The transcriptional repressor REST determines the cell-specific expression of the human MAPK8IP1 gene encoding IB1 (JIP-1).

Islet-brain 1 (IB1) is the human and rat homologue of JIP-1, a scaffold protein interacting with the c-Jun amino-terminal kinase (JNK). IB1 expression is mostly restricted to the endocrine pancreas and to the central nervous system. Herein, we explored the transcriptional mechanism responsible for this preferential islet and neuronal expression of IB1. A 731-bp fragment of the 5' regulatory region of the human MAPK8IP1 gene was isolated from a human BAC library and cloned upstream of a luciferase reporter gene. This construct drove high transcriptional activity in both insulin-secreting and neuron-like cells but not in unrelated cell lines. Sequence analysis of this promoter region revealed the presence of a neuron-restrictive silencer element (NRSE) known to bind repressor zinc finger protein REST. This factor is not expressed in insulin-secreting and neuron-like cells. By mobility shift assay, we confirmed that REST binds to the NRSE present in the IB1 promoter. Once transiently transfected in beta-cell lines, the expression vector encoding REST repressed IB1 transcriptional activity. The introduction of a mutated NRSE in the 5' regulating region of the IB1 gene abolished the repression activity driven by REST in insulin-secreting beta cells and relieved the low transcriptional activity of IB1 observed in unrelated cells. Moreover, transfection in non-beta and nonneuronal cell lines of an expression vector encoding REST lacking its transcriptional repression domain relieved IB1 promoter activity. Last, the REST-mediated repression of IB1 could be abolished by trichostatin A, indicating that deacetylase activity is required to allow REST repression. Taken together, these data establish a critical role for REST in the control of the tissue-specific expression of the human IB1 gene.

Fas-associated death domain protein (FADD) and caspase-8 mediate up-regulation of c-Fos by Fas ligand and tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) via a FLICE inhibitory protein (FLIP)-regulated pathway.

Fas, a death domain-containing member of the tumor necrosis factor receptor family and its ligand FasL have been predominantly studied with respect to their capability to induce cell death. However, a few studies indicate a proliferation-inducing signaling activity of these molecules too. We describe here a novel signaling pathway of FasL and the tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) that triggers transcriptional activation of the proto-oncogene c-fos, a typical target gene of mitogenic pathways. FasL- and TRAIL-mediated up-regulation of c-Fos was completely dependent on the presence of Fas-associated death domain protein (FADD) and caspase-8, but caspase activity seemed to be dispensable as a pan inhibitor of caspases had no inhibitory effect. Upon overexpression of the long splice form of cellular FADD-like interleukin-1-converting enzyme (FLICE) inhibitory protein (cFLIP) in Jurkat cells, FasL- and TRAIL-induced up-regulation of c-Fos was almost completely blocked. The short splice form of FLIP, however, showed a rather stimulatory effect on c-Fos induction. Together these data demonstrate the existence of a death receptor-induced, FADD- and caspase-8-dependent pathway leading to c-Fos induction that is inhibited by the long splice form FLIP-L.

IB1, a JIP-1-related nuclear protein present in insulin-secreting cells.

JIP-1 is a cytoplasmic inhibitor of the c-Jun amino-terminal kinase activated pathway recently cloned from a mouse brain cDNA library. We report herein the expression cloning of a rat cDNA encoding a JIP-1-related nuclear protein from a pancreatic beta-cell cDNA library that we named IB1 for Islet-Brain 1. IB1 was isolated by its ability to bind to GTII, a cis-regulatory element of the GLUT2 promoter. The IB1 cDNA encodes a 714-amino acid protein, which differs from JIP-1 by the insertion of 47 amino acids in the carboxyl-terminal part of the protein. The remaining 667 amino acids are 97% identical to JIP-1. The 47-amino acid insertion contains a truncated phosphotyrosine interaction domain and a putative helix-loop-helix motif. Recombinant IB1 (amino acids 1-714 and 280-714) was shown to bind in vitro to GTII. Functionally IB1 transactivated the GLUT2 gene. IB1 was localized within the cytoplasm and the nucleus of insulin-secreting cells or COS-7 cells transfected with an expression vector encoding IB1. Using a heterologous GAL4 system, we localized an activation domain of IB1 within the first 280 amino acids of the protein. These data demonstrate that IB1 is a DNA-binding protein related to JIP-1, which is highly expressed in pancreatic beta-cells where it functions as a transactivator of the GLUT2 gene.

Quantitative proteomics reveals subset-specific viral recognition in dendritic cells.

Dendritic cell (DC) populations consist of multiple subsets that are essential orchestrators of the immune system. Technological limitations have so far prevented systems-wide accurate proteome comparison of rare cell populations in vivo. Here, we used high-resolution mass spectrometry-based proteomics, combined with label-free quantitation algorithms, to determine the proteome of mouse splenic conventional and plasmacytoid DC subsets to a depth of 5,780 and 6,664 proteins, respectively. We found mutually exclusive expression of pattern recognition pathways not previously known to be different among conventional DC subsets. Our experiments assigned key viral recognition functions to be exclusively expressed in CD4(+) and double-negative DCs. The CD8alpha(+) DCs largely lack the receptors required to sense certain viruses in the cytoplasm. By avoiding activation via cytoplasmic receptors, including retinoic acid-inducible gene I, CD8alpha(+) DCs likely gain a window of opportunity to process and present viral antigens before activation-induced shutdown of antigen presentation pathways occurs.

The scaffold protein IB1/JIP-1 controls the activation of JNK in rat stressed urothelium.

The c-Jun N-terminal kinase (JNK) is critical for cell survival, differentiation, apoptosis and tumorigenesis. This signalling pathway requires the presence of the scaffold protein Islet-Brain1/c-Jun N-terminal kinase interacting protein-1 (IB1/JIP-1). Immunolabeling and in situ hybridisation of bladder sections showed that IB1/JIP-1 is expressed in urothelial cells. The functional role of IB1/JIP-1 in the urothelium was therefore studied in vivo in a model of complete rat bladder outlet obstruction. This parietal stress, which is due to urine retention, reduced the content of IB1/JIP-1 in urothelial cells and consequently induced a drastic increase in JNK activity and AP-1 binding activity. Using a viral gene transfer approach, the stress-induced activation of JNK was prevented by overexpressing IB1/JIP-1. Conversely, the JNK activity was increased in urothelial cells where the IB1/JIP-1 content was experimentally reduced using an antisense RNA strategy. Furthermore, JNK activation was found to be increased in non-stressed urothelial cells of heterozygous mice carrying a selective disruption of the IB1/JIP-1 gene. These data established that mechanical stress in urothelial cells in vivo induces a robust JNK activation as a consequence of regulated expression of the scaffold protein IB1/JIP-1. This result highlights a critical role for that scaffold protein in the homeostasis of the urothelium and unravels a new potential target to regulate the JNK pathway in this tissue.

MyD88, an adapter protein involved in interleukin-1 signaling.

MyD88 has a modular organization, an N-terminal death domain (DD) related to the cytoplasmic signaling domains found in many members of the tumor necrosis factor receptor (TNF-R) superfamily, and a C-terminal Toll domain similar to that found in the expanding family of Toll/interleukin-1-like receptors (IL-1R). This dual domain structure, together with the following observations, supports a role for MyD88 as an adapter in IL-1 signal transduction; MyD88 forms homodimers in vivo through DD-DD and Toll-Toll interactions. Overexpression of MyD88 induces activation of the c-Jun N-terminal kinase (JNK) and the transcription factor NF-kappaB through its DD. A point mutation in MyD88, MyD88-lpr (F56N), which prevents dimerization of the DD, also blocks induction of these activities. MyD88-induced NF-kappaB activation is inhibited by the dominant negative versions of TRAF6 and IRAK, which also inhibit IL-1-induced NF-kappaB activation. Overexpression of MyD88-lpr or MyD88-Toll (expressing only the Toll domain) acted to inhibit IL-1-induced NF-kappaB and JNK activation in a 293 cell line overexpressing the IL-1RI. MyD88 coimmunoprecipitates with the IL-1R signaling complex in an IL-1-dependent manner.

Fas triggers an alternative, caspase-8-independent cell death pathway using the kinase RIP as effector molecule.

Cell death is achieved by two fundamentally different mechanisms: apoptosis and necrosis. Apoptosis is dependent on caspase activation, whereas the caspase-independent necrotic signaling pathway remains largely uncharacterized. We show here that Fas kills activated primary T cells efficiently in the absence of active caspases, which results in necrotic morphological changes and late mitochondrial damage but no cytochrome c release. This Fas ligand-induced caspase-independent death is absent in T cells that are deficient in either Fas-associated death domain (FADD) or receptor-interacting protein (RIP). RIP is also required for necrotic death induced by tumor necrosis factor (TNF) and TNF-related apoptosis-inducing ligand (TRAIL). In contrast to its role in nuclear factor kappa B activation, RIP requires its own kinase activity for death signaling. Thus, Fas, TRAIL and TNF receptors can initiate cell death by two alternative pathways, one relying on caspase-8 and the other dependent on the kinase RIP.

FIST/HIPK3: a Fas/FADD-interacting serine/threonine kinase that induces FADD phosphorylation and inhibits fas-mediated Jun NH(2)-terminal kinase activation.

Fas is a cell surface death receptor that signals apoptosis. Several proteins have been identified that bind to the cytoplasmic death domain of Fas. Fas-associated death domain (FADD), which couples Fas to procaspase-8, and Daxx, which couples Fas to the Jun NH(2)-terminal kinase pathway, bind independently to the Fas death domain. We have identified a 130-kD kinase designated Fas-interacting serine/threonine kinase/homeodomain-interacting protein kinase (FIST/HIPK3) as a novel Fas-interacting protein. Binding to Fas is mediated by a conserved sequence in the COOH terminus of the protein. FIST/HIPK3 is widely expressed in mammalian tissues and is localized both in the nucleus and in the cytoplasm. In transfected cell lines, FIST/HIPK3 causes FADD phosphorylation, thereby promoting FIST/HIPK3-FADD-Fas interaction. Although Fas ligand-induced activation of Jun NH(2)-terminal kinase is impaired by overexpressed active FIST/HIPK3, cell death is not affected. These results suggest that Fas-associated FIST/HIPK3 modulates one of the two major signaling pathways of Fas.

The A-kinase anchoring protein (AKAP)-Lbc-signaling complex mediates alpha1 adrenergic receptor-induced cardiomyocyte hypertrophy.

In response to various pathological stresses, the heart undergoes a pathological remodeling process that is associated with cardiomyocyte hypertrophy. Because cardiac hypertrophy can progress to heart failure, a major cause of lethality worldwide, the intracellular signaling pathways that control cardiomyocyte growth have been the subject of intensive investigation. It has been known for more than a decade that the small molecular weight GTPase RhoA is involved in the signaling pathways leading to cardiomyocyte hypertrophy. Although some of the hypertrophic pathways activated by RhoA have now been identified, the identity of the exchange factors that modulate its activity in cardiomyocytes is currently unknown. In this study, we show that AKAP-Lbc, an A-kinase anchoring protein (AKAP) with an intrinsic Rho-specific guanine nucleotide exchange factor activity, is critical for activating RhoA and transducing hypertrophic signals downstream of alpha1-adrenergic receptors (ARs). In particular, our results indicate that suppression of AKAP-Lbc expression by infecting rat neonatal ventricular cardiomyocytes with lentiviruses encoding AKAP-Lbc-specific short hairpin RNAs strongly reduces both alpha1-AR-mediated RhoA activation and hypertrophic responses. Interestingly, alpha1-ARs promote AKAP-Lbc activation via a pathway that requires the alpha subunit of the heterotrimeric G protein G12. These findings identify AKAP-Lbc as the first Rho-guanine nucleotide exchange factor (GEF) involved in the signaling pathways leading to cardiomyocytes hypertrophy.

TCR-induced NF-kappaB activation: a crucial role for Carma1, Bcl10 and MALT1.

T-cell receptor (TCR) engagement induces the maturation of thymocytes and the activation and proliferation of peripheral T cells through signaling pathways that target several transcription factors. The transcription factor nuclear factor-κB (NF-κB) has an essential role in the activation of mature T cells but the signaling pathway leading from TCR stimulation to NF-κB activation is not well defined. Carma1, Bcl10 and MALT1 are recently identified proteins that have an important and previously unexpected role in antigen receptor-induced NF-κB activation and the control of lymphocyte proliferation. We believe that the recent advances in this field could stimulate research for the development of new immunomodulatory drugs and could lead to a better understanding of the molecular mechanisms underlying the formation of lymphomas and potentially of other immune disorders.

The proteolytic activity of the paracaspase MALT1 is key in T cell activation

The paracaspase MALT1 is pivotal in antigen receptor-mediated lymphocyte activation and lymphomagenesis. MALT1 contains a caspase-like domain, but it is unknown whether this domain is proteolytically active. Here we report that MALT1 had arginine-directed proteolytic activity that was activated after T cell stimulation, and we identify the signaling protein Bcl-10 as a MALT1 substrate. Processing of Bcl-10 after Arg228 was required for T cell receptor-induced cell adhesion to fibronectin. In contrast, MALT1 activity but not Bcl-10 cleavage was essential for optimal activation of transcription factor NF-kappaB and production of interleukin 2. Thus, the proteolytic activity of MALT1 is central to T cell activation, which suggests a possible target for the development of immunomodulatory or anticancer drugs

Variations in IB1/JIP1 expression regulate susceptibility of beta-cells to cytokine-induced apoptosis irrespective of C-Jun NH2-terminal kinase signaling.

We previously reported that interleukin-1beta (IL-1beta) alone does not cause apoptosis of beta-cells, whereas when combined with gamma-interferon (IFN-gamma) and tumor necrosis factor-alpha (TNF-alpha), it exerts a distinct apoptotic effect. Studies in beta-cell lines indicated that IL-1beta reduced expression of islet brain (IB)-1/JNK interacting protein (JIP)-1, a JNK scaffold protein with antiapoptotic action. We examined whether variations in IB1/JIP-1 expression in purified primary beta-cells affect their susceptibility to cytokine-induced apoptosis. Exposure to IL-1beta for 24 h decreased cellular IB1/JIP-1 content by 66 +/- 17%; this IL-1beta effect was maintained in the presence of TNF-alpha + IFN-gamma, which did not influence IB1/JIP-1 levels by themselves. Addition of IL-1beta to TNF-alpha + IFN-gamma increased apoptosis from 20 +/- 2% to 59 +/- 5%. A similar increase in TNF-alpha + IFN-gamma-induced apoptosis was produced by adenoviral expression of antisense IB1/JIP-1 and was not further enhanced by addition of IL-1beta, indicating that IL-1beta-mediated suppression of IB1/JIP-1 in beta-cells increases their susceptibility to cytokine-induced apoptosis. However, adenovirally mediated overexpression of IB1/JIP-1 also potentiated TNF-alpha + IFN-gamma-induced apoptosis, suggesting that the antiapoptotic effect of IB1/JIP-1 depends on well-defined cellular levels. We conclude that the IB1/JIP-1 level in beta-cells can control their susceptibility to apoptosis independent of JNK signaling.

Proximal 11p deletion syndrome (P11pDS): additional evaluation of the clinical and molecular aspects.

The combination of multiple exostoses (EXT) and enlarged parietal foramina (foramina parietalia permagna, FPP) represent the main features of the proximal 11p deletion syndrome (P11pDS), a contiguous gene syndrome (MIM 601224) caused by an interstitial deletion on the short arm of chromosome 11. Here we present clinical aspects of two new P11pDS patients and the clinical follow-up of one patient reported in the original paper describing this syndrome. Recognised clinical signs include EXT, FPP, mental retardation, facial asymmetry, asymmetric calcification of coronary sutures, defective vision (severe myopia, nystagmus, strabismus), skeletal anomalies (small hands and feet, tapering fingers), heart defect, and anal stenosis. In addition fluorescence in situ hybridisation and molecular analysis were performed to gain further insight in potential candidate genes involved in P11pDS.

Equine herpesvirus protein E10 induces membrane recruitment and phosphorylation of its cellular homologue, bcl-10.

v-E10, a caspase recruitment domain (CARD)-containing gene product of equine herpesvirus 2, is the viral homologue of the bcl-10 protein whose gene was found to be translocated in mucosa-associated lymphoid tissue (MALT) lymphomas. v-E10 efficiently activates the c-jun NH(2)-terminal kinase (JNK), p38 stress kinase, and the nuclear factor (NF)-kappaB transcriptional pathway and interacts with its cellular homologue, bcl-10, via a CARD-mediated interaction. Here we demonstrate that v-E10 contains a COOH-terminal geranylgeranylation consensus site which is responsible for its plasma membrane localization. Expression of v-E10 induces hyperphosphorylation and redistribution of bcl-10 from the cytoplasm to the plasma membrane, a process which is dependent on the intactness of the v-E10 CARD motif. Both membrane localization and a functional CARD motif are important for v-E10-mediated NF-kappaB induction, but not for JNK activation, which instead requires a functional v-E10 binding site for tumor necrosis factor receptor-associated factor (TRAF)6. Moreover, v-E10-induced NF-kappaB activation is inhibited by a dominant negative version of the bcl-10 binding protein TRAF1, suggesting that v-E10-induced membrane recruitment of cellular bcl-10 induces constitutive TRAF-mediated NF-kappaB activation.