FOXM1 Participates in Trophoblast Migration and Early Trophoblast Invasion: Potential Role in Blastocyst Implantation.

Successful implantation requires coordinated migration and invasion of trophoblast cells into a receptive endometrium. Reduced forkhead box M1 (FOXM1) expression limits trophoblast migration and angiogenesis in choriocarcinoma cell lines, and in a rat model, placental FOXM1 protein expression was significantly upregulated in the early stages of pregnancy compared to term pregnancy. However, the precise role of FOXM1 in implantation events remains unknown. By analyzing mice blastocysts at embryonic day (E3.5), we have demonstrated that FOXM1 is expressed as early as the blastocyst stage, and it is expressed in the trophectoderm of the blastocyst. Since controlled oxygen tension is determinant for achieving normal implantation and placentation and a chronic hypoxic environment leads to shallow trophoblast invasion, we evaluated if FOXM1 expression changes in response to different oxygen tensions in the HTR-8/SVneo first trimester human trophoblast cell line and observed that FOXM1 expression was significantly higher when trophoblast cells were cultured at 3% O2, which coincides with oxygen concentrations in the uteroplacental interface at the time of implantation. Conversely, FOXM1 expression diminished in response to 1% O2 that resembles a hypoxic environment in utero. Migration and angiogenesis were assessed following FOXM1 knockdown and overexpression at 3% O2 and 1% O2, respectively, in HTR-8/SVneo cells. FOXM1 overexpression increased transmigration ability and tubule formation. Using a 3D trophoblast invasion model with trophospheres from HTR-8/SVneo cells cultured on a layer of MATRIGEL and of mesenchymal stem cells isolated from menstrual fluid, we observed that trophospheres obtained from 3D trophoblast invasion displayed higher FOXM1 expression compared with pre-invasion trophospheres. Moreover, we have also observed that FOXM1-overexpressing trophospheres increased trophoblast invasion compared with controls. HTR-8/SVneo-FOXM1-depleted cells led to a downregulation of PLK4, VEGF, and MMP2 mRNA expression. Our current findings suggest that FOXM1 participates in embryo implantation by contributing to trophoblast migration and early trophoblast invasion, by inducing transcription activation of genes involved in these processes. Maternal-fetal communication is crucial for trophoblast invasion, and maternal stromal cells may induce higher levels of FOXM1 in trophoblast cells.

Mesenchymal Stem Cells-Induced Trophoblast Invasion Is Reduced in Patients with a Previous History of Preeclampsia.

Endometrial stromal cells play an important role in reproductive success, especially in implantation and placentation. Although Mesenchymal stem cells (MSCs) have been studied to assess decidualization disorders in preeclampsia (PE), their role during trophoblast invasion remains unclear. This study aims to determine: (i) whether MSCs isolated from menstrual fluid (MenSCs) from nulliparous, multiparous, and women with a previous history of preeclampsia exhibited different patterns of proliferation and migration and (ii) whether reproductive history (i.e., prior pregnancy or prior history of PE) was able to produce changes in MenSCs, thus altering trophoblast invasion capacity. MenSCs were collected from nulliparous and multiparous women without a history of PE and from non-pregnant women with a history of PE. Proliferation and migration assays were performed on MenSCs with sulforhodamine B and transwell assays, respectively. Trophoblast invasion was analyzed by culturing HTR-8/SVneo trophospheres on a matrigel overlying MenSCs for 72 h at 5% O2, simulating a 3D implantation model. A previous history of pregnancy or PE did not impact the proliferative capacity or migratory behavior of MenSCs. Following exposure to physiological endometrial conditions, MenSCs demonstrated upregulated expression of IGFBP-1 and LIF mRNA, decidualization and window of implantation markers, respectively. The mRNA expression of VIM, NANOG, and SOX2 was upregulated upon trophosphere formation. Relative to co-culture with multiparous MenSCs, co-culture with PE-MenSCs was associated with reduced trophoblast invasion. The findings of this study suggest a potential role for communication between maternal MenSCs and invading trophoblast cells during the implantation process that could be implicated in the etiology of PE.

Diagnostic potential of peri-implant crevicular fluid microRNA-21-3p and microRNA-150-5p and extracellular vesicles in peri-implant diseases.

BACKGROUND: To explore the diagnostic usefulness of extracellular vesicles (EVs), and their subpopulations (micro-vesicles and exosomes), and microRNAs (miRNA-21-3p, miRNA-150-5p, and miRNA-26a-5p) in peri-implant crevicular fluid (PICF) of subjects with healthy, peri-implant mucositis and peri-implantitis implants. METHODS: A total of 54 patients were enrolled into healthy, peri-implant mucositis, and peri-implantitis groups. PICF samples were collected, EVs subpopulations (MVs and Exo) were isolated and characterized by nanoparticle tracking analysis and transmission electron microscopy. The expression of miRNA-21-3p, miRNA-150-5p and miRNA-26a-5p was quantified by qRT-PCR. Logistic regression models and accuracy performance tests were estimated. RESULTS: PICF samples show the presence of EVs delimited by a bi-layered membrane, in accordance with the morphology and size (< 200 nm). The concentration of PICF-EVs, micro-vesicles and exosomes was significantly increased in peri-implantitis implants compared to healthy implants (P = 0.023, P = 0.002, P = 0.036, respectively). miRNA-21-3p and miRNA-150-5p expression were significantly downregulated in patients with peri-implantitis in comparison with peri-implant mucositis sites (P = 0.011, P = 0.020, respectively). The reduced expression of miRNA-21-3p and miRNA-150-5p was associated with peri-implantitis diagnosis (OR:0.23, CI 0.08-0.66, P = 0.007 and OR:0.07, CI 0.01-0.78, P = 0.031, respectively). The model which included the miRNA-21-3p and miRNA-150-5p expression had a sensitivity of 93.3%, a specificity of 76.5%, a positive predictive value of 77.8%, and a negative predictive value of 92.9%. The positive and negative likelihood ratios were 3.97 and 0.09, respectively. The area under the receiver operating characteristics curve for the model was 0.84. CONCLUSIONS: An increase concentration of EVs with a downregulation expression of miRNA-21-3p and miRNA-150-5p could be related with the peri-implantitis development.

Vesículas extracelulares como predictores tempranos de diabetes gestacional / Extracellular vesicle concentration in maternal plasma as an early marker of gestational diabetes

Background During pregnancy, there is an increase in the amount of extracellular vesicles, especially placental exosomes, in maternal plasma. Aim To isolate and characterize extracellular vesicles from blood during the three trimesters of pregnancy and to evaluate their capacity to identify patients at risk of developing gestational diabetes. Material and Methods A case-control study was conducted in a cohort of 50 pregnant women with plasma samples taken in each trimester. Six women who developed gestational diabetes were paired with three healthy controls per case (a total of 19). Clinical characteristics were recorded at first prenatal appointment, and blood samples were obtained during the first, second and third trimesters. Extracellular vesicles were isolated from plasma by the commercial kit, ExoQuick™. Nanoparticle tracking analysis, was used to characterize the obtained extracellular vesicles. Results The total concentration of extracellular particles isolated from maternal plasma increased along with gestational age. The size of the extracellular vesicles obtained in the first trimester of pregnancy was very similar between groups (144 ± 37 nm for controls and 143 ± 34 nm for patients with gestational diabetes mellitus). Moreover, the concentration of extracellular vesicles collected in the first trimester, was significantly higher in patients who developed gestational diabetes mellitus later in pregnancy compared to normoglycemic pregnant women (7.94 x 10 8 and 5.15 x 10 8 , p = 0.03). Conclusions Our results provide an insight into the potential capacity of first trimester plasma extracellular vesicles as early biomarkers for the prediction of gestational diabetes mellitus.

Oral extracellular vesicles in early pregnancy can identify patients at risk of developing gestational diabetes mellitus.

AIM: To isolate and characterize oral extracellular vesicles from gingival crevicular fluid at 11-14 weeks and evaluate their capacity to identify patients at risk of developing gestational diabetes mellitus. METHODS: A case-control study was conducted, including patients who developed gestational diabetes mellitus (n = 11) and healthy pregnant controls (n = 23). Obstetric and periodontal histories were recorded at 11-14 weeks of gestation, and samples of gingival crevicular fluid obtained. Extracellular vesicles were isolated from gingival crevicular fluid by ExoQuick. Nanoparticle tracking analysis, ELISA and transmission electron microscopy were used to characterize extracellular vesicles. RESULTS: Total extracellular vesicles isolated from gingival crevicular fluid were significantly higher in patients who developed gestational diabetes mellitus later in pregnancy compared to normoglycemic pregnant women (6.3x109 vs 1.7 x1010, p value = 0.0026), and the concentration of the extracellular vesicles delivered an area under the ROC curve of 0.81. The distribution size of extracellular vesicles obtained using ExoQuick was around 148 ± 57 nm. There were no significant differences in the periodontal status between cases and controls. The exosome transmembrane protein CD63 was also detected in the extracellular vesicles of gingival crevicular fluid. CONCLUSION: We were able to isolate extracellular vesicles from gingival crevicular fluid using a method that is suitable to be applied in a clinical setting. Our results provide an insight into the potential capacity of first trimester oral extracellular vesicles as early biomarkers for the prediction of gestational diabetes mellitus in pre-symptomatic women.

Reduced FOXM1 Expression Limits Trophoblast Migration and Angiogenesis and Is Associated With Preeclampsia.

Trophoblast cells are often compared to highly invasive carcinoma cells due to their capacity to proliferate in hypoxic conditions and to exhibit analogous vascular, proliferative, migratory, and invasive capacities. Thus, genes that are important for tumorigenesis, such as forkhead box M1 ( FOXM1) may also be involved in processes of trophoblast invasion. Indeed, we found Foxm1 protein and messenger RNA (mRNA) levels decreased as gestational age increased in rat's placentae. Accordingly, when mimicking early placental events in vitro, protein and mRNA expression of FOXM1 increased from 21% to 8% O2, reaching its highest expression at 3% oxygen tension, which reflects early implantation environment, and dropping to very low levels at 1% O2. Remarkably, FOXM1 silencing in JEG-3 cells was able to significantly decrease migration by 27.9%, in comparison with those cells transfected with control siRNA. Moreover, angiogenesis was compromised when conditioned media (CM) from FOXM1-siRNA -JEG-3 (3% O2) was added to human umbilical vein endothelial cells (HUVEC) cells; however, when CM of JEG-3 cells overexpressing FOXM1 at 1% O2 was added, the ability of HUVEC to form tubule networks was restored. Additionally, quantitative real-time polymerase chain reaction (PCR) assays of FOXM1 knockdown and overexpression experiments in JEG-3 cells revealed that the depletion of FOXM1 at 3% O2 and overexpression of FOXM1 at 1% O2 led to downregulation and upregulation of vascular endothelial growth factor transcriptional (VEGF) levels, respectively. Conversely, we also observed deregulation of FOXM1 in placentae derived from pregnancies complicated by preeclampsia (PE). Therefore, we demonstrate that FOXM1 may be a new regulatory protein of early placentation processes and that under chronic hypoxic conditions (1% O2) and in patients with severe PE, its levels decrease.

Placental Aromatase Is Deficient in Placental Ischemia and Preeclampsia.

INTRODUCTION: Preeclampsia is a maternal hypertensive disorder with uncertain etiology and a leading cause of maternal and fetal mortality worldwide, causing nearly 40% of premature births delivered before 35 weeks of gestation. The first stage of preeclampsia is characterized by reduction of utero-placental blood flow which is reflected in high blood pressure and proteinuria during the second half of pregnancy. In human placenta androgens derived from the maternal and fetal adrenal glands are converted into estrogens by the enzymatic action of placental aromatase. This implies that alterations in placental steroidogenesis and, subsequently, in the functionality or bioavailability of placental aromatase may be mechanistically involved in the pathophysiology of PE. METHODS: Serum samples were collected at 32-36 weeks of gestation and placenta biopsies were collected at time of delivery from PE patients (n = 16) and pregnant controls (n = 32). The effect of oxygen tension on placental cells was assessed by incubation JEG-3 cells under 1% and 8% O2 for different time periods, Timed-mated, pregnant New Zealand white rabbits (n = 6) were used to establish an in vivo model of placental ischemia (achieved by ligature of uteroplacental vessels). Aromatase content and estrogens and androgens concentrations were measured. RESULTS: The protein and mRNA content of placental aromatase significantly diminished in placentae obtained from preeclamptic patients compared to controls. Similarly, the circulating concentrations of 17-ß-estradiol/testosterone and estrone/androstenedione were reduced in preeclamptic patients vs. controls. These data are consistent with a concomitant decrease in aromatase activity. Aromatase content was reduced in response to low oxygen tension in the choriocarcinoma JEG-3 cell line and in rabbit placentae in response to partial ligation of uterine spiral arteries, suggesting that reduced placental aromatase activity in preeclamptic patients may be associated with chronic placental ischemia and hypoxia later in gestation. CONCLUSIONS: Placental aromatase expression and functionality are diminished in pregnancies complicated by preeclampsia in comparison with healthy pregnant controls.

NFAT5 Is Up-Regulated by Hypoxia: Possible Implications in Preeclampsia and Intrauterine Growth Restriction.

During gestation, low oxygen environment is a major determinant of early placentation process, while persistent placental hypoxia leads to pregnancy-related complications such as preeclampsia (PE) and intrauterine growth restriction (IUGR). PE affects 5%-8% of all pregnancies worldwide and is a cause of maternal and fetal morbidity and mortality. During placental development, persistent hypoxia due to poor trophoblast invasion and reduced uteroplacental perfusion leads to maternal endothelial dysfunction and clinical manifestation of PE. Here we hypothesized that nuclear factor of activated T cells-5 (NFAT5), a well-known osmosensitive renal factor and recently characterized hypoxia-inducible protein, is also activated in vivo in placentas of PE and IUGR complications as well as in the in vitro model of trophoblast hypoxia. In JAR cells, low oxygen tension (1% O2) induced NFAT5 mRNA and increased its nuclear abundance, peaking at 16 h. This increase did not occur in parallel with the earlier HIF1A induction. Real-time PCR and Western blot analysis confirmed up-regulation of NFAT5 mRNA and NFAT5 nuclear content in human preeclamptic placentas and in rabbit placentas of an experimentally induced IUGR model, as compared with the control groups. In vitro lambda protein phosphatase (lambda PPase) treatment revealed that increased abundance of NFAT5 protein in nuclei of either JAR cells (16 h of hypoxia) or PE and IUGR placentas is at least partially due to NFAT5 phosphorylation. NFAT5 downstream targets aldose reductase (AR) and sodium-myo-inositol cotransporter (SMIT; official symbol SLC5A3) were not significantly up-regulated either in JAR cells exposed to hypoxia or in placentas of PE- and IUGR-complicated pregnancies, suggesting that hypoxia-dependent activation of NFAT5 serves as a separate function to its tonicity-dependent stimulation. In conclusion, we propose that NFAT5 may serve as a novel marker of placental hypoxia and ischemia independently of HIF1A.

SIRT6 modulates paclitaxel and epirubicin resistance and survival in breast cancer.

In this study, we report the identification of a novel role of SIRT6 in both epirubicin and paclitaxel resistance in breast cancer. We found that SIRT6 protein levels are elevated in paclitaxel- and epirubicin-resistant MCF-7 cells compared with the parental sensitive cells. SIRT6 knockout and depletion sensitized cells to both paclitaxel and epirubicin treatment, whereas SIRT6 ectopic overexpression led to increased resistance to paclitaxel and epirubicin. Moreover, our data suggest that SIRT6 could be mediating epirubicin resistance through enhancing the DNA repair response to epirubicin-induced DNA damage. Clonogenic assays also revealed that mouse embryonic fibroblasts (MEFs) lacking SIRT6 have decreased long-term viability in response to epirubicin. The tumour suppressor FOXO3a increases its levels of acetylation in MEFs depleted of SIRT6, whereas its induction by epirubicin is attenuated in breast cancer cells overexpressing SIRT6. Further cell viability studies demonstrate that deletion of FOXO1/3/4 in MEFs can confer sensitivity to both paclitaxel and epirubicin, suggesting that SIRT6 reduces paclitaxel and epirubicin sensitivity, at least in part, through modulating FOXO acetylation and expression. Consistently, immunohistochemical analysis of 118 breast cancer patient samples revealed that high SIRT6 nuclear staining is significantly associated with poorer overall survival (P = 0.018; Kaplan-Meier analysis). Multivariate Cox analysis demonstrated that nuclear SIRT6 staining remained associated with death after correcting for tumour stage and lymph-node involvement (P = 0.033). Collectively, our data suggest that SIRT6 has a role in paclitaxel and epirubicin sensitivity via targeting FOXO proteins and that SIRT6 could be a useful biomarker and therapeutic target for paclitaxel- and epirubicin-resistant cancer.

The p38 MAPK-MK2 axis regulates E2F1 and FOXM1 expression after epirubicin treatment.

E2F1 is responsible for the regulation of FOXM1 expression, which plays a key role in epirubicin resistance. Here, we examined the role and regulation of E2F1 in response to epirubicin in cancer cells. We first showed that E2F1 plays a key role in promoting FOXM1 expression, cell survival, and epirubicin resistance as its depletion by siRNA attenuated FOXM1 induction and cell viability in response to epirubicin. We also found that the p38-MAPK activity mirrors the expression patterns of E2F1 and FOXM1 in both epirubicin-sensitive and -resistant MCF-7 breast cancer cells, suggesting that p38 has a role in regulating E2F1 expression and epirubicin resistance. Consistently, studies using pharmacologic inhibitors, siRNA knockdown, and knockout mouse embryonic fibroblasts (MEF) revealed that p38 mediates the E2F1 induction by epirubicin and that the induction of E2F1 by p38 is, in turn, mediated through its downstream kinase MK2 [mitogen-activated protein kinase (MAPK)-activated protein kinase 2; MAPKAPK2]. In agreement, in vitro phosphorylation assays showed that MK2 can directly phosphorylate E2F1 at Ser-364. Transfection assays also showed that E2F1 phosphorylation at Ser-364 participates in its induction by epirubicin but also suggests that other phosphorylation events are also involved. In addition, the p38-MK2 axis can also limit c-jun-NH(2)-kinase (JNK) induction by epirubicin and, notably, JNK represses FOXM1 expression. Collectively, these findings underscore the importance of p38-MK2 signaling in the control of E2F1 and FOXM1 expression as well as epirubicin sensitivity.

Phosphorylation of FOXO3a on Ser-7 by p38 promotes its nuclear localization in response to doxorubicin.

FOXO3a is a forkhead transcription factor that regulates a multitude of important cellular processes, including proliferation, apoptosis, differentiation, and metabolism. Doxorubicin treatment of MCF-7 breast carcinoma cells results in FOXO3a nuclear relocation and the induction of the stress-activated kinase p38 MAPK. Here, we studied the potential regulation of FOXO3a by p38 in response to doxorubicin. Co-immunoprecipitation studies in MCF-7 cells demonstrated a direct interaction between p38 and FOXO3a. We also showed that p38 can bind and phosphorylate a recombinant FOXO3a directly in vitro. HPLC-coupled phosphopeptide mapping and mass spectrometric analyses identified serine 7 as a major site for p38 phosphorylation. Using a phosphorylated Ser-7 FOXO3a antibody, we demonstrated that FOXO3a is phosphorylated on Ser-7 in response to doxorubicin. Immunofluorescence staining studies showed that upon doxorubicin treatment, the wild-type FOXO3a relocalized to the nucleus, whereas the phosphorylation-defective FOXO3a (Ala-7) mutant remained largely in the cytoplasm. Treatment with SB202190 also inhibits the doxorubicin-induced FOXO3a Ser-7 phosphorylation and nuclear accumulation in MCF-7 cells. In addition, doxorubicin caused the nuclear translocation of FOXO3a in wild-type but not p38-depleted mouse fibroblasts. Together, our results suggest that p38 phosphorylation of FOXO3a on Ser-7 is essential for its nuclear relocalization in response to doxorubicin.

iASPP and chemoresistance in ovarian cancers: effects on paclitaxel-mediated mitotic catastrophe.

PURPOSE: iASPP is a specific regulator of p53-mediated apoptosis. Herein, we provided the first report on the expression profile of iASPP in ovarian epithelial tumor and its effect on paclitaxel chemosensitivity. EXPERIMENTAL DESIGN: Expression and amplification status of iASPP was examined in 203 clinical samples and 17 cell lines using immunohistochemistry, quantitative real-time PCR, and immunoblotting, and correlated with clinicopathologic parameters. Changes in proliferation, mitotic catastrophe, apoptosis, and underlying mechanism in ovarian cancer cells of different p53 status following paclitaxel exposure were also analyzed. RESULTS: The protein and mRNA expression of iASPP was found to be significantly increased in ovarian cancer samples and cell lines. High iASPP expression was significantly associated with clear cell carcinoma subtype (P = 0.003), carboplatin and paclitaxel chemoresistance (P = 0.04), shorter overall (P = 0.003), and disease-free (P = 0.001) survival. Multivariate analysis confirmed iASPP expression as an independent prognostic factor. Increased iASPP mRNA expression was significantly correlated with gene amplification (P = 0.023). iASPP overexpression in ovarian cancer cells conferred resistance to paclitaxel by reducing mitotic catastrophe in a p53-independent manner via activation of separase, whereas knockdown of iASPP enhanced paclitaxel-mediated mitotic catastrophe through inactivating separase. Both securin and cyclin B1/CDK1 complex were involved in regulating separase by iASPP. Conversely, overexpressed iASPP inhibited apoptosis in a p53-dependent mode. CONCLUSIONS: Our data show an association of iASPP overexpression with gene amplification in ovarian cancer and suggest a role of iASPP in poor patient outcome and chemoresistance, through blocking mitotic catastrophe. iASPP should be explored further as a potential prognostic marker and target for chemotherapy.

ATM and p53 regulate FOXM1 expression via E2F in breast cancer epirubicin treatment and resistance.

In this report, we investigated the role and regulation of forkhead box M1 (FOXM1) in breast cancer and epirubicin resistance. We generated epirubicin-resistant MCF-7 breast carcinoma (MCF-7-EPI(R)) cells and found FOXM1 protein levels to be higher in MCF-7-EPI(R) than in MCF-7 cells and that FOXM1 expression is downregulated by epirubicin in MCF-7 but not in MCF-7-EPI(R) cells. We also established that there is a loss of p53 function in MCF-7-EPI(R) cells and that epirubicin represses FOXM1 expression at transcription and gene promoter levels through activation of p53 and repression of E2F activity in MCF-7 cells. Using p53(-/-) mouse embryo fibroblasts, we showed that p53 is important for epirubicin sensitivity. Moreover, transient promoter transfection assays showed that epirubicin and its cellular effectors p53 and E2F1 modulate FOXM1 transcription through an E2F-binding site located within the proximal promoter region. Chromatin immunoprecipitation analysis also revealed that epirubicin treatment increases pRB (retinoblastoma protein) and decreases E2F1 recruitment to the FOXM1 promoter region containing the E2F site. We also found ataxia-telangiectasia mutated (ATM) protein and mRNA to be overexpressed in the resistant MCF-7-EPI(R) cells compared with MCF-7 cells and that epirubicin could activate ATM to promote E2F activity and FOXM1 expression. Furthermore, inhibition of ATM in U2OS cells with caffeine or depletion of ATM in MCF-7-EPI(R) with short interfering RNAs can resensitize these resistant cells to epirubicin, resulting in downregulation of E2F1 and FOXM1 expression and cell death. In summary, our data show that ATM and p53 coordinately regulate FOXM1 via E2F to modulate epirubicin response and resistance in breast cancer.

Constitutively nuclear FOXO3a localization predicts poor survival and promotes Akt phosphorylation in breast cancer.

BACKGROUND: The PI3K-Akt signal pathway plays a key role in tumorigenesis and the development of drug-resistance. Cytotoxic chemotherapy resistance is linked to limited therapeutic options and poor prognosis. METHODOLOGY/PRINCIPAL FINDINGS: Examination of FOXO3a and phosphorylated-Akt (P-Akt) expression in breast cancer tissue microarrays showed nuclear FOXO3a was associated with lymph node positivity (p = 0.052), poor prognosis (p = 0.014), and P-Akt expression in invasive ductal carcinoma. Using tamoxifen and doxorubicin-sensitive and -resistant breast cancer cell lines as models, we found that doxorubicin- but not tamoxifen-resistance is associated with nuclear accumulation of FOXO3a, consistent with the finding that sustained nuclear FOXO3a is associated with poor prognosis. We also established that doxorubicin treatment induces proliferation arrest and FOXO3a nuclear relocation in sensitive breast cancer cells. Induction of FOXO3a activity in doxorubicin-sensitive MCF-7 cells was sufficient to promote Akt phosphorylation and arrest cell proliferation. Conversely, knockdown of endogenous FOXO3a expression reduced PI3K/Akt activity. Using MDA-MB-231 cells, in which FOXO3a activity can be induced by 4-hydroxytamoxifen, we showed that FOXO3a induction up-regulates PI3K-Akt activity and enhanced doxorubicin resistance. However FOXO3a induction has little effect on cell proliferation, indicating that FOXO3a or its downstream activity is deregulated in the cytotoxic drug resistant breast cancer cells. Thus, our results suggest that sustained FOXO3a activation can enhance hyperactivation of the PI3K/Akt pathway. CONCLUSIONS/SIGNIFICANCE: Together these data suggest that lymph node metastasis and poor survival in invasive ductal breast carcinoma are linked to an uncoupling of the Akt-FOXO3a signaling axis. In these breast cancers activated Akt fails to inactivate and re-localize FOXO3a to the cytoplasm, and nuclear-targeted FOXO3a does not induce cell death or cell cycle arrest. As such, sustained nuclear FOXO3a expression in breast cancer may culminate in cancer progression and the development of an aggressive phenotype similar to that observed in cytotoxic chemotherapy resistant breast cancer cell models.

FOXM1 confers acquired cisplatin resistance in breast cancer cells.

The transcription factor Forkhead box M1 (FOXM1) is a key regulator of cell proliferation and is overexpressed in many forms of primary cancers, leading to uncontrolled cell division and genomic instability. To address the role of FOXM1 in chemoresistance, we generated a cisplatin-resistant breast cancer cell line (MCF-7-CIS(R)), which had an elevated level of FOXM1 protein and mRNA expression relative to the parental MCF-7 cells. A close correlation was observed between FOXM1 and the expression of its proposed downstream targets that are involved in DNA repair; breast cancer-associated gene 2 (BRCA2) and X-ray cross-complementing group 1 (XRCC1) were expressed at higher levels in the resistant cell lines compared with the sensitive MCF-7 cells. Moreover, cisplatin treatment induced DNA damage repair in MCF-7-CIS(R) and not in MCF-7 cells. Furthermore, the expression of a constitutively active FOXM1 (DeltaN-FOXM1) in MCF-7 cells alone was sufficient to confer cisplatin resistance. Crucially, the impairment of DNA damage repair pathways through the small interfering RNA knockdown inhibition of either FOXM1 or BRCA2/XRCC1 showed that only the silencing of FOXM1 could significantly reduce the rate of proliferation in response to cisplatin treatment in the resistant cells. This suggests that the targeting of FOXM1 is a viable strategy in circumventing acquired cisplatin resistance. Consistently, the FOXM1 inhibitor thiostrepton also showed efficacy in causing cell death and proliferative arrest in the cisplatin-resistant cells through the downregulation of FOXM1 expression. Taken together, we have identified a novel mechanism of acquired cisplatin resistance in breast cancer cells through the induction of FOXM1.

Definition of microRNAs that repress expression of the tumor suppressor gene FOXO1 in endometrial cancer.

Endometrial cancer is the most common malignancy of the lower female reproductive tract. The tumor suppressor FOXO1 is downregulated in endometrial cancer compared with normal endometrium but the underlying mechanisms are not well understood. Using microRNA (miR) target prediction algorithms, we identified several miRs that potentially bind the 3'-untranslated region of FOXO1 transcripts. Expression profiling of normal and malignant endometrial samples by quantitative real-time PCR and Northern blot analysis revealed an inverse correlation between the levels of FOXO1 protein and the abundance of several of the in silico-predicted miRs, suggesting that loss of FOXO1 expression in endometrial cancer may be mediated by miRs. To determine the role of candidate miRs, we used the endometrial cancer cell lines HEC-1B and Ishikawa, which express FOXO1 at high and low levels, respectively. Expression of miR-9, miR-27, miR-96, miR-153, miR-182, miR-183, or miR-186, but not miR-29a, miR-128, miR-152, or miR-486 mimetics in HEC-1B cells was sufficient to significantly reduce the abundance of FOXO1. Conversely, FOXO1 expression was efficiently restored in the Ishikawa cell line upon simultaneous inhibition of miR-9, miR-27, miR-96, miR-153, miR-183, and miR-186. Moreover, induction of FOXO1 in Ishikawa cells by miR inhibitors was accompanied by G1 cell cycle arrest and cell death, and was attenuated by the small interfering RNA-mediated downregulation of FOXO1 expression. Our findings identify several miRs overexpressed in endometrial cancer that function in concert to repress FOXO1 expression. Further, aberrant miR expression results in deregulated cell cycle control and impaired apoptotic responses, and thus, may be central to endometrial tumorigenesis.