and folate receptor promoters were modulated by cav-1 in SKOV3 cells as demonstrated by transient transfection with or silencing of cav-1. Chromatin immunoprecipitation and supershift assays indicated that nuclear cav-1 can bind in vitro and in vivo to promoter sequences of both cyclin D1 and folate receptor genes. These data suggest that in ovarian carcinoma cells cav-1, localized in transcriptionally inactive chromatin, exerts a functional activity mediated, at least in part, by directly binding to sequences of genes involved in proliferation.

Cardiovascular abnormalities inFolr1 knockout mice and folate rescue

BACKGROUND

Periconceptional folic acid supplementation is widely believed to aid in the prevention of neural tube defects (NTDs), orofacial clefts, and congenital heart defects. Folate-binding proteins or receptors serve to bind folic acid and 5-methyltetrahydrofolate, representing one of the two major mechanisms of cellular folate uptake.

METHODS

We herein describe abnormal cardiovascular development in mouse fetuses lacking a functional folate-binding protein gene (Folr1). We also performed a dose-response study with folinic acid and determined the impact of maternal folate supplementation on Folr1 nullizygous cardiac development.

RESULTS

Partially rescued preterm Folr1(-/-) (formerly referred to as Folbp1) fetuses were found to have outflow tract defects, aortic arch artery abnormalities, and isolated dextracardia. Maternal supplementation with folinic acid rescued the embryonic lethality and the observed cardiovascular phenotypes in a dose-dependant manner. Maternal genotype exhibited significant impact on the rescue efficiency, suggesting an important role of in utero folate status in embryonic development. Abnormal heart looping was observed during early development of Folr1(-/-) embryos partially rescued by maternal folinic acid supplementation. Migration pattern of cardiac neural crest cells, genetic signals in pharyngeal arches, and the secondary heart field were also found to be affected in the mutant embryos.

CONCLUSIONS

Our observations suggest that the beneficial effect of folic acid for congenital heart defects might be mediated via its impact on neural crest cells and by gene regulation of signaling pathways involved in the development of the pharyngeal arches and the secondary heart field.

The role of folate receptor alpha in cancer development, progression and treatment: cause, consequence or innocent bystander?

Folate receptor alpha (FRalpha) is a membrane-bound protein with high affinity for binding and transporting physiologic levels of folate into cells. Folate is a basic component of cell metabolism and DNA synthesis and repair, and rapidly dividing cancer cells have an increased requirement for folate to maintain DNA synthesis, an observation supported by the widespread use of antifolates in cancer chemotherapy. FRalpha levels are high in specific malignant tumors of epithelial origin compared to normal cells, and are positively associated with tumor stage and grade, raising questions of its role in tumor etiology and progression. It has been suggested that FRalpha might confer a growth advantage to the tumor by modulating folate uptake from serum or by generating regulatory signals. Indeed, cell culture studies show that expression of the FRalpha gene, FOLR1, is regulated by extracellular folate depletion, increased homocysteine accumulation, steroid hormone concentrations, interaction with specific transcription factors and cytosolic proteins, and possibly genetic mutations. Whether FRalpha in tumors decreases in vivo among individuals who are folate sufficient, or whether the tumor's machinery sustains FRalpha levels to meet the increased folate demands of the tumor, has not been studied. Consequently, the significance of carrying a FRalpha-positive tumor in the era of folic acid fortification and widespread vitamin supplement use in countries such as Canada and the United States is unknown. Epidemiologic and clinical studies using human tumor specimens are lacking and increasingly needed to understand the role of environmental and genetic influences on FOLR1 expression in tumor etiology and progression. This review summarizes the literature on the complex nature of FOLR1 gene regulation and expression, and suggests future research directions.

Complement Activated by Chimeric Anti–Folate Receptor Antibodies Is an Efficient Effector System to Control Ovarian Carcinoma

Two chimeric monoclonal antibodies (mAb), cMOV18 and cMOV19, recognizing distinct epitopes of folate receptor highly expressed on epithelial ovarian cancer (EOC) cells were analyzed for their ability to activate complement (C) as a means to enhance their antitumor activity. The individual cMOVs failed to activate C on six EOC cell lines as documented by the marginal deposition of C components and the negligible C-dependent cytotoxicity (CDC). Conversely, the mixture of cMOVs was more effective, although the percentage of cell killing did not exceed 25%. Fluorescence-activated cell sorting analysis of EOC cells for surface expression of the membrane C regulatory proteins (mCRP) revealed high levels of CD46, variable expression of CD59, and absence of CD55. This finding was confirmed in tumor tissue specimens obtained from advanced-stage EOC patients and analyzed for the expression of mCRPs mRNA using a cDNA microarray and for the presence of proteins by immunohistochemistry. Incubation of EOC cells with neutralizing mAbs to CD46 and CD59 led to a significant increase in the CDC from 10%-20% to 45%-50%. The relative contribution of antibody-dependent cell cytoxicity (ADCC) and C-dependent killing of two EOC cell lines induced by the mixture of cMOV18 and cMOV19 was about 15% and 25%-35%, respectively, bringing the total killing to about 40%-50%. This value increased to 60%-70% after neutralization of CD46 and CD59 without an appreciable change of ADCC. These results suggest that C is the major contributor to the killing of EOC cells induced by the mixture of cMOV18 and cMOV19.

90Y Labeling of monoclonal antibody MOv18 and preclinical validation for radioimmunotherapy of human ovarian carcinomas

The monoclonal antibody (mAb) MOv18 binds the membrane alpha isoform of the folate receptor (FR) which is overexpressed in human ovarian carcinoma cells. Exploiting the targeting capacity of this mAb, we developed and preclinically validated a protocol for the stable labeling of the mAb with 90Y, an isotope which has shown promise in cancer radioimmunotherapy. MOv18 was derivatized with the stable macrocyclic ligand p-isothiocyanatobenzyl-1,4,7,10-tetraazacyclododecane-1,4,7,10- tetraacetic acid (Bz-DOTA). MOv18-Bz-DOTA conjugates were labeled with 90Y or 111In under metal-free and good laboratory practice conditions. At the optimal Bz-DOTA/mAb derivatization ratio of 4-5, conjugates maintained binding activity up to 6 months, were efficiently labeled with 90Y or 111In (mean labeling yield 85 and 64%, associated to a final mean specific activity of 74 and 37 MBq/mg) and displayed a mean immunoreactivity of 60 and 58%, respectively. The radiolabeled preparations were stable in human serum, with >97% radioactivity associated to mAb at 48 h after labeling. The ability of 90Y- and 111In-MOv18 to localize FR on tumors in vivo was analyzed in nude mice bearing tumors induced by isogenic cell lines differing only in the presence or absence of the relevant antigen [A431FR (FR-positive) and A431tMock (FR-negative)]. In vivo biodistribution in organs other than tumor was comparable in non-tumor-, A431tMock- and A431FR-bearing mice, whereas the median tumor uptake of the radiolabeled reagents, expressed as area under the curve (AUC) and maximum uptake (Umax), was significantly higher (sixfold to sevenfold) in A431FR than in A431tMock tumors (P=0.0465 and P=0.0332, respectively). Mean maximum uptake (% ID/g) for 90Y-MOv18 was 53.7 and 7.4 in A431FR and A431tMock respectively; corresponding values for 111In-Mov18 were 45.0 and 11.3. These data demonstrate the feasibility of 90Y-labeling of MOv18 without compromising antibody binding ability and the immunoreagent-specific localization in vivo on FR-expressing tumors, suggesting the suitability of 90Y-MOv18 for clinical studies.

Multivitamin and alcohol intake and folate receptor alpha expression in ovarian cancer

Folate receptor alpha (FRalpha) expression in epithelial ovarian cancer may be related to folate intake. We examined this association using multivitamin intake, a proxy for folic acid, and assessed whether the relation was modified by alcohol intake, a folate agonist. Cases (n = 148) with suspected epithelial ovarian cancer, of ages > or = 20 years, were seen at Mayo Clinic, Minnesota, between 2000 and 2004; those with tumor specimens (n = 108) were included in analyses. Outpatient controls (n = 148) without cancer and with at least one ovary intact were matched to cases by age (within 5 years) and state of residence. Multivitamin (> or = 4 pills/wk) and weekly alcohol (> or = 5 drinks) intakes were assessed. Tumor specimens were analyzed immunohistochemically for FRalpha. Multivariable rate ratios (RR) and 95% confidence intervals (CI) were estimated using unconditional logistic regression. In case-control analysis, the RRs of multivitamin intake with absent/weak/moderate and strong-expressing FRalpha tumors were 0.30 (95% CI, 0.12-0.70) and 0.47 (95% CI, 0.24-0.91), respectively. For alcohol, the associations were 0.84 (95% CI, 0.24-2.86) and 1.65 (95% CI, 0.69-3.93), respectively. In case-case analysis, the RR associated with developing strong-expressing versus other FRalpha tumors was 3.13 (95% CI, 1.14-8.65) for multivitamins and 1.58 (95% CI, 0.45-5.60) for alcohol. The data did not support evidence for an interaction between multivitamin and alcohol intake with risk of developing a strong-expressing FRalpha tumor. The association of multivitamin intake with ovarian cancer may depend on FRalpha expression level.

Simultaneous expression of caveolin-1 and E-cadherin in ovarian carcinoma cells stabilizes adherens junctions through inhibition of src-related kinases

Cadherin-mediated adhesion plays an important role in maintaining cell-cell contacts and reducing tumor metastasis. However, neo-expression of E-cadherin in ovarian carcinoma does not prevent the release and spread of cells from the primary tumor. Because caveolin-1 is down-regulated concomitantly with E-cad expression, we investigated whether the stability of adherens junctions in ovarian carcinoma was affected by caveolin-1 expression. We used IGROV1 cells transfected with caveolin-1 (IGtC3), mock-transfected control cells (IGtM87), and SKOV3 cells that endogenously express caveolin-1. Simultaneous expression of caveolin-1 and E-cadherin favored membrane distribution of E-cadherin and its associated catenin (p120ctn), even when caveolin-1 was only focally associated with adherens junctions. Silencing of caveolin-1 induced intracellular E-cadherin redistribution in IGtC3 and SKOV3 cells. Treatment with the specific src kinase inhibitor PP1 increased E-cadherin expression in IGtM87 and SKOV3 cells and enhanced membrane localization of both E-cadherin and p120ctn. However, PP1 could not completely reverse the detrimental effects on cell-cell adhesion induced by Ca2+ depletion in IGtM87 cells. Together, our data suggest that caveolin-1 expression indirectly promotes cell-cell adhesion in ovarian carcinoma cells by a mechanism involving inhibition of src-related kinases. Thus, down-regulation or loss of caveolin-1 might contribute significantly to the spread of tumor cells from the primary tumor.

Maternal fumonisin exposure and risk for neural tube defects: mechanisms in an in vivo mouse model

BACKGROUND

Fumonisin B1 (FB1) is a mycotoxin produced by the fungus Fusarium verticillioides, a common contaminant of corn worldwide. FB1 disrupts sphingolipid biosynthesis by inhibiting the enzyme ceramide synthase, resulting in an elevation of free sphingoid bases and depletion of downstream glycosphingolipids. A relationship between maternal ingestion of FB1-contaminated corn during early pregnancy and increased risk for neural tube defects (NTDs) has recently been proposed in human populations around the world where corn is a dietary staple. The current studies provide an in vivo mouse model of FB1 teratogenicity.

METHODS

Pregnant LM/Bc mice were injected with increasing doses of FB1 on GD 7.5 and 8.5, and exposed fetuses were examined for malformations. Sphingolipid profiles and (3)H-folate concentrations were measured in maternal and fetal tissues. Immunohistochemical expression of the GPI-anchored folate receptor (Folbp1) and its association with the lipid raft component, ganglioside GM1, were characterized. Rescue experiments were performed with maternal folate supplementation or administration of gangliosides.

RESULTS

Maternal FB1 administration (20 mg/kg of body weight) during early gestation resulted in 79% NTDs in exposed fetuses. Sphingolipid profiles were significantly altered in maternal and embryonic tissues following exposure, and (3)H-folate levels and immunohistochemical expression of Folbp1 were reduced. Maternal folate supplementation partially rescued the NTD phenotype, whereas GM1 significantly restored folate concentrations and afforded almost complete protection against FB1-induced NTDs.

CONCLUSIONS

Maternal FB1 exposure altered sphingolipid metabolism and folate concentrations in LM/Bc mice, resulting in a dose-dependent increase in NTDs that could be prevented when adequate folate levels were maintained.

Effects of dietary folate intake and folate binding protein-2 (Folbp2) on urinary speciation of sodium arsenate in mice

Folate binding protein-2 (Folbp2(-/-)) knockout mice have been previously shown to be highly susceptible to the teratogenic effects of arsenic. Arsenic biotransformation is achieved primarily by biomethylation. Given the potential close relationship between folate biochemistry and arsenic biotransformation, the aims of our study were to: (1) test whether Folbp2(-/-) mice have altered arsenic biotransformation which would suggest a potential mechanism for their enhanced susceptibility; (2) examine whether dietary folate deficiency alters arsenic biotransformation. Folbp2(-/-) mice were found to have slightly lower plasma folate levels than wildtype mice. No genotype-specific effects were observed in arsenic speciation thereby negating altered biotransformation of arsenic as the mechanism of the enhanced teratogenicity seen in Folbp2(-/-) mice. Reduction in excretion of organic arsenicals was observed during folate deficiency, suggesting an important role for folic acid homeostasis in arsenic biotransformation.

Antisense oligonucleotides targeted to the human α folate receptor inhibit breast cancer cell growth and sensitize the cells to doxorubicin treatment

Folates are essential for cell survival and are required for numerous biochemical processes. The human α isoform folate receptor (αhFR) has a very high affinity for folic acid and is considered an essential component in the cellular accumulation of folates and folate analogues used in chemotherapy. The expression of αhFR is not detected inmost normal tissues. In contrast, high levels of the expression of αhFR have been reported in a variety of cancer cells. The significance of αhFR overexpression in malignant tissues has not been elucidated, but it is possible that it promotes cell proliferation not only by mediating folate uptake but also by generating other regulatory signals. The purpose of the present study was to evaluate αhFR as a potential target for the treatment of breast cancer. Initial studies were done in nasopharyngeal carcinoma (KB) cells, which express high levels of αhFR. In KB cells, antisense oligodeoxyribonucleotides (ODN) complementary to the αhFR gene sequences were found to reduce newly synthesized αhFR protein up to 60%. To examine the effect of αhFR antisense ODNs in a panel of cultured human breast cancer cell lines, we used a tumor cell–targeted, transferrin-liposome–mediated delivery system. The data show that αhFR antisense ODNs induced a dose-dependent decrease in cell survival. Finally, we determined that αhFR antisense ODNs sensitized MDA-MB-435 breast cancer cells by 5-fold to treatment with doxorubicin. The data support the application of αhFR antisense ODNs as a potential anticancer agent in combination with doxorubicin.

Secreted and Placental Membrane Forms of Folate-Binding Protein Occur Sequentially During Pregnancy in Swine1

The objective was to understand how two forms of folate-binding protein interact to accomplish folate transport during pregnancy in swine. Specific folate binding was measured in uterine flushings during the estrous cycle and early pregnancy and in allantoic fluid (secreted form) and placental membranes (membrane form) throughout later pregnancy. In addition, the localization of the secreted form of folate-binding protein (sFBP) in uterine wall sections was assessed. Uterine flushings were collected on Days 10, 13, and 15 of the estrous cycle and pregnancy. Allantoic fluid and placentas were collected on Days 20, 35, 50, 70, 90, and 105 of pregnancy. Uterine-wall sections were collected on all days of the experiment. Folate binding was measured by incubation of aliquots of uterine flushings, allantoic fluid, or placental microsomal membranes with 0.5-4 nM [(3)H]folate. Uterine-wall sections were incubated with purified anti-FBP IgG or normal rabbit serum IgG to localize sFBP. Folate binding did not differ between early pregnancy and the estrous cycle in uterine flushings, was greatest from Day 50 to 70 of pregnancy in allantoic fluid, and was greatest from Day 50 of pregnancy onward in placental microsomal membranes. Staining for sFBP was present in the endometrial glands from Day 10 to 15 in cyclic gilts and from Day 10 to 20 in pregnant gilts. The pattern of folate binding and sFBP staining supports the concept that sFBP transports folate to the developing conceptus until placentation and then the placental form takes over folate transport.

Valproate-induced neural tube defects in folate-binding protein-2 (Folbp2) knockout mice

BACKGROUND

Folate is an important B vitamin that is transported into cells by way of folate-binding proteins and transporters. Folate-binding protein-2 nullizygous (Folbp2(-/-)) mice develop normally; however, we have found them to be more susceptible to the teratogenic effects of arsenate exposure than wild-type control mice.

METHODS

In the current study, we wanted to extend our findings and test the hypothesis that Folbp2(-/-) mice are more susceptible to the teratogenic effects of valproic acid (VPA), a commonly used antiepileptic drug that is known to induce neural tube defects (NTDs) in both humans and laboratory animals.

RESULTS

Folbp2(-/-) mice had higher VPA-induced frequencies of embryonic lethality and exencephaly than did the wild-type control mice during folate supplementation and a control diet, respectively. All other differences in response between the two genotypes were short of reaching statistical significance. Folate supplementation of wild-type, but not Folbp2(-/-) dams reduced embryonic lethality of VPA-treated wild-type embryos compared to the folate-deficient diet.

CONCLUSIONS

Unlike our previous findings with arsenate, enhanced susceptibility of Folbp2(-/-) mice to in utero VPA exposure was demonstrated in some dietary folate regimens. Thus, our data indicate a relatively frail relationship between Folbp2 and VPA-induced NTDs.

Spatial regulation of Galphai protein signaling in clathrin-coated membrane microdomains containing GAIP

Regulators of G-protein signaling (RGS) proteins are GTPase-activating proteins (GAPs) that bind to Galpha subunits and attenuate G protein signaling, but where these events occur in the cell is not yet established. Here we investigated, by immunofluorescence labeling and deconvolution analysis, the site at which endogenous Galpha-interacting protein (GAIP) (RGS19) binds to Galphai3-YFP and its fate after activation of delta-opioid receptor (DOR). In the absence of agonist, GAIP is spatially segregated from Galphai3 and DOR in clathrin-coated domains (CCPs) of the cell membrane (PM), whereas Galphai3-YPF and DOR are located in non-clathrin-coated microdomains of the PM. Upon addition of agonist, Galphai3 partially colocalizes with GAIP in CCPs at the PM. When endocytosis is blocked by expression of a dynamin mutant [dyn(K44A)], there is a striking overlap in the distribution of DOR and Galphai3-YFP with GAIP in CCPs. Moreover, Galphai3-YFP and GAIP form a coprecipitable complex. Our results support a model whereby, after agonist addition, DOR and Galphai3 move together into CCPs where Galphai3 and GAIP meet and turn off G protein signaling. Subsequently, Galphai3 returns to non-clathrin-coated microdomains of the PM, GAIP remains stably associated with CCPs, and DOR is internalized via clathrin-coated vesicles. This constitutes a novel mechanism for regulation of Galpha signaling through spatial segregation of a GAP in clathrin-coated pits.

Reversion of transformed phenotype in ovarian cancer cells by intracellular expression of anti folate receptor antibodies

The alpha-folate receptor (FR) is selectively overexpressed in 90% of nonmucinous ovarian carcinomas, whereas no expression is detectable in normal ovarian surface epithelium (OSE). Indirect evidence suggests that FR expression is associated with tumor progression and affects cell proliferation. To evaluate better the role of FR, we developed an approach based on intracellular expression of single-chain (sc) antibodies (intrabody) to downmodulate membrane expression of FR in ovary cancer cells. IGROV-1 and SKOV3 ovarian carcinoma cell lines were transfected with an anti-FR intrabody. Transfectants and parental cells were tested for FR, integrins and anti-FR intrabody expression by fluorescence-activated cell sorting (FACS), reverse transcription and polymerase chain reaction (RT-PCR) and/or immunoblotting. Cell growth characteristics and adhesion properties were evaluated in liquid, semisolid and organotypic cultures. The anti-FR scFv inhibited FR expression from 60 to 99%. At physiological concentrations of folate, proliferation varied directly as a function of FR expression. FR downmodulation was accompanied by reduced colony-forming ability in soft agar, morphological change of the cells, significant enhanced adhesion to laminin or Matrigel, a two- to three-fold increase in alpha6beta4 integrin expression, and a marked reduction in laminin production. In three-dimensional organotypic cultures, anti-FR intrabody-transfected IGROV1 cells grew as a single-ordered layer, reminiscent of normal OSE growth in vivo. In conclusion, the anti-FR intrabody reverses the transformed phenotype in ovary cancer cells and may provide an efficient means to inhibit selectively the growth of these cells.

Neural and orofacial defects in Folp1 knockout mice [corrected]

BACKGROUND

Folic acid is essential for the development of the nervous system and other associated structures. Mice deficient in the folic acid-binding protein one (Folbp1) gene display multiple developmental abnormalities, including neural and craniofacial defects. To better understand potential interactions between Folbp1 gene and selected genes involved in neural and craniofacial morphogenesis, we evaluated the expression patterns of a panel of crucial differentiation markers (Pax-3, En-2, Hox-a1, Shh, Bmp-4, Wnt-1, and Pax-1).

METHODS

Folbp1 mice were supplemented with low dosages of folinic add to rescue nullizygotes from dying in utero before gestational day 10. The gene marker analyses were carried out by in situ hybridization.

RESULTS

In nullizygote embryos with open cranial neural tube defects, the downregulation of Pax-3 and En-2 in the impaired midbrain, along with an observed upregulation of the ventralizing marker Shh in the expanded floor plate, suggested an important regulatory interaction among these three genes. Moreover, the nullizygotes also exhibit craniofacial abnormalities, such as cleft lip and palate. Pax-3 signals in the impaired medial nasal primordia were significantly increased, whereas Pax-1 showed no expression in the undeveloped lateral nasal processes. Although Shh was downregulated, Bmp-4 was strongly expressed in the medial and lateral nasal processes, highlighting the antagonistic activities of these molecules.

CONCLUSIONS

Impairment of Folbp1 gene function adversely impacts the expression of several critical signaling molecules. Mis-expression of these molecules, perhaps mediated by Shh, may potentially contribute to the observed failure of neural tube closure and the development of craniofacial defects in the mutant mice.

Functional effect of point mutations in the alpha-folate receptor gene of CABA I ovarian carcinoma cells

The alpha-folate receptor (alpha FR) is overexpressed in 90% of nonmucinous ovarian carcinomas. In addition to the known role of alpha FR binding and mediating the internalization of folates, functional interaction of alpha FR with signaling molecules was recently shown. To identify a model to study the role of alpha FR in ovarian carcinoma, we characterized the alpha FR gene in the ovarian carcinoma cell line CABA I in comparison to a reference line, IGROV1. In CABA I cells, Northern blot analysis revealed an alpha FR transcript of the expected length and FACS analysis indicated receptor expression on the cell membrane; however, RNase protection assay revealed no specific signals. Southern blot and genomic PCR analysis suggested the presence of a rearrangement(s) involving the 5' region of the gene in CABA I cells as compared to IGROV1 cells. Cloning and sequencing of CABA I alpha FR cDNA revealed several point mutations. The partitioning of alpha FR in membrane microdomains from CABA I cells and its association with regulatory molecules was comparable to that of IGROV1 cells. By contrast, the alpha FR expressed on the CABA I cell membrane bound folic acid with lower affinity, and ectopic expression of the corresponding cDNA in CHO cells confirmed impaired folic acid binding. Thus, CABA I cells may provide a tool to delineate functional domains of the alpha FR.

Rantes activates Jak2 and Jak3 to regulate engagement of multiple signaling pathways in T cells

The chemokine RANTES (regulated on activation normal T cell expressed and secreted) and its cognate receptor CC chemokine receptor 5 (CCR5) have been implicated in regulating immune cell function. Previously we reported that in T cells, RANTES activation of CCR5 results in Stat1 and Stat3 phosphorylation-activation, leading to Stat1:1 and Stat1:3 dimers that exhibit DNA binding activity and the transcriptional induction of a Stat-inducible gene, c-fos. Given that RANTES and CCR5 have been implicated in T cell activation, we have studied RANTES-induced signaling events in a CCR5-expressing T cell line, PM1. RANTES treatment of PM1 T cells results in the rapid phosphorylation-activation of CCR5, Jak2, and Jak3. RANTES-inducible Jak phosphorylation is insensitive to pertussis toxin inhibition, indicating that RANTES-CCR5-mediated tyrosine phosphorylation events are not coupled directly to Galpha(i) protein-mediated events. In addition to Jaks, several other proteins are rapidly phosphorylated on tyrosine residues in a RANTES-dependent manner, including the Src kinase p56(lck), which associates with Jak3. Additionally our data confirm that the amino-terminally modified RANTES proteins, aminooxypentane-RANTES and Met-RANTES, are agonists for CCR5 and induce early tyrosine phosphorylation events that are indistinguishable from those inducible by RANTES with similar kinetics. Our data also demonstrate that RANTES activates the p38 mitogen-activated protein (MAP) kinase pathway. This is evidenced by the rapid RANTES-dependent phosphorylation and activation of p38 MAP kinase as well as the activation of the downstream effector of p38, MAP kinase-activated protein (MAPKAP) kinase-2. Pharmacological inhibition of RANTES-dependent p38 MAP kinase activation blocks MAPKAP kinase-2 activity. Thus, activation of Jak kinases and p38 MAP kinase by RANTES regulates the engagement of multiple signaling pathways.

Downmodulation of caveolin-1 expression in human ovarian carcinoma is directly related to alpha-folate receptor overexpression

Caveolin (cav-1) and the GPI-anchored alpha-folate receptor (alphaFR) are membrane proteins both found associated to caveolar structures. Several studies in tumor cells independently reported cav-1 downregulation and alphaFR overexpression. Here we analysed the expression of the two molecules in normal and tumor ovarian samples derived from fresh specimens and from cultured cell lines. Whereas normal ovary surface epithelial cells displayed only cav-1 expression, ovarian tumor surgical samples and cell lines (COR, IGROV1, OVCAR3 and OVCA432) displayed high alphaFR and low-level or no cav-1 expression, except those cell lines (SKOV3 and SW626) with the lower alphaFR expression. SKOV3, but not two alphaFR-negative non-ovarian cell lines, exhibited down-regulation of cav-1 expression following stable alphaFR cDNA transfection. Conversely, cav-1 transfection in IGROV1 cells led to downregulated alphaFR expression, together with formation of caveolar structures and reduction of growth capability. Moreover, cav-1 expression was induced in IGROV1 cells by transfection with intracellular anti-alphaFR antibodies to downmodulate alphaFR expression. In cav-1 transfected cells, transcriptional activity of the alphaFR-specific promoter P1 was reduced by 70% and an additional specific DNA-protein complex was identified by gel-shift assay, indicating that cav-1 expression influences alphaFR gene transcription. Together these results support the notion that alphaFR and cav-1 protein expression is reciprocally regulated in ovary cancer cells.