Post-transcriptional regulation of CLMP mRNA is controlled by tristetraprolin in response to TNFalpha via c-Jun N-terminal kinase signalling

Inactivation of JNK signalling results in polarity loss and cell senescence of Sertoli cell

As major somatic cells in the testis, Sertoli cell development is precisely regulated by numerous factors, and aberrant development of these cells is associated with male reproductive diseases. JNK signalling is evolutionarily conserved and involved in multiple critical biological processes. Here, we found that the double knockout of Jnk1 and Jnk2 resulted in aberrant localisation of Sertoli cells at early developmental stages, with most Sertoli cells being lost at later stages. Further studies revealed that the inactivation of JNK signalling caused polarity loss in Sertoli cells. In vitro-cultured Jnk1/2-DKO Sertoli cells exhibited a senescence-associated phenotype. Mechanistic studies demonstrate that JNK signalling is likely involved in establishing Sertoli cell polarity by regulating the expression of TGF-β2, mediated by c-Jun. The senescence of Sertoli cells in JNKs-deficient mice is caused by aberrant proteolysis of P27KIP1, mediated by c-Myc. This study demonstrates the role of JNK signalling in Sertoli cell development and functional maintenance, which may also represent an aetiology of male infertility in humans.

Distinct Responses to IL4 in Macrophages Mediated by JNK

IL(Interleukin)-4 is the main macrophage M2-type activator and induces an anti-inflammatory phenotype called alternative activation. The IL-4 signaling pathway involves the activation of STAT (Signal Transducer and Activator of Transcription)-6 and members of the MAPK (Mitogen-activated protein kinase) family. In primary-bone-marrow-derived macrophages, we observed a strong activation of JNK (Jun N-terminal kinase)-1 at early time points of IL-4 stimulation. Using selective inhibitors and a knockout model, we explored the contribution of JNK-1 activation to macrophages' response to IL-4. Our findings indicate that JNK-1 regulates the IL-4-mediated expression of genes typically involved in alternative activation, such as Arginase 1 or Mannose receptor, but not others, such as SOCS (suppressor of cytokine signaling) 1 or p21^Waf-1 (cyclin dependent kinase inhibitor 1A). Interestingly, we have observed that after macrophages are stimulated with IL-4, JNK-1 has the capacity to phosphorylate STAT-6 on serine but not on tyrosine. Chromatin immunoprecipitation assays revealed that functional JNK-1 is required for the recruitment of co-activators such as CBP (CREB-binding protein)/p300 on the promoter of Arginase 1 but not on p21^Waf-1. Taken together, these data demonstrate the critical role of STAT-6 serine phosphorylation by JNK-1 in distinct macrophage responses to IL-4.

The IgSF Cell Adhesion Protein CLMP and Congenital Short Bowel Syndrome (CSBS)

The immunoglobulin-like cell adhesion molecule CLMP is a member of the CAR family of cell adhesion proteins and is implicated in human congenital short-bowel syndrome (CSBS). CSBS is a rare but very severe disease for which no cure is currently available. In this review, we compare data from human CSBS patients and a mouse knockout model. These data indicate that CSBS is characterized by a defect in intestinal elongation during embryonic development and impaired peristalsis. The latter is driven by uncoordinated calcium signaling via gap junctions, which is linked to a reduction in connexin43 and 45 levels in the circumferential smooth muscle layer of the intestine. Furthermore, we discuss how mutations in the CLMP gene affect other organs and tissues, including the ureter. Here, the absence of CLMP produces a severe bilateral hydronephrosis-also caused by a reduced level of connexin43 and associated uncoordinated calcium signaling via gap junctions.

Congenital Short-Bowel Syndrome Is Associated With a Novel Deletion Mutation in the CLMP Gene: Mutations in CLMP Caused CSBS

Objective: To describe the clinical presentation and novel mutation in the coxsackie and adenovirus receptor-like membrane protein (CLMP) gene in a Chinese family with congenital short bowel syndrome (CSBS). Methods: We collected clinical data from a Chinese family with inherited CSBS, and performed whole exon sequencing of the children and their parents. The pathogenic sites of candidate genes were targeted, and the detected exon deletions were verified by quantitative PCR. Results: Two siblings in this family presented with bilious vomiting, and were diagnosed with CSBS on laparotomy. Two siblings and their parents underwent complete exome sequencing of the peripheral blood. Both children had CLMP gene exons 3-5 homozygous deletion mutation, while the parents had a heterozygous mutation. Conclusion: This study identified a novel mutation of the CLMP gene in a Chinese family with CSBS. Identification of this mutation can help with genetic counseling and prenatal diagnosis of CSBS.

First Report of Congenital Short Bowel Syndrome in an Iranian Patient Caused by a Mutation in the CLMP Gene

Congenital short bowel syndrome (CSBS) is a rare congenital neonatal disorder. CSBS results from intestinal impairment during embryogenesis. Mutated CXADR-like membrane protein ( CLMP ) and Filamin A genes are involved in the cause of CSBS. In this study, due to our misdiagnosis, we had to perform whole exome sequencing on the patient, and also we implemented cosegregation analysis on his parents with consanguineous marriage and also parents' mothers. We identified a homozygous loss of function mutation in the CLMP gene in exon 5 (c.664C > T, p.R222X). Also, both parents and grandmothers of the proband were heterozygous for this mutation. Loss of function mutation in CLMP causes CSBS, leading to impaired intestinal development.

CXADR-like membrane protein (CLMP) in the rat ovary: stimulation by human chorionic gonadotrophin during the periovulatory period

CXADR-like membrane protein (CLMP) is a novel cell-cell adhesion molecule. The present study investigated the spatiotemporal expression pattern of CLMP and its regulation in the rat ovary during the periovulatory period. Real-time polymerase chain reaction analysis revealed that Clmp mRNA was rapidly stimulated in intact ovaries by 4h after human chorionic gonadotrophin (hCG) treatment. In situ hybridisation analysis demonstrated that Clmp mRNA expression was stimulated in theca cells at 4h after hCG and remained elevated until 12h. Clmp mRNA was also upregulated in granulosa cells and was present in forming corpora lutea. Our data indicate that the protein kinase A but not the protein kinase C pathway regulates the expression of Clmp mRNA in granulosa cells. Phosphatidylinositol 3 kinase and p38 kinase are also involved in regulating Clmp mRNA expression. The stimulation of Clmp mRNA by hCG requires new protein synthesis. Furthermore, inhibition of epidermal growth factor receptor activation significantly inhibited Clmp mRNA expression, whereas inhibition of prostaglandin synthesis or progesterone action had no effect. The stimulation of CLMP in the rat ovary may be important in cell adhesion events during ovulation and luteal formation such as maintaining the structure and communication of ovarian follicular and luteal cells.

Cell-cell communication mediated by the CAR subgroup of immunoglobulin cell adhesion molecules in health and disease

The immunoglobulin superfamily represents a diverse set of cell-cell contact proteins and includes well-studied members such as NCAM1, DSCAM, L1 or the contactins which are strongly expressed in the nervous system. In this review we put our focus on the biological function of a less understood subgroup of Ig-like proteins composed of CAR (coxsackievirus and adenovirus receptor), CLMP (CAR-like membrane protein) and BT-IgSF (brain and testis specific immunoglobulin superfamily). The CAR-related proteins are type I transmembrane proteins containing an N-terminal variable (V-type) and a membrane proximal constant (C2-type) Ig domain in their extracellular region which are implicated in homotypic adhesion. They are highly expressed during embryonic development in a variety of tissues including the nervous system whereby in adult stages the protein level of CAR and CLMP decreases, only BT-IgSF expression increases within age. CAR-related proteins are concentrated at specialized cell-cell communication sites such as gap or tight junctions and are present at the plasma membrane in larger protein complexes. Considerable progress has been made on the molecular structure and interactions of CAR while research on CLMP and BT-IgSF is at an early stage. Studies on mouse mutants revealed biological functions of CAR in the heart and for CLMP in the gastrointestinal and urogenital systems. Furthermore, CAR and BT-IgSF appear to regulate synaptic function in the hippocampus.

Transforming growth factor-β3 regulates cell junction restructuring via MAPK-mediated mRNA destabilization and Smad-dependent protein degradation of junctional adhesion molecule B (JAM-B)

Junctional adhesion molecule-B (JAM-B) is found between Sertoli cells at the blood-testis barrier (BTB) as well as between Sertoli and germ cells at the apical ectoplasmic specializations (ES) in the testis. The expression of JAM-B is tightly regulated to modulate the passage of spermatocytes across the BTB as well as the release of mature spermatozoa from the seminiferous epithelium. Transforming growth factor beta (TGF-β) family is implicated in the regulation of testicular cell junction dynamics during spermatogenesis. This study aims to investigate the effects of TGF-β3 on the expression of JAM-B as well as the underlying mechanisms on how TGF-β3 regulates JAM-B expression to facilitate the disassembly of the BTB and apical ES. Our results revealed that TGF-β3 suppresses JAM-B at post-transcriptional and post-translational levels. Inhibitor, siRNA knockdown and co-immunoprecipitation have shown that TGF-β3 induces JAM-B protein degradation via ubiquitin-proteasome pathway. Immunofluorescence staining further confirmed that blockage of ubiquitin-proteasome pathway could abrogate TGF-β3-induced loss of JAM-B at the cell-cell interface. siRNA knockdown and immunofluorescence staining also demonstrated that activation of Smad signaling is required for TGF-β3-induced JAM-B protein degradation. In addition, TGF-β3 reduces JAM-B mRNA levels, at least in part, via post-transcriptional regulation. mRNA stability assay has confirmed that TGF-β3 promotes the degradation of JAM-B transcript and TGF-β3-mediated mRNA destabilization requires the activation of ERK1/2 and p54 JNK signal cascades. Taken together, TGF-β3 significantly downregulates JAM-B expression via post-transcriptional and post-translational modulation and results in the disruption of BTB and apical ES.

Synergistic effect of interferon-gamma and tumor necrosis factor-alpha on coxsackievirus and adenovirus receptor expression: an explanation of cell sloughing during testicular inflammation in mice

Coxsackievirus and adenovirus receptor (CAR) is a junction molecule that expresses on Sertoli and germ cells. It mediates Sertoli-germ cell adhesion and facilitates migration of preleptotene/leptotene spermatocytes across the blood-testis barrier, suggesting that CAR-based cell adhesion and migration are crucial for spermatogenesis. Interferon-gamma (IFNG) and tumor necrosis factor alpha (TNF) are two major cytokines that are elevated during testicular inflammation and cause reduced fertility. We investigated the mechanism by which IFNG and TNF exert their disruptive effects on testicular cell adhesion. We have demonstrated that combined treatment with IFNG and TNF (IFNG+TNF) exerts a synergistic effect by downregulating CAR mRNA and protein levels. Immunofluorescence staining revealed that IFNG+TNF treatment effectively removes CAR from the site of cell-cell contact. Using inhibitor and co-immunoprecipitation, we confirmed that IFNG+TNF mediates CAR protein degradation via ubiquitin-proteasome and NFKB pathways. Blockage of ubiquitin-proteasome pathway significantly inhibits CAR degradation, as indicated by the reappearance of CAR at the site of cell-cell contact. Additionally, IFNG+TNF reduces CAR mRNA via transcriptional regulation. Mutational studies have shown that IFNG+TNF-induced CAR repression is achieved by suppression of the basal transcription. Electrophoretic mobility shift assay and chromatin immunoprecipitation assays further confirmed that IFNG+TNF treament not only inhibits binding of the basal transcription factors but also promotes binding of NFKB subunits and Sp1 (negative regulators) to the CAR promoter region. Taken together, IFNG+TNF treatment significantly downregulates CAR expression, which provides an explanation of how cell sloughing in the epithelium mediates, by loss of CAR-based cell adhesion, during testicular inflammation.

Transforming growth factor β regulates P-body formation through induction of the mRNA decay factor tristetraprolin

Transforming growth factor β (TGF-β) is a potent growth regulator and tumor suppressor in normal intestinal epithelium. Likewise, epithelial cell growth is controlled by rapid decay of growth-related mRNAs mediated through 3' untranslated region (UTR) AU-rich element (ARE) motifs. We demonstrate that treatment of nontransformed intestinal epithelial cells with TGF-β inhibited ARE-mRNA expression. This effect of TGF-β was promoted through increased assembly of cytoplasmic RNA processing (P) bodies where ARE-mRNA localization was observed. P-body formation was dependent on TGF-β/Smad signaling, as Smad3 deletion abrogated P-body formation. In concert with increased P-body formation, TGF-β induced expression of the ARE-binding protein tristetraprolin (TTP), which colocalized to P bodies. TTP expression was necessary for TGF-β-dependent P-body formation and promoted growth inhibition by TGF-β. The significance of this was observed in vivo, where colonic epithelium deficient in TGF-β/Smad signaling or TTP expression showed attenuated P-body levels. These results provide new insight into TGF-β's antiproliferative properties and identify TGF-β as a novel mRNA stability regulator in intestinal epithelium through its ability to promote TTP expression and subsequent P-body formation.

Tristetraprolin (TTP): interactions with mRNA and proteins, and current thoughts on mechanisms of action

Changes in mRNA stability and translation are critical control points in the regulation of gene expression, particularly genes encoding growth factors, inflammatory mediators, and proto-oncogenes. Adenosine and uridine (AU)-rich elements (ARE), often located in the 3' untranslated regions (3'UTR) of mRNAs, are known to target transcripts for rapid decay. They are also involved in the regulation of mRNA stability and translation in response to extracellular cues. This review focuses on one of the best characterized ARE binding proteins, tristetraprolin (TTP), the founding member of a small family of CCCH tandem zinc finger proteins. In this survey, we have reviewed the current status of TTP interactions with mRNA and proteins, and discussed current thinking about TTP's mechanism of action to promote mRNA decay. We also review the proposed regulation of TTP's functions by phosphorylation. Finally, we have discussed emerging evidence for TTP operating as a translational regulator. This article is part of a Special Issue entitled: RNA Decay mechanisms.

Transforming growth factor-β1 (TGF-β1) regulates cell junction restructuring via Smad-mediated repression and clathrin-mediated endocytosis of nectin-like molecule 2 (Necl-2)

Nectin-like molecule-2 (Necl-2), a junction molecule, is exclusively expressed by spermatogenic cells. It mediates homophilic interaction between germ cells and heterophilic interaction between Sertoli and germ cells. Knockout studies have shown that loss of Necl-2 causes male infertility, suggesting Necl-2-based cell adhesion is crucial for spermatogenesis. Transforming growth factor-βs (TGF-βs) are crucial for regulating cell junction restructuring that are required for spermatogenesis. In the present study, we aim to investigate the mechanism on how TGF-β1 regulates Necl-2 expression to achieve timely junction restructuring in the seminiferous epithelium during spermatogenesis. We have demonstrated that TGF-β1 reduces Necl-2 mRNA and protein levels at both transcriptional and post-translational levels. Using inhibitor and clathrin shRNA, we have revealed that TGF-β1 induces Necl-2 protein degradation via clathrin-dependent endocytosis. Endocytosis assays further confirmed that TGF-β1 accelerates the internalization of Necl-2 protein to cytosol. Immunofluorescence staining also revealed that TGF-β1 effectively removes Necl-2 from cell-cell interface. In addition, TGF-β1 reduces Necl-2 mRNA via down-regulating Necl-2 promoter activity. Mutational studies coupled with knockdown experiments have shown that TGF-β1-induced Necl-2 repression requires activation of Smad proteins. EMSA and ChIP assays further confirmed that TGF-β1 promotes the binding of Smad proteins onto MyoD and CCAATa motifs in vitro and in vivo. Taken together, TGF-β1 is a potent cytokine that provides an effective mechanism in controlling Necl-2 expression in the testis via Smad-dependent gene repression and clathrin-mediated endocytosis.

CLMP is essential for intestinal development, but does not play a key role in cellular processes involved in intestinal epithelial development

Loss-of-function mutations in CLMP have been found in patients with Congenital Short Bowel Syndrome (CSBS), suggesting that its encoded protein plays a major role in intestinal development. CLMP is a membrane protein that co-localizes with tight junction proteins, but its function is largely unknown. We expressed wild-type (WT)-CLMP and a mutant-CLMP (associated with CSBS) in human intestinal epithelial T84 cells that, as we show here, do not produce endogenous CLMP. We investigated the effects of WT-CLMP and mutant-CLMP proteins on key cellular processes that are important for intestinal epithelial development, including migration, proliferation, viability and transepithelial resistance. Our data showed that expression of WT-CLMP or mutant-CLMP does not affect any of these processes. Moreover, our aggregation assays in CHO cells show that CLMP does not act as a strong adhesion molecule. Thus, our data suggest that, in the in vitro model systems we used, the key processes involved in intestinal epithelial development appear to be unaffected by WT-CLMP or mutant-CLMP. Further research is needed to determine the role of CLMP in the development of the intestine.

MEKK1-MKK4-JNK-AP1 pathway negatively regulates Rgs4 expression in colonic smooth muscle cells

BACKGROUND

Regulator of G-protein Signaling 4 (RGS4) plays an important role in regulating smooth muscle contraction, cardiac development, neural plasticity and psychiatric disorder. However, the underlying regulatory mechanisms remain elusive. Our recent studies have shown that upregulation of Rgs4 by interleukin (IL)-1β is mediated by the activation of NFκB signaling and modulated by extracellular signal-regulated kinases, p38 mitogen-activated protein kinase, and phosphoinositide-3 kinase. Here we investigate the effect of the c-Jun N-terminal kinase (JNK) pathway on Rgs4 expression in rabbit colonic smooth muscle cells.

METHODOLOGY/PRINCIPAL FINDINGS

Cultured cells at first passage were treated with or without IL-1β (10 ng/ml) in the presence or absence of the selective JNK inhibitor (SP600125) or JNK small hairpin RNA (shRNA). The expression levels of Rgs4 mRNA and protein were determined by real-time RT-PCR and Western blot respectively. SP600125 or JNK shRNA increased Rgs4 expression in the absence or presence of IL-1β stimulation. Overexpression of MEKK1, the key upstream kinase of JNK, inhibited Rgs4 expression, which was reversed by co-expression of JNK shRNA or dominant-negative mutants for MKK4 or JNK. Both constitutive and inducible upregulation of Rgs4 expression by SP600125 was significantly inhibited by pretreatment with the transcription inhibitor, actinomycin D. Dual reporter assay showed that pretreatment with SP600125 sensitized the promoter activity of Rgs4 in response to IL-1β. Mutation of the AP1-binding site within Rgs4 promoter increased the promoter activity. Western blot analysis confirmed that IL-1β treatment increased the phosphorylation of JNK, ATF-2 and c-Jun. Gel shift and chromatin immunoprecipitation assays validated that IL-1β increased the in vitro and ex vivo binding activities of AP1 within rabbit Rgs4 promoter.

CONCLUSION/SIGNIFICANCE

Activation of MEKK1-MKK4-JNK-AP1 signal pathway plays a tonic inhibitory role in regulating Rgs4 transcription in rabbit colonic smooth muscle cells. This negative regulation may aid in maintaining the transient level of RGS4 expression.

Intratesticular expression of mRNAs of both interferon γ and tumor necrosis factor α is significantly increased in experimental autoimmune orchitis in mice

Experimental autoimmune orchitis (EAO) is one of the models of immunological male infertility. Murine EAO is CD4+T cell-dependent and classically induced by immunization with a testicular homogenate and adjuvants. We previously established that immunization with viable syngeneic testicular germ cells (TGC) can also induce murine EAO with no use of any adjuvant. Analyses of this EAO model have already revealed that cultured spleen cells of immunized mice secreted interferon (IFN)-γ and that treatment of the immunized mice with anti-IFN-γ monoclonal antibodies significantly suppressed the EAO. It is known that both IFN-γ and tumor necrosis factor (TNF)-α are representative cytokines of Th1 cells and exhibit local toxicity toward the seminiferous epithelium in vivo. However, changes in these two cytokines in EAO-affected testes have not yet been investigated. Therefore, in the present study, we investigated the expression of intratesticular IFN-γ and TNF- α mRNAs in TGC-induced EAO using real-time RT-PCR. The results demonstrated that the intratesticular mRNAs for both IFN-γ and TNF-α significantly increased, while other cytokines such as IL-1α, IL-1β, IL-6 and TGF-β did not show dramatic changes in the immunized mice. These results suggest that secretion of significant amounts of IFN-γ and TNF-α in situ contributes to the spermatogenic disturbance in EAO.

Inflammation: cytokines and RNA-based regulation

The outcome of an inflammatory response depends upon the coordinated regulation of a variety of both pro-inflammatory and anti-inflammatory cytokines and other proteins. Regulation of these inflammation mediators can occur at multiple levels, including transcription, mRNA translation, post-translational modifications, and mRNA degradation. Post-transcriptional regulation has been shown to play an important role in controlling the expression of these mediators, allowing for normal initiation and resolution of the inflammatory response. Many inflammatory mediators have unstable mRNAs due, in part, to the presence of AU-rich elements in their 3'-untranslated regions. Increasing numbers of RNA-binding proteins have been identified that can bind to these AU-rich elements and then regulate the stability and/or translation of the mRNA. This review summarizes current knowledge about the role of several RNA-binding proteins that act through AU-rich elements to post-transcriptionally regulate the biosynthesis of proteins involved in inflammation.