Activation protein 1-dependent transcriptional activation of interleukin 2 gene by Ca2+/calmodulin kinase type IV/Gr

Inhibition of calmodulin increases intracellular survival of Salmonella in chicken macrophage cells

Calcium (Ca²⁺) is a pivotal intracellular second messenger and calmodulin (CaM) acts as a multifunctional Ca²⁺-binding protein that regulates downstream Ca²⁺ dependent signaling. Together they play an important role in regulating various cellular functions, including gene expression, maturation of phagolysosome, apoptosis, and immune response. Intracellular Ca²⁺ has been shown to play a critical role in Toll-like receptor-mediated immune response to microbial agonists in the HD11 chicken macrophage cell line. The role of that the Ca²⁺/CaM pathway plays in the intracellular survival of Salmonella in chicken macrophages has not been reported. In this study, kinome peptide array analysis indicated that the Ca²⁺/CaM pathway was significantly activated when chicken macrophage HD11 cells were infected with S. Enteritidis or S. Heidelberg. Further study demonstrated that treating cells with a pharmaceutical CaM inhibitor W-7, which disrupts the formation of Ca²⁺/CaM, significantly inhibited macrophages to produce nitric oxide and weaken the control of intracellular Salmonella replication. These results strongly indicate that CaM plays an important role in the innate immune response of chicken macrophages and that the Ca²⁺/CaM mediated signaling pathway is critically involved in the host cell response to Salmonella infection.

Ex Vivo Expansion of Hematopoietic Stem and Progenitor Cells from Umbilical Cord Blood

Transplantation of umbilical cord blood cells is currently widely used in modern cell therapy. However, the limited number of hematopoietic stem and progenitor cells (HSPCs) and prolonged time of recovery after the transplantation are significant limitations in the use of cord blood. Ex vivo expansion with various cytokine combinations is one of the most common approaches for increasing the number of HSPCs from one cord blood unit. In addition, there are protocols that enable ex vivo amplification of cord blood cells based on native hematopoietic microenvironmental cues, including stromal components and the tissue-relevant oxygen level. The newest techniques for ex vivo expansion of HSPCs are based on data from the elucidation of the molecular mechanisms governing the hematopoietic niche function. Application of these methods has provided an improvement of several important clinical outcomes. Alternative methods of cord blood transplantation enhancement based on optimization of HPSC homing and engraftment in patient tissues have also been successful. The goal of the present review is to analyze recent methodological approaches to cord blood HSPC ex vivo amplification.

Cytokines induced by long-term potentiation (LTP) recording: a potential explanation for the lack of correspondence between learning/memory performance and LTP

The relationship between learning/memory performance and long-term potentiation (LTP) induction is ambiguous. Although a large body of data supports a strong correspondence between learning/memory performance and LTP, many studies have also provided evidence to the contrary. In this study, we found that 2-month-old senescence-accelerated mice/prone 8 (SAMP8 mice) displayed both impaired performance in a Morris Water Maze (MWM) and enhanced LTP compared to senescence-accelerated mice/resistance 1 (SAMR1). BALB/c mice challenged with Complete Freund's Adjuvant (CFA) performed better in the shuttle-box test but displayed impaired LTP compared to intact animals. It is interesting that BALB/c mice challenged with Incomplete Freund's Adjuvant (IFA) performed better than intact animals, with no LTP impairment. Cytokine analysis showed no significant differences between the interleukin-6 (IL-6), interleukin-10 (IL-10) or TNF-α content in the intact hippocampal tissues of either the SAMR1 and SAMP8 mice or the immune-challenged BALB/c and intact animals. Further analysis demonstrated that the increase in cytokine content was higher in the hippocampal tissues used for LTP recording in the SAMR1 and CFA-challenged animals compared to the SAMP8 and intact BALB/c mice. A correlation analysis demonstrated that pro-inflammatory cytokines (IL-6 and TNF-α) displayed a negative correlation with LTP, while an anti-inflammatory cytokine (IL-10) displayed a positive correlation with LTP. These results suggest that pro-inflammatory cytokines induced by LTP manipulation in experiments (e.g., via tissue injury caused by electrode insertion) may be one of the factors contributing to the observed lack of correspondence between memory/learning ability and LTP.

PLC/CAMK IV-NF-kappaB involved in the receptor for advanced glycation end products mediated signaling pathway in human endothelial cells

Advanced glycation end products (AGEs) and their interaction with the receptor for advanced glycation end products (RAGE) play an important role in diabetic vascular complications. The current study demonstrated that AGEs significantly increased RAGE expression and the release of tumor necrosis factor-alpha (TNF-alpha), interleukin-6 (IL-6) in human umbilical vein endothelial cell-derived line ECV304 cells. RAGE antisense RNA partially inhibited the expression of TNF-alpha and IL-6 induced by AGEs. Oligonucleotide microarray was used to identify the genes that respond to RAGE activation. Phospholipase C beta 1 (PLC beta 1), phospholipase C beta 4 (PLC beta 4) and calcium/calmodulin-dependent protein kinase IV (CAMK IV) which associated with Ca(2+) signaling were upregulated. The rise of intracellular calcium and the NF-kappaB promoter activity induced by AGEs were suppressed by RAGE antisense RNA, PLC inhibitor U73122 and dominant negative CAMK IV, respectively. These findings suggest that PLC/CAMK IV-NF-kappaB is involved in RAGE mediated signaling pathway in human endothelial cells.

Expression, localisation and functional activation of NFAT-2 in normal human skin, psoriasis, and cultured keratocytes

Ciclosporin A (CsA) is widely utilized for the treatment of inflammatory skin diseases such as psoriasis. The therapeutic effects of CsA are thought to be mediated via its immunosuppressive action on infiltrating lymphocytes in skin lesions. CsA and tacrolimus block T cell activation by inhibiting the phosphatase calcineurin and preventing translocation from the cytoplasm to the nucleus of the transcription factor Nuclear Factor of Activated T cells (NFAT). As calcineurin and NFAT 1 have been shown to be functionally active in cultured human keratocytes, expression of other NFAT family members such as NFAT-2 and possible functional activation was investigated in human keratocytes. RT-PCR and Western Analysis were used to investigate the presence of NFAT-2 mRNA and protein in human keratocytes. Tissue culture of human keratocytes and immunostaining of cells on coverslips and confocal microscopy were used to assess the degree of nuclear localisation of NFAT-2 in cultured cells. Keratome biopsies were taken from patients with psoriasis (lesional and non-lesional skin) and normal skin and immunohistochemistry was used to assess the NFAT-2 localisation in these biopsies using a well characterized anti-NFAT-2 antibody. The NFAT-2 mRNA and protein expression was demonstrated using RT-PCR and Western blotting. Moreover, the expression of NFAT-2 in normal skin, non-lesional and lesional psoriasis showed a striking basal staining suggesting a role for NFAT-2 in keratocytes proliferation. A range of cell types in the skin express NFAT-2. The expression of NFAT-2 in human keratocytes and response to different agonists provides perhaps a unique opportunity to examine the regulation, subcellular localization and kinetics of translocation of different NFATs in primary cultured human cells. In these experiments the author assessed the expression, localization of NFAT-2 in cultured human keratocytes and measured the degree of nuclear localisaion of NFAT-2 using immunofluorescence and confocal microscopy and whether CsA and tacrolimus inhibit NFAT-2 nuclear translocation. As with NFAT 1, differentiation-promoting agents that increase intracellular calcium concentration induced nuclear translocation of NFAT-2 in cultured keratocytes but with different kinetics. These data provide the first evidence of that NFAT-2 is expressed in normal skin, psoriasis and that NFAT-2 functionally active in human keratocytes and that nuclear translocation of NFAT-2 in human skin cells has different kinetics than NFAT 1 suggesting that NFAT-2 may play an important role in regulation of keratocytes proliferation and differentiation at a different stage. Inhibition of this pathway in human epidermal keratocytes many account, in part for the therapeutic effects of CsA and tacrolimus in skin disorders such as psoriasis. Thus, supporting our previous work data that calcineurin/NFAT is functionally active not only in T cells, but in skin cells.

Calmodulin-dependent phosphatase, kinases, and transcriptional corepressors involved in T-cell activation

The second messenger calcium plays an essential role in mediating the T-cell receptor (TCR) signaling pathway leading to cytokine production and T-cell clonal expansion. The immunosuppressive drugs cyclosporine A and FK506 have served both as therapeutic agents and as molecular probes for unraveling the protein phosphatase calcineurin as a rate-limiting enzyme involved in the transmission of calcium signal from the cytosol into the nucleus to reprogram gene expression. The use of mouse knockout models has helped to verify and further elucidate the functions of different isoforms of calcineurin in both helper T-cell activation and thymocyte development. In addition to calcineurin, three other classes of calmodulin-binding proteins have also been shown to play important roles in calcium signaling in T cells. Thus, Cabin1 and class II histone deacetylases have been found to constitute a novel calcium-signaling module in conjunction with the transcription factor myocyte enhance factor family and the transcriptional coactivator p300 to suppress and activate cytokine gene transcription in a calcium-dependent manner. The calmodulin-dependent protein kinases II and IV were also shown to play negative and positive regulatory functions, respectively, in TCR-mediated cytokine production. The crosstalks among these and other signal transducers in T cells form an extensive nonlinear signaling network that dictates the final outcome of the TCR signaling pathway.

Calcium signaling in immune cells

Calcium acts as a second messenger in many cell types, including lymphocytes. Resting lymphocytes maintain a low concentration of Ca2+. However, engagement of antigen receptors induces calcium influx from the extracellular space by several routes. A chief mechanism of Ca2+ entry in lymphocytes is through store-operated calcium (SOC) channels. The identification of two important molecular components of SOC channels, CRACM1 (the pore-forming subunit) and STIM1 (the sensor of stored calcium), has allowed genetic and molecular manipulation of the SOC entry pathway. In this review, we highlight advances in the understanding of Ca2+ signaling in lymphocytes with special emphasis on SOC entry. We also discuss outstanding questions and probable future directions of the field.

Calcium/calmodulin-dependent kinase IV in immune and inflammatory responses: novel routes for an ancient traveller

Ca(2+) is a pivotal second messenger controlling the activation of lymphocytes. Crucial events in the social life of immunocytes are regulated by the calcium/calmodulin complex (Ca(2+)/CaM), which controls the activation status of many enzymes, including the Ca(2+)/CaM-dependent Ser-Thr kinases (CaMK) I, II and IV. Although CaMKI and CaMKII are expressed ubiquitously, CaMKIV is found predominately in cells of the nervous and immune systems. To be active, CaMKIV requires binding of Ca(2+)/CaM and phosphorylation by CaMKKalpha or beta. The requirement of two CaM kinases in the same signalling pathway led to the concept of a CaM kinase cascade. In this review, we focus on the roles of CaMKK and CaMKIV cascades in immune and inflammatory responses.

o-GlcNAc transferase is activated by CaMKIV-dependent phosphorylation under potassium chloride-induced depolarization in NG-108-15 cells

Post-translational modification of cellular proteins by beta-o-linked N-acetylglucosamine (o-GlcNAc) moieties plays a significant role in signal transduction by modulating protein stability, protein-protein interactions, transactivation processes, and the enzyme activities of target proteins. Though various classes of proteins are known to be regulated by o-GlcNAc modification (o-GlcNAcylation), the mechanism that regulates o-linked GlcNAc transferase (OGT) activity remains unknown. Here, we report that potassium chloride-induced depolarization provokes the activation of OGT and subsequent o-GlcNAcylation of proteins in neuroblastoma NG-108-15 cells. Moreover, such an induction of protein o-GlcNAcylation was abolished by treating cells with either a voltage-gated calcium channel inhibitor or a calcium/calmodulin-dependent protein kinase (CaMK) inhibitor. In addition, CaMKIV was found to specifically phosphorylate and activate OGT in vivo and in vitro, which implies that CaMKIV is required for depolarization-induced activation of OGT. Furthermore, we found that OGT is involved in depolarization-induced and CaMKIV-dependent activation of activator protein-1 (AP-1) and subsequent tissue inhibitor of metalloproteinase-1 (Timp-1) gene expression. Taken together, our findings suggest that CaMKIV activated OGT, and OGT has an essential role on the process of CaMKIV-dependent AP-1 activation under depolarization in neuronal cells.

CaMKII and CaMKIV mediate distinct prosurvival signaling pathways in response to depolarization in neurons

By fusing the CaMKII-inhibitory peptide AIP to GFP, we constructed a specific and effective CaMKII inhibitor, GFP-AIP. Expression of GFP-AIP and/or dominant-inhibitory CaMKIV in cultured neonatal rat spiral ganglion neurons (SGNs) shows that CaMKII and CaMKIV act additively and in parallel to mediate the prosurvival effect of depolarization. Depolarization or expression of constitutively active CaMKII functionally inactivates Bad, indicating that this is one means by which CaMKII promotes neuronal survival. CaMKIV, but not CaMKII, requires CREB to promote SGN survival, consistent with the exclusively nuclear localization of CaMKIV and indicating that the principal prosurvival function of CaMKIV is activation of CREB. Consistent with this, a constitutively active CREB construct that provides a high level of CREB activity promotes SGN survival, although low levels of CREB activity did not do so. Also, in apoptotic SGNs, activation of CREB by depolarization is disabled, presumably as part of a cellular commitment to apoptosis.

Cyclosporin A and FK506 inhibit IL-12p40 production through the calmodulin/calmodulin-dependent protein kinase-activated phosphoinositide 3-kinase in lipopolysaccharide-stimulated human monocytic cells

Cyclosporine-A (CyA) and FK506 are potent immunosuppressive agents because of their ability to suppress the production of Th1 cytokines including interleukin (IL)-12. However, the mechanisms underlying the inhibitory effects of CyA and FK506 on the production of IL-12p40, a critical component of IL-12, remain unknown. Both CyA and FK506 are potent inhibitors of calcineurin in the calcium signaling pathway. Interestingly, calcium and phosphoinositide 3-kinase (PI3K) signaling pathways have been shown to negatively regulate lipopolysaccharide (LPS)-induced murine IL-12p40 production. Contrary to these observations, we show that LPS-induced IL-12p40 production in human monocytic cells is positively regulated by the calcium pathway and in particular by calmodulin-(CaM) and CaM-dependent protein kinase-II (CaMK-II)-activated PI3K. Furthermore, LPS-induced IL-12p40 production was regulated by the p110alpha catalytic subunit of PI3K. Moreover, LPS induced IL-12p40 production through the CaM/CaMK-II-activated NFkappaB and AP-1 transcription factors. LPS-induced IL-12p40 production is known to be regulated by the c-Jun N-terminal kinase (JNK) pathway. Importantly, both CyA and FK506 down-regulated LPS-induced IL-12p40 transcription by inhibiting CaM/CaMK-II-activated PI3K and their downstream transcription factors NFkappaB and AP-1 independent of the JNK pathway.

Nuclear Ca2+/calmodulin-dependent protein kinase II in the murine heart

Ca(2+) signaling through CaMKII is critical in regulating myocyte function with regard to excitation-contraction-relaxation cycles and excitation-transcription coupling. To investigate the role of nuclear CaMKII in cardiac function, transgenic mice were designed and generated to target the expression of a CaMKII inhibitory peptide, AIP (KKALRRQEAVDAL), to the nucleus. The transgenic construct consists of the murine alpha-myosin heavy chain promoter followed by the expression unit containing nucleotides encoding a four repeat concatemer of AIP (AIP(4)) and a nuclear localization signal (NLS). Western blot and immunohistochemical analyses demonstrate that AIP(4) is expressed only in the nucleus of cardiac myocytes of the transgenic mice (NLS-AIP(4)). The function of cytoplasmic CaMKII is not affected by the expression of AIP(4) in the nucleus. Inhibition of nuclear CaMKII activity resulted in reduced translocation of HDAC5 from nucleus to cytoplasm in NLS-AIP(4) mouse hearts. Loss of nuclear CaMKII activity causes NLS-AIP(4) mice to have smaller hearts than their nontransgenic littermates. Transcription factors including CREB and NFkappaB are not regulated by cardiac nuclear CaMKII. With physiological stresses such as pregnancy or aging (8 months), NLS-AIP(4) mice develop hypertrophy symptoms including enlarged atria, systemic edema, sedentariness, and morbidity. RT-PCR analyses revealed that the hypertrophic marker genes, such as ANF and beta-myosin heavy chain, were upregulated in pregnancy stressed mice. Our results suggest that absence of adequate Ca2+signaling through nuclear CaMKII regulated pathways leads to development of cardiac disease.

Alteration of neuronal firing properties after in vivo experience in a FosGFP transgenic mouse

Identifying the cells and circuits that underlie perception, behavior, and learning is a central goal of contemporary neuroscience. Although techniques such as lesion analysis, functional magnetic resonance imaging, 2-deoxyglucose studies, and induction of gene expression have been helpful in determining the brain areas responsible for particular functions, these methods are technically limited. Currently, there is no method that allows for the identification and electrophysiological characterization of individual neurons that are associated with a particular function in living tissue. We developed a strain of transgenic mice in which the expression of the green fluorescent protein (GFP) is controlled by the promoter of the activity-dependent gene c-fos. These mice enable an in vivo or ex vivo characterization of the cells and synapses that are activated by particular pharmacological and behavioral manipulations. Cortical and subcortical fosGFP expression could be induced in a regionally restricted manner after specific activation of neuronal ensembles. Using the fosGFP mice to identify discrete cortical areas, we found that neurons in sensory-spared areas rapidly regulate action potential threshold and spike frequency to decrease excitability. This method will enhance our ability to study the way neuronal networks are activated and changed by both experience and pharmacological manipulations. In addition, because activated neurons can be functionally characterized, this tool may enable the development of better pharmaceuticals that directly affect the neurons involved in disease states.

Generation of Silent Synapses by Acute In Vivo Expression of CaMKIV and CREB

The transcription factor CREB is critical for several forms of experience-dependent plasticity in a range of species and is commonly activated in neurons by calcium/calmodulin-dependent protein kinase IV (CaMKIV). Surprisingly, little is known about the neural circuit adaptations caused by activation of CaMKIV and CREB. Here, we use viral-mediated gene transfer in vivo to examine the consequences of acute expression of constitutively active forms of CaMKIV and CREB on synaptic function in the rodent hippocampus. Acute expression of active CaMKIV or CREB caused an enhancement of both NMDA receptor-mediated synaptic responses and long-term potentiation (LTP). This was accompanied by electrophysiological and morphological changes consistent with the generation of "silent synapses," which provide an ideal substrate for further experience-dependent modifications of neural circuitry and which may also be important for the consolidation of long-term synaptic plasticity and memories.

Calcium/calmodulin-dependent protein kinase I in Xenopus laevis

Calcium/calmodulin (CaM) dependent protein kinase I (CaM-KI) is a member of a well-defined multi-functional CaM-K family, but its physiological and developmental functions have yet to be determined. Here, we have cloned two cDNAs encoding CaM-KI from a Xenopus laevis (X. laevis) oocyte cDNA library. One is a novel isoform of CaM-KI, named CaM-KI LiKbeta (XCaM-KI LiKbeta). The other is an alpha isoform of CaM-KI (XCaM-KIalpha), which is a highly related to previously cloned mammalian isoform. XCaM-KIalpha was constantly expressed through embryogenesis, whereas XCaM-KI LiKbeta expression dramatically increased in the neurula stage. Both XCaM-KI isoforms exhibited kinase activity in a Ca(2+)/CaM-dependent manner. Overexpression of a constitutively active mutant of CaM-KI isoforms inhibited cell cleavage in X. laevis embryos and caused a marked change of cell morphology in Hela cells. Taken together, these results suggest that CaM-KI plays a role in cell-structure regulation during early embryonic development.

Cyclic AMP differentially modulates CD40L expression on human nai;ve and memory CD4(+) T cells

Although differences in nai;ve and memory T cell signaling have been recognized, how these differences relate to cell regulation and function is not well understood. In this study, we investigated CD40 ligand (CD40L) regulation by cyclic AMP (cAMP) and prostaglandin E(2) (PGE(2)) and observed differential effects depending upon the cell subset and mode of activation. cAMP inhibited CD3-induced CD40L in both nai;ve and memory subsets, although greater inhibition was observed in memory cells. With CD3/CD28 costimulation, cAMP inhibited CD40L in memory cells but had a minimal effect on nai;ve cells. In primed T cells, cAMP increased CD40L on nai;ve cells but inhibited expression on memory cells. Differential cAMP effects appear interrelated to calcium signaling since the level of CD40L induced by calcium ionophore was increased by cAMP in both cell subsets, although nai;ve cells were more calcium responsive. Calcium-dependent calcineurin activity appeared necessary for CD40L expression, although no interaction of calcineurin and cAMP regulation was demonstrable. In contrast, inhibitors of Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) blocked cAMP effects to increase CD40L and resulted in marked CD40L inhibition. The importance of CaMKIV in cAMP regulation was confirmed by transfection studies using a dominant negative CaMKIV construct. We conclude that cAMP differentially regulates CD40L expression in a manner that appears dependent upon CaMKIV activation. In view of the central role of CD40L expression in immunity as well as the pathophysiology of common diseases, it is of interest that cAMP can either increase or decrease CD40L expression depending upon the T cell subtype and mechanism of cell activation.

Ca(2+)/calmodulin-dependent protein kinase IV expression in epithelial ovarian cancer

Ca(2+)/calmodulin-dependent protein kinase IV (CaMKIV) is a multifunctional protein kinase expressed abundantly in the central nervous system. Because changes in intracellular Ca(2+) concentrations affect progression through the mitotic cell cycle, enhanced expression of CaMKIV has been reported in small cell lung carcinoma and hepatocellular carcinoma. To elucidate the involvement of CaMKIV in epithelial ovarian carcinogenesis, we analyzed serial frozen sections for CaMKIV protein expression in 26 patients with ovarian epithelial carcinoma and ten patients with benign cystadenoma of the ovary by fluorescent immunohistochemistry. We analyzed the relationship between the percentages of CaMKIV-stained cells and the patient's characteristics, including histological classification, clinical stage, histological grade, and clinical outcome. In the benign ovarian cystadenoma, CaMKIV was detected in none of the cases examined. Most of the CaMKIV proteins were found in the nucleus of epithelial ovarian cancer tissue. CaMKIV expression was significantly associated with clinical stage (P<0.01), histological grade (P<0.01), and clinical outcome (P<0.01). Survival data were available for all patients, and univariate Cox regression analysis showed that CaMKIV expression was significantly associated with poor prognosis (P<0.05). Our results demonstrate that CaMKIV expression in epithelial ovarian cancer correlates with the malignant potential of this tumor.

Calcium regulation of dendritic growth via CaM kinase IV and CREB-mediated transcription

We report that CaM kinase IV and CREB play a critical role in mediating calcium-induced dendritic growth in cortical neurons. Calcium-dependent dendritic growth is suppressed by CaM kinase inhibitors, a constitutively active form of CaM kinase IV induces dendritic growth in the absence of extracellular stimulation, and a kinase-dead form of CaM kinase IV suppresses dendritic growth induced by calcium influx. CaM kinase IV activates the transcription factor CREB, and expression of a dominant negative form of CREB blocks calcium- and CaM kinase IV-induced dendritic growth. In cortical slice cultures, dendritic growth is attenuated by inhibitors of voltage-sensitive calcium channels and by dominant negative CREB. These experiments indicate that calcium-induced dendritic growth is regulated by activation of a transcriptional program that involves CaM kinase IV and CREB-mediated signaling to the nucleus.

New human myelodysplastic cell line, TER-3: G-CSF specific downregulation of Ca2+/calmodulin-dependent protein kinase IV

We have established a new hematopoietic cell line from a patient with myelodysplastic syndrome (MDS), which was refractory anemia with excess blasts (RAEB). This cell line, designated TER-3, depends on several cytokines for long-term survival and growth, and requires interleukin-3 (IL-3) for continuous growth. Cytochemical analysis revealed that TER-3 cells are weakly dianisidine positive and nonspecific esterase positive, but peroxidase negative. The surface marker profile shows that the TER-3 cells are strongly positive for myeloid, lymphoid, and megakaryocytic antigens such as CD15, CD19, and CD61, and negative for some common multilineage antigens such as CD13, CD33, and CD34. Thus, this cell line has a multilineage phenotype, suggesting that the transformation event occurred in multipotent stem cells. Dianisidine- and nonspecific esterase-positive TER-3 cells increase with granulocyte-colony stimulating factor (G-CSF) rather than with IL-3. These results suggest that the cell line is useful for understanding the mechanism underlying G-CSF-associated hematopoietic cell differentiation and activation in the patient with MDS.

Chemokine receptors and stromal cells in the homing and homeostasis of chronic lymphocytic leukemia B cells

Chronic lymphocytic leukemia (CLL) is a disease characterized by an accumulation, of mature, functionally incompetent B lymphocytes in the blood, secondary lymphoid tissues, and marrow. Lymphocyte trafficking and homing to specialized microenvironments is an active process that depends on the sequential engagement of adhesion molecules and activation through chemokine receptors. CLL B cells express functional CXCR3, CXCR4, and CXCR5 chemokine receptors that can direct leukemia cell chemotaxis in vitro. Marrow stromal cells, blood-derived "nurse-like cells", and extramedullary stromal cells of mesenchymal origin secrete high amounts of stromal cell-derived factor-1 (SDF-1) and thereby can attract CLL B cells via CXCR4. In vitro, CLL cells are rescued from apoptosis by cell-cell contact with such cells. Moreover, we found that the capacity of these cells to protect leukemia cells from apoptosis in vitro is mediated, at least in part, by the SDF-1 chemokine. Taken together, these findings suggest that chemokines and their receptors on CLL B cells can govern the homing and survival of leukemia B cells in vivo and therefore may contribute to their noted resistance to chemotherapy-induced apoptosis. Conceivably, CXCR4, and possibly other chemokine receptors, may represent a novel target for the development of effective treatment of this disease.

Requirement for Ca2+/calmodulin-dependent kinase type IV/Gr in setting the thymocyte selection threshold

The outcome of thymocyte selection is influenced by the nature of Ca2+ signals transduced by the TCR. Robust Ca2+ responses characterize high-affinity, negatively selecting peptide/TCR interactions, while modest responses typify lower-affinity, positively selecting interactions. To elucidate mechanisms by which thymocytes decode distinct Ca2+ signals, we examined selection events in mice lacking Ca2+/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr), which is enriched in thymocytes. CaMKIV/Gr-deficient thymocytes exhibited impaired positive selection and defective Ca2+-dependent gene transcription. Significantly, CaMKIV/Gr deficiency raised the selection threshold of peptide/TCR interactions such that a peptide that normally induced weak negative selection instead promoted positive selection. These results demonstrate an important role for CaMKIV/Gr in sensitizing thymocytes to selection by low-affinity peptides.

Transcriptional activity of the distal CD40 ligand promoter

CD40 ligand (CD40L, CD154) is a T cell cytokine with highly regulated expression that requires the transcription factor nuclear factor of activated T cells (NF-AT) to bind at two sites in the proximal CD40L promoter. We have determined that the distal CD40L promoter (-500 to -1300 bp from start of transcription) conveys superior promoter activity in reporter gene assays. Within the distal promoter, we have identified a third NF-AT binding site, at -761 to -756. Oligonucleotides incorporating each of the three NF-AT sites cross-compete for binding of nuclear extracts from activated T cells and bind NF-ATc2 by antibody supershift. Mutation of the distal NF-AT site reduces activity of the 1300 bp CD40L promoter construct to that of the proximal 500 bp construct, which includes only two NF-AT sites. This suggests that the newly identified NF-AT site is the major mediator of transcriptional activation in the distal CD40L promoter.

Life and death decisions: regulation of apoptosis by proteolysis of signaling molecules

Caspases are the major executioners of cell death, serving as molecular guillotines to behead many proteins required for maintenance of cellular homeostasis. Identification of caspase substrates has taken on increasing importance as we attempt to better understand the molecular mechanisms involved in regulating the struggle between life and death. Many caspase substrates have been described and include RNA binding proteins such as La and U1-70 kD, structural proteins such as keratin and nuclear lamins, and transcription factors or their regulatory proteins that include IkappaB, SP1, and SREBP. Kinases and other signaling proteins are perfectly suited to regulate life and death decisions in response to cellular stressors and have only recently been identified as important caspase substrates. Here we review the current status of signaling pathways that are activated, inactivated or dysregulated by proteases such as caspases and calpain to control entry into apoptosis. The emerging concept that some caspase pathways may be inhibited by cellular and viral apoptosis inhibitory proteins while other caspase pathways are preserved suggests that a subset of these kinases may exist as cleaved 'isoforms' in cells that are not destined to perish. By acting as executioners and as important 'molecular sensors' of the degree of cellular injury, the signaling proteins described in this review are strong candidates to mediate downstream events, both in condemned and in viable cells.

CaM kinase signaling induces cardiac hypertrophy and activates the MEF2 transcription factor in vivo

Hypertrophic growth is an adaptive response of the heart to diverse pathological stimuli and is characterized by cardiomyocyte enlargement, sarcomere assembly, and activation of a fetal program of cardiac gene expression. A variety of Ca(2+)-dependent signal transduction pathways have been implicated in cardiac hypertrophy, but whether these pathways are independent or interdependent and whether there is specificity among them are unclear. Previously, we showed that activation of the Ca(2+)/calmodulin-dependent protein phosphatase calcineurin or its target transcription factor NFAT3 was sufficient to evoke myocardial hypertrophy in vivo. Here, we show that activated Ca(2+)/calmodulin-dependent protein kinases-I and -IV (CaMKI and CaMKIV) also induce hypertrophic responses in cardiomyocytes in vitro and that CaMKIV overexpressing mice develop cardiac hypertrophy with increased left ventricular end-diastolic diameter and decreased fractional shortening. Crossing this transgenic line with mice expressing a constitutively activated form of NFAT3 revealed synergy between these signaling pathways. We further show that CaMKIV activates the transcription factor MEF2 through a posttranslational mechanism in the hypertrophic heart in vivo. Activated calcineurin is a less efficient activator of MEF2-dependent transcription, suggesting that the calcineurin/NFAT and CaMK/MEF2 pathways act in parallel. These findings identify MEF2 as a downstream target for CaMK signaling in the hypertrophic heart and suggest that the CaMK and calcineurin pathways preferentially target different transcription factors to induce cardiac hypertrophy.

MEF2 responds to multiple calcium-regulated signals in the control of skeletal muscle fiber type

Different patterns of motor nerve activity drive distinctive programs of gene transcription in skeletal muscles, thereby establishing a high degree of metabolic and physiological specialization among myofiber subtypes. Recently, we proposed that the influence of motor nerve activity on skeletal muscle fiber type is transduced to the relevant genes by calcineurin, which controls the functional activity of NFAT (nuclear family of activated T cell) proteins. Here we demonstrate that calcineurin-dependent gene regulation in skeletal myocytes is mediated also by MEF2 transcription factors, and is integrated with additional calcium-regulated signaling inputs, specifically calmodulin-dependent protein kinase activity. In skeletal muscles of transgenic mice, both NFAT and MEF2 binding sites are necessary for properly regulated function of a slow fiber-specific enhancer, and either forced expression of activated calcineurin or motor nerve stimulation up-regulates a MEF2-dependent reporter gene. These results provide new insights into the molecular mechanisms by which specialized characteristics of skeletal myofiber subtypes are established and maintained.

A protein encoded within the Down syndrome critical region is enriched in striated muscles and inhibits calcineurin signaling

Here we describe a small family of proteins, termed MCIP1 and MCIP2 (for myocyte-enriched calcineurin interacting protein), that are expressed most abundantly in striated muscles and that form a physical complex with calcineurin A. MCIP1 is encoded by DSCR1, a gene located in the Down syndrome critical region. Expression of the MCIP family of proteins is up-regulated during muscle differentiation, and their forced overexpression inhibits calcineurin signaling to a muscle-specific target gene in a myocyte cell background. Binding of MCIP1 to calcineurin A requires sequence motifs that resemble calcineurin interacting domains found in NFAT proteins. The inhibitory action of MCIP1 involves a direct association with the catalytic domain of calcineurin, rather than interference with the function of downstream components of the calcineurin signaling pathway. The interaction between MCIP proteins and calcineurin may modulate calcineurin-dependent pathways that control hypertrophic growth and selective programs of gene expression in striated muscles.

Ca(2+)-dependent gene expression mediated by MEF2 transcription factors

Ca(2+) induction of a subset of cellular and viral immediate-early activation genes in lymphocytes has been previously mapped to response elements recognized by the MEF2 family of transcription factors. Here, we demonstrate that Ca(2+) activation of MEF2 response elements in T lymphocytes is mediated in synergy by two Ca(2+)/calmodulin-dependent enzymes, the phosphatase calcineurin, and the kinase type IV/Gr (CaMKIV/Gr), which promote transcription by the MEF2 family members MEF2A and MEF2D. Calcineurin up-regulates the activity of both factors by an NFAT-dependent mechanism, while CaMKIV/Gr selectively and independently activates MEF2D. These results identify MEF2 proteins as effectors of a pathway of gene induction in T lymphocytes which integrates diverse Ca(2+) activation signals and may be broadly operative in several tissues.

Peptide specificity determinants at P-7 and P-6 enhance the catalytic efficiency of Ca2+/calmodulin-dependent protein kinase I in the absence of activation loop phosphorylation

Phosphorylation of Ca2+/calmodulin-dependent protein kinase I (CaM KI) at Thr-177 by recombinant rat Ca2+/calmodulin-dependent kinase kinase B (CaM KKB) modulates the kinetics of synapsin-(4-13) peptide phosphorylation by reducing the Km 44-fold and decreasing the KCaM 4-fold. There is also a slight decrease in Km for ATP and increase in enzyme Vmax. A synthetic peptide substrate from the yeast transcription factor, ADR1-(222-234)G233 is a 15-fold better substrate for the Thr-177 dephospho-form of CaM KI than synapsin-(4-13). The Thr-177 dephospho-enzyme has a Km and Vmax for ADR1-(222-234)G233 similar to the values with synapsin-(4-13) using the Thr-177 phosphorylated enzyme. Likewise, with ADR1-(222-234)G233 as substrate, phosphorylation of Thr-177 or substitution of T177A had very little effect on the kinetic values. Using chimeric peptides between synapsin-(4-13) and ADR1-(222-234)G233 we found that N-terminal basic residues at P-7 and P-6 positions were sufficient to allow efficient phosphorylation by the Thr-177 dephospho-form of CaM KI. Phosphorylation of Thr-177 expands the substrate specificity of CaM KI and is not merely an "on-off" switch for kinase activity.

A late phase of cerebellar long-term depression requires activation of CaMKIV and CREB

Recently, it has been shown that cerebellar LTD has a late phase that may be blocked by protein synthesis inhibitors. To understand the mechanisms underlying the late phase, we interfered with the activation of transcription factors that might couple synaptic activation to protein synthesis. Particle-mediated transfection of cultured Purkinje neurons with an expression vector encoding a dominant inhibitory form of CREB resulted in a nearly complete blockade of the late phase. Kinases that activate CREB were inhibited, and LTD was assessed. Inhibition of PKA or the MAPK/RSK cascades were without effect on the late phase, while constructs designed to interfere with CaMKIV function attenuated the late phase. These results indicate that the activation of CaMKIV and CREB are necessary to establish a late phase of cerebellar LTD.

Calcium Mobilization in Human Myeloid Cells Results in Acquisition of Individual Dendritic Cell-Like Characteristics Through Discrete Signaling Pathways

We have shown previously that calcium ionophore (CI) treatment of various myeloid origin cells results in rapid acquisition of properties associated with mature, activated dendritic cells. These properties include increased CD83 and costimulatory molecule expression, tendencies to form dendritic processes, loss of CD14 expression by monocytes, and typically an enhanced capacity to sensitize T lymphocytes to Ag. We here analyze the intracellular signaling pathways by which CI induces acquisition of such properties. Thapsigargin, which raises intracellular Ca2+ levels by antagonizing its sequestration, induced immunophenotypic and morphologic changes that paralleled CI treatment. CI-induced activation was broadly attenuated by the Ca2+ chelating compound EGTA and by calmodulin antagonists trifluoperazine dimaleate and W-7. However, antagonists of signaling pathways downstream to calmodulin displayed more selective inhibitory effects. Calcineurin antagonists cyclosporin A and the FK-506 analogue, ascomycin, diminished costimulatory molecule and CD83 expression, as well as formation of dendritic processes in CI-treated myeloid cells, and strongly attenuated the T cell allosensitizing capacity of CI-treated HL-60 cells. These calcineurin antagonists displayed minimal effect on CI-induced CD14 down-regulation in monocytes. In contrast, the calmodulin-dependent protein kinase antagonists, K252a and KT5926, while displaying only modest effects on CI-induced costimulatory molecule and CD83 expression, strongly blocked CD14 down-regulation. These results are consistent with a Ca2+-dependent mechanism for CI-induced differentiation of myeloid cells, and indicate that multiple discrete signaling pathways downstream to calcium mobilization and calmodulin activation may be essential in regulating this process.

5-Hydroxytryptamine2A receptor stimulation induces activator protein-1 and cyclic AMP-responsive element binding with cyclic AMP-responsive element-binding protein and Jun D as common components in cerebellar neurons

Previous studies from our laboratory have demonstrated that stimulation of 5-hydroxytryptamine2A receptors in rat cerebellar granule cells produces an increase in the levels of 5-hydroxytryptamine2A receptor messenger RNA and binding sites, and that this up-regulation requires de novo RNA and protein synthesis. Here we showed that up-regulation of 5-hydroxytryptamine2A receptor binding sites induced by stimulation with the 5-hydroxytryptamine2A/2C receptor agonist, (+/-)-(2,5-dimethoxy-4-iodophenyl)-2-aminopropane (DOI), is associated with an increase in the 5-hydroxytryptamine2A receptor transcription rate. To examine the possible role of transcriptional activation in DOI-induced 5-hydroxytryptamine2A receptor up-regulation, we studied the effects of DOI on transcription factor binding to activator protein-1 and cyclic AMP-responsive element (CRE) DNA consensus sequences. We found that DOI induces a time-dependent increase in activator protein-1 and CRE transcription factor binding activity, which is blocked by 5-hydroxytryptamine2A receptor antagonists. Similar to 5-hydroxytryptamine2A receptor up-regulation, DOI-induced activator protein-1 binding is suppressed by inhibitors of calmodulin and Ca2+/calmodulin-dependent kinases. The increased activator protein-1 binding is effectively competed by excessive activator protein-1 and CRE sequences as well as endogenous activator protein-1-like sequences present in the rat 5-hydroxytryptamine2A receptor gene. Supershift assays revealed that cAMP-responsive element-binding protein (CREB) and Jun D are common components of both activator protein-1 and CRE binding complexes. DOI also increased the level of phospho-CREB in a time-dependent manner. The binding of phospho-CREB transcription factor to the activator protein-1 site suggests that CREB may modulate the transcription of genes that contain activator protein-1 but lack CRE site in their promoters, through interaction with the activator protein-1 site. The rat 5-hydroxytryptamine2A receptor up-regulation may involve such a mechanism.

Calcium-Dependent Activation of TNF Family Gene Expression by Ca2+/Calmodulin Kinase Type IV/Gr and Calcineurin

CD40 ligand (L), FasL, and TNF-α are members of the TNF family of cytokines. All are expressed by T lymphocytes shortly after activation but have distinct effector functions. Transcription of these genes can be induced by stimulation of T cells by calcium ionophore alone and requires the calcineurin-dependent transcription factor NF of activated T cells. We have examined a second calcium-dependent signaling pathway, mediated by calcium/calmodulin-dependent kinase IV (CaMKIV) in transcriptional activation of TNF family genes. In reporter gene assays using constructs driven by the promoters of human CD40L, FasL, or TNF-α along with vectors expressing constitutively active CaMKIV and calcineurin, we have demonstrated that each promoter is activated by calcineurin and CaMKIV in a synergistic fashion. Furthermore, specific inhibition of CaMKIV by chemical means and by a dominant negative mutant of CaMKIV impairs the ionomycin-induced activity of all three promoters as well as protein expression of CD40L and TNF-α. Our results indicate that activation of gene expression by calcineurin and CaMKIV is common to members of the TNF cytokine family.

Immunohistochemical localization of Ca2+/Calmodulin-dependent protein kinase IV in outer hair cells

A smooth membrane system consisting of subsurface cisternae (SSC) underlies the lateral plasmalemma of auditory outer hair cells (OHCs). The SSC contain Ca-ATPase and are regarded as an intracellular Ca2+ reservoir like the sarcoplasmic reticulum of myocytes. Recently, it has been demonstrated that Ca-ATPase activity in sarcoplasmic reticulum is regulated by Ca2+/calmodulin-dependent protein kinases (CaM kinases). Here we investigated the presence of CaM kinases in OHCs and their possible association with the SSC. Inner ears collected from adult gerbils and from neonates at 2-day intervals between 0 and 20 days after birth were immunostained with antibodies specific for different CaM kinases. A polyclonal antiserum against CaM kinase IV yielded a strong immunostaining reaction along the lateral wall of OHCs. The staining appeared after the tenth postnatal day and continued into adulthood. No other site in the inner ear, including cochlear inner hair cells and vestibular hair cells, was reactive. The kinase's apparent association with the SSC strongly supports its involvement in intracellular Ca2+ homeostasis and suggests a role in regulating the OHCs' slow motile responses.

Calcium/calmodulin-dependent protein kinase IV is cleaved by caspase-3 and calpain in SH-SY5Y human neuroblastoma cells undergoing apoptosis

We have previously demonstrated cleavage of alpha-spectrin by caspase-3 and calpain during apoptosis in SH-SY5Y neuroblastoma cells (Nath, R., Raser, K. J., Stafford, D., Hajimohammadreza, I., Posner, A., Allen, H., Talanian, R. V., Yuen, P., Gilbertsen, R. B., and Wang, K. K. (1996) Biochem. J. 319, 683-690). We demonstrate here that calcium/calmodulin-dependent protein kinase IV (CaMK IV) is cleaved during apoptosis by caspase-3 and calpain. We challenged SH-SY5Y cells with the pro-apoptotic agent thapsigargin. Western blot analysis revealed major CaMK IV breakdown products of 40, 38, and 33 kDa. Digestion of control SH-SY5Y lysate with purified caspase-3 produced a 38-kDa CaMK IV fragment; digestion with purified calpain produced a major fragment of 40 kDa. Pretreatment with carbobenzoxy-Asp-CH2OC(O)-2,6-dichlorobenzene or Z-Val-Ala-Asp-fluoromethylketone was able to block the caspase-3-mediated production of the 38-kDa fragment both in situ and in vitro. Calpain inhibitor II similarly blocked formation of the calpain-mediated 40-kDa fragment both in situ and in vitro. Digestion of recombinant CaMK IV by other caspase family members revealed that only caspase-3 produces a fragmentation pattern consistent to that seen in situ. The major caspase-3 and calpain cleavage sites are respectively identified as PAPD176*A and CG201*A, both within the CaMK IV catalytic domain. Furthermore, calmodulin-stimulated protein kinase activity decreases within 6 h in thapsigargin-treated SH-SY5Y. The loss of activity precedes cell death.

Identification of a signaling pathway involved in calcium regulation of BDNF expression

A signaling pathway by which calcium influx regulates the expression of the major activity-dependent transcript of BDNF in cortical neurons has been elucidated. Deletion and mutational analysis of the promoter upstream of exon III reveals that transactivation of the BDNF gene involves two elements 5' to the mRNA start site. The first element, located between 72 and 47 bp upstream of the mRNA start site, is a novel calcium response element and is required for calcium-dependent BDNF expression in both embryonic and postnatal cortical neurons. The second element, located between 40 and 30 bp upstream of the mRNA start site, matches the consensus sequence of a cAMP response element (CRE) and is required for transactivation of the promoter in postnatal but not embryonic neurons. The CRE-dependent component of the response appears to be mediated by CREB since it is part of the complex that binds to this CRE, and since dominant negative mutants of CREB attenuate transactivation of the promoter. A constitutively active mutant of CaM kinase IV, but not of CaM kinase II, leads to activation of the promoter in the absence of extracellular stimuli, and partially occludes calcium-dependent transactivation. The effects of CaM kinase IV on the promoter require an intact CRE. These mechanisms, which implicate CaM kinase IV and CREB in the control of BDNF expression, are likely to be centrally involved in activity-dependent plasticity during development.

The Epstein-Barr virus-induced Ca2+/calmodulin-dependent kinase type IV/Gr promotes a Ca(2+)-dependent switch from latency to viral replication

The switch from latency to viral replication in Epstein-Barr virus (EBV)-transformed human B cells is mediated by Zta, the protein product of immediate-early EBV gene BZLF1. BZLF1 transcription is normally suppressed in EBV-transformed B cells but can be induced in some cell lines upon ligation of surface immunoglobulin by mechanisms that include the activation of Ca(2+)-dependent signaling pathways. The multifunctional Ca2+/calmodulin-dependent kinase type IV/Gr (CaMKIV/Gr) is normally absent in primary human B cells, but its expression is induced by the EBV oncoprotein LMP1 in the course of B-cell growth transformation by EBV. In this study, we demonstrate that activated CaMKIV/Gr induces transcription from the BZLF1 promoter and upregulates the expression of Zta in permissive cells. Transcriptional activation of the BZLF1 promoter by CaMKIV/Gr is dependent on the CREB/AP1 binding element ZII and is greatly augmented by the Ca2+/calmodulin-dependent phosphatase calcineurin. These results outline a virus-regulated mechanism involving CaMKIV/Gr which promotes transition from latency to productive viral replication in response to Ca(2+)-mobilizing extracellular signals.

Defective survival and activation of thymocytes in transgenic mice expressing a catalytically inactive form of Ca2+/calmodulin-dependent protein kinase IV

We have generated transgenic mice that express a catalytically inactive form of Ca2+/calmodulin-dependent protein kinase IV (CaMKIV) specifically in thymic T cells. The presence of this protein results in a markedly reduced thymic cellularity, although the distribution of the remaining cells is normal based on evaluation of the CD4 and CD8 cell surface antigens that are used to gauge T cell development. Isolated thymic T cells from the transgenic mice also show a dramatically decreased survival rate when evaluated in culture under conditions that do not favor activation. When challenged with an activating stimulus such as alpha-CD3 or a combination of phorbol ester plus ionophore, the cells are severely compromised in their ability to produce the cytokine interleukin-2 (IL-2). Reduction of IL-2 production is secondary to the inability to phosphorylate the cAMP response element binding protein, CREB, and induce expression of the immediate early genes such as Fos B that are required to transactivate the IL-2 promoter. Because transgene expression was regulated by the proximal promoter of the murine lck gene and this promoter is inactivated in T cells that exit the thymus, the mutant hCaMKIV is not present in peripheral T cells. Consequently, T lymphocytes present in the spleen can be activated normally in response to either stimulus mentioned above, demonstrating that the effects of the inactive CaMKIV on activation are reversible. Our results suggest that CaMKIV may represent a physiologically relevant CREB kinase in T cells and that the enzyme is also required to ensure normal expansion of T cells in the thymus. Whereas the pathway responsible for this latter role is yet to be elucidated, it is unlikely to include CREB phosphorylation.

Ca2+-dependent regulation in neuronal gene expression

Ca2+ is an important signal-transduction molecule that plays a role in many intracellular signaling pathways. Recent advances have indicated that in neurons, Ca2+-controlled signaling mechanisms cooperate in order to discriminate amongst incoming cellular inputs. Ca2+-dependent transcriptional events can thereby be made selectively responsive to bursts of synaptic activity of specific intensity or duration.

Regulation of microtubule dynamics by Ca2+/calmodulin-dependent kinase IV/Gr-dependent phosphorylation of oncoprotein 18

Oncoprotein 18 (Op18; also termed p19, 19K, p18, prosolin, and stathmin) is a regulator of microtubule (MT) dynamics and is phosphorylated by multiple kinase systems on four Ser residues. In addition to cell cycle-regulated phosphorylation, external signals induce phosphorylation of Op18 on Ser-25 by the mitogen-activated protein kinase and on Ser-16 by the Ca2+/calmodulin-dependent kinase IV/Gr (CaMK IV/Gr). Here we show that induced expression of a constitutively active mutant of CaMK IV/Gr results in phosphorylation of Op18 on Ser-16. In parallel, we also observed partial degradation of Op18 and a rapid increase of total cellular MTs. These results suggest a link between CaMK IV/Gr, Op18, and MT dynamics. To explore such a putative link, we optimized a genetic system that allowed conditional coexpression of a series of CaMK IV/Gr and Op18 derivatives. The result shows that CaMK IV/Gr can suppress the MT-regulating activity of Op18 by phosphorylation on Ser-16. In line with these results, by employing a chemical cross-linking protocol, it was shown that phosphorylation of Ser-16 is involved in weakening of the interactions between Op18 and tubulin. Taken together, these data suggest that the mechanism of CaMK IV/Gr-mediated suppression of Op18 activity involves both partial degradation of Op18 and direct modulation of the MT-destabilizing activity of this protein. These results show that Op18 phosphorylation by CaMK IV/Gr may couple alterations of MT dynamics in response to external signals that involve Ca2+.

Cyclosporin A-sensitive induction of the Epstein-Barr virus lytic switch is mediated via a novel pathway involving a MEF2 family member

Induction of the Epstein-Barr virus (EBV) lytic cycle by crosslinking surface immunoglobulin is inhibited by the immunosuppressants cyclosporin A (CsA) and FK506. This correlates with the ability of CsA to inhibit Ca2+-dependent transcription of the lytic cycle switch gene BZLF1. It is shown here that CsA sensitivity maps to three sites (ZIA, ZIB and ZID) that bind the serum response factor-related protein MEF2D. A synthetic promoter containing multiple copies of a MEF2D site from Zp, in conjunction with a CREB/AP-1 site (ZII) from Zp, exhibits CsA-sensitive inducibility. Furthermore, the Zp MEF2D sites were functionally interchangeable with MEF2 sites derived from heterologous promoters. While no evidence of a NFAT family member binding to either the MEF2 or CREB/AP-1 sites was obtained, it could be demonstrated that CsA-sensitive induction of Zp was mediated by calcineurin and NFATc2 in synergy with either phorbol ester or especially with the EBV-induced Ca2+/calmodulin-dependent kinase type IV/Gr. These studies identify Zp as prototypic of a novel class of CsA-sensitive and NFAT-dependent promoters defined by the presence of MEF2 sites.

Transcription factors of the NFAT family: regulation and function

As targets for the immunosuppressive drugs cyclosporin A and FK506, transcription factors of the NFAT (nuclear factor of activated T cells) family have been the focus of much attention. NFAT proteins, which are expressed in most immune-system cells, play a pivotal role in the transcription of cytokine genes and other genes critical for the immune response. The activity of NFAT proteins is tightly regulated by the calcium/calmodulin-dependent phosphatase calcineurin, a primary target for inhibition by cyclosporin A and FK506. Calcineurin controls the translocation of NFAT proteins from the cytoplasm to the nucleus of activated cells by interacting with an N-terminal regulatory domain conserved in the NFAT family. The DNA-binding domains of NFAT proteins resemble those of Rel-family proteins, and Rel and NFAT proteins show some overlap in their ability to bind to certain regulatory elements in cytokine genes. NFAT is also notable for its ability to bind cooperatively with transcription factors of the AP-1 (Fos/Jun) family to composite NFAT:AP-1 sites, found in the regulatory regions of many genes that are inducibly transcribed by immune-system cells. This review discusses recent data on the diversity of the NFAT family of transcription factors, the regulation of NFAT proteins within cells, and the cooperation of NFAT proteins with other transcription factors to regulate the expression of inducible genes.

A unique phosphorylation-dependent mechanism for the activation of Ca2+/calmodulin-dependent protein kinase type IV/GR

The activity of the Ca2+/calmodulin-dependent protein kinase IV/Gr (CaMKIV/Gr) is shown to be strictly regulated by phosphorylation of three residues both in vitro and in response to antigen receptor-mediated signaling in lymphocytes. One residue, Thr-200, is indispensable for enhancement of Ca2+/calmodulin-dependent basal activity by CaMKIV/Gr kinase. This event requires Ca2+/calmodulin in the full-length CaMKIV/Gr but is Ca2+/calmodulin-independent when a truncated version of CaMKIV/Gr is used as a substrate (DeltaCaMKIV/Gr1-317 (Delta1-317)). The other two residues, Ser12 and Ser13, are apparently autophosphorylated by the Ca2+/calmodulin-bound CaMKIV/Gr. Phosphorylation of neither Ser12-Ser13 nor Thr312 (the residue in a homologous position to Thr286 of CaMKIIalpha influences the development of Ca2+/calmodulin-independent activity or any other property of CaMKIV/Gr examined. Similarly, removal of the NH2-terminal 20 amino acids has no effect on the activation or function of CaMKIV/Gr. However, mutation of both Ser12 and Ser13 residues to Ala in Delta1-317 completely abrogates activity, while individual substitutions have no effect. These results indicate that the NH2-terminal Ser cluster mediates a novel type of intrasteric inhibition and suggest that three events are required for CaMKIV/Gr activation: 1) Ca2+/calmodulin binding; 2) phosphorylation of the Ca2+/calmodulin-bound enzyme on Thr200 by a Ca2+/calmodulin-dependent protein kinase kinase; and 3) autophosphorylation of Ser12-Ser13. This three-step requirement is unique among the multifunctional Ca2+/calmodulin-dependent kinases.