Expression of a Ca2+/calmodulin-dependent protein kinase, CaM kinase-Gr, in human T lymphocytes. Regulation of kinase activity by T cell receptor signaling

Understanding the pathogenic significance of altered calcium-calmodulin signaling in T cells in autoimmune diseases

Calcium/calmodulin-dependent protein kinase IV (CaMK4) serves as a pivotal mediator in the regulation of gene expression, influencing the activity of transcription factors within a variety of immune cells, including T cells. Altered CaMK4 signaling is implicated in autoimmune diseases such as systemic lupus erythematosus, rheumatoid arthritis, and psoriasis, which are characterized by dysregulated immune responses and clinical complexity. These conditions share common disturbances in immune cell functionality, cytokine production, and autoantibody generation, all of which are associated with disrupted calcium-calmodulin signaling. This review underscores the consequences of dysregulated CaMK4 signaling across these diseases, with an emphasis on its impact on Th17 differentiation and T cell metabolism-processes central to maintaining immune homeostasis. A comprehensive understanding of roles of CaMK4 in gene regulation across various autoimmune disorders holds promise for the development of targeted therapies, particularly for diseases driven by Th17 cell dysregulation.

Identifying changes in immune cells and constructing prognostic models using immune-related genes in post-burn immunosuppression

BACKGROUND

Burn patients are prone to infection as well as immunosuppression, which is a significant cause of death. Currently, there is a lack of prognostic biomarkers for immunosuppression in burn patients. This study was conducted to identify immune-related genes that are prognosis biomarkers in post-burn immunosuppression and potential targets for immunotherapy.

METHODS

We downloaded the gene expression profiles and clinical data of 213 burn patients and 79 healthy samples from the Gene Expression Omnibus (GEO) database. Immune infiltration analysis was used to identify the proportion of circulating immune cells. Functional enrichment analyses were carried out to identify immune-related genes that were used to build miRNA-mRNA networks to screen key genes. Next, we carried out correlation analysis between immune cells and key genes that were then used to construct logistic regression models in GSE77791 and were validated in GSE19743. Finally, we determined the expression of key genes in burn patients using quantitative reverse transcription polymerase chain reaction (qRT-PCR).

RESULTS

A total of 745 differently expressed genes were screened out: 299 were up-regulated and 446 were down-regulated. The number of Th-cells (CD4+) decreased while neutrophils increased in burn patients. The enrichment analysis showed that down-regulated genes were enriched in the T-cell activation pathway, while up-regulated genes were enriched in neutrophil activation response in burn patients. We screened out key genes (NFATC2, RORA, and CAMK4) that could be regulated by miRNA. The expression of key genes was related to the proportion of Th-cells (CD4+) and survival, and was an excellent predictor of prognosis in burns with an area under the curve (AUC) value of 0.945. Finally, we determined that NFATC2, RORA, and CAMK4 were down-regulated in burn patients.

CONCLUSION

We found that NFATC2, RORA, and CAMK4 were likely prognostic biomarkers in post-burn immunosuppression and potential immunotherapeutic targets to convert Th-cell dysfunction.

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation

The incidence and prevalence of inflammatory bowel disease (IBD) are increasing worldwide. IBD is known to be multifactorial, but inflammatory signaling within the intestinal epithelium and a subsequent failure of the intestinal epithelial barrier have been shown to play essential roles in disease pathogenesis. CaMKIV is a multifunctional protein kinase associated with inflammation and cell cycle regulation. CaMKIV has been extensively studied in autoimmune diseases, but a role in idiopathic intestinal inflammation has not been described. In this study, active CaMKIV was highly expressed within the intestinal epithelium of humans with ulcerative colitis and wild-type (WT) mice with experimental induced colitis. Clinical disease severity directly correlates with CaMKIV activation, as does expression of proinflammatory cytokines and histologic features of colitis. In WT mice, CaMKIV activation is associated with increases in expression of 2 cell cycle proarrest signals: p53 and p21. Cell cycle arrest inhibits proliferation of the intestinal epithelium and ultimately results in compromised intestinal epithelial barrier integrity, further perpetuating intestinal inflammation during experimental colitis. Using a CaMKIV null mutant mouse, we demonstrate that a loss of CaMKIV protects against murine DSS colitis. Small molecules targeting CaMKIV activation may provide therapeutic benefit for patients with IBD.-Cunningham, K. E., Novak, E. A., Vincent, G., Siow, V. S., Griffith, B. D., Ranganathan, S., Rosengart, M. R., Piganelli, J. D., Mollen, K. P. Calcium/calmodulin-dependent protein kinase IV (CaMKIV) activation contributes to the pathogenesis of experimental colitis via inhibition of intestinal epithelial cell proliferation.

The role of CaMK4 in immune responses

Calcium/calmodulin-dependent protein kinase IV (CaMK4) is a multifunctional serine/threonine kinase that regulates gene expression by activating transcription factors in a wide range of immune cells including T cells and antigen-presenting cells. The function of CaMK4 is suggested to be abnormal mainly in systemic lupus erythematosus (SLE), which is characterized by autoantibody production, immune complex formation, and immune dysregulation. Although accumulating evidence indicates that CaMK4 plays important roles in the immune responses, the precise molecular mechanisms underlying the development of autoimmune diseases and inflammatory disorders have not been established. In this review, we briefly summarize the role of CaMK4 in immune responses. We also discuss T-cell signaling pathways that control interleukin (IL)-17 production in patients with lupus nephritis and in glomerulonephritis in lupus-prone mice. A better understanding of the signaling and gene regulation of CaMK4 will lead to the identification of novel therapeutic targets in Th17 driven-autoimmune diseases.

Genistein protects hippocampal neurons against injury by regulating calcium/calmodulin dependent protein kinase IV protein levels in Alzheimer's disease model rats

Genistein has a neuroprotective effect in Alzheimer's disease, but its mechanism of action needs further clarification. Accumulating evidence suggests that excessive phosphorylation of tau protein causes production of neurofibrillary tangles, which is one of the main pathological characteristics of Alzheimer's disease, and tau protein can be phosphorylated by calcium/calmodulin dependent protein kinase IV (CAMK4). After 7 days of pre-administration of genistein (90 mg/kg), an Alzheimer's disease rat model was established using an intraperitoneal injection of D-galactose combined with an intracerebral injection of amyloid-β peptide (25-35). The rat was then continuously administered genistein (90 mg/kg) for 42 days. The Morris water maze test, western blotting and hematoxylin-eosin staining results showed that genistein significantly decreased the escape latency and increased the number of times crossing the platform, reduced p-tau, CALM, CAMKK1 and p-CAMK4 protein levels in the hippocampus, and alleviated hippocampal neuron damage. These findings indicate that genistein may play a neuroprotective role in Alzheimer's disease through regulating CAMK4 to modulate tau hyperphosphorylation.

Binding studies and biological evaluation of β-carotene as a potential inhibitor of human calcium/calmodulin-dependent protein kinase IV

Human calcium/calmodulin-dependent protein kinase IV (CAMKIV), a member of Ser/Thr kinase family, is associated with cancer, cerebral hypoxia and neurodegenerative diseases. β-carotene is a colored organic compound, abundant in plants and fruits and is used in cancer prevention. Here, we report a strong binding affinity of β-carotene with CAMKIV using molecular docking, fluorescence binding and isothermal titration calorimetry methods. Furthermore, β-carotene also reduces the enzyme activity of CAMKIV moderately as observed during ATPase assay. To see the role of β-carotene on cell proliferation and apoptosis, cancerous cells (HeLa, HuH7and MCF-7) and normal (HEK-293-T) cell lines were used. Admirable anticancer activity of β-carotene was observed. We further performed propidium iodide and DAPI (4',6-diamidino-2-phenylindole) assays to understand the mechanism of anticancer activity of β-carotene at molecular level. Our findings provide a newer insight into the use of β-carotene in cancer prevention and protection via inhibition of CAMKIV by regulating the signaling pathways.

Implications of the thyroid hormone on neuronal development with special emphasis on the calmodulin-kinase IV pathway

Thyroid hormones influence brain development through regulation of gene expression. This is especially true for Ca²⁺-dependent regulation since a major pathway is controlled by the Ca²⁺/calmodulin-dependent protein kinase IV (CaMKIV) which in turn is induced by the thyroid hormone T₃. In addition, CaMKIV is involved in regulation of alternative splicing of a number of protein isoforms, among them PMCA1a, the neuronal specific isoform of the plasma membrane calcium pump. On the other hand, hypothyroidism or CaMKIV deficiency can have a severe influence on brain development. This article is part of a Special Issue entitled: ECS Meeting edited by Claus Heizmann, Joachim Krebs and Jacques Haiech.

Urea-induced denaturation of human calcium/calmodulin-dependent protein kinase IV: a combined spectroscopic and MD simulation studies

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a multifunctional enzyme which belongs to the Ser/Thr kinase family. CaMKIV plays important role in varieties of biological processes such as gene expression regulation, memory consolidation, bone growth, T-cell maturation, sperm motility, regulation of microtubule dynamics, cell-cycle progression, and apoptosis. To measure stability parameters, urea-induced denaturation of CaMKIV was carried out at pH 7.4 and 25°C, using three different probes, namely far-UV CD, near-UV absorption, and tryptophan fluorescence. A coincidence of normalized denaturation curves of these optical properties suggests that urea-induced denaturation is a two-state process. Analysis of these denaturation curves gave values of 4.20 ± 0.12 kcal mol^-1, 2.95 ± 0.15 M, and 1.42 ± 0.06 kcal mol^-1 M^-1 for [Formula: see text] (Gibbs free energy change (ΔG_D) in the absence of urea), C_m (molar urea concentration ([urea]) at the midpoint of the denaturation curve), and m (=∂ΔG_D/∂[urea]), respectively. All these experimental observations have been fully supported by 30 ns molecular dynamics simulation studies.

Calcium/calmodulin-dependent protein kinase IV: A multifunctional enzyme and potential therapeutic target

The calcium/calmodulin-dependent protein kinase IV (CAMKIV) belongs to the serine/threonine protein kinase family, and is primarily involved in transcriptional regulation in lymphocytes, neurons and male germ cells. CAMKIV operates the signaling cascade and regulates activity of several transcription activators by phosphorylation, which in turn plays pivotal roles in immune response, inflammation and memory consolidation. In this review, we tried to focus on different aspects of CAMKIV to understand the significance of this protein in the biological system. This enzyme is associated with varieties of disorders such as cerebral hypoxia, azoospermia, endometrial and ovarian cancer, systemic lupus, etc., and hence it is considered as a potential therapeutic target. Structure of CAMKIV is comprised of five distinct domains in which kinase domain is responsible for enzyme activity. CAMKIV is involved in varieties of cellular functions such as regulation of gene expression, T-cell maturation, regulation of survival phase of dendritic cells, bone growth and metabolism, memory consolidation, sperm motility, regulation of microtubule dynamics, cell-cycle progression and apoptosis. In this review, we performed an extensive analysis on structure, function and regulation of CAMKIV and associated diseases.

Integrative genomic and transcriptomic analysis identified candidate genes implicated in the pathogenesis of hepatosplenic T-cell lymphoma

Hepatosplenic T-cell lymphoma (HSTL) is an aggressive lymphoma cytogenetically characterized by isochromosome 7q [i(7)(q10)], of which the molecular consequences remain unknown. We report here results of an integrative genomic and transcriptomic (expression microarray and RNA-sequencing) study of six i(7)(q10)-positive HSTL cases, including HSTL-derived cell line (DERL-2), and three cases with ring 7 [r(7)], the recently identified rare variant aberration. Using high resolution array CGH, we profiled all cases and mapped the common deleted region (CDR) at 7p22.1p14.1 (34.88 Mb; 3506316-38406226 bp) and the common gained region (CGR) at 7q22.11q31.1 (38.77 Mb; 86259620–124892276 bp). Interestingly, CDR spans a smaller region of 13 Mb (86259620–99271246 bp) constantly amplified in cases with r(7). In addition, we found that TCRG (7p14.1) and TCRB (7q32) are involved in formation of r(7), which seems to be a byproduct of illegitimate somatic rearrangement of both loci. Further transcriptomic analysis has not identified any CDR-related candidate tumor suppressor gene. Instead, loss of 7p22.1p14.1 correlated with an enhanced expression of CHN2 (7p14.1) and the encoded β2-chimerin. Gain and amplification of 7q22.11q31.1 are associated with an increased expression of several genes postulated to be implicated in cancer, including RUNDC3B, PPP1R9A and ABCB1, a known multidrug resistance gene. RNA-sequencing did not identify any disease-defining mutation or gene fusion. Thus, chromosome 7 imbalances remain the only driver events detected in this tumor. We hypothesize that the Δ7p22.1p14.1-associated enhanced expression of CHN2/β2-chimerin leads to downmodulation of the NFAT pathway and a proliferative response, while upregulation of the CGR-related genes provides growth advantage for neoplastic δγT-cells and underlies their intrinsic chemoresistance. Finally, our study confirms the previously described gene expression profile of HSTL and identifies a set of 24 genes, including three located on chromosome 7 (CHN2, ABCB1 and PPP1R9A), distinguishing HSTL from other malignancies.

Plasma and cerebrospinal proteomes from children with cerebral malaria differ from those of children with other encephalopathies

Clinical signs and symptoms of cerebral malaria in children are nonspecific and are seen in other common encephalopathies in malaria-endemic areas. This makes accurate diagnosis difficult in resource-poor settings. Novel malaria-specific diagnostic and prognostic methods are needed. We have used 2 proteomic strategies to identify differentially expressed proteins in plasma and cerebrospinal fluid from children with a diagnosis of cerebral malaria, compared with those with a diagnosis of malaria-slide-negative acute bacterial meningitis and other nonspecific encephalopathies. Here we report the presence of differentially expressed proteins in cerebral malaria in both plasma and cerebrospinal fluid that could be used to better understand pathogenesis and help develop more-specific diagnostic methods. In particular, we report the expression of 2 spectrin proteins that have known Plasmodium falciparum–binding partners involved in the stability of the infected red blood cell, suppressing further invasion and possibly enhancing the red blood cell's ability to sequester in microvasculature.

Calcium/calmodulin-dependent protein kinase IV suppresses IL-2 production and regulatory T cell activity in lupus

The activity of calcium/calmodulin-dependent protein kinase IV (CaMK4) is increased in T cells from patients with systemic lupus erythematosus (SLE) and has been shown to reduce IL-2 production by promoting the effect of the transcriptional repressor cAMP responsive element modulator-α on the IL2 promoter. In this article, we demonstrate that T cells from MRL/lpr mice display increased levels of CaMK4 in the nucleus, and that genetic deletion of Camk4 results in improved survival. We demonstrate that absence of CaMK4 restores IL-2 production, curbs increased T cell activation, and augments the number and activity of regulatory T cells. Analogously, silencing of CaMK4 in T cells from patients with SLE increases the expression of FoxP3 on stimulation in the presence of TGF-β. Our results demonstrate the importance of the serine/threonine kinase CaMK4 in the generation and function of regulatory T cells in patients with SLE and lupus-prone mice, and its potential to serve as a therapeutic target.

Regulation of calcium/calmodulin-dependent kinase IV by O-GlcNAc modification

Similar to phosphorylation, GlcNAcylation (the addition of O-GlcNAc to Ser(Thr) residues on polypeptides) is an abundant, dynamic, and inducible post-translational modification. GlcNAcylated proteins are crucial in regulating virtually all cellular processes, including signaling, cell cycle, and transcription. Here we show that calcium/calmodulin-dependent kinase IV (CaMKIV) is highly GlcNAcylated in vivo. In addition, we show that upon activation of HEK293 cells, hemagglutinin-tagged CaMKIV GlcNAcylation rapidly decreases, in a manner directly opposing its phosphorylation at Thr-200. Correspondingly, there is an increase in CaMKIV interaction with O-GlcNAcase during CaMKIV activation. Furthermore, we identify at least five sites of GlcNAcylation on CaMKIV. Using site-directed mutagenesis, we determine that the GlcNAcylation sites located in the active site of CaMKIV can modulate its phosphorylation at Thr-200 and its activity toward cAMP-response element-binding transcription factor. Our results strongly indicate that the O-GlcNAc modification participates in the regulation of CaMKIV activation and function, possibly coordinating nutritional signals with the immune and nervous systems. This is the first example of an O-GlcNAc/phosphate cycle involving O-GlcNAc transferase/kinase cross-talk.

The Balpha and Bdelta regulatory subunits of PP2A are necessary for assembly of the CaMKIV.PP2A signaling complex

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a serine/threonine kinase that is important in synaptic plasticity and T cell maturation. Activation of CaMKIV requires calcium/calmodulin binding and phosphorylation at T200 by CaMK kinase. Our previous work has shown that protein serine/threonine phosphatase 2A (PP2A) forms a complex with CaMKIV and negatively regulates its activity. Here we demonstrate that PP2A tightly regulates T200 phosphorylation of endogenous CaMKIV, but has little effect on the phosphorylation of the ectopically-expressed kinase. This differential regulation of endogenous versus exogenous CaMKIV is due to differences in their ability to associate with PP2A, as exogenous CaMKIV associates poorly with PP2A in comparison to endogenous CaMKIV. The inability of exogenous CaMKIV to associate with PP2A appears to be due to limiting amounts of endogenous PP2A regulatory B subunits, since coexpression of Balpha or Bdelta causes the recruitment of PP2Ac to ectopic CaMKIV, leading to formation of a CaMKIV.PP2A complex. Together, these data indicate that the B subunits are essential for the interaction of PP2A with CaMKIV.

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.

Physiological roles of the Ca2+/CaM-dependent protein kinase cascade in health and disease

Numerous hormones, growth factors and physiological processes cause a rise in cytosolic Ca2+, which is translated into meaningful cellular responses by interacting with a large number of Ca2(+)-binding proteins. The Ca2(+)-binding protein that is most pervasive in mediating these responses is calmodulin (CaM), which acts as a primary receptor for Ca2+ in all eukaryotic cells. In turn, Ca2+/CaM functions as an allosteric activator of a host of enzymatic proteins including a considerable number of protein kinases. The topic of this review is to discuss the physiological roles of a sub-set of these protein kinases which can function in cells as a Ca2+/CaM-dependent kinase signaling cascade. The cascade was originally believed to consist of a CaM kinase kinase that phosphorylates and activates one of two CaM kinases, CaMKI or CaMKIV. The unusual aspect of this cascade is that both the kinase kinase and the kinase require the binding of Ca2+/CaM for activation. More recently, one of the CaM kinase kinases has been found to activate another important enzyme, the AMP-dependent protein kinase so the concept of the CaM kinase cascade must be expanded. A CaM kinase cascade is important for many normal physiological processes that when misregulated can lead to a variety of disease states. These processes include: cell proliferation and apoptosis that may conspire in the genesis of cancer; neuronal growth and function related to brain development, synaptic plasticity as well as memory formation and maintenance; proper function of the immune system including the inflammatory response, activation of T lymphocytes and hematopoietic stem cell maintenance; and the central control of energy balance that, when altered, can lead to obesity and diabetes. Although the study of the CaM-dependent kinase cascades is still in its infancy continued analysis of the pathways regulated by these Ca2(+)-initiated signaling cascades holds considerable promise for the future of disease-related research.

Cytobiological consequences of calcium-signaling alterations induced by human viral proteins

Since calcium-signaling regulates specific and fundamental cellular processes, it represents the ideal target of viral proteins, in order for the virus to control cellular functions and favour its persistence, multiplication and spread. A detailed analysis of reports focused on the impact of viral proteins on calcium-signaling has shown that virus-related elevations of cytosolic calcium levels allow increased viral protein expression (HIV-1, HSV-1/2), viral replication (HBx, enterovirus 2B, HTLV-1 p12(I), HHV-8, EBV), viral maturation (rotavirus), viral release (enterovirus 2B) and cell immortalization (EBV). Interestingly, virus-induced decreased cytosolic calcium levels have been found to be associated with inhibition of immune cells functions (HIV-1 Tat, HHV-8 K15, EBV LMP2A). Finally, several viral proteins are able to modulate intracellular calcium-signaling to control cell viability (HIV-1 Tat, HTLV-1 p13(II), HCV core, HBx, enterovirus 2B, HHV-8 K7). These data point out calcium-signaling as a key cellular target for viral infection and should stimulate further studies exploring new calcium-related therapeutic strategies.

Systemic lupus erythematosus serum IgG increases CREM binding to the IL-2 promoter and suppresses IL-2 production through CaMKIV

Systemic lupus erythematosus (SLE) T cells express high levels of cAMP response element modulator (CREM) that binds to the IL-2 promoter and represses the transcription of the IL-2 gene. This study was designed to identify pathways that lead to increased binding of CREM to the IL-2 promoter in SLE T cells. Ca(2+)/calmodulin-dependent kinase IV (CaMKIV) was found to be increased in the nucleus of SLE T cells and to be involved in the overexpression of CREM and its binding to the IL-2 promoter. Treatment of normal T cells with SLE serum resulted in increased expression of CREM protein, increased binding of CREM to the IL-2 promoter, and decreased IL-2 promoter activity and IL-2 production. This process was abolished when a dominant inactive form of CaMKIV was expressed in normal T cells. The effect of SLE serum resided within the IgG fraction and was specifically attributed to anti-TCR/CD3 autoantibodies. This study identifies CaMKIV as being responsible for the increased expression of CREM and the decreased production of IL-2 in SLE T cells and demonstrates that anti-TCR/CD3 antibodies present in SLE sera can account for the increased expression of CREM and the suppression of IL-2 production.

Mechanism of the Generation of Autonomous Activity of Ca2+/Calmodulin-dependent Protein Kinase IV

Ca2+/calmodulin-dependent protein kinase IV (CaM-KIV) is phosphorylated at Thr196 by Ca2+/calmodulin-dependent protein kinase kinase (CaM-KK), resulting in induction of both autonomous activity and a high level of Ca2+/CaM-dependent activity. We have shown that the kinetics of Thr196 phosphorylation of CaM-KIV by CaM-KK is well correlated with the generation of its autonomous activity, although Thr177 phosphorylation of CaM-KI does not induce its autonomous activity. The activities of CaM-KI chimera mutants fused with C-terminal regions (residues 296-469 and 296-350) of CaM-KIV are completely dependent on Ca2+/CaM, which is also the case for CaM-KI. Unlike wild-type CaM-KI, however, phosphorylation of Thr177 in the chimera mutants by CaM-KK resulted in generation of significant autonomous activities, indicating that the phosphorylation of Thr in the activation loop is sufficient to partially release the autoinhibitory region of CaM-KIV from the catalytic core. Indeed, the CaM-KIV peptide (residues 304-325) containing minimum autoinhibitory sequences (residues 314-321) suppressed the activity of non-phosphorylated CaM-KIV with an IC50 of approximately 50 microm, and this suppression was competitive with respect to the peptide substrate; however, the CaM-KIV peptide was not capable of inhibiting Thr196-phosphorylated CaM-KIV. Taken together, these results indicated that the Thr196 phosphorylation of CaM-KIV by CaM-KK reduced the interaction of the catalytic core with the autoinhibitory region, resulting in generation of the autonomous activity.

Regulation and function of the calcium/calmodulin-dependent protein kinase IV/protein serine/threonine phosphatase 2A signaling complex

Calcium/calmodulin-dependent protein kinase IV (CaMKIV) is a member of the broad substrate specificity class of Ca(2+)/calmodulin (CaM)-dependent protein kinases and functions as a potent stimulator of Ca(2+)-dependent gene expression. Activation of CaMKIV is a transient, tightly regulated event requiring both Ca(2+)/CaM binding and phosphorylation of the kinase on T200 by an upstream CaMK kinase (CaMKK). Previously, CaMKIV was shown to stably associate with protein serine/threonine phosphatase 2A (PP2A), which was proposed to play a role in negatively regulating the kinase. Here we report that the Ca(2+)/CaM binding-autoinhibitory domain of CaMKIV is required for association of the kinase with PP2A and that binding of PP2A and Ca(2+)/CaM appears to be mutually exclusive. We demonstrate that inhibition of the CaMKIV/PP2A association in cells results in enhanced CaMKIV-mediated gene transcription that is independent of Ca(2+)/CaM. The enhanced transcriptional activity correlates with the elevated level of phospho-T200 that accumulates when CaMKIV is prevented from interacting with PP2A. Collectively, these data suggest a molecular basis for the sequential activation and inactivation of CaMKIV. First, in response to an increase in intracellular Ca(2+), CaMKIV binds Ca(2+)/CaM and becomes phosphorylated on T200 by CaMKK. These events result in the generation of autonomous activity required for CaMKIV-mediated transcriptional regulation. The CaMKIV-associated PP2A then dephosphorylates CaMKIV T200, thereby terminating autonomous activity and CaMKIV-mediated gene transcription.

Critical role of cAMP-response element-binding protein for angiotensin II-induced hypertrophy of vascular smooth muscle cells

We reported previously an important role of cyclic AMP-response element (CRE) for the induction of interleukin-6 gene expression by angiotensin II (AngII). We examined signaling pathways that are responsible for AngII-induced phosphorylation of CRE-binding protein (CREB) at serine 133 that is a critical marker for the activation in rat vascular smooth muscle cells (VSMC). AngII time dependently induced phosphorylation of CREB with a peak at 5 min. The AngII-induced phosphorylation of CREB was blocked by CV11974, an AngII type I receptor antagonist, suggesting that AngII type I receptor may mediate the phosphorylation of CREB. Inhibition of extracellular signal-regulated protein kinase (ERK) by PD98059 or inhibition of p38 mitogen-activated protein kinase (MAPK) by SB203580 partially inhibited AngII-induced CREB phosphorylation. A protein kinase A inhibitor, H89, also partially suppressed AngII-induced CREB phosphorylation. Inhibition of epidermal growth factor-receptor by AG1478 suppressed the AngII-induced CREB phosphorylation as well as activation of ERK and p38MAPK. Overexpression of the dominant negative form of CREB by an adenovirus vector suppressed AngII-induced c-fos expression and incorporation of [(3)H]leucine to VSMC. These findings suggest that AngII may activate multiple signaling pathways involving two MAPK pathways and protein kinase A, all of which contribute to the activation of CREB. Transactivation of epidermal growth factor-receptor is also critical for AngII-induced CREB phosphorylation. Activation of CREB may be important for the regulation of gene expression and hypertrophy of VSMC induced by AngII.

Regulation of microtubule-associated proteins

Microtubule-associated proteins (MAPs) function to regulate the assembly dynamics and organization of microtubule polymers. Upstream regulation of MAP activities is the major mechanism used by cells to modify and control microtubule assembly and organization. This review summarizes the functional activities of MAPs found in animal cells and discusses how these MAPs are regulated. Mechanisms controlling gene expression, isoform-specific expression, protein localization, phosphorylation, and degradation are discussed. Additional regulatory mechanisms include synergy or competition between MAPs and the activities of cofactors or binding partners. For each MAP it is likely that regulation in vivo reflects a composite of multiple regulatory mechanisms.

Defective signaling in a subpopulation of CD4(+) T cells in the absence of Ca(2+)/calmodulin-dependent protein kinase IV

Ca(2+)/calmodulin-dependent protein kinase IV-deficient (CaMKIV(-/-)) mice have been used to investigate the role of this enzyme in CD4(+) T cells. We identify a functional defect in a subpopulation of CD4(+) T cells, characterized by a cell surface marker profile usually found on memory phenotype CD4(+) T cells. Upon T-cell receptor engagement, the mutant cells produce diminished levels of interleukin-2 (IL-2), IL-4, and gamma interferon protein and mRNA. The defect is secondary to an inability to phosphorylate CREB and to induce CREB-dependent immediate-early genes, including c-jun, fosB, fra2, and junB, which are required for cytokine gene induction. In contrast, stimulated naive CD4(+) T cells from CaMKIV(-/-) mice show normal CREB phosphorylation, induction of immediate-early genes, and cytokine production. Thus, in addition to defining an important signaling role for CaMKIV in a subpopulation of T cells, we identify differential signaling requirements for cytokine production between naive T cells and T cells that express cell surface markers characteristic of the memory phenotype.

Genetic dissection of corticosterone receptor function in the rat hippocampus

The hippocampus, a brain structure with a crucial role in learning and memory and an involvement in stress-related neurological or psychiatric disorders, is extremely sensitive to aberrant levels of corticosteroid stress hormones (CORT). We hypothesized that CORT-affected brain disorders are the result of aberrant expression of specific CORT-responsive genes. In order to identify such genes, we have applied several gene expression profiling techniques such as differential display, DNA micro-arrays and in particular the highly sensitive serial analysis of gene expression (SAGE). Using SAGE, a total of 76,790 hippocampal tags were generated which together represent 28,748 unique mRNAs of which 4626 gave a hit with rat sequences in Genbank. By comparing SAGE profiles derived from rat hippocampi treated with different concentrations of corticosteroids, we have identified over 200 CORT-responsive genes with significant differential expression in hippocampus. The identified products include genes that are important for the plasticity of hippocampal neurones such as neural cell adhesion molecules, growth-promoting proteins, genes involved in axogenesis, synaptogenesis and signal-transduction. One novel corticosteroid-responsive gene, classified as Ca2+/calmodulin-dependent protein kinase (CaMK)-VI, exhibited structural resemblance with the family of CaMKs, in particular with that of CaMK-IV. We also identified an alternatively spliced mRNA of this gene encoding a peptide (CaMK-kinase related peptide or CARP) which may function in an autoregulatory feedback loop. These findings suggest a novel mode of operation of the CaMK pathway in control of Ca2+ homeostasis relevant for CORT-related brain disorders.

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.

CaMKIV/Gr is dispensable for spermatogenesis and CREM-regulated transcription in male germ cells

The calcium/calmodulin-dependent protein kinase type IV/Gr (CaMKIV/Gr) is expressed in male germ cells and spermatids and has been implicated in controlling the differentiation of germ cells into mature spermatozoa. The function of CaMKIV/Gr in spermatogenesis was investigated using CaMKIV/Gr-deficient mice generated by targeted gene disruption. CaMKIV/Gr-deficient males exhibited normal spermatogenesis, and their fertility was similar to that of wild-type littermates. Notwithstanding the function of CaMKIV/Gr as an activator of cAMP response element (CRE)-dependent transcription, mRNA levels of several testis-specific CRE modulator (CREM)-regulated genes were unaltered. These results indicate that CaMKIV/Gr is not essential for spermatogenesis or for CRE-regulated gene transcription in the testis.

Ca(2+)/CaM-dependent kinases: from activation to function

Calmodulin (CaM) is an essential protein that serves as a ubiquitous intracellular receptor for Ca(2+). The Ca(2+)/CaM complex initiates a plethora of signaling cascades that culminate in alteration of cellular functions. Among the many Ca(2+)/CaM-binding proteins to be discovered, the multifunctional protein kinases CaMKI, II, and IV play pivotal roles. Our review focuses on this class of CaM kinases to illustrate the structural and biochemical basis for Ca(2+)/CaM interaction with and regulation of its target enzymes. Gene transcription has been chosen as the functional endpoint to illustrate the recent advances in Ca(2+)/CaM-mediated signal transduction mechanisms.

Calcium-induced ERK activation in human T lymphocytes occurs via p56(Lck) and CaM-kinase

We previously demonstrated that stimulation of human T-lymphocytes with calcium ionophores induced the phosphorylation and enzymatic activation of ERK2. We now report on the mechanism by which calcium-ionophore-induced activation of ERK1 and 2 occurs in these cells. The activation of ERK1 and 2 by increases in intracellular calcium was inhibited by calmidazolium suggesting the involvement of calmodulin in this response. To further elucidate the mechanism by which calcium-induced ERK activation occurs, we used the CaM-kinase inhibitor KN-93 and an inactive analog of KN-93 (KN-92). KN-93, but not KN-92, blocked ionomycin-induced activation of ERK1 and 2 in human T lymphocytes. We previously demonstrated that stimulation of T lymphocytes with ionomycin or A23187 resulted in a CaM-kinase-dependent shift in the mobility of p56(Lck). To determine if p56(Lck) was involved in calcium-induced ERK activation, we stimulated the p56(Lck) negative Jurkat cell derivatives, J.CaM1.6 and J.CaM1/Rep3, with ionomycin. In these p56(Lck) negative cell lines, activation of ERK1 and 2 in response to ionomycin was only minimally detected. When J.CaM1 cells were reconstituted with p56(Lck), ionomycin induced ERK1 and 2 activation. Treatment of Jurkat cells with PP2, an inhibitor of p56(Lck), inhibited calcium-induced, but not PMA-induced, ERK1 and 2 activation. Treatment of Jurkat cells with the MEK inhibitor PD98059 blocked ionomycin-induced ERK activation, but not the shift in the mobility of p56(Lck). Our data suggests that increases in intracellular calcium induce the activation of ERK1 and 2 in human T lymphocytes via sequential activation of CaM-kinase and phosphorylation of p56(Lck).

Potentiation of CD3-induced expression of the linker for activation of T cells (LAT) by the calcineurin inhibitors cyclosporin A and FK506

The activation of blood cells, including T cells, triggers intracellular signals that control the expression of critical molecules, including cytokines and cytokine receptors. We show that T-cell receptor (TCR) ligation increases the cellular level of the protein linker for activation of T cells (LAT), a molecule critical for T-cell development and function. T-cell activation increased LAT messenger RNA, as determined by reverse transcription–polymerase chain reaction and by Northern blotting. The TCR-induced increase in LAT expression involved the activation of the serine/threonine kinases PKC and MEK, because inhibitors of these kinases blocked the increase in LAT. Accordingly, the PKC activator phorbol myristate acetate up-regulated LAT expression. Strikingly, the calcineurin inhibitors cyclosporin A (CsA) and FK506 strongly potentiated TCR-induced LAT expression, suggesting that the activation of calcineurin following TCR ligation negatively regulates LAT expression. Accordingly, Ca++ ionophores, which can activate calcineurin by increasing intracellular Ca++, blocked the TCR-induced increase in cellular LAT. CsA and FK506 blocked the Ca++ionophores' inhibitory effect on LAT expression. Notably, CsA and FK506 preferentially up-regulated TCR-induced LAT expression; under the same conditions, these compounds did not increase the expression of 14 other molecules that previously had been implicated in T-cell activation. These data show that TCR-induced LAT expression involves the activation of the PKC-Erk pathway and is negatively regulated by the activation of calcineurin. Furthermore, the potentiation of TCR-induced LAT expression by CsA and FK506 suggests that the action of these agents involves up-regulating the cellular level of critical signaling molecules. These findings may have important therapeutic implications.

Influence of aging and caloric restriction on activation of Ras/MAPK, calcineurin, and CaMK-IV activities in rat T cells

The signaling cascade mediated by Ras (p21ras) and MAPK (mitogen-activated protein kinase) and calcium/calmodulin regulating enzymes, calcineurin (CaN) and CaMK-IV, are considered to be essential for T-cell growth and function. In the present study, the effect of aging and caloric restriction (CR) on the induction of Ras and MAPK activation by concanavalin A (ConA) was studied. Splenic T cells were isolated from young (4-6 months) and old (22-24 months) rats that had free access to food (control group), and from caloric restricted old (22-24 months) rats that beginning at 6 weeks of age were fed 60%(40% caloric restriction) of the diet consumed by the control rats. We found that the induction of Ras activity in T cells isolated from control old rats was lower (P<0.001) than that in control young rats. However, the levels of Ras activity in T cells isolated from CR old rats were similar to the levels in the age-matched control rats. The induction of MAPK activity in T cells isolated from control old rats and CR old rats was significantly less than in T cells isolated from control young rats, and caloric restriction significantly (P<0.05) reduced the age-related decline in MAPK activation. We also measured the induction of CaN and CaMK-IV activities by ConA in T cells from control young and old and CR old rats. The induction of both CaN and CaMK-IV activity decreased with age. Caloric restriction significantly (P<0.05) reduced the age-related decline in CaN activity, but had no significant effect on CaMK-IV activity. The changes in Ras/MAPK activation and in CaN and CaMK-IV activity with age or with CR were not associated with alterations in their corresponding protein levels. Thus, caloric restriction has a differential effect on the activation of the upstream signaling molecules that are altered with age.

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.

T Cell Activation Up-Regulates the Expression of the Focal Adhesion Kinase Pyk2: Opposing Roles for the Activation of Protein Kinase C and the Increase in Intracellular Ca2+

T cell activation initiates signals that control gene expression of molecules important for T cell function. The focal adhesion kinase Pyk2 has been implicated in T cell signaling. To further analyze the involvement of Pyk2 in T cell processes, we examined the effect of T cell stimulation on the expression of Pyk2. We found that TCR ligation or PMA increased Pyk2 expression in Jurkat T cells and in normal T cells. In contrast, TCR ligation and PMA failed to induce any detectable increase in the expression of the other member of the focal adhesion kinase family, Fak, in Jurkat T cells and induced only a weak increase in Fak expression in normal T cells. The serine/threonine kinases, protein kinase C and mitogen-activated protein/extracellular signal-related kinase kinase (MEK), regulated Pyk2 expression, as inhibitors of these kinases blocked stimulus-induced Pyk2 expression. Cyclosporin A, FK506, and KN-62 did not block Pyk2 expression; thus, calcineurin and Ca2+/calmodulin-activated kinases are not critical for augmenting Pyk2 expression. TCR ligation increased Pyk2 mRNA, and the transcriptional inhibitor actinomycin D blocked Pyk2 expression. Strikingly, Ca2+ ionophores, at concentrations that in combination with other stimuli induced IL-2 expression, blocked TCR- and PMA-induced up-regulation of Pyk2 expression. Thus, the increase in Ca2+ has opposing effects on IL-2 and Pyk2 expression. Cyclosporin A and FK506, but not KN-62, blocked Ca2+ ionophore-mediated inhibition of Pyk2 expression, implicating calcineurin in down-regulating Pyk2 expression. These results show that TCR-triggered intracellular signals increase Pyk2 expression and shed light on the molecular mechanisms that regulate Pyk2 expression in T cells.

Age-related decline in activation of calcium/calmodulin-dependent phosphatase calcineurin and kinase CaMK-IV in rat T cells

We have previously shown that the DNA binding activity of the transcription factor NFAT which plays a predominant role in IL-2 transcription decreases with age. Because the transactivation (dephosphorylation and nuclear translocation) of the NFAT-c (cytoplasmic component of the NFAT complex) is mediated by the calcium/calmodulin-dependent phosphatase, calcineurin (CaN), and because Ca2+/calmodulin-dependent kinases (CaMK-II and IV/Gr) have been shown to play a critical role in calcium signaling in T cells, it was of interest to determine what effect aging has on the activation and the levels of these calcium regulating enzymes. The induction of calcineurin phosphatase activity, and CaMK-II and IV/Gr activities, were studied in splenic T cells isolated from Fischer 344 rats at 6, 15, and 24 months of age. In addition, the changes in the protein levels of these enzymes were measured by Western blot. The calcineurin phosphatase activity and CaMK-II and IV kinase activities were at a maximum after the cells were incubated with anti-CD3 antibody for 5-10 minutes. The induction of calcineurin activity by anti-CD3 and by calcium ionophore (A23187) declined 65 and 55%, respectively, between 6 and 24 months of age. The induction of CaMK-IV activity, but not CaMK-II activity by anti-CD3, was significantly less (by 54%) in T cells from old rats compared to T cells from young rats. The decline in the activation of these enzymes with age was not associated with changes in their corresponding protein levels. These results demonstrate that alterations in calcineurin phosphatase activity and CaMK-IV activity may contribute to the well-documented age-related decline in T cell function.

The Ca-calmodulin-dependent protein kinase cascade

The Ca2+-calmodulin-dependent protein kinase (CaM kinase) cascade includes three kinases: CaM-kinase kinase (CaMKK); and the CaM kinases CaMKI and CaMKIV, which are phosphorylated and activated by CaMKK. Members of this cascade respond to elevation of intracellular Ca2+ levels and are particularly abundant in brain and in T cells. CaMKK and CaMKIV localize both to the nucleus and to the cytoplasm, whereas CaMKI is only cytosolic. Nuclear CaMKIV regulates transcription through phosphorylation of several transcription factors, including CREB. In the cytoplasm, there is extensive cross-talk between CaMKK, CaMKIV and other signaling cascades, including those that involve the cAMP-dependent kinase (PKA), MAP kinases and protein kinase B (PKB; also known as Akt). Activation of PKB by CaMKK appears to be important in protection of neurons from programmed cell death during development.

hSK4/hIK1, a calmodulin-binding KCa channel in human T lymphocytes. Roles in proliferation and volume regulation

Human T lymphocytes express a Ca2+-activated K+ current (IK), whose roles and regulation are poorly understood. We amplified hSK4 cDNA from human T lymphoblasts, and we showed that its biophysical and pharmacological properties when stably expressed in Chinese hamster ovary cells were essentially identical to the native IK current. In activated lymphoblasts, hSK4 mRNA increased 14.6-fold (Kv1.3 mRNA increased 1.3-fold), with functional consequences. Proliferation was inhibited when Kv1.3 and IK were blocked in naive T cells, but IK block alone inhibited re-stimulated lymphoblasts. IK and Kv1.3 were involved in volume regulation, but IK was more important, particularly in lymphoblasts. hSK4 lacks known Ca2+-binding sites; however, we mapped a Ca2+-dependent calmodulin (CaM)-binding site to the proximal C terminus (Ct1) of hSK4. Full-length hSK4 produced a highly negative membrane potential (Vm) in Chinese hamster ovary cells, whereas the channels did not function when either Ct1 or the distal C terminus was deleted (Vm approximately 0 mV). Native IK (but not expressed hSK4) current was inhibited by CaM and CaM kinase antagonists at physiological Vm values, suggesting modulation by an accessory molecule in native cells. Our results provide evidence for increased roles for IK/hSK4 in activated T cell functions; thus hSK4 may be a promising therapeutic target for disorders involving the secondary immune response.

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.

Calmodulin-dependent protein kinase IV: regulation of function and expression

Calmodulin-dependent protein kinase IV (CaMKIV) is a key mediator of Ca2+-induced gene expression. This serine/threonine kinase is itself activated by a calmodulin kinase kinase. In the present contribution the gene structure, regulation of activity, the role in Ca2+-dependent gene expression, and the hormonal induction and controlled expression of CaMKIV during tissue development are reviewed.

Components of a calmodulin-dependent protein kinase cascade. Molecular cloning, functional characterization and cellular localization of Ca2+/calmodulin-dependent protein kinase kinase beta

Ca2+/calmodulin-dependent protein kinases I and IV (CaMKI and CaMKIV, respectively) require phosphorylation on an equivalent single Thr in the activation loop of subdomain VIII for maximal activity. Two distinct CaMKI/IV kinases, CaMKKalpha and CaMKKbeta, were purified from rat brain and partially sequenced (Edelman, A. M., Mitchelhill, K., Selbert, M. A., Anderson, K. A., Hook, S. S., Stapleton, D., Goldstein, E. G., Means, A. R., and Kemp, B. E. (1996) J. Biol. Chem. 271, 10806-10810). We report here the cloning and sequencing of cDNAs for human and rat CaMKKbeta, tissue and regional brain localization of CaMKKbeta protein, and mRNA and functional characterization of recombinant CaMKKbeta in vitro and in Jurkat T cells. The sequences of human and rat CaMKKbeta demonstrate 65% identity and 80% similarity with CaMKKalpha and 30-40% identity with CaMKI and CaMKIV themselves. CaMKKbeta is broadly distributed among rat tissues with highest levels in CaMKIV-expressing tissues such as brain, thymus, spleen, and testis. In brain, CaMKKbeta tracks more closely with CaMKIV than does CaMKKalpha. Bacterially expressed CaMKKbeta undergoes intramolecular autophosphorylation, is regulated by Ca2+/CaM, and phosphorylates CaMKI and CaMKIV on Thr177 and Thr200, respectively. CaMKKbeta activates both CaMKI and CaMKIV when coexpressed in Jurkat T cells as judged by phosphorylated cAMP response element-binding protein-dependent reporter gene expression. CaMKKbeta activity is enhanced by elevation of intracellular Ca2+, although substantial activity is observed at the resting Ca2+ concentration. The strict Ca2+ requirement of CaMKIV-dependent phosphorylation of cAMP response element-binding protein, is therefore controlled at the level of CaMKIV rather than CaMKK.

Regulation of adenylyl cyclase activity in human peripheral blood mononuclear cells: effects of protein kinase inhibitors and of a calcium ionophore

In a previous paper we presented evidence for a negative regulation of adenylyl cyclase activity by tyrosine protein kinase(s) in the human leukemic T cell line Jurkat. In order to examine this point in non malignant cells, we conducted the present study in human peripheral blood mononuclear cells (PBMC). In these cells, staurosporine, a broad spectrum protein kinase inhibitor, enhanced not only the receptor-mediated, induced by prostaglandin E2 (PGE2), but also the direct (forskolin-induced) stimulation of adenylyl cyclase activity. Herbimycin A, a specific protein tyrosine kinase inhibitor, reproduced only in part the effect of staurosporine, whereas bisindolylmaleimide, the most specific protein kinase C (PKC) inhibitor known at present time, was ineffective. All these observations were made both in the absence and presence of isobutylmethylxanthine, a phosphodiesterase inhibitor, indicating that the effects of staurosporine and herbimycin A on cAMP accumulation were not due to phosphodiesterase inhibition. The calcium ionophore A 23187 also enhanced the PGE2-induced cAMP accumulation, and this effect was not additive to that of staurosporine, but additive to that of herbimycin A. These results confirm and extend those obtained in Jurkat cells. Taken together, they indicate that in human PBMC the adenylyl cyclase activity is negatively regulated by tyrosine kinase(s) and not by PKC, and positively regulated by Ca2+. They also suggest that the major enhancement by staurosporine of the PGE2-induced cAMP accumulation, although chiefly mediated by protein tyrosine kinase inhibition, also depends on another, presently undetermined, effect of the drug simulating that of Ca2+.

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.

Serine 16 of Stathmin as a Cytosolic Target for Ca2+/Calmodulin-Dependent Kinase II After CD2 Triggering of Human T Lymphocytes

We investigated specific signaling events initiated after T cell triggering through the costimulatory surface receptors CD2 and CD28 as compared with activation via the Ag receptor (TCR/CD3). We therefore followed the phosphorylation of stathmin, a ubiquitous cytoplasmic phosphoprotein proposed as a general relay integrating diverse intracellular signaling pathways through the combinatorial phosphorylation of serines 16, 25, 38, and 63, the likely physiologic substrates for Ca2+/calmodulin (CaM)-dependent kinases, mitogen-activated protein (MAP) kinase, cyclin-dependent kinases (cdks), and protein kinase A, respectively. We addressed the specific protein kinase systems involved in the CD2 pathway of T cell activation through the analysis of stathmin phosphorylation patterns in exponentially growing Jurkat T cells, as revealed by phosphopeptide mapping. Stimulation via CD2 activated multiple signal transduction pathways, resulting in phosphorylation of distinct sites of stathmin, the combination of which only partially overlaps the CD3- and CD28-induced patterns. The partial redundancy of the three T cell activation pathways was evidenced by the phosphorylation of Ser25 and Ser38, substrates of MAP kinases and of the cdk family kinase(s), respectively. Conversely, the phosphorylation of Ser16 of stathmin was observed in response to both CD2 and CD28 triggering, but not CD3 triggering, with a kinetics compatible with the lasting activation of CaM kinase II in response to CD2 triggering. In vitro, Ser16 of recombinant human stathmin was phosphorylated also by purified CaM kinase II, and in vivo, CaM kinase II activity was indeed stimulated in CD2-triggered Jurkat cells. Altogether, our results favor an association of CaM kinase II activity with costimulatory signals of T lymphocyte activation and phosphorylation of stathmin on Ser16.

A signaling complex of Ca2+-calmodulin-dependent protein kinase IV and protein phosphatase 2A

Stimulation of T lymphocytes results in a rapid increase in intracellular calcium concentration ([Ca2+]i) that parallels the activation of Ca2+-calmodulin-dependent protein kinase IV (CaMKIV), a nuclear enzyme that can phosphorylate and activate the cyclic adenosine monophosphate (cAMP) response element-binding protein (CREB). However, inactivation of CaMKIV occurs despite the sustained increase in [Ca2+]i that is required for T cell activation. A stable and stoichiometric complex of CaMKIV with protein serine-threonine phosphatase 2A (PP2A) was identified in which PP2A dephosphorylates CaMKIV and functions as a negative regulator of CaMKIV signaling. In Jurkat T cells, inhibition of PP2A activity by small t antigen enhanced activation of CREB-mediated transcription by CaMKIV. These findings reveal an intracellular signaling mechanism whereby a protein serine-threonine kinase (CaMKIV) is regulated by a tightly associated protein serine-threonine phosphatase (PP2A).

The Ca2+/calmodulin-dependent kinase type IV is involved in the CD5-mediated signaling pathway in human T lymphocytes

The CD5 receptor on T lymphocytes is involved in T cell activation and T-B cell interactions. In the present study, we have characterized the signaling pathways induced by anti-CD5 stimulation in human T lymphocytes. In T lymphocytes, anti-CD5 co-stimulation enhances the phytohemagglutinin/anti-CD28-induced interleukin-2 (IL-2) mRNA accumulation 1.6-fold and IL-2 protein secretion 2. 2-fold, whereby the up-regulation is mediated at both the transcriptional and post-transcriptional level. The CD5 signaling pathway up-regulates the IL-2 gene expression by increasing the DNA binding and transactivation activity of activator protein 1 but affects none of the other transcription factors like nuclear factor of activated T cells, nuclear factor kappaB, Oct, and CD28-responsive complex/nuclear factor of mitogen-activated T cells involved in the regulation of the IL-2 promoter activity. The CD5-induced increase of the activator protein 1 activity is mediated through the activation of calcium/calmodulin-dependent (CaM) kinase type IV, and is independent of the activation of mitogen-activated protein kinases Jun N-terminal kinase, extracellular signal-regulated kinase, and p38/Mpk2, and calcium/calmodul-independent kinase type II. The expression of a dominant negative mutant of CaM kinase IV in T lymphocytes transfected with an IL-2 promoter-driven reporter construct completely abrogates the response to CD5 stimulation, indicating that CaM kinase IV is essential to the CD5 signaling pathway. In addition, it is demonstrated that calcium/calmodulin-dependent kinase type IV is also involved in the stabilization of the IL-2 transcripts, which is observed after co-stimulation of phytohemagglutinin/anti-CD28 activated T lymphocytes with anti-CD5.

Inhibitory cross-talk by cAMP kinase on the calmodulin-dependent protein kinase cascade

The calmodulin-dependent kinase (CaM-K) cascade, a Ca2+-triggered system involving phosphorylation and activation of CaM-KI and CaM-KIV by CaM kinase kinase (CaM-KK), regulates transcription through direct phosphorylation of transcription factors such as cAMP response element-binding protein. We have shown previously that activated CaM-KIV can activate the mitogen-activated protein kinases (Enslen, H., Tokumitsu, H., Stork, P. J. S., Davis, R. J., and Soderling, T. R. (1996) Proc. Natl. Acad. Sci. U. S. A. 93, 10803-10808), and the present paper describes a novel regulatory cross-talk between cAMP kinase (PKA) and CaM-KK. PKA gave rapid phosphorylation in vitro and in cells of recombinant CaM-KK, resulting in 50-75% inhibition of CaM-KK activity, part of which was due to suppression of CaM-binding by phosphorylation of Ser458 in the CaM-binding domain. However, the Ser458 --> Ala mutant, or a truncation mutant in which the CaM-binding and autoinhibitory domains were deleted, was still partially suppressed by PKA-mediated phosphorylation. The second inhibitory site was identified as Thr108 by site-specific mutagenesis. Treatments of COS-7, PC12, hippocampal, or Jurkat cells with the PKA activators forskolin or isoproterenol gave 30-90% inhibition of either endogenous or transfected CaM-KK and/or CaM-KIV activities. These results demonstrate that the CaM kinase cascade is negatively regulated in cells by the cAMP/PKA pathway.

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.

Regulation of phospholipid biosynthesis by Ca(2+)-calmodulin-dependent protein kinase inhibitors

Inhibitors of Ca(2+)-calmodulin (CaM)-dependent protein kinases strongly modify phospholipid metabolism. Two compounds, KN62 and KT5926 recognized as blockers of Ca(2+)-CaM-dependent protein kinase II, induced a specific increase in phosphatidylserine (PtdSer) synthesis without noticeable changes in phosphatidylcholine (PtdCho) and phosphatidylethanolamine (PtdEtn) biosynthesis. The increase of PtdSer synthesis was dependent on the presence of Ca2+ in the incubation medium and was impaired in cells whose Ca2+ stores were depleted by pretreatment with CD3 mAb, thapsigargin or EGTA. The mechanism of the stimulation of PtdSer synthesis by these two compounds seems to involve an accumulation of Ca2+ into the endoplasmic reticulum, possibly due to an increased activity of the endoplasmic reticulum Ca(2+)-ATPase. By contrast, ML-7 and ML-9, two inhibitors of the myosin light chain kinase (MLCK), another Ca(2+)-CaM-dependent kinase, were both capable of increasing PtdSer synthesis and decreasing PtdCho and PtdEtn synthesis, reproducing the effect previously described with CaM-antagonists. The increase of PtdSer caused by ML-7 and ML-9 was Ca(2+)-dependent while the inhibition of PtdCho and PtdEtn synthesis was not. The use of these four protein kinase inhibitors thus suggests the possible existence of two CaM-dependent pathways that differentially regulates phospholipid metabolism in T cells.

CREB phosphorylation and dephosphorylation: a Ca(2+)- and stimulus duration-dependent switch for hippocampal gene expression

While changes in gene expression are critical for many brain functions, including long-term memory, little is known about the cellular processes that mediate stimulus-transcription coupling at central synapses. In studying the signaling pathways by which synaptic inputs control the phosphorylation state of cyclic AMP-responsive element binding protein (CREB) and determine expression of CRE-regulated genes, we found two important Ca2+/calmodulin (CaM)-regulated mechanisms in hippocampal neurons: a CaM kinase cascade involving nuclear CaMKIV and a calcineurin-dependent regulation of nuclear protein phosphatase 1 activity. Prolongation of the synaptic input on the time scale of minutes, in part by an activity-induced inactivation of calcineurin, greatly extends the period over which phospho-CREB levels are elevated, thus affecting induction of downstream genes.