Receptor tyrosine kinase Ron is expressed in mouse reproductive tissues during embryo implantation and is important in trophoblast cell function

The role of circular RNA in preeclampsia: From pathophysiological mechanism to clinical application

Preeclampsia (PE) is a common pregnancy-induced hypertension disorder that poses a significant threat to the health of pregnant women and fetuses, and has become a leading cause of maternal, fetal, and neonatal mortality. Currently, the therapy strategy for PE is mainly prevention management and symptomatic treatment, and only delivery can completely terminate PE. Therefore, a deeper understanding of the pathogenesis of PE is needed to make treatment and prevention more effective and targeted. With the deepening of molecular etiology research, circular RNAs (circRNAs) have been found to be widely involved in various processes of PE pathogenesis. As a kind of RNA with a special "head to tail" loop structure, the characteristics of circRNAs enable them to play diverse roles in the pathophysiology of PE, and can also serve as ideal biomarkers for early prediction and monitoring progression of PE. In this review, we summarized the latest research on PE-related circRNAs, trying to elucidate the unique or shared roles of circRNAs in various pathophysiological mechanisms of PE, aiming to provide a whole picture of current research on PE-related circRNAs, and extend a new perspective for the precise screening and targeted therapy of PE.

An Introduction and Overview of RON Receptor Tyrosine Kinase Signaling

RON is a receptor tyrosine kinase (RTK) of the MET receptor family that is canonically involved in mediating growth and inflammatory signaling. RON is expressed at low levels in a variety of tissues, but its overexpression and activation have been associated with malignancies in multiple tissue types and worse patient outcomes. RON and its ligand HGFL demonstrate cross-talk with other growth receptors and, consequentially, positions RON at the intersection of numerous tumorigenic signaling programs. For this reason, RON is an attractive therapeutic target in cancer research. A better understanding of homeostatic and oncogenic RON activity serves to enhance clinical insights in treating RON-expressing cancers.

circCRAMP1L is a novel biomarker of preeclampsia risk and may play a role in preeclampsia pathogenesis via regulation of the MSP/RON axis in trophoblasts

Background

Preeclampsia is a severe disease in pregnant women, which is primarily managed by early screening and prevention. Circular RNAs (circRNAs) have increasingly been shown to be important biological regulators involved in numerous diseases. Further, increasing evidence has demonstrated that circRNAs can be used as diagnostic biomarkers. This study was conducted to evaluate the potential of circCRAMP1L, previously identified to be downregulated in preeclampsia, as a novel biomarker for predicting the development of preeclampsia.

Methods

We measured the expression of circCRAMP1L, which is reportedly relevant to trophoblast physiology, in plasma samples from 64 patients with preeclampsia and 64 age-, gestational age-, and body mass index-matched healthy pregnant women by qRT-PCR. MTT proliferation and transwell invasion assays revealed the biological role of circCRAMP1L in preeclampsia pathogenesis. RNA immunoprecipitation and dual-luciferase reporter assays clarified the mechanism underlying the biological function of circCRAMP1L in TEV-1 cells.

Results

circCRAMP1L circulating levels were significantly lower in patients with preeclampsia (2.66 ± 0.82, △Ct value) than in healthy pregnant women (3.95 ± 0.67, △Ct value, p <  0.001). The area under the receiver operating characteristic curve for circCRAMP1L was 0.813. Univariate and multivariate analyses identified circCRAMP1L as an independent predictor of preeclampsia. Furthermore, when circCRAMP1L was utilised in combination with its target protein macrophage stimulating protein (MSP), the predictive performance increased, with an area under the receiver operating characteristic curve of 0.928 (95% CI 0.882–0.974), 80.0% sensitivity, and 80.0% specificity. The in vitro results indicated that circCRAMP1L regulates cell proliferation, and invasion via MSP and RON proteins. We investigated the molecular mechanisms of these effects. In vitro, relative to the control group, circCRAMP1L overexpression significantly enhanced cell proliferation; furthermore, trophoblast cell invasion increased proportionally with circCRAMP1L expression. RNA immunoprecipitation and luciferase reporter gene illustrated that circCRAMP1L participated in regulation of trophoblast cell by regulating MSP.

Conclusion

Reduced plasma levels of circCRAMP1L may be associated with an increased risk of preeclampsia, and circCRAMP1L may be a novel biomarker of preeclampsia risk.

Supplementary information

Supplementary information accompanies this paper at 10.1186/s12884-020-03345-5.

Macrophage-stimulating protein is decreased in severe preeclampsia and regulates the biological behavior of HTR-8/SVneo trophoblast cells

Preeclampsia (PE) is a major challenge for obstetricians. There is no effective way to block the development of PE other than terminating the pregnancy. The biological behavior of trophoblast cells, which are similar to cancer cells, may be closely related to the onset of PE. The vital role of macrophage-stimulating protein (MSP) in the development and progression of cancer has been recognized, while a role for this protein in PE has rarely been reported. This study aimed to explore whether MSP affects severe PE (sPE) and, if so, to characterize the mechanism. Patient information, blood samples and/or placental tissues were collected. An enzyme-linked immunosorbent assay (ELISA) was used to determine the plasma MSP concentration. The relationships between the plasma MSP concentration and clinical characteristics were analyzed. Immunofluorescence was performed to localize MSP in placental tissues. Western blotting and reverse transcription quantitative polymerase chain reaction (RT-qPCR) were used to determine MSP protein and mRNA expression in placental tissues. MSP was overexpressed or underexpressed in the trophoblastic cell line HTR-8/SVneo by lentiviral transfection and the proliferation, apoptosis, migration, invasion and angiogenesis of cells were detected. MSP was downregulated in sPE, and the underexpression of MSP inhibited HTR-8/SVneo cell proliferation, migration, invasion and angiogenesis. We further verified that MSP affects the biological behavior of trophoblast cells through the β-catenin/ZEB1 signaling pathway. These results suggest that decreased MSP in the blood and placental tissues of patients with sPE, especially those with early-onset sPE, leads to reduced trophoblast cell invasion, which plays an important role in the pathogenesis of PE.

Plasma Level of Placenta-Derived Macrophage-Stimulating Protein -Chain in Preeclampsia before 20 Weeks of Pregnancy

Object

This study aimed to investigate the diagnostic value of placenta-derived macrophage-stimulating protein α-chain (MSP-α) before the 20^th week of gestation for the early diagnosis of preeclampsia (PE).

Methods and Materials

Two parts of this nested case-control study were simultaneously executed, and 1500 pregnant women were recruited. A total of 124 pregnant women were included in the plasma analysis part of this study. The MSP-α plasma level was measured before the 20^th week of gestation, and the participants were followed until delivery. A case group of 62 women with PE and a control group of 62 women matched by gestational age, maternal age, and pre-pregnancy BMI (with normotensive pregnancies) were evaluated. In the placenta analysis part of this nested case-control study, the placentas of 34 pregnant women were randomly obtained. The placental levels of MSP were measured in 17 individuals with PE (case group) and in 17 women with a normotensive pregnancy matched by gestational age and maternal age (control group).

Results

The plasma level of MSP-α was higher in the PE group than in the control group before the 20^th week of gestation (p < 0.001). In addition, compared to the women with severe features in the PE group, those without severe features had a significantly higher plasma MSP-α level before the 20^th week of gestation (p < 0.001). The area under the receiver operating characteristic curve (AUC) of MSP-α before the 20^th week of gestation was 0.905 (95% CI, 0.811–0.962) for the women with early-onset PE without severe features. With regard to the placenta, the PE group (accumulated optical density, IOD [SUM] = 8862.37 ± 2064.42) exhibited increased MSP staining (more intense MSP staining or more extensive staining) compared with the control group (normal pregnancies (IOD [SUM] = 447.92 ± 114.72, P < 0.001). Furthermore, increased MSP staining was detected among the women without severe features compared with those with severe features in the PE group (IOD [SUM]: 12192.65 ± 5325.56 vs. 4104.83 ± 2383.06, P = 0.021).

Conclusion

According to the findings of this study, the plasma level of MSP-α may be associated with PE, and MSP-α may be considered a candidate protein for further analysis in studies of PE. Multicenter studies with larger sample sizes must be performed in the future to obtain accurate results regarding the predictive value of MSP-α in combination with other protein factors for the early diagnosis of PE.

Id2 Mediates Differentiation of Labyrinthine Placental Progenitor Cell Line, SM10

The placenta is an organ that is formed transiently during pregnancy, and appropriate placental development is necessary for fetal survival and growth. Proper differentiation of the labyrinthine layer of the placenta is especially crucial, as it establishes the fetal-maternal interface that is involved in physiological exchange processes. Although previous studies have indicated the importance of inhibitor of differentiation/inhibitor of DNA binding-2 (Id2) helix-loop-helix transcriptional regulator in mediating cell differentiation, the ability of Id2 to regulate differentiation toward the labyrinthine (transport) lineage of the placenta has yet to be determined. In the current study, we have generated labyrinthine trophoblast progenitor cells with increased (SM10-Id2) or decreased (SM10-Id2-shRNA) Id2 expression and determined the effect on TGF-β-induced differentiation. Our Id2 overexpression and knockdown analyses indicate that Id2 mediates TGF-β-induced morphological differentiation of labyrinthine trophoblast cells, as Id2 overexpression prevents differentiation and Id2 knockdown results in differentiation. Thus, our data indicate that Id2 is an important molecular mediator of labyrinthine trophoblast differentiation. An understanding of the regulators of trophoblast progenitor differentiation toward the labyrinthine lineage may offer insights into events governing pregnancy-associated disorders, such as placental insufficiency, fetal growth restriction, and preeclampsia.

The progesterone-responsive gene 14-3-3τ enhances the transcriptional activity of progesterone receptor in uterine cells

Members of the 14-3-3 family are intracellular dimeric phosphoserine-binding proteins that can associate with and modulate the activities of many proteins. In our efforts to isolate the genes regulated by progesterone (P(4)) using suppressive subtractive hybridization, we previously found that 14-3-3τ is one of the genes upregulated by P(4). In this study, we demonstrated by quantitative RT-PCR (qRT-PCR), western blot analyses, and immunohistochemistry that 14-3-3τ mRNA and protein levels were increased in the rat uterus after P(4) treatment. Furthermore, qRT-PCR indicated that P(4) increased 14-3-3τ mRNA levels in human endometrial epithelial cells and endometrial stromal cells (ESCs). Western blot and qRT-PCR analyses revealed that in vitro decidualization using cAMP and medroxyprogesterone 17-acetate increased levels of 14-3-3τ mRNA and protein in ESCs. We have shown by qRT-PCR and western blot analyses that P(4) increased the mRNA and protein levels of 14-3-3τ in Ishikawa cells that stably express P(4) receptor-B (PR-B). Immunocytochemistry revealed that 14-3-3τ colocalizes with PR and translocates from the cytoplasm to the nucleus in response to P(4). Moreover, by luciferase reporter assay, we demonstrated that 14-3-3τ enhances the transcriptional activity of PR-B. Taken together, we propose that 14-3-3τ is a P(4)-responsive gene in uterine cells that modulates P(4) signaling.

Ron receptor tyrosine kinase signaling as a therapeutic target

INTRODUCTION

Since its discovery nearly 20 years ago, the Ron receptor tyrosine kinase has been extensively studied. These studies have elucidated many of the major signaling pathways activated by Ron. In the context of the inflammation and cancer, studies have shown that Ron plays differential roles; Ron activation limits the inflammatory response, whereas in cancer, Ron activation is associated with increased metastases and poor prognosis.

AREAS COVERED

This review discusses the current literature with regard to Ron signaling and consequences of its activation in cancer as well as its role in cancer therapy. Further, we discuss the mechanisms by which Ron influences the inflammatory response and its role in chronic inflammatory diseases. Finally, we discuss Ron's connection between chronic inflammation and progression to cancer.

EXPERT OPINION

The complex nature of Ron's signaling paradigm necessitates additional studies to understand the pathways by which Ron is functioning and how these differ in inflammation and cancer. This will be vital to understanding the impact that Ron signaling has in disease states. Additional studies of targeted therapies, either alone or in conjunction with current therapies are needed to determine if inhibition of Ron signaling will provide long-term benefits to cancer patients.

Met-related receptor tyrosine kinase Ron in tumor growth and metastasis

The Ron receptor is a member of the Met family of cell surface receptor tyrosine kinases and is primarily expressed on epithelial cells and macrophages. The biological response of Ron is mediated by binding of its ligand, hepatocyte growth factor-like protein/macrophage stimulating-protein (HGFL). HGFL is primarily synthesized and secreted from hepatocytes as an inactive precursor and is activated at the cell surface. Binding of HGFL to Ron activates Ron and leads to the induction of a variety of intracellular signaling cascades that leads to cellular growth, motility and invasion. Recent studies have documented Ron overexpression in a variety of human cancers including breast, colon, liver, pancreas, and bladder. Moreover, clinical studies have also shown that Ron overexpression is associated with both worse patient outcomes as well as metastasis. Forced overexpression of Ron in transgenic mice leads to tumorigenesis in both the lung and the mammary gland and is associated with metastatic dissemination. While Ron overexpression appears to be a hallmark of many human cancers, the mechanisms by which Ron induces tumorigenesis and metastasis are still unclear. Several strategies are currently being undertaken to inhibit Ron as a potential therapeutic target; current strategies include the use of Ron blocking proteins, small interfering RNA (siRNA), monoclonal antibodies, and small molecule inhibitors. In total, these data suggest that Ron is a critical factor in tumorigenesis and that inhibition of this protein, alone or in combination with current therapies, may prove beneficial in the treatment of cancer patients.

Association of RON tyrosine kinase with the Jaagsiekte sheep retrovirus envelope glycoprotein

The envelope (Env) of Jaagsiekte sheep retrovirus (JSRV) functions as an oncoprotein. One of the mechanisms of JSRV-induced cell transformation that has been proposed for epithelial cells involves JSRV Env binding Hyaluronidase 2 (the JSRV receptor), thereby inducing its degradation and allowing the release and activation of RON tyrosine kinase which is normally suppressed by HYAL-2. In this study, we report that HYAL-2 and RON are not critical for the JSRV Env-induced transformation of the rat epithelial cell line IEC-18, while the cytoplasmic tail of the JSRV Env is critical to transform this cell line. We have also determined that RON can associate with the JSRV Env under normal and stringent conditions. In addition, the cytoplasmic tail of the JSRV and the enJS5F16 (non oncogenic JSRV-related endogenous retrovirus) Env proteins appears to have a major influence on the activation status of RON. Thus, it appears that the interaction of the JSRV Env with RON is more complex than previously thought and requires further investigation.

Identification of committed placental stem cell lines for studies of differentiation

Trophoblasts provide a model to investigate fundamental mechanisms of stem cell differentiation, but the availability of trophoblast stem cell lines is limited. Here we report the development of an RT-PCR-based lineage-specific profile as a method to identify the lineages of placental trophoblast cells routinely and specifically. This profiling method was used to analyze the mouse SM10 and rat HRP-1 cell lines, isolated from a region of the placental labyrinth, but of previously unidentified lineage. Using this profile, the expression of trophoblast stem cell markers was detected in the SM10 and HRP-1 cells. In contrast, no expression of a marker of differentiated labyrinthine trophoblast was detected. Additionally, both cell lines expressed labyrinthine trophoblast-specific genes and did not express lineage-specific markers of spongiotrophoblasts or trophoblast giant cells. Our results suggest that SM10 and HRP-1 cell lines are trophoblast stem cell-like cell lines that can be maintained in undifferentiated but committed state in cell culture. These cell lines express labyrinthine-specific genes and are committed to differentiate solely into functional labyrinthine trophoblasts. Our profiling method provides a new technique to identify stem cells and their lineage-specific differentiation. This method additionally indicates that SM10 and HRP-1 cell lines provide new systems for future studies of stem cell differentiation, allowing investigation of basic mechanisms of differentiation, which may provide insights into the biophysics of development of a specialized system. This method should also prove to be useful for identification of other stem cell lines and examination of lineage-specific commitment.

Ron receptor signaling augments mammary tumor formation and metastasis in a murine model of breast cancer

The tyrosine kinase receptor Ron has been implicated in several types of cancer, including overexpression in human breast cancer. This is the first report describing the effect of Ron signaling on tumorigenesis and metastasis in a mouse model of breast cancer. Mice with a targeted deletion of the Ron tyrosine kinase signaling domain (TK-/-) were crossed to mice expressing the polyoma virus middle T antigen (pMT) under the control of the mouse mammary tumor virus promoter. Both pMT-expressing wild-type control (pMT+/- TK+/+) and pMT+/- TK-/- mice developed mammary tumors and lung metastases. However, a significant decrease in mammary tumor initiation and growth was found in the pMT+/- TK-/- mice compared with controls. An examination of mammary tumors showed that there was a significant decrease in microvessel density, significantly decreased cellular proliferation, and a significant increase in terminal deoxynucleotidyl transferase-mediated nick end labeling-positive staining in mammary tumor cells from the pMT+/- TK-/- mice compared with the pMT+/- TK+/+ mice. Biochemical analyses on mammary tumor lysates showed that whereas both the pMT-expressing TK+/+ and TK-/- tumors have increased Ron expression compared with normal mammary glands, the pMT-expressing TK-/- tumors have deficits in mitogen-activated protein kinase and AKT activation. These results indicate that Ron signaling synergizes with pMT signaling to induce mammary tumor formation, growth, and metastasis. This effect may be mediated in part through the regulation of angiogenesis and through proliferative and cell survival pathways regulated by mitogen-activated protein kinase and AKT.

The receptor tyrosine kinase Ron is expressed in the mouse ovary and regulates inducible nitric oxide synthase levels and ovulation

OBJECTIVE

To determine the reproductive effects in mice of the deletion of the tyrosine kinase domain of the Ron receptor.

DESIGN

Controlled animal studies.

SETTING

Academic research environment.

ANIMAL(S)

Immature mice with deletion of the tyrosine kinase domain of the Ron receptor (TK-/-) at 22-30 days of age and adult black Swiss female mice at 5-6 weeks of age.

INTERVENTION(S)

Hormonal stimulation of immature female TK-/- animals to induce ovulation.

MAIN OUTCOME MEASURE(S)

Ovulation rates measured by counting the total number of cumulus oocyte complexes in the ampullar region of the murine oviduct after hormonal stimulation. Western blot analysis measured murine ovarian protein levels of endothelial and inducible nitric oxide synthase (iNOS). Immunohistochemical analysis localized iNOS in the developing murine ovarian follicle.

RESULT

Immature TK-/- mice (22-30 days) ovulate significantly fewer cumulus oocyte complexes. Western blot analyses demonstrated increased levels of iNOS before and after ovulation compared with controls. Conversely, endothelial nitric oxide synthase levels were similar and remained constant during corresponding time periods. Immunohistochemical analyses demonstrated a significant increase in iNOS staining throughout the ovary in TK-/- mice with a significant amount of iNOS in granulosa cells surrounding the oocyte when compared with controls.

CONCLUSION(S)

The increased level of nitric oxide in the TK-/- mice is likely due to an elevated level of iNOS, which may contribute to a decrease in the size of the ovaries and ovulation rates of immature TK-/- animals.