A key feature of memory processes is to link different input signals by association and to preserve this coupling at the level of synaptic connections. Late-phase long-term potentiation (L-LTP), a form of synaptic plasticity thought to encode long-term memory, requires gene transcription and protein synthesis. In this study, we report that a recently cloned coactivator of cAMP-response elementbinding protein (CREB), called transducer of regulated CREB activity 1 (TORC1), contributes to this process by sensing the coincidence of calcium and cAMP signals in neurons and by converting it into a transcriptional response that leads to the synthesis of factors required for enhanced synaptic transmission. We provide evidence that TORC1 is involved in L-LTP maintenance at the Schaffer collateral-CA1 synapses in the hippocampus.BDNF ͉ calcineurin ͉ cAMP-response element-binding protein ͉ long-term potentiation ͉ memory T ransducers of regulated cAMP-response element-binding protein (CREB) activity (TORCs) are newly discovered coactivators that dramatically increase CREB's transcriptional activity independently of CREB Ser-133 phosphorylation (1, 2). Recently, it has been shown that TORC2 functions as a pancreatic coincidence detector. In insulinoma cells, glucose and gut hormones, via respective activation of L-type calcium channels and the cAMP pathway, synergistically promote the dephosphorylation and the concomitant nuclear translocation of TORC2 (3). In the brain, encoding and storing associative memories requires detection of the coincidence of different input signals and translation of these associations into changes in the number, structure, or function of synapses. Therefore, it appears that short-lived coincidences result in the transcriptional activation of genes encoding factors required for enhanced synaptic transmission. TORCs present two features that neurons could use to create an association: they can detect the coincidence of the two most important second messengers, calcium and cAMP, and they are potent coactivators of CREB, a transcription factor known to drive the expression of genes underlying synaptic plasticity, late-phase long-term potentiation (L-LTP), learning, and memory (4-7).CREB-dependent promoters have been generally thought to respond to various intracellular and extracellular cues by the stimulus-dependent phosphorylation of CREB at Ser-133 and resultant recruitment of the coactivator CREB binding protein (CBP) (5,6,8,9). Modification of CREB at this site often mirrors the activation of neurons, leading to the idea that the expression of plasticity-related genes relies on CREB/CBP interaction. However, some studies revealing a discrepancy between CREB phosphorylation and CREB-mediated gene transcription have challenged this model. For instance, monocular deprivation induces LacZ expression in the visual cortex of cAMP-response element (CRE)-LacZ transgenic mice (10), whereas phosphorylation of CREB at Ser-133 remains static (11). Similarly, the mechanism underlying CREB activation during L...

Type 2 diabetes is a polygenic and genetically heterogeneous disease . The age of onset of the disease is usually late and environmental factors may be required to induce the complete diabetic phenotype. Susceptibility genes for diabetes have not yet been identified. Islet-brain-1 (IB1, encoded by MAPK8IP1), a novel DNA-binding transactivator of the glucose transporter GLUT2 (encoded by SLC2A2), is the homologue of the c-Jun amino-terminal kinase-interacting protein-1 (JIP-1; refs 2-5). We evaluated the role of IBi in beta-cells by expression of a MAPK8IP1 antisense RNA in a stable insulinoma beta-cell line. A 38% decrease in IB1 protein content resulted in a 49% and a 41% reduction in SLC2A2 and INS (encoding insulin) mRNA expression, respectively. In addition, we detected MAPK8IP1 transcripts and IBi protein in human pancreatic islets. These data establish MAPK8IP1 as a candidate gene for human diabetes. Sibpair analyses performed on i49 multiplex French families with type 2 diabetes excluded MAPK8IP1 as a major diabetogenic locus. We did, however, identify in one family a missense mutation located in the coding region of MAPK8IP1 (559N) that segregated with diabetes. In vitro, this mutation was associated with an inability of IB1 to prevent apoptosis induced by MAPK/ERK kinase kinase 1 (MEKK1) and a reduced ability to counteract the inhibitory action of the activated c-JUN amino-terminal kinase (JNK) pathway on INS transcriptional activity. Identification of this novel non-maturity onset diabetes of the young (MODY) form of diabetes demonstrates that IB1 is a key regulator of 3-cell function.

CCAAT/enhancer-binding protein (C/EBP) family members are transcription factors involved in important physiological processes, such as cellular proliferation and differentiation, regulation of energy homeostasis, inflammation, and hematopoiesis. Transcriptional activation by C/EBP␣ and C/EBP␤ involves the coactivators CREB-binding protein (CBP) and p300, which promote transcription by acetylating histones and recruiting basal transcription factors. In this study, we show that C/EBP␦ is also using CBP as a coactivator. Based on sequence homology with C/EBP␣ and -␤, we identify in C/EBP␦ two conserved amino acid segments that are necessary for the physical interaction with CBP. Using reporter gene assays, we demonstrate that mutation of these residues prevents CBP recruitment and diminishes the transactivating potential of C/EBP␦. In addition, our results indicate that C/EBP family members not only recruit CBP but specifically induce its phosphorylation. We provide evidence that CBP phosphorylation depends on its interaction with C/EBP␦ and define point mutations within one of the two conserved amino acid segments of C/EBP␦ that abolish CBP phosphorylation as well as transcriptional activation, suggesting that this new mechanism could be important for C/EBP-mediated transcription.The CCAAT/enhancer-binding protein (C/EBP) 1 family is composed of pleiotropic transcription factors involved in tissuespecific metabolic gene transcription, in signal transduction activated by several cytokines, and in cell differentiation (for a review, see Refs. 1-7). Six members of the family have been described so far: C/EBP␣, C/EBP␤, C/EBP␦, C/EBP␥, C/EBP⑀, and C/EBP (8). C/EBP isoforms bind to their cognate DNA element through a bipartite domain called bZIP. This domain consists of a basic region, contacting DNA, and a homo-or heterodimer-forming region called the leucine zipper (9). Because of the high conservation in the bZIP domain, C/EBP family members are able to form homo-or heterodimers, and all, except C/EBP , bind to the same cis-regulatory elements.C/EBP␣, C/EBP␤, and C/EBP␦ are involved in terminal differentiation of a variety of cells including adipocytes (10), hepatocytes (11,12), gut epithelial cells (13), macrophages (14), myelomonocytes (15), and neurons (16,17). In the nervous system, the role of C/EBP family members is not characterized as well as, for instance, in adipocytes or hepatocytes. However, a recent study suggests that they are essential for cortical progenitor cells to become postmitotic neurons (16). Interestingly, certain C/EBP isoforms appear to be involved in learning and memory processes (18 -20), glial or neuronal cell functions (21-23), and neurotrophic factor expression (24).Knock-out mice were generated for different C/EBP isoforms (reviewed in Refs. 7,8,and 10). These C/EBP-deficient mice display various phenotypes extending from perinatal lethality (for C/EBP␣) to subtle abnormalities. These different phenotypes suggest that C/EBP family members are not functionally redundant, which, to a cer...

IB1/JIP-1 are recently characterized mammalian scaffold proteins involved in the regulation of the JNK 1 signaling pathway (1-3). These two isoforms bind to and associate in a single transduction complex three kinases, MLK3, MKK7, and JNK, which together constitute an ordered unit of sequential signaling molecules transducing a variety of stress signals (2, 3). To date, five different isoforms of the protein have been cloned, which are mainly N-terminal splice variants that arise from expression of one single gene on human chromosome 11p11.2-p12 (1, 4, 5). A S59N mutation close to the JNK binding domain of IB1 has recently been associated with a late onset type 2 diabetes (6). Functionally, this mutation led to an increased susceptibility of JNK-mediated apoptosis in different cell systems, implying a presumably important functional role of IB1 in controlling the cell response to proapoptotic stimuli (6).Interleukin 1 (IL-1␤), which activates JNK essentially through the MKK7 pathway in several cells and tissues (7-10), is believed to play a key role in the process of selective ␤ cell destruction observed in type 1 diabetes. Chronic exposure of pancreatic islets or of ␤-derived cell lines to IL-1␤ had been shown to lead to the selective death of the ␤ cells, whereas non-␤ cells such as glucagon-producing cells appeared more resistant to the action of the cytokine (reviewed in Refs. 11-15). The molecular basis for the preferential killing of pancreatic ␤ versus ␣ cells by IL-1␤ is not fully understood. One important player in this phenomenon is the inducible nitric-oxide synthase gene iNOS, which is specifically expressed in the ␤ cells upon IL-1␤ treatment (16 -20). A number of reports have indeed clearly shown that ␤ cell apoptosis is NO-dependent (see for example two recent reports (21, 22)). In line with this, pancreatic islets from iNOS KO mice show a better resistance to IL-1␤ cytotoxicity (23).This NO-dependent killing of ␤ cells has been, however, challenged by several reports pointing to the existence of NOindependent death signaling pathways (24, 25). For example, there is no direct correlation between expression of iNOS and sensitivity to IL-1␤ between ␤ cells at different stages of differentiation (26). Importantly, the iNOS inhibitor L-NMMA does not prevent IL-1␤-induced ␤ cell death in rat or human islets (24,25). It is also possible to block NO synthesis by blocking the extracellular signal-regulated kinase and p38 MAP kinase pathways, however, without any positive effect on cell survival (17).To better understand the molecular mechanisms that specifically sensitize ␤ cells to IL-1␤-induced death, we recently used two different subclones of the pluripotent pancreatic endocrine stem cell clone (MSL). The MSL AN697C1 subclone gave rise to two derived cell lines, namely the glucagon-secreting AN-glu, and after stable transfection with the transcription factor pancreatic duodenal homeobox factor-1, the insulin secreting ANins (27). Despite having similar rates of NO synthesis, we found that the AN-ins c...