Acidic calponin immunoreactivity in postnatal rat brain and cultures: subcellular localization in growth cones, under the plasma membrane and along actin and glial filaments

Mechanoregulation and function of calponin and transgelin

It is well known that chemical energy can be converted to mechanical force in biological systems by motor proteins such as myosin ATPase. It is also broadly observed that constant/static mechanical signals potently induce cellular responses. However, the mechanisms that cells sense and convert the mechanical force into biochemical signals are not well understood. Calponin and transgelin are a family of homologous proteins that participate in the regulation of actin-activated myosin motor activity. An isoform of calponin, calponin 2, has been shown to regulate cytoskeleton-based cell motility functions under mechanical signaling. The expression of the calponin 2 gene and the turnover of calponin 2 protein are both under mechanoregulation. The regulation and function of calponin 2 has physiological and pathological significance, as shown in platelet adhesion, inflammatory arthritis, arterial atherosclerosis, calcific aortic valve disease, post-surgical fibrotic peritoneal adhesion, chronic proteinuria, ovarian insufficiency, and tumor metastasis. The levels of calponin 2 vary in different cell types, reflecting adaptations to specific tissue environments and functional states. The present review focuses on the mechanoregulation of calponin and transgelin family proteins to explore how cells sense steady tension and convert the force signal to biochemical activities. Our objective is to present a current knowledge basis for further investigations to establish the function and mechanisms of calponin and transgelin in cellular mechanoregulation.

Proteomic Screen of Brain Glycoproteome Reveals Prion Specific Marker of Pathogenesis

Transmissible spongiform encephalopathies (TSEs) are neurodegenerative disorders caused by the presence of an infectious prion protein. The primary site of pathology is the brain characterized by neuroinflammation, astrogliosis, prion fibrils, and vacuolation. The events preceding the observed pathology remain in question. We sought to identify biomarkers in the brain of TSE-infected and aged-matched control mice using two-dimensional fluorescence difference gel electrophoresis (2D-DIGE). Since the brain proteome is too complex to resolve all proteins using 2D-DIGE, protein samples are initially filtered through either concanavalin A (ConA) or wheat-germ agglutinin (WGA) columns. Four differentially abundant proteins are identified through screening of the two different glycoproteomes: Neuronal growth regulator 1 (NEGR1), calponin-3 (CNN3), peroxiredoxin-6 (Prdx6), and glial fibrillary acidic protein (GFAP). Confirmatory Western blots are performed with samples from TSE-infected and comparative Alzheimer's disease (AD) affected brains and their respective controls from time points throughout the disease courses. The abundance of three of the four proteins increases significantly during later stages of prion disease whereas NEGR1 decreases in abundance. Comparatively, no significant changes are observed in later stages of AD. Our lab is the first to associate the glycosylated NEGR1 protein with prion disease pathology.

Astroglial Modulation of Hydromineral Balance and Cerebral Edema

Maintenance of hydromineral balance (HB) is an essential condition for life activity at cellular, tissue, organ and system levels. This activity has been considered as a function of the osmotic regulatory system that focuses on hypothalamic vasopressin (VP) neurons, which can reflexively release VP into the brain and blood to meet the demand of HB. Recently, astrocytes have emerged as an essential component of the osmotic regulatory system in addition to functioning as a regulator of the HB at cellular and tissue levels. Astrocytes express all the components of osmoreceptors, including aquaporins, molecules of the extracellular matrix, integrins and transient receptor potential channels, with an operational dynamic range allowing them to detect and respond to osmotic changes, perhaps more efficiently than neurons. The resultant responses, i.e., astroglial morphological and functional plasticity in the supraoptic and paraventricular nuclei, can be conveyed, physically and chemically, to adjacent VP neurons, thereby influencing HB at the system level. In addition, astrocytes, particularly those in the circumventricular organs, are involved not only in VP-mediated osmotic regulation, but also in regulation of other osmolality-modulating hormones, including natriuretic peptides and angiotensin. Thus, astrocytes play a role in local/brain and systemic HB. The adaptive astrocytic reactions to osmotic challenges are associated with signaling events related to the expression of glial fibrillary acidic protein and aquaporin 4 to promote cell survival and repair. However, prolonged osmotic stress can initiate inflammatory and apoptotic signaling processes, leading to glial dysfunction and a variety of brain diseases. Among many diseases of brain injury and hydromineral disorders, cytotoxic and osmotic cerebral edemas are the most common pathological manifestation. Hyponatremia is the most common cause of osmotic cerebral edema. Overly fast correction of hyponatremia could lead to central pontine myelinolysis. Ischemic stroke exemplifies cytotoxic cerebral edema. In this review, we summarize and analyze the osmosensory functions of astrocytes and their implications in cerebral edema.

Review on PACAP-Induced Transcriptomic and Proteomic Changes in Neuronal Development and Repair

Pituitary adenylate cyclase activating polypeptide (PACAP) is a neuropeptide with widespread occurrence and diverse biological effects. Among its several different effects, of special importance is the action of PACAP on neuronal proliferation, differentiation and migration, and neuroprotection. The neuroprotective mechanism of PACAP is both direct and indirect, via neuronal and non-neuronal cells. Several research groups have performed transcriptomic and proteomic analysis on PACAP-mediated genes and proteins. Hundreds of proteins have been described as being involved in the PACAP-mediated neuroprotection. In the present review we summarize the few currently available transcriptomic data potentially leading to the proteomic changes in neuronal development and protection. Proteomic studies focusing on the neuroprotective role of PACAP are also reviewed and discussed in light of the most intriguing and promising effect of this neuropeptide, which may possibly have future therapeutic potential.

Cnn3 regulates neural tube morphogenesis and neuronal stem cell properties

Calponin 3 (Cnn3) is a member of the Cnn family of actin-binding molecules that is highly expressed in the mammalian brain and has been shown to control dendritic spine morphology, density, and plasticity by regulating actin cytoskeletal reorganization and dynamics. However, little is known about the role of Cnn3 during embryonic development. In this study, we analyzed mutant animals deficient in Cnn3 to gain a better understanding of its role in brain morphogenesis. Embryos lacking Cnn3 exhibited massive malformation of the developing brain including exoencephaly, closure defects at the rostral neural tube, and strong enlargement of brain tissue. In wild-type animals, we found Cnn3 being localized to the apical lining of the neuroepithelium in close vicinity to beta-Catenin and N-cadherin. By performing immunohistochemistry on beta-Catenin and p-Smad, and furthermore taking advantage of Wnt-reporter animals, we provide evidence that the loss of Cnn3 during development can affect signaling pathways crucial for correct morphogenesis of the neural tube. In addition, we used embryonic neurosphere cultures to investigate the role of Cnn3 in embryonic neuronal stem cells (NSC). Here, we observed that Cnn3 deficiency in NSCs increased the number of newly formed neurospheres and increased neurosphere size without perturbing their differentiation potential. Together, our study provides evidence for an important role of Cnn3 during development of the embryonic brain and in regulating NSC function.

Calponin isoforms CNN1, CNN2 and CNN3: Regulators for actin cytoskeleton functions in smooth muscle and non-muscle cells

Calponin is an actin filament-associated regulatory protein expressed in smooth muscle and many types of non-muscle cells. Three homologous genes, CNN1, CNN2 and CNN3, encoding calponin isoforms 1, 2, and 3, respectively, are present in vertebrate species. All three calponin isoforms are actin-binding proteins with functions in inhibiting actin-activated myosin ATPase and stabilizing the actin cytoskeleton, while each isoform executes different physiological roles based on their cell type-specific expressions. Calponin 1 is specifically expressed in smooth muscle cells and plays a role in fine-tuning smooth muscle contractility. Calponin 2 is expressed in both smooth muscle and non-muscle cells and regulates multiple actin cytoskeleton-based functions. Calponin 3 participates in actin cytoskeleton-based activities in embryonic development and myogenesis. Phosphorylation has been extensively studied for the regulation of calponin functions. Cytoskeleton tension regulates the transcription of CNN2 gene and the degradation of calponin 2 protein. This review summarizes our knowledge learned from studies over the past three decades, focusing on the evolutionary lineage of calponin isoform genes, their tissue- and cell type-specific expressions, structure-function relationships, and mechanoregulation.

Conversion of nanoscale topographical information of cluster-assembled zirconia surfaces into mechanotransductive events promotes neuronal differentiation

Background

Thanks to mechanotransductive components cells are competent to perceive nanoscale topographical features of their environment and to convert the immanent information into corresponding physiological responses. Due to its complex configuration, unraveling the role of the extracellular matrix is particularly challenging. Cell substrates with simplified topographical cues, fabricated by top-down micro- and nanofabrication approaches, have been useful in order to identify basic principles. However, the underlying molecular mechanisms of this conversion remain only partially understood.

Results

Here we present the results of a broad, systematic and quantitative approach aimed at understanding how the surface nanoscale information is converted into cell response providing a profound causal link between mechanotransductive events, proceeding from the cell/nanostructure interface to the nucleus. We produced nanostructured ZrO₂ substrates with disordered yet controlled topographic features by the bottom-up technique supersonic cluster beam deposition, i.e. the assembling of zirconia nanoparticles from the gas phase on a flat substrate through a supersonic expansion. We used PC12 cells, a well-established model in the context of neuronal differentiation. We found that the cell/nanotopography interaction enforces a nanoscopic architecture of the adhesion regions that affects the focal adhesion dynamics and the cytoskeletal organization, which thereby modulates the general biomechanical properties by decreasing the rigidity of the cell. The mechanotransduction impacts furthermore on transcription factors relevant for neuronal differentiation (e.g. CREB), and eventually the protein expression profile. Detailed proteomic data validated the observed differentiation. In particular, the abundance of proteins that are involved in adhesome and/or cytoskeletal organization is striking, and their up- or downregulation is in line with their demonstrated functions in neuronal differentiation processes.

Conclusion

Our work provides a deep insight into the molecular mechanotransductive mechanisms that realize the conversion of the nanoscale topographical information of SCBD-fabricated surfaces into cellular responses, in this case neuronal differentiation. The results lay a profound cell biological foundation indicating the strong potential of these surfaces in promoting neuronal differentiation events which could be exploited for the development of prospective research and/or biomedical applications. These applications could be e.g. tools to study mechanotransductive processes, improved neural interfaces and circuits, or cell culture devices supporting neurogenic processes.

Electronic supplementary material

The online version of this article (doi:10.1186/s12951-016-0171-3) contains supplementary material, which is available to authorized users.

Overexpressed Calponin3 by Subsonic Vibration Induces Neural Differentiation of hUC-MSCs by Regulating the Ionotropic Glutamate Receptor

In this study, we used proteomics to investigate the effects of sonic vibration (SV) on mesenchymal stem cells derived from human umbilical cords (hUC-MSCs) during neural differentiation to understand how SV enhances neural differentiation of hUC-MSCs. We investigated the levels of gene and protein related to neural differentiation after 3 or 5 days in a group treated with 40-Hz SV. In addition, protein expression patterns were compared between the control and the 40-Hz SV-treated hUC-MSC groups via a proteomic approach. Among these proteins, calponin3 (CNN3) was confirmed to have 299 % higher expression in the 40-Hz SV stimulated hUC-MSCs group than that in the control by Western blotting. Notably, overexpression of CNN3-GFP in Chinese hamster ovary (CHO)-K1 cells had positive effects on the stability and reorganization of F-actin compared with that in GFP-transfected cells. Moreover, CNN3 changed the morphology of the cells by making a neurite-like form. After being subjected to SV, messenger RNA (mRNA) levels of glutamate receptors such as PSD95, GluR1, and NR1 as well as intracellular calcium levels were upregulated. These results suggest that the activity of glutamate receptors increased because of CNN3 characteristics. Taken together, these results demonstrate that overexpressed CNN3 during SV increases expression of glutamate receptors and promotes functional neural differentiation of hUC-MSCs.

A Conditional Knockout Mouse Model Reveals That Calponin-3 Is Dispensable for Early B Cell Development

Calponins form an evolutionary highly conserved family of actin filament-associated proteins expressed in both smooth muscle and non-muscle cells. Whereas calponin-1 and calponin-2 have already been studied to some extent, little is known about the role of calponin-3 under physiological conditions due to the lack of an appropriate animal model. Here, we have used an unbiased screen to identify novel proteins implicated in signal transduction downstream of the precursor B cell receptor (pre-BCR) in B cells. We find that calponin-3 is expressed throughout early B cell development, localizes to the plasma membrane and is phosphorylated in a Syk-dependent manner, suggesting a putative role in pre-BCR signaling. To investigate this in vivo, we generated a floxed calponin-3-GFP knock-in mouse model that enables tracking of cells expressing calponin-3 from its endogenous promoter and allows its tissue-specific deletion. Using the knock-in allele as a reporter, we show that calponin-3 expression is initiated in early B cells and increases with their maturation, peaking in the periphery. Surprisingly, conditional deletion of the Cnn3 revealed no gross defects in B cell development despite this regulated expression pattern and the in vitro evidence, raising the question whether other components may compensate for its loss in lymphocytes. Together, our work identifies calponin-3 as a putative novel mediator downstream of the pre-BCR. Beyond B cells, the mouse model we generated will help to increase our understanding of calponin-3 in muscle and non-muscle cells under physiological conditions.

Differentiated markers in undifferentiated cells: expression of smooth muscle contractile proteins in multipotent bone marrow mesenchymal stem cells

In studying the differentiation of stem cells along smooth muscle lineage, smooth muscle cell (SMC) contractile proteins serve as markers for the relative state of maturation. Yet, recent evidence suggests that some SMC markers are probably expressed in multipotent mesenchymal stem cells (MSCs). Such a paradox necessitates investigations to re-examine their role as differentiated markers in MSCs. We tried to detect the expression of four widely used SMC markers including α-smooth muscle actin (α-SMA), h1-calponin, desmin and smooth muscle myosin heavy chain (SM-MHC), as well as the other isoforms of calponin family in resting MSCs. Then we used three different conditions to initiate MSCs differentiation along SMC lineage, and examined the alternation of SMC markers expression at both the transcript level and protein level. Desmin and h1-calponin are expressed in MSCs, in the presence or absence of SMC induction conditions. Moreover, MSCs are shown to express all known isoforms of calponin. Double-staining reveals that h1-calponin +/α-SMA - cells constitute the majority of resting MSCs. Under differentiated conditions, expression of SM-MHC was initiated and expression of α-SMA was promoted. The expression of SM-MHC and upregulation of α-SMA are relatively reliable indications of a mature smooth muscle phenotype in MSCs. Given that the cells are particularly rich in calponins expression, we postulate possible roles of these proteins in regulating cellular function by taking part in actin cytoskeleton and signaling. These findings imply that an extensive study of the cell physiology of MSCs should focus on the functional roles for these proteins, rather than simply regard them as differentiated markers.

Rock-dependent calponin 3 phosphorylation regulates myoblast fusion

Myogenesis occurs during embryonic development as well as regeneration following postnatal muscle fiber damage. Herein, we show that acidic calponin or calponin 3 (CNN3) regulates both myoblast cell fusion and muscle-specific gene expressions. Overexpression of CNN3 impaired C2C12 cell fusion, whereas CNN3 gene knockdown promoted skeletal myosin expression and fusion. CNN3 was phosphorylated at Ser293/296 in the C-terminal region. The basal inhibitory property of CNN3 against myoblast differentiation was enhanced by Ser293/296Ala mutation or deletion of the C-terminal region, and this inhibition was reversed by Ser293/296Asp mutation. Ser293/296 phosphorylation was required for CNN3 to bind actin and was dependent on Rho-associated kinases 1/2 (ROCK 1/2). Gene knockdown of ROCK1/2 suppressed CNN3 phosphorylation and impaired myoblast fusion, and these effects were partially attenuated by additional CNN3 overexpression of Ser293/296Asp CNN3. These findings indicated that CNN3 phosphorylation by ROCK blunts CNN3's inhibitory effects on muscle cell differentiation and fusion. In muscle tissues, satellite cells, but not mature myofibrils, expressed CNN3. CNN3 was also expressed and phosphorylated during myotube induction in isolated muscle satellite cells. Taken together, these results indicate that CNN3 is a downstream regulator of the ROCK signaling pathway for myogenesis.

Dynamics of signaling, cytoskeleton and cell cycle regulation proteins in glioblastoma cells after sub-lethal photodynamic treatment: antibody microarray study

BACKGROUND

Photodynamic therapy (PDT) that induces oxidative stress and cell death is used for tumor destruction in oncology. To characterize early molecular events in photosensitized glioblastoma cells, we studied expression of 224 proteins after sublethal PDT that doesn't kill but wounds cells.

METHODS

Cultured glioblastoma D54Mg cells were photosensitized with 5-aminolevulinic acid so that cell survival was 95-100%. At following 0.5-5.5h protein expression and phosphorylation was assayed using proteomic antibody microarrays.

RESULTS

Within the first post-treatment hour we observed phosphorylation of protein kinase Raf, adhesion-related kinases FAK and Pyk2, and microtubule-associated protein tau. Protein kinase Cγ and microtubule-associated protein MAP-1B were overexpressed. Dystrophin, calponin, and vinculin, components of the actin cytoskeleton scaffold, microtubule-associated proteins MAP2 and CNP, cytokeratins 4 and 7 were down-regulated that indicated changes in adhesion and cell shape. Down-regulation of cyclins A, D1 and D3, c-Myc, checkpoint proteins chk1/2 and up-regulation of Smad4 could arrest the cell cycle. Overexpression of Bcl-xL and down-regulation of caspase 9 demonstrated anti-apoptotic response. At 2h post-treatment protein expression changed lesser but at 5.5h levels of PKCγ and β-synuclein and phosphorylation of Raf, FAK, Pyk2, and tau increased again.

CONCLUSIONS

Sub-lethal PDT induces complex response of glioblastoma cells including changes in activity and expression of proteins involved in adhesion-mediated signaling, signal transduction, cytoskeleton remodeling, cell cycle regulation and anti-apoptotic processes.

GENERAL SIGNIFICANCE

Multiple reactions of various cellular subsystems including adhesion, cytoskeleton, signal transduction, cell cycle, and apoptosis are integrated into the general cell response to a sublethal impact.

Increased expression of calponin-3 in epileptic patients and experimental rats

Calponin-3 is an actin-interacting protein and is expressed in the brain. Our previous microarray scan has found an up-regulation of calponin-3 gene CNN3 in the temporal lobe of patients with drug-resistant epilepsy. Here we investigated in epileptic patients the changes of brain and cerebrospinal fluid (CSF) calponin-3 expressions, and assessed calponin-3 expression pattern in a rat model of pilocarpine-induced epilepsy. We showed that in the temporal neocortices of 30 patients with drug-resistant epilepsy, both mRNA and protein level of calponin-3 were significantly increased. In addition, the augmentation of CSF calponin-3 from 126 epileptic patients was closely correlated with disease duration. Moreover, in the cortices of temporal lobes of pilocarpine-treated rats, calponin-3 increased along with the time and maintained at significant high levels for up to 2 months, while the up-regulation of hippocampal calponin-3 only occurred at 24h and 1 week. The elevated calponin-3 suggests that deregulation of actin filament dynamics in axonal and dendritic outgrowth and synaptic rearrangement may contribute to pathophysiology of epilepsy.

Two distinct regions of calponin share common binding sites on actin resulting in different modes of calponin-actin interaction

Calponins are a small family of proteins that alter the interaction between actin and myosin II and mediate signal transduction. These proteins bind F-actin in a complex manner that depends on a variety of parameters such as stoichiometry and ionic strength. Calponin binds G-actin and F-actin, bundling the latter primarily through two distinct and adjacent binding sites (ABS1 and ABS2). Calponin binds other proteins that bind F-actin and considerable disagreements exist as to how calponin is located on the filament, especially in the presence of other proteins. A study (Galkin, V.E., Orlova, A., Fattoum, A., Walsh, M.P. and Egelman, E.H. (2006) J. Mol. Biol. 359, 478-485.), using EM single-particle reconstruction has shown that there may be four modes of interaction, but how these occur is not yet known. We report that two distinct regions of calponin are capable of binding some of the same sites on actin (such as 18-28 and 360-372 in subdomain 1). This accounts for the finding that calponin binds the filament with different apparent geometries. We suggest that the four modes of filament binding account for differences in stoichiometry and that these, in turn, arise from differential binding of the two calponin regions to actin. It is likely that the modes of binding are reciprocally influenced by other actin-binding proteins since members of the alpha-actinin group also adopt different actin-binding positions and bind actin principally through a domain that is similar to calponin's ABS1.

Calponin control of cerebrovascular reactivity: therapeutic implications in brain trauma

Calponin (Cp) is an actin-binding protein first characterized in chicken gizzard smooth muscle (SM). This review discusses the role of Cp in mediating SM contraction, the biochemical process by which Cp facilitates SM contraction and the function of Cp in the brain. Recent work on the role of Cp in pathological states with emphasis on traumatic brain injury is also discussed. Based on past and present data, the case is presented for targeting Cp for novel genetic and pharmacological therapies aimed at improving outcome following traumatic brain injury (TBI).

Enhancement of axonal regeneration by in vitro conditioning and its inhibition by cyclopentenone prostaglandins

Axonal regeneration is enhanced by the prior ;conditioning' of peripheral nerve lesions. Here we show that Xenopus dorsal root ganglia (DRG) with attached peripheral nerves (PN-DRG) can be conditioned in vitro, thereafter showing enhanced neurotrophin-induced axonal growth similar to preparations conditioned by axotomy in vivo. Actinomycin D inhibits axonal outgrowth from freshly dissected PN-DRG, but not from conditioned preparations. Synthesis of mRNAs that encode proteins necessary for axonal elongation might therefore occur during the conditioning period, a suggestion that was confirmed by oligonucleotide microarray analysis. Culturing PN-DRG in a compartmentalized system showed that inhibition of protein synthesis (but not RNA synthesis) in the distal nerve impaired the conditioning response, suggesting that changes in gene expression in cultured DRG depend on the synthesis and retrograde transport of protein(s) in peripheral nerves. The culture system was also used to demonstrate retrograde axonal transport of several proteins, including thioredoxin (Trx). Cyclopentenone prostaglandins, which react with Trx, blocked the in vitro conditioning effect, whereas inhibition of other signalling pathways thought to be involved in axonal regeneration did not. This suggests that Trx and/or other targets of these electrophilic prostaglandins regulate axonal regeneration. Consistent with this hypothesis, morpholino-induced suppression of Trx expression in dissociated DRG neurons was associated with reduced neurite outgrowth.

Calponin in non-muscle cells

Calponin is an actin filament-associated regulatory protein expressed in smooth muscle and non-muscle cells. Calponin is an inhibitor of the actin-activated myosin ATPase. Three isoforms of calponin have been found in the vertebrates. Whereas the role of calponin in regulating smooth muscle contractility has been extensively investigated, the function and regulation of calponin in non-muscle cells is much less understood. Based on recent progresses in the field, this review focuses on the studies of calponin in non-muscle cells, especially its regulation by cytoskeleton tension and function in cell motility. The ongoing research has demonstrated that calponin plays a regulatory role in non-muscle cell motility. Therefore, non-muscle calponin is an attractive target for the control of cell proliferation, migration and phagocytosis, and the treatment of cancer metastasis.

Identification of calponin 3 as a novel Smad-binding modulator of BMP signaling expressed in cartilage

Bone morphogenetic proteins (BMP) play a prominent role in cartilage tissue homeostasis and perturbations of BMP signaling contribute to pathological processes like osteoarthritis. The response to BMP is determined by intracellular proteins interacting with the signal mediators Smads 1 and 5. Applying the yeast two-hybrid technique we could identify the actin-binding protein calponin 3 as a novel Smad-binding protein expressed in chondrocytes. It interacted with Smads 1 and 5 and overexpression led to an attenuation of BMP-dependent transcription. Calponin 3 mRNA and protein were expressed in cartilage tissue and isolated chondrocytes and a slight, but statistically significant reduction of mRNA expression levels could be detected in osteoarthritic cartilage. Our results suggest a role of calponin 3 in the regulation of BMP-dependent cellular responses. By interaction with the Smad proteins 1 and 5 and the inhibition of BMP-induced transcription, calponin 3 provides a negative regulatory mechanism for the BMP signaling pathway. This inhibitory effect likely depends on a sequestration of the Smads to the cytoskeleton due to the actin-binding properties of calponin 3. The down-regulation of calponin 3 expression in osteoarthritic joints could contribute to the increased responsiveness to BMPs described previously. Furthermore, our data provide a possible explanation for the effect of the related protein calponin 1 on bone and cartilage development.

Calponin is expressed by subpopulations of connective tissue cells but not olfactory ensheathing cells in the neonatal olfactory mucosa

BACKGROUND

Debate has been ongoing on the relative merits of olfactory ensheathing cells (OECs) and Schwann cells as candidates for transplant-mediate repair of CNS lesions. Both glial cells exhibit similar molecular and cellular properties and to date there has been no antigenic marker identified that can clearly distinguish the two cell types. This inability to distinguish between the two cells types prevents confirmation of a controversial statement that cultures of OECs are contaminated with Schwann cells. Recently, proteomic analysis of foetal OECs and adult Schwann cells identified an actin-binding protein, calponin, as a specific marker for OECs. However, at the same time a recent report suggested that adult OECs do not express calponin. It was not clear if this discrepancy was due to methodology, as cells had to be treated with proteinase K to maximize calponin staining or developmental differences with only foetal/neonatal OECs expressing calponin. For this reason we have examined calponin expression in the peripheral olfactory system of embryonic and neonatal rats in vivo and from cells in vitro to assess if calponin is expressed in a developmental manner.

RESULTS

In this study we show that: i) proteinase K pretreatment had no effect on calponin staining in both OECs and Schwann cells. ii) calponin immunoreactivity was not expressed by embryonic or neonatal OECs in vitro and in vivo although connective tissue from the olfactory mucosa was strongly positive in neonatal rats but not embryonic rats, iii) calponin expression in the olfactory mucosa was heterogeneous, defining subpopulations of connective tissue cells iv) using functional confrontation assays between OECs or Schwann cells with astrocytes, calponin was expressed heterogeneously by astrocytes.

CONCLUSION

It is concluded that calponin is heterogeneously expressed by neonatal mucosal connective tissue but not expressed by neonatal OECs, embryonic OECs, and neonatal Schwann cells. Furthermore, we propose that calponin is not a specific marker for OECs generated from any developmental age.

Calponins: adaptable modular regulators of the actin cytoskeleton

Over 20 years ago Katsuhito Takahashi isolated a heat stable, calmodulin and actin binding protein from chicken gizzard smooth muscle. Considered initially as a mainly structural component of the vertebrate smooth muscle contractile machinery, the 34-kDa calcium- and calmodulin-binding troponin T-like protein, calponin quickly appeared to also be involved in a number of regulatory and signal transduction events in the actin cytoskeleton. Calponins regulate actomyosin contraction, and reduce metastatic cell motility and tissue invasion. From these various cellular functions the biological role of calponin is now slowly emerging, namely that of an actin filament-stabilizing molecule that contributes to physiological thin filament turnover rates in different cell types.

Calponin binds G-actin and F-actin with similar affinity

Calponins are actin-binding proteins that are implicated in the regulation of actomyosin. Calponin binds filamentous actin (F-actin) through two distinct sites ABS1 and ABS2, with an affinity in the low micromolar range. We report that smooth muscle calponin binds monomeric actin with a similar affinity (K(d) of 0.15 microM). We show that the arrangement of binding is similar to that of F-actin by a number of criteria, most notably that the distance between Cys273 on calponin and Cys374 of actin is 29A when measured by fluorescent resonance energy transfer, the same distance as previously reported for F-actin.

A direct interaction with calponin inhibits the actin-nucleating activity of gelsolin

Gelsolin and calponin are well-characterized cytoskeletal proteins that are abundant and widely expressed in vertebrate tissues. It is also becoming apparent, however, that they are involved in cell signalling. In the present study, we show that gelsolin and calponin interact directly to form a high-affinity (K(d)=16 nM) 1:1 complex, by the use of fluorescent probes attached to both proteins, by affinity chromatography and by immunoprecipitation. These methods show that gelsolin can form high-affinity complexes with two calponin isoforms (basic h1 and acidic h3). They also show that gelsolin binds calponin through regions that have been identified previously as being calponin's actin-binding sites. Moreover, gelsolin does not interact with calponin while calponin is bound to F-actin. Reciprocal experiments to find calponin-binding sites on gelsolin show that these are in both the N- and C-terminal halves of gelsolin. Calponin has minimal effects on actin severing by gelsolin. In contrast, calponin markedly affects the nucleation activity of gelsolin. The maximum inhibition of nucleation by gelsolin was 50%, which was achieved with a ratio of two calponins for every gelsolin. Thus the interaction of calponin with gelsolin may play a regulatory role in the formation of actin filaments through modulation of gelsolin's actin-binding function and through the prevention of calponin's actin-binding activities.

Change in the shape and density of dendritic spines caused by overexpression of acidic calponin in cultured hippocampal neurons

Dendritic spines are morphing structures believed to provide a cellular substrate for synaptic plasticity. It has been suggested that the actin cytoskeleton is the target of molecular mechanisms regulating spine morphology. Here we hypothesized that acidic calponin, an actin-binding protein, is one of the key regulators of actin filaments during spine plasticity. Our data showed that the overexpression of acidic calponin-GFP (green fluorescent protein) in primary cultures of rat hippocampal neurons causes an elongation of spines and an increase of their density as compared with those of GFP-expressing neurons. These effects required the actin-binding domains of acidic calponin. The close apposition of the presynatic marker synaptophysin to these long spines and the presence of specific postsynaptic markers actin, PSD-95, NR1, and GluR1 suggested the existence of functional excitatory synaptic contacts. Indeed, electrophysiological data showed that the postsynaptic overexpression of acidic calponin enhanced the frequency of miniature excitatory postsynaptic currents as compared with that of GFP-expressing neurons, but did not affect their properties such as amplitude, rise time, and half width. Studies in heterologous cells revealed that acidic calponin reorganized the actin filaments and stabilized them. Taken together, these findings show that acidic calponin regulates dendritic spine morphology and density, likely via regulation of the actin cytoskeleton reorganization and dynamic. Furthermore, the acidic calponin-induced spines are able to establish functional glutamatergic synapses. Such data suggest that acidic calponin is a key factor in the regulation of spine plasticity and synaptic activity.

Identification of differentially expressed genes in scrapie-infected mouse brains by using global gene expression technology

The pathogenesis of prion diseases, a class of transmissible fatal neurodegenerative diseases in humans and animals, is still unclear. The aim of this study was to identify the differentially regulated genes that correlate with the development of prion diseases for a better understanding of their pathological mechanisms. We employed Affymetrix Mouse Expression Arrays 430A containing >22,000 transcripts and compared the global gene expression profiles from brains of mice who were intracerebrally inoculated with scrapie strains ME7 and RML with those from brains of uninfected and mock-infected mice. The microarray data were analyzed by Significance Analysis of Microarrays, revealing 121 genes whose expression increased at least twofold in both ME7- and RML-infected mouse brains, with an estimated false discovery rate of < or =5%. These genes encode proteins involved in proteolysis, protease inhibition, cell growth and maintenance, the immune response, signal transduction, cell adhesion, and molecular metabolism. The time course of expression generally showed up-regulation of these genes from 120 days postinoculation (dpi) for ME7-inoculated mouse brains and from 90 dpi for RML-inoculated mouse brains. The onset of elevated expression correlated temporally with the onset of PrP(Sc) accumulation and the activation of glia, which may have contributed to neuronal cell death. Among the differentially regulated genes reported in the present study, the emergence of genes for several cathepsins and S100 calcium binding proteins was conspicuous. These and other genes reported here may represent novel potential diagnostic and therapeutic targets for prion disease.

Tyrosine phosphorylation of calponins. Inhibition of the interaction with F-actin

The phosphorylation-dephosphorylation of serine and threonine residues of calponin is known to modulate in vitro its interaction with F-actin and is thought to regulate several biological processes in cells, involving either of the calponin isoforms. Here, we identify, for the first time, tyrosine-phosphorylated calponin h3 within COS 7 cells, before and after their transfection with the pSV vector containing cDNA encoding the cytoplasmic, Src-related, tyrosine kinase, Fyn. We then describe the specific tyrosine phosphorylation in vitro of calponin h1 and calponin h3 by this kinase. 32P-labeling of tyrosine residues was monitored by combined autoradiography, immunoblotting with a specific phosphotyrosine monoclonal antibody and dephosphorylation with the phosphotyrosine-specific protein phosphatase, YOP. PhosphorImager analyses showed the incorporation of maximally 1.4 and 2.0 mol of 32P per mol of calponin h3 and calponin h1, respectively. As a result, 75% and 68%, respectively, of binding to F-actin was lost by the phosphorylated calponins. Furthermore, F-actin, added at a two- or 10-fold molar excess, did not protect, but rather increased, the extent of 32P-labeling in both calponins. Structural analysis of the tryptic phosphopeptides from each 32P-labeled calponin revealed a single, major 32P-peptide in calponin h3, with Tyr261 as the phosphorylation site. Tyr261 was also phosphorylated in calponin h1, together with Tyr182. Collectively, the data point to the potential involvement, at least in living nonmuscle cells, of tyrosine protein kinases and the conserved Tyr261, located in the third repeat motif of the calponin molecule, in a new level of regulation of the actin-calponin interaction.

The role of calponin in the gene profile of metastatic cells: inhibition of metastatic cell motility by multiple calponin repeats

Metastasis of diseased cells is the basic event leading to death in individuals with cancer. Establishment of metastasis requires that tumour cells migrate from the site of the primary tumour into the circulation system, escape from the vasculature and form secondary tumours at novel sites. These processes depend to a large degree on cytoskeletal remodeling. We show here that multiple copies of the short actin-binding module CLIK(23) from human or Caenorhabditis elegans calponin proteins effectively inhibit cell motility on two dimensional matrices and suppress soft agar colony formation of metastatic melanoma and adenocarcinoma cells of murine and human origin. Ectopic expression of CLIK(23) modules for 30 days results in the formation of multinucleated cells. The repeat displays true modular behaviour, resulting in increased cytoskeletal effects in direct correlation with the increase in number of modules. Our results demonstrate that the role of calponin in the signature profile of metastasising cells is that of a mechanical stabiliser of the actin cytoskeleton, which interferes with actin turnover by binding at a unique interface along the actin filament.

Cytoskeletal dynamics and transport in growth cone motility and axon guidance

Recent studies indicate the actin and microtubule cytoskeletons are a final common target of many signaling cascades that influence the developing neuron. Regulation of polymer dynamics and transport are crucial for the proper growth cone motility. This review addresses how actin filaments, microtubules, and their associated proteins play crucial roles in growth cone motility, axon outgrowth, and guidance. We present a working model for cytoskeletal regulation of directed axon outgrowth. An important goal for the future will be to understand the coordinated response of the cytoskeleton to signaling cascades induced by guidance receptor activation.

Gene Expression Profile Changes Are Commonly Modulated across Models and Species after Traumatic Brain Injury

Brain trauma is a major cause of morbidity and mortality, both in adult and pediatric populations. Much of the functional deficit derives from delayed cell death resulting from induction of neurotoxic factors that overwhelm endogenous neuroprotective responses. To identify the potential molecular mechanisms underlying such delayed responses, we compared gene expression patterns using high-density oligonucleotide arrays at 4, 8, 24, and 72 h after moderate levels of lateral fluid percussion-induced brain injury in rats and lateral controlled cortical impact injury in mice (a total of 47 profiles). Expression of 82 genes in 12 functional categories was significantly changed in both species after trauma. The largest number of gene expression changes were found in the functional groups related to inflammation (17%), transcription regulation (16%), and cell adhesion/extracellular matrix (15%). Fifty percent of genes similarly altered across models had not been previously implicated in traumatic brain injury. Of particular interest were expression changes in genes linked to neurodegeneration, such as ATF3 and lysosomal membrane glycoprotein 2, and to neuroprotection including lipocortin 1, calponin 3, gelsolin, Id-1, and p45 NF-E2. Gene expression profiling across species and models may help identify candidate molecular pathways induced by brain injury, some of which may provide novel targets for therapeutic intervention.

Age-associated changes in hypothalamic and pituitary neuroendocrine gene expression in the rat

A cDNA membrane array displaying 1183 probes was used to detect hypothalamic and pituitary changes in gene expression accompanying ageing and age-associated pituitary macroadenomas. Four groups of male Sprague-Dawley rats (3-, 15-, 24-month-old and 24-month-old with prolactinoma) were compared in two independent hybridizations. cDNA array data were confirmed and completed by comparative reverse transcriptase-polymerase chain reaction on selected genes. The expression of 454 and 116 mRNAs was detected in hypothalamus and pituitary, respectively. Growth hormone (GH) mRNA alone represented 85% of total gene expression in the gland of young rats, and other pituitary hormone transcripts 2.8%, while melanin-concentrating hormone (MCH) mRNA, the most expressed neuropeptide transcript involved in neuroendocrine regulation, accounted for only 0.8% of total hypothalamic transcripts. The proportion of genes modified in the hypothalamus and pituitary was rather modest: 1.5% and 5.2%, respectively, for ageing per se, and 1.1% and 5.2% for age-associated macroprolactinomas. Among pituitary specific RNAs, GH mRNA expression was notably decreased with age. At the hypothalamic level, expression of genes directly involved in GH regulation, such as somatostatin and growth hormone-releasing hormone, was not altered, while neuropeptide transcripts involved in feeding behaviour [orexin/hypocretin, MCH, pro-opiomelanocortin (POMC), cocaine- and amphetamine-regulated transcript (CART)] were significantly altered. In addition, a few ubiquitous transcripts (hnRNP-K, PFKm, CCND 2, calponin and set) were differently affected in both tissues. Modifications in hypothalamic orexigenic (orexin, MCH) and anorexigenic (POMC, CART) gene expression are in keeping with an age-associated decrease in energy consumption but a higher one in the presence of macroprolactinomas.

Increased levels of acidic calponin during dendritic spine plasticity after pilocarpine-induced seizures

We have previously shown that, in HEK 293 cells, overexpression of acidic calponin, an actin-binding protein, induces remodeling of actin filaments, leading to a change in cell morphology. In addition, this protein is found in dendritic spines of adult hippocampal neurons. We hypothesized that this protein plays a role in regulating actin-based filaments during dendritic spine plasticity. To assess this hypothesis, the pilocarpine model of temporal lobe epilepsy was selected because an important reorganization of the glutamatergic network, which includes an aberrant sprouting of granule cell axons, neo-synaptogenesis, and dendritic spine remodeling, is well established in the dentate gyrus. This reorganization begins after the initial period of status epilepticus after pilocarpine injection, during the silent period when animals display a normal behavior, and reaches a plateau at the chronic stage when the animals have developed spontaneous recurrent seizures. Our data show that the intensity of immunolabeling for acidic calponin was clearly increased in the inner one-third of the molecular layer of the dentate gyrus, the site of mossy fiber sprouting, and neo-synaptogenesis, at 1 and 2 weeks after pilocarpine injection (silent period) when the reorganization was taking place. In contrast, in chronic pilocarpine-treated animals, when the reorganization was established, the levels of labeling for acidic calponin in the inner molecular layer were similar to those observed in control rats. In addition, double immunostaining studies suggested that the increase in acidic calponin levels occurred within the dendritic spines. Altogether, these results are consistent with an involvement of acidic calponin in dendritic spine plasticity.

Genomic responses of the brain to ischemic stroke, intracerebral haemorrhage, kainate seizures, hypoglycemia, and hypoxia

RNA expression profiles in rat brain were examined 24 h after ischemic stroke, intracerebral haemorrhage, kainate-induced seizures, insulin-induced hypoglycemia, and hypoxia and compared to sham- or untouched controls. Rat oligonucleotide microarrays were used to compare expression of over 8000 transcripts from three subjects in each group (n = 27). Of the somewhat less than 4000 transcripts called 'present' in normal or treated cortex, 5-10% of these were up-regulated 24 h after ischemia (415), haemorrhage (205), kainate (187), and hypoglycemia (302) with relatively few genes induced by 6 h of moderate (8% oxygen) hypoxia (15). Of the genes induced 24 h after ischemia, haemorrhage, and hypoglycemia, approximately half were unique for each condition suggesting unique components of the responses to each of the injuries. A significant component of the responses involved immune-process related genes likely to represent responses to dying neurons, glia and vessels in ischemia; to blood elements in haemorrhage; and to the selectively vulnerable neurons that die after hypoglycemia. All of the genes induced by kainate were also induced either by ischemia, haemorrhage or hypoglycemia. This strongly supports the concept that excitotoxicity not only plays an important role in ischemia, but is an important mechanism of brain injury after intracerebral haemorrhage and hypoglycemia. In contrast, there was only a single gene that was down-regulated by all of the injury conditions suggesting there is not a common gene down-regulation response to injury.

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.

Proteomic analysis of normal and malignant prostate tissue to identify novel proteins lost in cancer

BACKGROUND

Alterations of important protein pathways, including loss of prostate secretory granules, and disruption of the prostatic secretory pathway have been identified as early events in malignancy. In this study, proteomics was used to map the differences in protein expression between normal and malignant prostate tissues and to identify and analyze differentially expressed proteins in human prostate tissue with particular regard to the proteins lost in malignancy.

METHODS

Small quantities of normal and malignant prostate tissue were taken fresh from 34 radical prostatectomy cases. After histological examination, proteins were solubilized from selected tissues and separated using two-dimensional electrophoresis. Using image analysis, the proteome of normal and malignant tissues were mapped and differentially expressed proteins (present in normal and absent in malignant tissue) were identified and subsequently analyzed using peptide mass finger printing and N-terminal sequencing. Western blotting and immunohistochemistry were performed to examine expression profiles and tissue localization of candidate proteins.

RESULTS

Comparison of protein maps of normal and malignant prostate were used to identify 20 proteins which were lost in malignant transformation, including prostate specific antigen (PSA), alpha-1 antichymotrypsin (ACT), haptoglobin, and lactoylglutathione lyase. Three of the 20 had not previously been reported in human prostate tissue (Ubiquitin-like NEDD8, calponin, and a follistatin-related protein). Western blotting confirmed differences in the expression profiles of NEDD8 and calponin, and immunohistochemistry demonstrated differences in the cellular localization of these two proteins in normal and malignant prostate glands.

CONCLUSIONS

The expression of NEDD8, calponin, and the follistatin-related protein in normal prostate tissues is a novel finding and the role of these important functional proteins in normal prostate and their loss or reduced expression in prostate malignancy warrants further investigations.

Process formation results from the imbalance between motor-mediated forces

Several reports have suggested that neurite outgrowth is mediated by opposing forces generated on microtubules and microfilaments but the molecular basis underlying these forces have not been determined. Here, we show that in non-neuronal cell lines, the inhibition of actomyosin activity by acidic calponin promotes the formation of processes. This effect is blocked by inhibition of the motor activity of cytoplasmic dynein. Therefore, neurite formation is due to an imbalance between tensile and compressive forces mediated by myosins and dyneins, respectively. We propose a mechanism that involves the motor-mediated forces in a tight regulation of the process formation.

Subcellular distribution of calponin and caldesmon in rat hippocampus

Caldesmon and calponin are two actin- and calmodulin-binding proteins involved in the 'actin-linked' regulation of smooth muscle and non-muscle Mg(2+)-actin-activated myosin II ATPase activity. In the present report we show that caldesmon and calponin are present in the post-synaptic side of symmetric synapses and accumulate in the post-synaptic densities of asymmetric synapses. Caldesmon- and calponin-immunoreactivities are also observed at the plasma membrane of the hippocampal neurones. Finally, while caldesmon seems strictly distributed to neurones, acidic calponin is present in both neurones and astrocytes.