Localization of the multiple calmodulin messenger RNAs in differentiated PC12 cells

Calm1 signaling pathway is essential for the migration of mouse precerebellar neurons

The calcium ion regulates many aspects of neuronal migration, which is an indispensable process in the development of the nervous system. Calmodulin (CaM) is a multifunctional calcium ion sensor that transduces much of the signal. To better understand the role of Ca(2+)-CaM in neuronal migration, we investigated mouse precerebellar neurons (PCNs), which undergo stereotyped, long-distance migration to reach their final position in the developing hindbrain. In mammals, CaM is encoded by three non-allelic CaM (Calm) genes (Calm1, Calm2 and Calm3), which produce an identical protein with no amino acid substitutions. We found that these CaM genes are expressed in migrating PCNs. When the expression of CaM from this multigene family was inhibited by RNAi-mediated acute knockdown, inhibition of Calm1 but not the other two genes caused defective PCN migration. Many PCNs treated with Calm1 shRNA failed to complete their circumferential tangential migration and thus failed to reach their prospective target position. Those that did reach the target position failed to invade the depth of the hindbrain through the required radial migration. Overall, our results suggest the participation of CaM in both the tangential and radial migration of PCNs.

Effects of decreased calmodulin protein on the survival mechanisms of alveolar macrophages during Pneumocystis pneumonia

Pneumocystis infection causes increased intracellular levels of reactive oxygen species (ROS) and the subsequent apoptosis of alveolar macrophages (Amø). Assessments of key prosurvival molecules in Amø and bronchoalveolar lavage fluids from infected rats and mice showed low levels of granulocyte-macrophage colony-stimulating factor (GM-CSF) and reduced activation of phosphoinositide-3 kinase (PI-3K). Ubiquitous calcium-sensing protein calmodulin protein and mRNA levels were also reduced in Amø during Pneumocystis pneumonia (Pcp). Calmodulin has been implicated in control of GM-CSF production and PI-3K activation in other immune cell types. Experiments to determine the control of GM-CSF and PI-3K by calmodulin in Amø showed that GM-CSF expression and PI-3K activation could not be induced when calmodulin was inhibited. Calmodulin inhibition also led to increased levels of ROS and apoptosis in cells exposed to bronchoalveolar lavage fluids from infected animals. Supplementation of Amø with exogenous calmodulin increased survival signaling via GM-CSF and PI-3K and reduced ROS and apoptosis. These data support the hypotheses that calmodulin levels at least partially control survival signaling in Amø and that restoration of GM-CSF or PI-3K signaling will improve host response to the organism.

Multiple calmodulin mRNAs are selectively transported to functionally different neuronal and glial compartments in the rat hippocampus. An electron microscopic in situ hybridization study

The ultrastructural distribution of the calmodulin (CaM) mRNAs transcribed from the three CaM genes was studied in the CA1 region of the adult rat hippocampus by means of electron microscopic in situ hybridization. Digoxigenin-labeled CaM gene-specific riboprobes were detected with nanogold-anti-digoxigenin antibody conjugate. The CaM mRNAs were differentially distributed in both the neuronal and glial cell compartments. The greatest difference in neuronal distribution of the CaM mRNAs was found in the dendrites, where the mRNAs transcribed from the CaM I and III genes were much more abundant than the CaM II mRNA. The neuronal perikarya were heavy labeled for all the CaM mRNAs. Interestingly, the myelinated axons and axon terminals also contained small amounts of nanogold particles for all the CaM mRNAs, which diminished with increasing distance from the soma. Most of the synaptic profiles, however, contained labeling only in the postsynaptic region. The CaM mRNAs were differentially distributed in the glial cells. While the glial cell somata were only lightly labeled, surprisingly concentrated labeling was present in the perisynaptic and perivascular astrocytic processes. In general, the CaM II mRNA was the least represented in the glial processes. Only a very low CaM gene expression was observed in the endothelial and resting microglial cells. These results provide ultrastructural evidence for differential targeting of the multiple CaM mRNA transcripts to the intracellular compartments and suggest their microdomain-specific regulation.

Cell type-specific regulation of calmodulin 2 expression by mutant p53

To identify genes that are stimulated by oncogenic forms of mutant p53, we studied, by microarray analysis and PCR-select subtractive hybridization, gene expression changes in human wild-type (wt) p53-negative immortal 041 fibroblasts infected to stably express p53 mutant 175H. In contrast to the wt p53 transactivator, 175H induced only few and weak, gene expression changes. We report here the stimulation of calmodulin 2 (CaM 2), but not CaM 1 or 3, gene expression specifically in 041 cells. The stimulation of the CaM 2 promoter required the 5' untranslated sequences as well as the integrity of the transactivation domain of 175H. However, direct binding of 175H to the 5'UT in vitro could not be demonstrated.

Intracellular targeting of calmodulin mRNAs in primary hippocampal cells

We investigated the intracellular distribution of the mRNAs corresponding to the three non-allelic CaM genes in cultured hippocampal cells by in situ hybridization with digoxigenin-labeled gene-specific riboprobes. In neurons the perikaryon was heavily stained and strong dendritic mRNA targeting was detected for all three CaM genes. The color labeling exhibited a punctate distribution, suggesting that CaM mRNAs are transported in RNA granules. Immunocytochemistry for S100 demonstrated that glial cells express CaM mRNAs at a very low level. A minority of the cultured cells were negative for either labeling.

Ontogeny of calmodulin gene expression in rat brain

Calmodulin (CaM), a multifunctional intracellular calcium receptor, is a key element in signaling mechanisms. It is encoded in vertebrates by multiple apparently redundant genes (CaM I, II, III). To investigate whether differential expression takes place in the developing rat brain, a quantitative in situ hybridization analysis was carried out involving 15 brain areas at six ages between embryonic day 19 and postnatal day 20 (PD20) with gene-specific [(35)S]cRNA probes. A widespread, developmental stage-specific and differential expression of the three CaM genes was observed. The characteristic changes in the CaM mRNA levels in the examined time frame allowed the brain regions to be classified into three categories. For the majority of the areas (e.g. the piriform cortex for CaM III), the signal intensities peaked at around PD10 and the expression profile was symmetric (type 1). Other regions (e.g. the cerebral cortex, layer 1 for CaM II) displayed their highest signal intensities at the earliest age measured, followed by a gradual decrease (type 2). The signal intensities in the regions in the third group (e.g. the hypothalamus for CaM III) fluctuated from age to age (type 3). Marked CaM mRNA levels were measured for each transcript corresponding to the three CaM genes in the molecular layers of the cerebral and cerebellar cortici and hippocampus, suggesting their dendritic translocation. The highest signal intensity was measured for CaM II mRNA, followed by those for CaM III and CaM I mRNAs on PD1. However, the CaM II and CaM III mRNAs subsequently decreased steeply, while the CaM I mRNAs were readily detected even on PD20. Our results suggest that during development (1) the transcription of the CaM genes is under differential, area-specific control, and (2) a large population of CaM mRNAs is targeted to the dendritic compartment in a gene-specific manner.

Regulation of calmodulin mRNAs in differentiating human IMR-32 neuroblastoma cells

Calmodulin (CaM), the principal mediator of the calcium signal, regulates numerous processes pertinent to neural function. Mammalian CaM is generated from three genes that give rise to five distinct transcripts. To determine the regulation of individual CaM transcripts in neurons, we assessed their abundance during differentiation of human IMR-32 neuroblastoma cells. Northern analysis revealed that the 4.1 kb CALM1 transcript was specifically upregulated about two-fold during differentiation, and that this increase correlated with neurite extension. By contrast, the CALM2 and CALM3 mRNAs as well as the 1.7 kb CALM1 transcript showed an initial increase but then returned to levels close to, or only slightly above, controls. The increase in the 4.1 kb transcript was largely due to its specific stabilization in differentiated cells. However, total cellular CaM levels did not change significantly throughout differentiation. To begin to address whether the 4.1 kb CALM1 transcript might play a unique role in providing local CaM pools, we determined its localization in differentiated IMR-32 cells using in situ hybridization. The 4.1 kb CALM1 transcript localized to the cell body, but was also present within extending neurites. This finding agrees with in vivo studies showing elevated levels of the 4.1 kb CALM1 transcript in adult rat central neurons and the presence of CALM1 transcripts in dendrites, and establishes a human in vitro model system to study individual CaM transcripts with respect to neuronal functions.

Differential calmodulin gene expression in the rodent brain

Apparently redundant members of the calmodulin (CaM) gene family encode for the same amino acid sequence. CaM, a ubiquitous cytoplasmic calcium ion receptor, regulates the function of a variety of target molecules even in a single cell. Maintenance of the fidelity of the active CaM-target interactions in different compartments of the cell requires a rather complex control of the total cellular CaM pool comprising multiple levels of regulatory circuits. Among these mechanisms, it has long been proposed that a multigene family maximizes the regulatory potentials at the level of the gene expression. CaM genes are expressed at a particularly profound level in the mammalian central nervous system (CNS), especially in the highly polarized neurons. Thus, in the search for clear evidence of the suggested differential expression of the CaM genes, much of the research has been focused on the elements of the CNS. This review aims to give a comprehensive survey on the current understanding of this field at the level of the regulation of CaM mRNA transcription and distribution in the rodent brain. The results indicate that the CaM genes are indeed expressed in a gene-specific manner in the developing and adult brain under physiological conditions. To establish local CaM pools in distant intracellular compartments (dendrites and glial processes), local protein synthesis from differentially targeted mRNAs is also employed. Moreover, the CaM genes are controlled in a unique, gene-specific fashion when responding to certain external stimuli. Additionally, putative regulatory elements have been identified on the CaM genes and mRNAs.

Multiple calmodulin genes exhibit systematically differential responses to chronic ethanol treatment and withdrawal in several regions of the rat brain

Ethanol induces profound alterations in the neuronal signaling systems, including the calcium (Ca(2+)) signaling. Prolonged exposure to ethanol evokes adaptive changes in the affected systems as they strive to restore the normal neuronal function. We investigated the involvement of calmodulin (CaM) genes, coding for the major mediator protein of intracellular Ca(2+) signals, in these adaptive processes at the mRNA level. The changes induced in the regional abundances of the CaM I, II, and III mRNA classes by chronic ethanol treatment and withdrawal were examined by means of quantitative in situ hybridization, employing gene-specific [35S]cRNA probes on rat brain cryostat sections. Regional analysis of the resulting changes in mRNA levels highlighted brain areas that belong in neuronal systems known to be especially sensitive to the action of ethanol. The results revealed systematically differential regulation for the three mRNA classes: the CaM I and CaM III mRNA levels displayed increases, and CaM II levels decreases in the affected brain regions, in both chronic ethanol- and withdrawal-treated animals. As regards the numbers of brain regions undergoing significant alterations in mRNA content, the CaM I mRNA levels exhibited changes in most brain areas, the CaM II levels did so in a lower number of brain regions, and the CaM III levels changed in only a few brain areas. These results suggest a differential regulation for the CaM genes in the rat brain and may help towards elucidation of the functional significance of the multiple CaM genes in the mammalian genome.

Differential regulation of calmodulin content and calmodulin messenger RNA levels by acute and repeated, intermittent amphetamine in dopaminergic terminal and midbrain areas

Repeated doses of psychoactive drugs often produce adaptive responses that differ from the initial drug application and additional adaptive processes occur following cessation of the drug. The relationship between alterations in calmodulin protein and messenger RNA produced by an initial versus a repeated dose of amphetamine was examined, as well as changes following drug cessation. Calmodulin protein and messenger RNA of the three individual calmodulin genes were measured in rat dopaminergic cell body and terminal areas following acute or repeated amphetamine. Rats were either injected once with 2.5mg/kg amphetamine or saline and decapitated after 3h, or given 10 injections of amphetamine three to four days apart and decapitated 3h after the final injection. Calmodulin messenger RNA and protein were also measured three and seven days after ceasing drug treatment. Acute amphetamine increased calmodulin 1.7-fold in the striatum and threefold in the ventral mesencephalon, with corresponding elevations in calmodulin messenger RNAs. In response to the 10th dose of amphetamine, however, the degree of increase in calmodulin was diminished in the striatum and ablated in the ventral mesencephalon. Correspondingly, select species of calmodulin messenger RNA were decreased from control levels. In the frontal cortex or nucleus accumbens, calmodulin levels were basically unaltered by the first or 10th doses of amphetamine, but both calmodulin and its messenger RNA were altered with time upon cessation of the drug. Three days later, both calmodulin protein and messenger RNA were decreased in select brain areas. By seven days after the 10th injection, calmodulin content was altered compared to saline controls in all areas, but the change in messenger RNA no longer paralleled the change in protein.Our findings demonstrate that both calmodulin protein and select species of calmodulin messenger RNA are altered by acute amphetamine, but this effect is attenuated after repeated, intermittent amphetamine. There are further time-dependent changes after cessation of repeated amphetamine, which may reflect compensatory neuronal responses. The alterations in calmodulin content and synthesis could contribute to changes in patterns or duration of behaviors that occur upon cessation of repeated amphetamine.

The calmodulin multigene family as a unique case of genetic redundancy: multiple levels of regulation to provide spatial and temporal control of calmodulin pools?

Calmodulin (CaM) is a ubiquitous, highly conserved calcium sensor protein involved in the regulation of a wide variety of cellular events. In vertebrates, an identical CaM protein is encoded by a family of non-allelic genes, raising questions concerning the evolutionary pressure responsible for the maintenance of this apparently redundant family. Here we review the evidence that the control of the spatial and temporal availability of CaM may require multiple regulatory levels to ensure the proper localization, maintenance and size of intracellular CaM pools. Differential transcription of the CaM genes provides one level of regulation to meet tissue-specific, developmental and cell-specific needs for altered CaM levels. Post-transcriptional regulation occurs at the level of mRNA stability, perhaps dependent on alternative polyadenylation and differences in the untranslated sequences of the multiple gene transcripts. Recent evidence indicates that trafficking of specific CaM mRNAs may occur to specialized cellular locales such as the dendrites of neurons. This could allow local CaM synthesis and thereby help generate local pools of CaM. Local CaM activity may be further regulated by post-translational mechanisms such as phosphorylation or storage of CaM in a 'masked' form. The spatial resolution of CaM activity is enhanced by the limited free diffusion of CaM combined with differential affinity for and availability of target proteins. Preserving multiple CaM genes with divergent noncoding sequences may be necessary in complex organisms to ensure that the many CaM-dependent processes occur with the requisite spatial and temporal resolution. Transgenic mouse models and studies on mice carrying single and double gene 'knockouts' promise to shed further light on the role of specificity versus redundancy in the evolutionary maintenance of the vertebrate CaM multigene family.

Differential distribution and intracellular targeting of mRNAs corresponding to the three calmodulin genes in rat brain. A quantitative in situ hybridization study

To investigate the pattern of expression of the three calmodulin (CaM) genes by in situ hybridization, gene-specific [35S]-cRNA probes complementary to the multiple CaM mRNAs were hybridized in rat brain sections and subsequently detected by quantitative film or high-resolution nuclear emulsion autoradiography. A widespread and differential area-specific distribution of the CaM mRNAs was detected. The expression patterns corresponding to the three CaM genes differed most considerably in the olfactory bulb, the cerebral and cerebellar cortices, the diagonal band, the suprachiasmatic and medial habenular nuclei, and the hippocampus. Moreover, the significantly higher CaM I and CaM III mRNA copy numbers than that of CaM II in the molecular layers of certain brain areas revealed a differential dendritic targeting of these mRNAs. The results indicate a differential pattern of distribution of the multiple CaM mRNAs at two levels of cellular organization in the brain: (a) region-specific expression and (b) specific intracellular targeting. A precise and gene-specific regulation of synthesis and distribution of CaM mRNAs therefore exists under physiological conditions in the rat brain.

Effect of antisense oligodeoxynucleotides directed to individual calmodulin gene transcripts on the proliferation and differentiation of PC12 cells

Calmodulin (CaM) is encoded by three different genes that collectively give rise to five transcripts. In the present study, we used antisense oligodeoxynucleotides targeted to unique sequences in the transcripts from the individual CaM genes to selectively block the expression of the different genes and to investigate the roles these individual genes play in the proliferation and nerve growth factor (NGF)-induced differentiation of PC12 cells. Culturing PC12 cells in the presence of oligodeoxynucleotide antisense to the transcripts from CaM genes I and II caused a significant decrease in the proliferation and a significant delay in the NGF-induced differentiation of PC12 cells when compared with untreated cells and with cells treated with the corresponding randomized oligodeoxynucleotides. However, an oligodeoxynucleotide antisense to CaM gene III did not significantly alter the proliferation or the NGF-induced differentiation of PC12 cells. The inhibition of cell proliferation could be reversed by washing out the antisense oligodeoxynucleotides. The levels of CaM in cells treated with oligodeoxynucleotides antisense to CaM genes I or II were reduced 52% or 63%, respectively, of the levels found in the control cells. However, the levels of CaM were not significantly reduced in PC12 cells treated with CaM gene III antisense oligodeoxynucleotide. None of the randomized oligodeoxynucleotides had any effect on the levels of CaM in PC12 cells. The reduced levels of CaM in PC12 cells treated with an oligodeoxynucleotide antisense to CaM gene I were accompanied by a reduction in the levels of the CaM gene I mRNAs, supporting a true antisense mechanism of action for these oligodeoxynucleotides. These results suggest that altering the level of CaM by using antisense oligodeoxynucleotides targeted to the dominant CaM transcripts in a particular cell type will specifically inhibit their proliferation and, in the case of neuronal cells, alter the course of their differentiation.

Reduced level of calmodulin in PC12 cells induced by stable expression of calmodulin antisense RNA inhibits cell proliferation and induces neurite outgrowth

The role calmodulin plays in the growth and differentiation of nerve cells was assessed by altering the levels of calmodulin in the PC12 rat pheochromocytoma cell line and determining the effects of altering these levels on cellular proliferation and differentiation. Calmodulin levels in the PC12 cells were increased or decreased by transfecting the cells with a mammalian expression vector into which the rat calmodulin gene I had been cloned in the sense or antisense orientation, respectively. The cells transfected with the calmodulin sense gene showed increased levels of calmodulin immunoreactivity and increased levels of calmodulin messenger RNA as ascertained by immunocytochemistry and slot-blot analysis, respectively. Cells transfected with the calmodulin antisense construct showed reduced levels of calmodulin immunoreactivity. Reducing the levels of calmodulin by expression of antisense calmodulin messenger RNA resulted in a marked inhibition of cell growth, whereas increasing the levels of calmodulin by overexpressing calmodulin messenger RNA resulted in an acceleration of cell growth. Transfected PC12 cells having reduced levels of calmodulin immunoreactivity exhibited spontaneous outgrowth of long, stable and highly branched neuritic processes. PC12 cells in which calmodulin was overexpressed showed no apparent changes in cell morphology, but did show an altered response to the addition of nerve growth factor. While nerve growth factor slowed cellular proliferation and induced extensive neurite outgrowth, in parental PC12 cells nerve growth factor induced little or no neurite outgrowth and little inhibition of cell proliferation in transfected cells overexpressing calmodulin. These results indicate that calmodulin is essential for the proliferation of nerve cells and for the morphological changes that nerve cells undergo during differentiation. The study also suggests the possibility that a calmodulin antisense approach may be used to inhibit the proliferation of neuronal tumors.

CaM I mRNA is localized to apical dendrites during postnatal development of neurons in the rat brain

In the rat, a single calmodulin (CaM) protein is encoded by three separate genes which produce five different transcripts. The significance of the multiple CaM genes is not known; however, individual CaM transcripts could be targeted to specific intracellular sites. In this report, the cellular distribution of CaM I mRNAs was analyzed in the postnatal rat brain. The 4.0-kb CaM I transcript was present in neuronal cell bodies and also localized to apical dendritic processes. In cerebral cortical neurons, the 4.0-kb CaM I mRNA was detected in apical dendrites at postnatal day (PD) 5 to 15. In hippocampal neurons, this CaM message was present in dendritic processes from PD S to 20, whereas in Purkinje neurons it was detected in dendrites at PD 15 and 20. The presence of the 4.0-kb CaM I mRNA in dendrites of the rat brain supports the notion of targeting transcripts derived from the CaM multigene family to discrete intracellular destinations.

Developmental expression of calmodulin mRNA and protein in regions of the postnatal rat brain

The expression of calmodulin (CaM) protein and mRNA was analyzed in specific regions of the rat brain during postnatal development. CaM levels in the adult brain were more abundant in the cerebral hemispheres and thalamus compared to brain stem and superior plus inferior colliculus. All brain regions contained higher CaM protein and mRNA levels than in non-neural tissues such as the kidney. During postnatal development of the brain, maximal levels of CaM protein and CaM I mRNAs were attained at day 10 or 15. Protein levels declined thereafter in the adult in all regions except the thalamus. With respect to products of the rat CaM I gene, the 4.0 kb neural transcript demonstrated a pronounced increase during postnatal development, whereas the 1.8 kb message showed little change.

Immunocytochemical localization of calmodulin in PC12 cells and its possible interaction with histones

The subcellular localization of calmodulin, a multi-functional calcium-binding regulatory protein, was examined immunocytochemically in undifferentiated PC12 rat pheochromocytoma cells and cells differentiated with nerve growth factor (NGF) and dibutyryl cyclic AMP. In undifferentiated PC12 cells, diffuse immunostaining for calmodulin was observed in the cytoplasm, and weak, patch-like staining was found in the nucleus. In differentiated cells, intense immunostaining for calmodulin was observed in the cytoplasm, while nuclear immunostaining was still evident. Immunoreactivity for calmodulin was also observed along newly-formed neuritic processes, with strong staining in varicosity-like structures and growth cones. Using double-label immunochemistry, the relative intensity of immunostaining for calmodulin among the nuclei was found to correlate with the relative intensity of immunostaining for histones in the same nuclei. A comparison of a profile of 125I-calmodulin binding in the nuclear fraction from PC12 cells to that of immunoblotting for histones in the same fraction indicated that some of the histones are calmodulin-binding proteins in PC12 cells. These results show that the level and subcellular distribution of calmodulin are altered during the course of nerve cell differentiation and suggest the possibility that histones may function as major nuclear binding proteins for calmodulin.