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Results for “Cyclic AMP Response Element Modulator”

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PubMed1997

Ectopic ICER expression in pituitary corticotroph AtT20 cells: effects on morphology, cell cycle, and hormonal production.

The products of the cAMP response element modulator (CREM) gene play an important role in the transcriptional response to cAMP in endocrine cells. By virtue of an alternative, intronic promoter within the gene, the inducible cAMP early repressor (ICER) isoform is generated. ICER was shown to act as a dominant negative regulator and to be cAMP-inducible in various neuroendocrine cells and tissues. ICER negatively autoregulates its own expression and has been postulated to participate in the molecular events governing oscillatory hormonal regulations. To elucidate ICER function in pituitary physiology, we have generated AtT20 corticotroph cell lines expressing the sense or antisense ICER transcript under the control of the cadmium-inducible human methallothionein IIA promoter. Here we demonstrate that changes in the regulated levels of ICER have drastic consequences on the physiology of the corticotrophs. Ectopic ICER expression induces remarkable modifications in AtT20 morphology. Cells with persistent, nonregulated high levels of ICER are blocked in the G2/M phase of the cell cycle, while the opposite effect is obtained in cells expressing an antisense ICER transcript. We show that the effect of ICER on the AtT20 cell cycle is correlated to a direct down-regulation of the cyclin A gene promoter by ICER. Finally, we show that ACTH hormonal secretion from the corticotrophs is completely blocked by ICER ectopic expression. Interestingly, this effect is not due to a direct regulation of the POMC gene, but is mediated by a transcriptional control of the prohormone convertase 1 gene. These results point to a key regulatory function of CREM in pituitary physiology.

Animals↗

PubMed2001

Molecular basis of deficient IL-2 production in T cells from patients with systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) is a multifactorial autoimmune disease characterized by diverse cellular and biochemical aberrations, including decreased production of IL-2. Here we show that nuclear extracts from unstimulated SLE T cells, unlike extracts from normal T cells, express increased amounts of phosphorylated cAMP-responsive element modulator (p-CREM) that binds the -180 site of the IL-2 promoter. Nuclear extracts from stimulated normal T cells display increased binding of phosphorylated cAMP-responsive element binding protein (p-CREB) to the -180 site of the IL-2 promoter, whereas nuclear extracts from stimulated SLE T cells display primarily p-CREM and decreased p-CREB binding. In SLE T cells, p-CREM bound to the transcriptional coactivators, CREB binding protein and p300. Increased expression of p-CREM correlated with decreased production of IL-2. The transcription of a reporter gene driven by the -180 site was enhanced in normal T cells, but was suppressed in SLE T cells. These experiments demonstrate that transcriptional repression is responsible for the decreased production of IL-2 by SLE T cells.

5' Untranslated Regions↗

PubMed1998

Dynamic changes in the subnuclear organisation of pre-mRNA splicing proteins and RBM during human germ cell development.

RBM is a germ-cell-specific RNA-binding protein encoded by the Y chromosome in all mammals, implying an important and evolutionarily conserved (but as yet unidentified) function during male germ cell development. In order to address this function, we have developed new antibody reagents to immunolocalise RBM in the different cell types in the human testis. We find that RBM has a different expression profile from its closest homologue hnRNPG. Despite its ubiquitous expression in all transcriptionally active germ cell types, RBM has a complex and dynamic cell biology in human germ cells. The ratio of RBM distributed between punctate nuclear structures and the remainder of the nucleoplasm is dynamically modulated over the course of germ cell development. Moreover, pre-mRNA splicing components are targeted to the same punctate nuclear regions as RBM during the early stages of germ cell development but late in meiosis this spatial association breaks down. After meiosis, pre-mRNA splicing components are differentially targeted to a specific region of the nucleus. While pre-mRNA splicing components undergo profound spatial reorganisations during spermatogenesis, neither heterogeneous ribonucleoproteins nor the transcription factor Sp1 show either developmental spatial reorganisations or any specific co-localisation with RBM. These results suggest dynamic and possibly multiple functions for RBM in germ cell development.

Cyclic AMP Response Element Modulator↗

PubMed1999

Regulation of cAMP responsive element binding modulator isoforms in cultured rat ovarian granulosa cells.

A pituitary glycoprotein hormone FSH stimulates ovarian granulosa cells to induce ovarian follicular development. In this study we identified rat ovarian genes that were rapidly induced by FSH in the cultured rat granulosa cells by means of subtraction cloning. Complementary DNA clones encoding cAMP responsive element binding modulator (CREM) were identified as one of the FSH inducible genes. Northern blotting and reverse transcription and polymerase chain reaction (RT-PCR) analyses revealed that only the repressor type of CREM gene products, ICER (inducible cAMP early repressor) isoforms, were induced by FSH treatment in cultured rat granulosa cells. The induction of ICER by FSH was mimicked by reagents known to increase intracellular cAMP levels, indicating that the induction is through cAMP and protein kinase A signal transduction system. Induction of ICER was also confirmed as the protein levels. Electrophoretic mobility shift assay of granulosa cell extracts with a radiolabeled double stranded oligonucleotide corresponding to somatostatin cAMP responsive element also revealed that only the ICER proteins were induced by FSH treatment, whereas levels of CREM proteins were nearly constant regardless of the FSH treatment. Our present study demonstrates that FSH-induced and cAMP-mediated induction and attenuation of transcriptional responses by CREM gene products may be a key mechanistic component for the granulosa cell differentiation and proliferation.

Animals↗

PubMed1996

cAMP-response element modulator tau is a positive regulator of testis angiotensin converting enzyme transcription.

Testis angiotensin-converting enzyme (ACE) is a unique form of ACE, only produced by male germ cells, and results from a testis-specific promoter found within the ACE gene. We have investigated the role of cAMP-response element modulator (CREM)tau in testis ACE transcription. In gel shift experiments, testes nuclear proteins retard an oligonucleotide containing the cAMP-response element (CRE) found at position -55 in the testis ACE promoter. Anti-CREM antibody supershifts this complex. Competitive gel shift shows that recombinant CREM tau protein and testis nuclear proteins have a similar specificity of binding to the tests ACE CRE. Functional analysis using in vitro transcription and transfection studies also demonstrate that CREM tau protein is a transcriptional activator of the testis ACE promoter. Western blot analysis identifies CREM tau protein in the protein-DNA complex formed between nuclear proteins and the testis ACE CRE motif. This analysis also identified other CREM isoforms in the gel-shifted complex, which are thought to be CREM tau 1/2, CREM alpha/beta, and S-CREM. These data indicate that CREM tau isoforms play an important role as a positive regulator in the tissue-specific expression of testis ACE.

Animals↗

PubMed1999

Altered emotional and locomotor responses in mice deficient in the transcription factor CREM.

Various transcription factors act as nuclear effectors of the cAMP-dependent signaling pathway. These are the products of three genes in the mouse, CREB, CRE modulator (CREM), and ATF-1. CREM proteins are thought to play important roles within the hypothalamic-pituitary axis and in the control of rhythmic functions in the pineal gland. We have generated CREM-mutant mice and investigated their response in a variety of behavioral tests. CREM-null mice show a drastic increase in locomotion. In contrast to normal mice, the CREM-deficient mice show equal locomotor activity during the circadian cycle. The anatomy of the hypothalamic suprachiasmatic nuclei, the center of the endogenous pacemaker, is normal in mutant mice. Remarkably, CREM mutant mice also elicit a different emotional state, revealed by a lower anxiety in two different behavioral models, but they preserve the conditioned reactiveness to stress. These results demonstrate the high degree of functional specificity of each cAMP-responsive transcription factor in behavioral control.

Animals↗

PubMed1998

Identification and expression of a novel isoform of cAMP response element modulator in the human heart.

In end-stage human heart failure, excessive beta-adrenergic stimulation of the cAMP-dependent signaling pathway due to enhanced endogenous catecholamines is hypothesized to contribute to expressional alterations of myocardial regulatory proteins. The cAMP response element modulator (CREM) regulates the transcription of cAMP-responsive genes and might be involved in the regulation of cardiac gene expression. Using the reverse transcription polymerase chain reaction, we identified a novel CREM mRNA, CREM-Ib deltaC-X, in the human heart. Overexpression of CREM-Ib deltaC-X decreased cAMP response element (CRE) -mediated gene transcription in HIT-T15 cells, and this activity was assigned to the part of the sequence encoding putative internally translated proteins. Two of three possible internally translated proteins were immunologically identified in cells overexpressing CREM-Ib deltaC-X tagged with the hemagglutinin epitope of the influenza virus. Both proteins were expressed in bacteria and showed CRE-specific DNA binding, formation of heterodimers with the cAMP response element binding protein (CREB), and inhibition of CREB's binding to the CRE. CREM expression was detected on the mRNA and protein levels in the human heart. We conclude that CREM-Ib deltaC-X generates internally translated repressors of CRE-mediated gene transcription, suggesting the first example for the existence and function of human cardiac CREM.

Animals↗

PubMed1998

Transcriptional repressors are increased in pancreatic islets of type 2 diabetic rats.

To further clarify the mechanism of impaired insulin gene transcription in the diabetic state, we investigated the expression and function of the transcriptional repressor CREM (CRE modulator) in rat pancreatic islets. The CREM gene generates both transcriptional activators and repressors by alternative splicing and an intronic promoter. We isolated a novel alternatively spliced CREM isoform, CREM-17X, which efficiently represses insulin gene transcription, in addition to the three previously reported repressors. We also compared mRNA levels of insulin and the CREM repressors in pancreatic islets of Wistar and GK (Goto-Kakizaki) rats, the well-characterized spontaneous animal model of type 2 diabetes. The CREM repressor levels are increased, and the expression of insulin mRNA is decreased in GK rats, suggesting that increased CREM repressor expression in pancreatic islets could contribute to the decreased insulin gene transcription that results in impaired insulin secretion in type 2 diabetes.

Animals↗

PubMed2000

Induction of cAMP response element modulator (CREM) and inducible cAMP early repressor (ICER) expression in rat brain by uncompetitive N-methyl-D-aspartate receptor antagonists.

The N-methyl-D-aspartate (NMDA) subtype of glutamate receptor mediates fast excitatory neurotransmission, and agents that attenuate this function are neuroprotective, anesthetic, and psychotropic. To determine whether cAMP regulatable transcription factors play a role in the neurochemical actions of agents acting through NMDA receptors, the effects of the acute administration of uncompetitive and competitive antagonists on the expression of cAMP response element modulator (CREM) and inducible cAMP early repressor (ICER) transcription factors were examined. In situ hybridization to rat brain sections revealed that ICER mRNA expression was significantly increased by uncompetitive NMDA receptor antagonists (MK-801, phencyclidine, ketamine, memantine) but not by the competitive antagonist CPP [(+/-)-3-(2-carboxypiperazin-4-yl)-propyl-1-phosphonic acid] or other psychotropic agents (clozapine, haloperidol, desipramine). Major brain regions where ICER transcripts were increased were the hippocampus, parietal cortex layers IV and VI, temporal cortex, cingulate cortex, thalamus, and granule cell layer of the olfactory bulb. Northern and Western blot analyses indicated that CREM mRNA and protein, respectively, were also increased after MK-801 treatment, but ICER isoforms predominate during both basal and induced conditions. MK-801 also transiently increased the binding of proteins to cAMP response element, which was supershifted by anti-CREM antibody, indicating that increased mRNA and protein levels have functional consequences on gene transcription. These results provide evidence for the involvement of CREM and ICER family transcription factors in the pharmacologic effects of uncompetitive NMDA receptor antagonists.

Animals↗

PubMed1995

Developmental maturation of pineal gland function: synchronized CREM inducibility and adrenergic stimulation.

The cAMP response element modulator (CREM) gene encodes multiple activators and repressors of cAMP-responsive transcription. Differential splicing generates a developmental switch in CREM function during spermatogenesis, while the use of an alternative promoter is responsible for the production of a cAMP-inducible transcriptional repressor, ICER (inducible cAMP early repressor). The ICER promoter is strongly inducible by cAMP because of the presence of four tandemly repeated cAMP response elements. Furthermore, ICER negatively autoregulates the ICER promoter activity, thus generating a feedback loop. CREM constitutes an early response gene of the cAMP pathway in several neuroendocrine cells. We have previously shown that CREM is highly expressed in the adult rat pineal gland at nighttime. Here, we show that the only additional site of rhythmic ICER expression within the photoneuroendocrine system is the lamina intercalaris. Ontogenetically, the ICER day-night switch and cAMP inducibility mature in the pineal gland at the end of the first postnatal week. Importantly, this correlates with the onset of melatonin synthesis and the establishment of functional adrenergic innervation. At this developmental phase we document a significant increase in protein kinase A levels, thus suggesting that ICER inducibility reflects a complete maturation of the cAMP-dependent signaling pathway at the nuclear level.

Animals↗

PubMed2003

The cyclic adenosine 5'-monophosphate response element modulator suppresses IL-2 production in stimulated T cells by a chromatin-dependent mechanism.

The production of IL-2 is tightly controlled by several transcription factors that bind to the IL-2 promoter. The cAMP response element modulator (CREM) is known to form complexes with CREB and bind to the -180 site of the IL-2 promoter in anergic and in systemic lupus erythematosus T cells. In this study we show that CREM is transcriptionally induced in T cells following stimulation through CD3 and CD28, binds to the IL-2 promoter in vivo, and suppresses IL-2 production. Transfection of an antisense CREM plasmid into T cells blocked the expression and binding of CREM to the IL-2 promoter and the decrease of IL-2 production, which follows the early increase after T cell stimulation with CD3 and CD28. In addition, as assessed by chromatin immunoprecipitation experiments, antisense CREM prevented the binding of protein 300 and cAMP response element binding protein and promoted the acetylation of histones. Antisense CREM also enhanced the accessibility of the IL-2 promoter to endonucleases and prevented the condensation of chromatin in vivo. Our data suggest that upon T cell activation, CREM gradually replaces phosphorylated CREB at the -180 site of the IL-2 promoter. CREM, in turn, binds protein 300 and cAMP response element binding protein, but CREM is unable to activate its histone acetyltransferase activity, which results in condensation of chromatin and down-regulation of IL-2 production.

Acetyltransferases↗

PubMed2003

Transcriptional control in male germ cells: general factor TFIIA participates in CREM-dependent gene activation.

Regulation of gene expression in haploid male germ cells follows a number of specific rules that differ from somatic cells. In this physiological context, transcriptional control mediated by the activator CREM (cAMP-responsive element modulator) represents an established paradigm. In somatic cells activation by CREM requires its phosphorylation at a unique regulatory site (Ser117) and subsequent interaction with the ubiquitous coactivator CBP (cAMP response element binding protein-binding protein). In testis, CREM transcriptional activity is controlled through interaction with a tissue-specific partner, ACT (activator of CREM in testis), which confers a powerful, phosphorylation-independent activation capacity. In addition to specialized transcription factors and coactivators, a variety of general factors of the basal transcriptional machinery, and their distinct tissue-specific isoforms, are highly expressed in testis, supporting the general notion that testis-specific gene expression requires specialized mechanisms. Here, we describe that CREM interacts with transcription factor IIA (TFIIA), a general transcription factor that stimulates RNA polymerase II-directed transcription. This association was identified by a two-hybrid screen, using a testis-derived cDNA library, and confirmed by coimmunoprecipitation. The interaction is restricted to the activator isoforms of CREM and does not require Ser117. Importantly, CREM does not interact with TFIIAtau-ALF, a testis-specific TFIIA homolog. CREM and TFIIA are expressed in a spatially and temporally coordinated fashion during the differentiation program of germ cells. The two proteins also colocalize intracellularly in spermatocyte and spermatid cells. These findings contribute to the understanding of the highly specialized rules of transcriptional regulation in haploid germ cells.

Animals↗

PubMed1998

Cyclic adenosine 3',5'-monophosphate-responsive element modulator gene expression in germ cells of normo- and oligoazoospermic men.

In about one third of infertile men the cause of impaired spermatogenesis is not known. Spermatogenesis appears to be mediated at least in part by the pituitary gonadotropins, which activate the cAMP-dependent signaling pathway. The end point of this pathway is the activation of nuclear transcription factors, such as cAMP-responsive element-binding protein and cAMP-responsive element modulator (CREM). These factors, upon binding to gene sequences identified as cAMP response elements, modulate the expression of germ cell-specific genes that, in turn, promote the completion of spermatogenesis. The expressions of the cAMP-responsive element-binding protein and CREM genes create different isoforms, which can be divided into two groups: activators or repressors of gene regulation. Only CREM repressors are expressed in premeiotic germ cells in mice, whereas a switch to the expression of the CREM activator tau is observed from postmeiotic germ cells onward. Completion of germ cell maturation appears to be dependent on this phenomenon. Recently, mice lacking CREM gene expression have been generated. These animals were infertile and presented a developmental arrest of germ cell maturation at the stage of early spermatid. In this report we demonstrate that CREM gene expression also occurs in human germ cells. In particular, we determined by RT-PCR that a switch from the expression of CREM repressors to CREM activators is present in postmeiotic germ cells in normospermic men. Conversely, in oligoazoospermic patients only the expression of CREM repressors was detected. These data were confirmed by in situ hybridization studies in which transcripts for CREM activators were detected in postmeiotic germ cells in testis specimens showing conserved spermatogenesis, but not in specimens showing maturation arrest at the spermatid stage. Thus, our results indicate that the lack of a switch in the expression of CREM gene isoforms may be related to impaired spermatogenesis in humans.

Cyclic AMP Response Element Modulator↗

PubMed2003

Novel regulation of cardiac force-frequency relation by CREM (cAMP response element modulator).

The cAMP response element modulator (CREM) plays pivotal roles in the hypothalamic-pituitary-gonadal axis. CREM mRNA is robustly expressed in human myocardium, and identified isoforms may suppress cAMP response element-mediated transcription. However, little is known about the physiological importance of CREM in intact hearts remains unknown. We studied CREM-null mice and age-matched control littermates by in vivo pressure-volume loops to analyze basal and reserve cardiac function. Basal systolic and diastolic function, echocardiographic morphology, and myocardial histology were normal in CREM-null animals. However functional reserve with increasing heart rate was markedly depressed, with less contractile augmentation (+22+/-9% CREM-/- vs.+62+/-11% controls, P<0.05) and relaxation shortening (5+/-5% CREM-/- vs. -18+/-3% controls; P<0.05) at faster rates. In contrast, isoproterenol dose-responses were similar, suggesting normal beta-adrenergic receptor-coupled signaling. Gene expression of calcium handling proteins (SERCA, phospholamban) and stress-response genes (e.g., alpha-skeletal actin, beta-myosin heavy chain, natriuretic peptides) were similar between groups. However, total and serine-phosphorylated phospholamban protein declined -38 and -64% respectively, and protein phosphatase-1 (PP1) activity increased 44% without increased protein levels (all P<0.01) in CREM-/- vs. controls. These results demonstrate novel involvement of CREM in regulation of PP1 activity and of PLB, likely resulting in a potent frequency-dependent influence on cardiac function.

Adrenergic beta-Agonists↗

PubMed1999

Cyclic adenosine 3',5'-monophosphate(cAMP)/cAMP-responsive element modulator (CREM)-dependent regulation of cholesterogenic lanosterol 14alpha-demethylase (CYP51) in spermatids.

Lanosterol 14alpha-demethylase (CYP51) produces MAS sterols, intermediates in cholesterol biosynthesis that can reinitiate meiosis in mouse oocytes. As a cholesterogenic gene, CYP51 is regulated by a sterol/sterol-regulatory element binding protein (SREBP)-dependent pathway in liver and other somatic tissue. In testis, however, cAMP/cAMP-responsive element modulator CREMtau-dependent regulation of CYP51 predominates, leading to increased levels of shortened CYP51 mRNA transcripts. CREM-/- mice lack the abundant germ cell-specific CYP51 mRNAs in testis while expression of somatic CYP51 transcripts is unaffected. The mRNA levels of squalene synthase (an enzyme preceding CYP51 in cholesterol biosynthesis in testis of CREM-/- mice are unchanged as compared with wild-type animals, showing that regulation by CREMtau is not characteristic for all cholesterogenic genes expressed during spermatogenesis. The -334/+314 bp CYP51 region can mediate both the sterol/SREBP-dependent as well as the cAMP/CREMtau-dependent transcriptional activation. SREBP-1a from somatic cell nuclear extracts binds to a conserved CYP51-SRE1 element in the CYP51 proximal promoter. The cAMP-dependent transcriptional activator CREMtau from germ cell nuclear extracts binds to a conserved CYP51-CRE2 element while no SREBP-1 binding is observed in germ cells. The two regulatory pathways mediating expression of CYP51 describe this gene as a cholesterogenic gene (SREBP-dependent expression in liver and other somatic cells) and also as a haploid expressed gene (CREMtau-dependent expression in haploid male germ cells). While in somatic cells all genes involved in cholesterol biosynthesis are regulated coordinately by the sterol/SREBP-signaling pathway, male germ cells contain alternate routes to control expression of cholesterogenic genes.

Animals↗

PubMed2002

Differential inducibility of the transcriptional repressor ICER and its role in modulation of Fas ligand expression in T and NK lymphocytes.

The engagement of antigen receptor can initiate apoptosis of T lymphocytes through the induced expression of Fas ligand (FasL). Forskolin, an activator of the cAMP/PKA pathway, results in antagonism of Fas-dependent, activation-induced cell death (AICD) by suppressed expression of the FasL. We report that forskolin-mediated induction of inducible cAMP early repressor (ICER) correlates with transcriptional attenuation of FasL expression in the AICD model 2B4 T cell hybridoma. ICER is inducible in human peripheral blood CD3(+) T cells, but in CD19(+) B cells, its induction is less responsive to forskolin treatment. Increased expression of ICER correlates with decreased FasL expression in both T and NK cells. ICER binds specifically to the proximal DNA binding site of the nuclear factor of activated T cells (NFAT) in the FasL promoter and in the presence of the minimal NFAT DNA-binding domain, the proximal NFAT motif allows ICER and NFAT to form an NFAT/ICER ternary complex in vitro. Moreover, in the activated 2B4 T cell hybridoma, the proximal NFAT motif participates in the down-regulation of the FasL promoter mediated by ICER. These findings provide further insight into the mechanism involved in cAMP-mediated transcriptional attenuation of FasL expression in T and NK lymphocytes.

Antigens, CD19↗

PubMed2004

Distribution of transcription factor inducible cyclicAMP early repressor (ICER) in rodent brain and pituitary.

In morphogenetic dynamics of neurons, and in adaptive physiology of brain function, transcription factors of the cyclicAMP signaling pathway, such as activator cyclicAMP responsive element binding protein (CREB) and inhibitor inducible cyclicAMP early repressor (ICER), play an important role. In particular, the presence of the transcription factor ICER in neurons or neuroendocrine cells suggests the need for the gating of an up-regulated gene expression. Little is known, however, about the natural distribution of the inhibitory transcription factor ICER. We, therefore, mapped the rodent brain and pituitary for an ICER immunoreaction and found a nuclear staining for this transcription factor. ICER-positive glial cells were found throughout the brain. ICER-positive neurons were found in sensory input centers, like the olfactory bulb, or sensory brain stem nuclei, and in hypothalamic nuclei involved in central neuroendocrine control. In addition, neuroendocrine/endocrine transducers, like the pituitary and the pineal gland showed a high basal presence of ICER. Our data show that a basic ICER level is required by many cell systems and can be seen as an anticipatory and/or a protective measure in systems with superior reactive dynamics.

Animals↗

PubMed2002

Trafficking of PLP/DM20 and cAMP signaling in immortalized jimpy oligodendrocytes.

The synthesis, transport, and insertion of jimpy proteolipid protein and DM20 were studied in normal (158N) and jimpy (158JP) immortalized oligodendrocyte lines. Four different expression vectors encoding fusion proteins composed of native PLP and DM20 or jimpy PLP or DM20 were linked to enhanced green fluorescent protein (EGFP). All four transfected fusion proteins had similar distributions in the cell bodies and processes of the two cell types. Both normal and jimpy PLP-EGFP and DM20-EGFP were detected in both cell lines as far as 200 microM from the cell body, indicating synthesis and transport of mutated PLP and DM20 toward the plasma membrane. Immunocytochemistry of fixed normal and jimpy cells with the O10 antibody, which recognizes a conformationally sensitive PLP/DM20 epitope, confirmed that normal and jimpy PLP and DM20 were transported to the plasma membrane. Live staining of normal and jimpy cells transiently transfected with the native PLP showed positive staining, indicating PLP was correctly inserted into the membrane of both normal and jimpy oligodendrocytes. However, live staining of normal and jimpy cells transiently transfected with jimpy PLP showed no positive staining, indicating the mutated protein is abnormally inserted into the plasma membrane. Electrophysiological recordings of the resting membrane potential measured in the whole cell mode of the patch-clamp technique showed the absence of a developmentally regulated negative shift in the membrane potential in jimpy cells compared to normal native or immortalized oligodendrocytes. Treatment of 158N cells and native oligodendrocytes with dibutyryl cAMP (dbcAMP) caused morphological and biochemical differentiation, but failed to do so in 158JP cells, suggesting an abnormal signaling pathway in jimpy. The defect in cAMP signaling in jimpy oligodendrocytes was associated with the suppression of increase in mRNA level of the inducible cAMP early repressor (ICER). When the jimpy oligodendrocyte line was transfected with normal PLP or DM20 and exposed to dbcAMP, the cells failed to differentiate. This finding suggests that improper insertion of jimpy protein into the plasma membrane alters the membrane in such a way that certain signaling pathways are permanently altered. The abnormal insertion of jimpy PLP/DM20 into the plasma membrane may be the basis for the lack of cell signaling and abnormal resting potential in jimpy oligodendrocytes.

Animals↗