Caldesmon: a calmodulin-binding actin-regulatory protein

Phenotypic Characterization of Colorectal Liver Metastases: Capsule versus No Capsule and the Potential Role of Epithelial Mesenchymal Transition

Background: Colorectal liver metastases (CRLM) can be encased in a fibrous capsule separating cancer from normal liver tissue, which correlates with increased patient survival. This study investigated the cellular and molecular components of capsule formation and the possible role of epithelial mesenchymal transition (EMT). Methods: From 222 patients with CRLM, 84 patients (37.8%) were categorized to have CRLM encased with a capsule. A total of 34 CRLM from 34 selected patients was analyzed in detail by EMT pathway-profiling and custom PCR arrays to identify differences in gene expression between CRLM with (n = 20) and without capsule (n = 14). In parallel, those 34 CRLM were used to analyze 16 gene products at the metastasis margin via immunohistochemistry. Results: Encapsulated CRLM showed an elevated expression of signal transduction pathways and effector molecules involved in EMT. E-cadherin and keratin-19 were more prevalent, and transcription as well as translation (immunohistochemistry) of pGSK-3-β, SOX10, tomoregulin-1, and caldesmon were increased. By contrast, the loss of E-cadherin and the prevalence of snail-1 were increased in CRLM without capsule. Collagen I and III and versican were identified as capsule components with extracellular matrix fibers running concentrically around the malignant tissue and parallel to the invasive front. Caldesmon was also demonstrated as a capsule constituent. Conclusions: The fibrous capsule around CRLM can be produced by cells with mesenchymal characteristics. It functions as a protective border by both the features of fiber architecture and the inhibition of invasive growth through EMT recruiting mesenchymal cells such as myofibroblasts by transformation of surrounding epithelial or even carcinoma cells. By contrast, EMT demonstrated in non-encapsulated CRLM may lead to a more mesenchymal, mobile, and tissue-destructive carcinoma cell phenotype and facilitate malignant spread.

Construction and prognostic analysis of miRNA-mRNA regulatory network in liver metastasis from colorectal cancer

Background

Colorectal cancer (CRC) is one of the most common cancers in the world, and liver metastasis is the leading cause of colorectal cancer-related deaths. However, the mechanism of liver metastasis in CRC has not been clearly elucidated.

Methods

Three datasets from the Gene Expression Omnibus (GEO) database were analyzed to obtain differentially expressed genes (DEGs), which were subjected to functional enrichment analysis and protein-protein interaction analysis. Subsequently, mRNA-miRNA network was constructed, and the associated DEGs and DEMs were performed for prognostic analysis. Finally, we did infiltration analysis of growth arrest specific 1 (GAS1)-associated immune cells.

Results

We obtained 325 DEGs and 9 differentially expressed miRNAs (DEMs) between primary CRC and liver metastases. Enrichment analysis and protein-protein interactions (PPI) further revealed the involvement of DEGs in the formation of the inflammatory microenvironment and epithelial-mesenchymal transition (EMT) during the liver metastases process in CRC. Survival analysis demonstrated that low-expressed GAS1 as well as low-expressed hsa-miR-33b-5p was a favorable prognostic indicator of overall survival. Further exploration of GAS1 revealed that its expression was interrelated with the infiltration of immune cells in tumor tissues.

Conclusions

In summary, DEGs, DEMs, and their interactions found in liver metastasis of CRC may provide a basis for further understanding of the mechanism of CRC metastasis.

Mouse Gamma Herpesvirus MHV-68 Induces Severe Gastrointestinal (GI) Dilatation in Interferon Gamma Receptor-Deficient Mice (IFNγR-/-) That Is Blocked by Interleukin-10

Inflammatory bowel disease (IBD) and Clostridium difficile infection cause gastrointestinal (GI) distension and, in severe cases, toxic megacolon with risk of perforation and death. Herpesviruses have been linked to severe GI dilatation. MHV-68 is a model for human gamma herpesvirus infection inducing GI dilatation in interleukin-10 (IL-10)-deficient mice but is benign in wildtype mice. MHV-68 also causes lethal vasculitis and pulmonary hemorrhage in interferon gamma receptor-deficient (IFNγR-/-) mice, but GI dilatation has not been reported. In prior work the Myxomavirus-derived anti-inflammatory serpin, Serp-1, improved survival, reducing vasculitis and pulmonary hemorrhage in MHV-68-infected IFNγR-/- mice with significantly increased IL-10. IL-10 has been investigated as treatment for GI dilatation with variable efficacy. We report here that MHV-68 infection produces severe GI dilatation with inflammation and gut wall degradation in 28% of INFγR-/- mice. Macrophage invasion and smooth muscle degradation were accompanied by decreased concentrations of T helper (Th2), B, monocyte, and dendritic cells. Plasma and spleen IL-10 were significantly reduced in mice with GI dilatation, while interleukin-1 beta (IL-1β), IL-6, tumor necrosis factor alpha (TNFα) and INFγ increased. Treatment of gamma herpesvirus-infected mice with exogenous IL-10 prevents severe GI inflammation and dilatation, suggesting benefit for herpesvirus-induced dilatation.

Calmodulin-binding proteins: A journey of 40 years

The proteins which bind to calmodulin in a Ca²⁺-dependent and reversible manner are known as calmodulin-binding proteins. These proteins are involved in a multitude of processes in which Ca²⁺ and calmodulin play crucial roles. Our group elucidated the mechanism and importance of these proteins in normal and diseased conditions. Various calmodulin-binding proteins were discovered and purified from bovine tissue including a heat stable calmodulin-binding protein 70, calmodulin-dependent protein kinase VI and a high molecular weight calmodulin-binding protein (HMWCaMBP). We observed a complex interplay occurs between these and other Ca²⁺ and calmodulin-binding proteins during cardiac ischemia and reperfusion. Purified cardiac HMWCaMBP is a homolog form of calpastatin and an inhibitor of the Ca²⁺-activated cysteine proteases, calpains and therefore can have cardioprotective role in ischemic conditions. Calcineurin is a Ca²⁺ and calmodulin-dependent serine/threonine protein phosphatase showed increased phosphatase activity in ischemic heart through its direct interaction with Hsp70 and expression of calcineurin following ischemia suggests self-repair and favorable survival outcomes. Calcineurin was also found to be present in other tissues including the eye; where its expression and calcineurin phosphatase activity varied. In neurons, calcineurin may play a key role in initiating apoptosis-related pathways especially in epilepsy. In colorectal cancer we demonstrated high calcineurin phosphatase activity and simultaneous overexpression of calcineurin. The impact of calcineurin signaling on neuronal apoptosis in epilepsy and its use as a diagnostic marker for colorectal cancer requires in-depth study.

Expression of von Willebrand factor and caldesmon in the placental tissues of pregnancies complicated with intrauterine growth restriction

PURPOSE

The decreased placental perfusion is the underlying reason for intrauterine growth restriction that in turn leads to reduced placental perfusion and ischemia. However, there are several issues to be understood in the pathophysiology of intrauterine growth restriction. We aimed to study whether any compensatory response in placental vascular bed occur in pregnancies complicated with intrauterine growth restriction by the immunohistochemical staining of von Willebrand factor and caldesmon in placental tissues.

MATERIALS AND METHODS

A total of 103 pregnant women was enrolled in the study including 50 patients who were complicated with IUGR and 50 uncomplicated control patients. The study was designed in a prospective manner. All placentas were also stained with von Willebrand factor and caldesmon monoclonal kits.

RESULTS

The immunohistochemical staining of von Willebrand factor and caldesmon expressions in placental tissues were different between normal and intrauterine growth restriction group. The percentages of 2+ and 3+ von Willebrand factor expression were higher in the intrauterine growth restriction group comparing with the normal group, although the difference was not statistically significant. The intensity of caldesmon expression was significantly lower in the intrauterine growth restriction group in comparison with the normal group (p < .001).

CONCLUSION

Angiogenesis occurs as a placental response to intrauterine growth restriction which is a hypoxic condition. But newly formed vessels are immature and not strong enough. Our study is important to clarify the pathophysiology and placental compensatory responses in intrauterine growth restriction.

Customizable engineered blood vessels using 3D printed inserts

Current techniques for tissue engineering blood vessels are not customizable for vascular size variation and vessel wall thickness. These critical parameters vary widely between the different arteries in the human body, and the ability to engineer vessels of varying sizes could increase capabilities for disease modeling and treatment options. We present an innovative method for producing customizable, tissue engineered, self-organizing vascular constructs by replicating a major structural component of blood vessels - the smooth muscle layer, or tunica media. We utilize a unique system combining 3D printed plate inserts to control construct size and shape, and cell sheets supported by a temporary fibrin hydrogel to encourage cellular self-organization into a tubular form resembling a natural artery. To form the vascular construct, 3D printed inserts are adhered to tissue culture plates, fibrin hydrogel is deposited around the inserts, and human aortic smooth muscle cells are then seeded atop the fibrin hydrogel. The gel, aided by the innate contractile properties of the smooth muscle cells, aggregates towards the center post insert, creating a tissue ring of smooth muscle cells. These rings are then stacked into the final tubular construct. Our methodology is robust, easily repeatable and allows for customization of cellular composition, vessel wall thickness, and length of the vessel construct merely by varying the size of the 3D printed inserts. This platform has potential for facilitating more accurate modeling of vascular pathology, serving as a drug discovery tool, or for vessel repair in disease treatment.

Transcriptional and proteomic profiling of flatfish (Solea senegalensis) spermatogenesis

The Senegalese sole (Solea senegalensis) is a marine flatfish of high economic value and a target species for aquaculture. The efforts to reproduce this species in captivity have been hampered by the fact that farmed males (F1) often show lower sperm production and fertilization capacity than wild-type males (F0). Our knowledge on spermatogenesis is however limited to a few studies. In a previous work, we identified by 2-D DIGE several potential protein markers in testis for the poor reproductive performance of F1 males. Therefore, the objectives of the present study were, first, to investigate changes in genes and proteins expressed in the testis throughout spermatogenesis in F0 males by using a combination of transcriptomic and proteomic approaches and, second, to further compare the testis proteome between late spermatogenic stages of F0 and F1 fish to identify potential indicators of hampered reproductive performance in F1 fish. We identified approximately 400 genes and 49 proteins that are differentially expressed during the progression of spermatogenesis and that participate in processes such as transcriptional activation, the ubiquitin-proteasome system, sperm maturation and motility or cytoskeletal remodeling. Interestingly, a number of these proteins differed in abundance between F0 and F1 fish, pointing toward alterations in cytoskeleton, sperm motility, the ubiquitin-proteasome system and the redox state during spermiogenesis as possible causes for the decreased fertility of F1 fish.

Mutational and genotype-phenotype correlation analyses in 28 Polish patients with Cornelia de Lange syndrome

Cornelia de Lange syndrome (CdLS) is a multisystem congenital anomaly disorder characterized by prenatal and postnatal growth retardation, developmental delay, distinctive facial dysmorphism, limb malformations, and multiple organ defects. Mutations in the NIPBL gene have been discovered recently as a major etiology for this syndrome, and were detected in 27-56% of patients. Two groups have found significant differences in the severity or penetrance of some phenotypes between mutation positive and mutation negative patients. Different clinical features have also been described among patients with missense versus truncating mutations. In this study, we identified 13 NIPBL mutations in 28 unrelated Polish CdLS patients (46.4%), 11 were novel. Mutation positive patients were more severely affected in comparison to mutation negative individuals with respect to weight, height, and mean head circumference at birth, facial dysmorphism and speech impairment. Analyses of combined data from this and the two previous studies revealed that the degree of growth, developmental delay and limb defects showed significant differences between patients with and without mutations and between patients with missense and truncating mutations, whereas only a portion of these features differed significantly in any individual study. Furthermore, bioinformatic analyses of the NIPBL protein revealed several novel domains, which may give further clues about potential functions of this protein.

Over Expression of Smooth Muscle Specific Caldesmon by Transfection and Intermittent Agonist Induced Contraction Alters Cellular Morphology and Restores Differentiated Smooth Muscle Phenotype

PURPOSE

The thin filament associated protein h-caldesmon (h-CaD) modulates actin myosin interaction and contraction. Bladder outlet obstruction and detrusor hypertrophy are associated with the over expression of the nonmuscle CaD isoform l-CaD. It implies a poorly differentiated state of bladder myocytes and cytoskeletal remodeling in detrusor hypertrophy. We determined if h-CaD expression can be increased in a unique bladder smooth muscle (BSM) cell line derived from obstructed rabbit bladder smooth muscle that over expresses l-CaD. We examined whether the genetic restoration of h-caldesmon is possible in bladder smooth muscle cells by transfection or by agonist mediated contraction and whether this manipulation would alter cellular morphology.

MATERIALS AND METHODS

BSM cells were transfected with chicken h-CaD cDNA inserted into a mammalian vector. In another experiment BSM cells underwent intermittent bethanechol induced stimulation. h-CaD mRNA and protein were quantified with reverse transcriptase-polymerase chain reaction and Western blot analyses. Cell morphology was assessed using phase, video and confocal microscopy after double immunostaining with antibodies against alpha-actin and caldesmon.

RESULTS

Reverse transcriptase-polymerase chain reaction using primers specific for the transfected vector and h-CaD cDNA confirmed stable transfection of cells and increased content of h-CaD mRNA. Following bethanechol induced intermittent contraction Western blotting revealed 80% relative over expression of h-CaD in treated transfected cell lines (p <0.05) and 74% (not significant) in treated nontransfected controls. Confocal immunofluorescence microscopy revealed CaD in the cytoplasmic filaments co-localized to alpha-actin in the main cell body and perinuclear region in transfected cells, in contrast to the diffuse, irregular distribution of these filaments in control cells.

CONCLUSIONS

A unique bladder myocyte cell line was successfully and stably transfected with h-CaD cDNA. We show that agonist induced intermittent contraction preferentially increases h-CaD expression, the predominant CaD in nonobstructed bladder smooth muscle, and the restoration of h-CaD alters cell morphology and the organization of cytoplasmic filaments in cells derived from obstructed rabbit detrusor musculature.

ERK inhibition attenuates 5-HT-induced contractions in fetal and adult ovine carotid arteries

Growth and differentiation-related pathways are much more active in immature than in mature, fully differentiated smooth muscle. Because mitogen-activated protein kinases (MAPK) are intimately involved with growth and differentiation, and the extracellular signal-regulated kinase (ERK) subfamily of MAPKs are involved in some contractile responses, the present studies examined the hypothesis that ERKs play an important and age-dependent role in smooth muscle contraction. The MAPK inhibitors PD098059 and UO126 both inhibited serotonin (5-HT) concentration-response relations more effectively in carotid arteries from term fetal lambs, than in corresponding arteries from mature non-pregnant adult sheep. This inhibition involved significant decreases in both the pD2 (adult: 2-fold; fetus: 4- to 15-fold) and the maximum efficacy (adult: 15-19%; fetus: 34-39%) of 5-HT. Accompanying this age-dependent effect on contraction, quantitative Western blot assays revealed that ERK1 and ERK2 abundances were 39% and 164% greater, respectively, in fetal than in adult carotid arteries. The abundance of the putative ERK target, caldesmon, however, was about 7-fold greater in adult than in fetal arteries. Together, the present results support the view that ERK abundance and activity is upregulated in fetal relative to adult arteries, and that one consequence of this upregulation is that the contribution of ERKs to contraction, at least that initiated by 5-HT2a receptors, is greater in fetal than adult carotid arteries. Whereas the phosphorylation mechanisms through which ERKs augment contraction remain uncertain and controversial, the present results suggest that emphasis should be shifted away from caldesmon and toward other critical contractile proteins, and how these proteins may contribute differently to development of agonist-induced contractile force in immature and mature arteries.

Evidence for modulation of smooth muscle force by the p38 MAP kinase/HSP27 pathway

Mitogen-activated protein (MAP) kinases signal to proteins that could modify smooth muscle contraction. Caldesmon is a substrate for extracellular signal-related kinases (ERK) and p38 MAP kinases in vitro and has been suggested to modulate actin-myosin interaction and contraction. Heat shock protein 27 (HSP27) is downstream of p38 MAP kinases presumably participating in the sustained phase of muscle contraction. We tested the role of caldesmon and HSP27 phosphorylation in the contractile response of vascular smooth muscle by using inhibitors of both MAP kinase pathways. In intact smooth muscle, PD-098059 abolished endothelin-1 (ET-1)-stimulated phosphorylation of ERK MAP kinases and caldesmon, but p38 MAP kinase activation and contractile response remained unaffected. SB-203580 reduced muscle contraction and inhibited p38 MAP kinase and HSP27 phosphorylation but had no effect on ERK MAP kinase and caldesmon phosphorylation. In permeabilized muscle fibers, SB-203580 and a polyclonal anti-HSP27 antibody attenuated ET-1-dependent contraction, whereas PD-098059 had no effect. These results suggest that ERK MAP kinases phosphorylate caldesmon in vivo but that activation of this pathway is unnecessary for force development. The generation of maximal force may be modulated by the p38 MAP kinase/HSP27 pathway.

Expression of smooth muscle caldesmon in developing chicken gizzard

Caldesmon is an actin/calmodulin/tropomyosin protein located in the thin filaments of smooth muscle cells and microfilaments of nonmuscle cells. Two isoforms of caldesmon, h- and l-types, shown to exist in vertebrate smooth and nonmuscle cells respectively, are produced by alternative splicing of the caldesmon mRNA encoded by a single gene. To study the expression of smooth muscle specific h-caldesmon during the differentiation of mesenchymal cells into smooth muscle cells, soluble protein and total RNA from the gizzard primordium in the gut region of 5-day and gizzards of 7-, 9-, 13-, 17- and 21-day embryos and 2-days post-hatch chicks were extracted and analyzed for caldesmon expression at both protein and mRNA levels. Western blot analysis of proteins and immunofluorescence microscopy of tissue section were carried out using an antibody specific for h-caldesmon. Total RNA was analyzed by Northern blotting using a caldesmon cDNA probe, and h- and l-caldesmon cDNAs were identified due to the difference in their molecular sizes (4.8 and 4.1 kb respectively). The mRNA was also analyzed by reverse transcribed-polymerase chain reaction (RT-PCR) and Southern blot analysis. Our results show that the I-caldesmon mRNA was expressed at higher levels in the gizzard primordium during the early stages of development, and decreased gradually during growth. The h-caldesmon protein and mRNA, not expressed at day 5, is minimally expressed at day 7 and is fully turned on by day 9. Additionally, sequence analyses of the RT-PCR products of I-caldesmon showed that it lacked the spacer region, as predicted. RT-PCR analysis of total RNA gave two h-caldesmon fragments. These two fragments were identified as two different isoforms of h-caldesmon since they both contained the spacer region. They also showed homology in the region of exon 4 had differences in the region of exon 3b.

Membrane mechanisms and intracellular signalling in cell volume regulation

Recent work on selected aspects of the cellular and molecular physiology of cell volume regulation is reviewed. First, the physiological significance of the regulation of cell volume is discussed. Membrane transporters involved in cell volume regulation are reviewed, including volume-sensitive K+ and Cl- channels, K+, Cl- and Na+, K+, 2Cl- cotransporters, and the Na+, H+, Cl-, HCO3-, and K+, H+ exchangers. The role of amino acids, particularly taurine, as cellular osmolytes is discussed. Possible mechanisms by which cells sense their volumes, along with the sensors of these signals, are discussed. The signals are mechanical changes in the membrane and changes in macromolecular crowding. Sensors of these signals include stretch-activated channels, the cytoskeleton, and specific membrane or cytoplasmic enzymes. Mechanisms for transduction of the signal from sensors to transporters are reviewed. These include the Ca(2+)-calmodulin system, phospholipases, polyphosphoinositide metabolism, eicosanoid metabolism, and protein kinases and phosphatases. A detailed model is presented for the swelling-initiated signal transduction pathway in Ehrlich ascites tumor cells. Finally, the coordinated control of volume-regulatory transport processes and changes in the expression of organic osmolyte transporters with long-term adaptation to osmotic stress are reviewed briefly.

Calcium and smooth muscle contraction

The fact that smooth muscle exists in almost every hollow organ and is involved in a large number of disease states has led to a vast increase in smooth muscle research, covering areas from testing response to antagonists and agonists to measuring the molecular force generated by a single actin filament. Yet, the exact mechanisms regulating contractile response of smooth muscle remain unsolved. Calcium has been a central player in mediating smooth muscle contraction through binding with calmodulin, although there is evidence showing that under special circumstances smooth muscle can contract without change in intracellular Ca2+. In addition to the major regulatory pathway of Ca(2+)-calmodulin-myosin light chain kinase, there are other thin filament linked regulatory mechanisms in which Ca(2+)-calmodulin dependent phosphorylation of calponin and caldesmon may be involved. Ca2+ sensitivity of smooth muscle contraction may vary under different situations and this has recently been recognized as an important regulatory mechanism. Examples are protein kinase C (PKC) dependent phosphorylation of myosin light chain kinase which results in partial inhibition of contraction, and activation of myosin light chain phosphatase. There is new evidence showing that not only does Ca2+ regulate contraction by regulating the interaction of contractile proteins in smooth muscle, but also that shortening of smooth muscle itself reduces intracellular Ca2+ concentration, via a negative feedback.

The caldesmon content of vertebrate smooth muscle

Caldesmon and tropomyosin can be selectively and quantitatively extracted from vascular and visceral smooth muscle following heat treatment; all other smooth muscle proteins are precipitated by this procedure. Estimates of the caldesmon/tropomyosin molar ratio in heat-extracts determined by SDS-PAGE densitometry are 1 caldesmon:5.1-5.3 tropomyosin for rabbit and sheep aorta, and 1 caldesmon:5.9 tropomyosin for rabbit stomach and chicken gizzard. If the assumption is made that tropomyosin serves as a true reference of thin-filament content in intact muscle, it follows that the relative caldesmon contents in the above tissues are similar to each other. Caldesmon in heat extracts was identified by Western blotting, by its anomalous migration on several different SDS-PAGE systems and by its position on two-dimensional PAGE. Values of caldesmon contents in unfractionated total tissue homogenates were found to be similar to those cited above. Smooth muscles contain different thin-filament classes and only one type appears to possess caldesmon. By comparing values for the molar composition of caldesmon-specific filaments (1 caldesmon:2 tropomyosin:14 actin) with the values above determined for intact tissue, we conclude that the caldesmon filaments account for approx. 35-45% of the total thin-filament pool in arterial smooth muscle and slightly less in visceral muscles.

Interaction of caldesmon with phospholipids

The interaction of caldesmon with liposomes composed of various phospholipids has been examined by tryptophan fluorescence spectroscopy. The results indicate that caldesmon makes its strongest complex with phosphatidylserine (PS) vesicles (Kass. = 1.45 x 10(5) M-1). Both electrostatic and hydrophobic interactions contribute to the stability of this complex. The site for strong binding of PS seems to be located in the N-terminal part of the 34 kDa C-terminal fragment of caldesmon. Binding of PS at this site results in displacement of calmodulin from its complex with caldesmon.

Relation between cytoskeleton, hypo-osmotic treatment and volume regulation in Ehrlich ascites tumor cells

Pretreatment with cytochalasin B, which is known to disrupt microfilaments, significantly inhibits regulatory volume decrease (RVD) in Ehrlich ascites tumor cells, suggesting that an intact microfilament network is a prerequisite for a normal RVD response. Colchicine, which is known to disrupt microtubules, has no significant effect on RVD. Ehrlich cells have a cortical three-dimensional, orthogonal F-actin filament network which makes the cells look completely black in light microscopy following immunogold/silver staining using anti-actin antibodies. After addition of cytochalasin B, the stained cells get lighter with black dots localized to the plasma membrane and appearance of multiple knobby protrusions at cell periphery. Also, a significant decrease in the staining of the cells is seen after 15 min of RVD in hypotonic medium. This microfilament reorganization appears during RVD in the presence of external Ca2+ or Ca(2+)-ionophore A23187. It is, however, abolished in the absence of extracellular calcium, with or without prior depletion of intracellular Ca2+ stores. An effect of increased calcium influx might therefore be considered. The microfilament reorganization during RVD is abolished by the calmodulin antagonists pimozide and trifluoperazine, suggesting the involvement of calmodulin in the process. The microfilament reorganization is also prevented by addition of quinine. This quinine inhibition is overcome by addition of the K+ ionophore valinomycin.

Actin polymerization in murine B lymphocytes is stimulated by cytochalasin D but not by anti-immunoglobulin

One might predict that cytochalasin D, which slows polymerization of actin in solution and which inhibits actin-containing microfilament function in live B lymphocytes, would also prevent actin polymerization in these cells. However, we have used the NBD-Phallacidin flow cytometric assay for F-actin and the DNase I inhibition assay for G-actin to demonstrate that cytochalasin D (at 20 micrograms/ml and higher) stimulates actin polymerization in murine B lymphocytes within the first 30 sec of exposure. A similar response was seen in human neutrophils. Actin polymerization induced in neutrophils by chemotactic peptides has been linked to activation of the polyphosphoinositide-calcium increase-protein kinase C signal transduction pathway. As B lymphocytes also transduce signals using this pathway, we investigated whether cytochalasin D induced actin polymerization by activating this pathway. Cytochalasin D and ionomycin both stimulated a rapid increase in internal calcium (by 1 min) in the B cell which was inhibitable by EGTA, implicating calcium influx. Ionomycin also induced actin polymerization, detectable later, by 10 min. EGTA blocked the ionomycin-induced actin polymerization, but not that induced by cytochalasin D. Cytochalasin D-induced actin polymerization was not associated with detectable hydrolysis of polyphosphoinositides, nor was it inhibited by H7 (a protein kinase C inhibitor) or by HA1004 (an inhibitor of cyclic nucleotide-dependent kinases). Furthermore, anti-immunoglobulin antibodies, which stimulate B lymphocytes through the polyphosphoinositide hydrolysis-calcium increase-protein kinase C pathway, failed to induce actin polymerization in these cells. These antibodies did, however, stimulate the cells to perform activities that involve actin-containing microfilaments. Other primary activators of B lymphocytes (dextran sulfate, PMA, and LPS) and a panel of lymphokines previously shown to enhance B lymphocyte activation (IL-1, IL-2, IL-4, IL-5) were also screened in the F-actin assay and no evidence for actin polymerization was found. We conclude that the actin polymerization response to cytochalasin D in the B cell does not involve the polyphosphoinositide hydrolysis-calcium increase-protein kinase C pathway, nor does it depend on cyclic nucleotide-dependent kinases. Furthermore, our studies failed to provide any evidence that early actin polymerization occurs in murine B lymphocyte activation.

Spectrofluorimetric studies on C-terminal 34 kDa fragment of caldesmon

Analysis of the tryptophan fluorescence emission spectra of caldesmon and its 34 kDa C-terminal fragment indicates that all tryptophan residues are located on the surface of the molecule, accessible to solvent. All three tryptophan residues of the 34 kDa fragment and four of the five tryptophan residues of intact protein are accessible to free water, whereas one located in the N-terminal region of molecule is accessible only to bound water molecules. The temperature dependence of the fluorescence parameters indicates higher thermal stability of the 34 kDa fragment than the whole caldesmon molecule. The interaction of the 34 kDa fragment of caldesmon (like that of the intact molecule) with calmodulin is accompanied by a blue shift of the fluorescence emission maximum and an increase in the relative quantum yield. Computer-calculated binding constants show that the binding of calmodulin to the 34 kDa fragment (K = 2.5 x 10(5) M-1) is of two orders of magnitude weaker than that to intact caldesmon (K = 1.4 x 10(7) M-1). The interaction with tropomyosin results in a blue shift of the spectrum of the 34 kDa fragment, yet there is no effect on the spectrum of intact caldesmon. Binding constants of tropomyosin to caldesmon (K = 3.8 x 10(5) M-1) and its 34 kDa fragment (K = 2.3 x 10(5) M-1) are similar. Binding of calmodulin to caldesmon and to the 34 kDa fragment affects their interaction with tropomyosin.

Electron microscopic studies of chicken gizzard caldesmon and its complex with calmodulin

Caldesmon samples mounted on a stage rotating about a horizontal axis were shadowed keeping the shadow angle at about 3 degrees. This technique minimizes background metal deposits compared with the conventional method. The identity of caldesmon was confirmed by comparing the images of caldesmon alone with those of the caldesmon-calmodulin complex. In these samples the caldesmon molecules appeared to be elongated; most were between 30 and 80 nm in length. The maximum length was in good agreement with the earlier estimate of 74 nm based on hydrodynamic studies. Our observations also suggested the presence of a rather rigid 30-40 nm stretch in the middle of the caldesmon molecule, which was always visible under rotary shadowing, and a flexible structure of about 20 nm in length at each end of the molecule, which may or may not be visible depending on their orientation on the mica surface. In the samples of caldesmon crosslinked with calmodulin, we noticed the existence of complexes containing two calmodulin molecules per caldesmon molecule, separated by a distance of 60 nm, consistent with the suggestion that each end of caldesmon can interact with calmodulin.

Phorbol 12,13-diacetate-induced contraction of the canine basilar artery: role of protein kinase C

The pharmacological and biochemical mechanisms of contractile responses to the protein kinase C (PKC) activator phorbol-12,13-diacetate (PDA) were investigated in canine basilar arteries. In the normal medium, PDA elicited a strong, dose-related, and slow-developing sustained contraction. Among the constrictors examined, including serotonin, prostaglandin F2 alpha, and endothelin, only PDA yielded contractions in a Ca2(+)-free medium. In both media, the PDA-induced contractions were virtually inhibited by either staurosporine, H-7, or quinacrine, while neither neurotransmitter blockades nor R24571 (calmidazolium) exerted significant effects. In addition, it was shown that 8-bromocyclic GMP, but not 8-bromocyclic AMP, markedly curtailed the PDA-induced contractions. Biochemical analysis, furthermore, showed that PDA induced increased phosphorylations of 27- and 96-kDa and proteins other than the myosin light chain (MLC) 20-kDa protein. Thus, the present results open up a novel mechanism of sustained cerebral artery contractions, where PKC activation rather than Ca2+/calmodulin/MLC system plays a key role that is regulated both by phospholipase A2 and by cyclic GMP.

Calmodulin and wound healing in the coenocytic green alga Ernodesmis verticillata (Kützing) Børgesen : Immunofluorescence and effects of antagonists

The involvement of calmodulin (CaM) in wound-induced cytoplasmic contractions in E. verticillata was investigated. Indirect immunofluorescence of CaM in intact cells showed a faint, reticulate pattern of fluorescence in the cortical cytoplasm. Diffuse fluorescence was evident deeper within the cytoplasm. In contracted cells, CaM co-localizes with actin in the cortical cytoplasm in extensive, longitudinal bundles of microfilaments (MFs), and in an actin-containing reticulum. No association of CaM with tubulin was ever observed in the cortical cytoplasm at any stage of wound-healing. When contraction rates in wounded cells are measured, a lag period of 2 min is followed by a rapid, steady rate of movement over the subsequent 10 min. The delay in the initiation of longitudinal contraction corresponds to the time necessary for the assembly of the longitudinal MF bundles. Cytoplasmic motility was inhibited in a dose-dependent manner by CaM antagonists. In these inhibited cells, MF bundles did not assemble, or were poorly formed. In the latter case, CaM was always found associated with MFs. These results indicate a direct spatial and temporal correlation between CaM and actin, and a potential role for CaM in regulating the formation of functional MF bundles during wound-induced cytoplasmic contraction in Ernodesmis.

Structural study of gizzard caldesmon and its interaction with actin. Binding involves residues of actin also recognised by myosin subfragment 1

The interaction between actin and caldesmon that is associated with the inhibition of actomyosin ATPase activity in smooth muscle has been studied using 1H-NMR spectroscopy. Binding studies using the intact molecules were complemented by the use of thrombic cleavage fragments of both turkey and chicken gizzard caldesmon as well as defined peptides of actin, in order to investigate the conformational properties of caldesmon and to localise regions of the primary structures that participate in protein-protein contacts. The binding of caldesmon is shown to involve distinct segments on the N-terminal region (residues 1-44) of actin, as previously observed for the inhibitory component of the thin filament of striated muscle, troponin I [Levine et al. (1988) Eur. J. Biochem. 153, 389-397]. The comparable structural properties of these tissue-specific inhibitors of actomyosin ATPase and the similarities in their mode of interaction at the N-terminal region of actin suggest common aspects to the structural mechanism for thin-filament regulation in smooth and striated muscle. Unlike the inhibitory interaction of troponin I, however, the binding of caldesmon to the N-terminal region of actin directly involves groups within residues 20-41 of actin that are also recognised by myosin subfragment 1. The complementary segment of caldesmon has been localised to a 15-kDa thrombic fragment (residues 483-578) derived from the N-terminal portion of a 35-kDa proteolytic cleavage product from the C-terminal of caldesmon whose interaction with actin is modulated by calmodulin. The results are discussed in relation to the calcium-mediated mechanism for thin-filament regulation in smooth and striated muscle.

Caldesmon has two calmodulin-binding domains

Chicken gizzard caldesmon was cleaved with chymotrypsin or CNBr, and the calmodulin-binding fragments were isolated using an affinity column. Limited chymotryptic digestion gives rise to a 38 kDa calmodulin-binding fragment (CT40) as described previously (Szpacenko, A. & Dabrowska, R., FEBS Lett. 202, 182-186, 1986; Fujii, T., Imai, M., Rosenfeld, G. C. & Bryan, J., J. Biol. Chem. 261, 16155-16160, 1987; Yazawa, M., Yagi, K. & Sobue, K., J. Biochem. 102, 1065-1073, 1987). In the case of CNBr cleavage a 37 kDa calmodulin-binding fragment (CB40) was obtained. Both CT40 and CB40 contain a reactive thiol group, but these thiols are apparently in different environments as judged by the responses of attached fluorescent labels to calmodulin-binding. A comparison of the N-terminal sequences of CB40 and CT40 with the complete sequence of caldesmon shows that the two calmodulin-binding fragments in fact originate from different parts of the parent molecule. Thus there exist two calmodulin-binding sites in caldesmon, one in the N-terminal half and the other in the C-terminal half of the molecule. This is consistent with the recent finding that up to two calmodulin molecules can be crosslinked to each caldesmon molecule (Wang, C.-L.A., Biochem. Biophys. Res. Commun., 156, 1033-1038, 1988).

The effect of caldesmon on assembly and dynamic properties of actin

Our earlier fluorescence measurements using N-(1-pyrenyl)iodoacetamide-labeled actin revealed that caldesmon interacts with G-actin accelerating its nucleation at low salt concentration and causing polymerization in the absence of sale [Gałazkiewicz, B., Mossakowska, M., Osińska, H. & Dabrowska, R. (1985) FEBS Lett. 184, 144-149]. In this work the caldesmon-induced process of actin polymerization as well as the dynamic properties of the polymers formed have been investigated with the use of fluorescence, electron paramagnetic resonance (EPR) and electron microscopy techniques. Fluorescence titration of N-(1-pyrenyl)iodoacetamide-labeled actin with caldesmon showed saturation of the polymerization at a 1:3 molar ratio of caldesmon/actin monomer. Parallel pelleting experiments revealed, however, that the process of polymer formation is biphasic and only at higher concentrations of caldesmon does the copolymer contain around one caldesmon/three actin monomers. At low concentration of caldesmon a complex of one caldesmon/nine actin monomers is formed. EPR spectroscopy, using maleimide spin label bound at Cys374 of actin, also indicated that one caldesmon molecule polymerizes nine actin monomers. Taken together, these results might suggest the existence of weak and strong forms of actin binding to caldesmon and detection of only the latter by the fluorescence method. Copolymers of actin and caldesmon are indistinguishable from actin polymerized by salt with respect to their appearance in the electron microscope and their ability to interact with heavy meromyosin, although they are characterized by lower torsional flexibility as indicated by immobilization of spin labels attached to actin.

Location of the calmodulin- and actin-binding domains at the C-terminus of caldesmon

Digestion of caldesmon with carboxypeptidase Y is accompanied by loss of its ability to inhibit actomyosin ATPase activity and to bind actin and calmodulin. Similarly, carboxypeptidase Y digestion of a terminal 40 kDa chymotryptic fragment of caldesmon abolishes its inhibition of the actomyosin ATPase and binding to actin and calmodulin. This represents the first direct demonstration that these functional domains of caldesmon are located close to the carboxy-terminus of the molecule.

Calmodulin-binding proteins are developmentally regulated in gametes and embryos of fucoid algae

Calcium-binding proteins and calmodulin-binding proteins were identified in gametes and zygotes of the marine brown algae Fucus vesiculosus, Fucus distichus, and Pelvetia fastigiata using gel (SDS-PAGE) overlay techniques. A calcium current appears to be important during cell polarization in fucoid zygotes (K.R. Robinson and L.F. Jaffe, 1975, Science 187, 70-72; K.R. Robinson and R. Cone, 1980, Science 207, 77-78), but there are no biochemical data on calcium-binding proteins in these algae. By using a sensitive 45Ca2+ overlay method designed to detect high-affinity calcium-binding proteins, at least 9-11 polypeptides were detected in extracts of fucoid gametes and zygotes. All samples had calcium-binding proteins with apparent molecular weights of about 17 and 30 kDa. A 17-kDa calcium-binding protein was purified by calcium-dependent hydrophobic chromatography and was identified as calmodulin by immunological and enzyme activator criteria. A 125I-calmodulin overlay assay was used to identify potential targets of calmodulin action. Sperm contained one major calmodulin-binding protein of about 45 kDa. Eggs lacked major calmodulin-binding activity. A 72-kDa calmodulin-binding protein was prominent in zygotes from 1-65 hr postfertilization. Both calmodulin-binding proteins showed calcium-dependent binding activity. Overall, the data suggest that the appearance and distribution of certain calcium-binding and calmodulin-binding proteins are under developmental regulation, and may reflect the different roles of calcium during fertilization and early embryogenesis.

Photocrosslinking of calmodulin and/or actin to chicken gizzard caldesmon

The two sulfhydryl groups of chicken gizzard caldesmon were specifically labeled with a photoreactive crosslinker, benzophenone-maleimide, to study its interactions with calmodulin and/or actin. When incubated with F-actin caldesmon crosslinks to a single actin monomer; it can, however, crosslink to up to two calmodulin molecules in the presence, but not in the absence, of Ca2+. Thus caldesmon may have two calmodulin-binding sites, each containing, or being near, one of the two thiol residues. One of these two sites may also be adjacent to the actin-binding site. A calmodulin-binding fragment of caldesmon resulting from cyanogen bromide digestion crosslinks to a single calmodulin molecule, also in a Ca2+-dependent manner. Crosslinking of calmodulin to caldesmon does not prevent the latter from binding F-actin, suggesting that calmodulin and actin do not compete with each other for the same binding site(s) on the caldesmon molecule.

Comparison of Ca2+-dependent effects of caldesmon-tropomyosin-calmodulin and troponin-tropomyosin complexes on the structure of F-actin in ghost fibers and its interaction with myosin heads

Comparison of two types of Ca2+-regulated thin filament, reconstructed in ghost fibers by incorporating either caldesmon-gizzard tropomyosin-calmodulin or skeletal muscle troponin-tropomyosin complex, was performed by polarized microphotometry. The changes in actin structure under the influence of these regulatory complexes, as well as those upon the binding of the myosin heads, were followed by measurements of F-actin intrinsic tryptophan fluorescence and the fluorescence of phalloidin-rhodamine complex attached to F-actin. The results show that in the presence of smooth muscle tropomyosin and calmodulin, caldesmon causes Ca2+-dependent alterations of actin conformation and flexibility similar to those induced by skeletal muscle troponin-tropomyosin complex. In both cases, transferring of the fiber from '-Ca2+' to '+Ca2+' solution increases the number of turned-on actin monomers. However, whereas troponin in the absence of Ca2+ potentiates the effect of skeletal muscle tropomyosin, caldesmon-calmodulin complex inhibits the effect of smooth muscle tropomyosin. This difference seems to be due to the qualitatively different alterations in the structure and flexibility of F-actin in ghost fibers evoked by smooth and skeletal muscle tropomyosins. Troponin can bind to F-actin-smooth muscle tropomyosin-caldesmon complex and, in the presence of Ca2+, release the restraint by caldesmon for S-1-induced alterations of conformation, and reduce that for flexibility of actin in ghost fibers. This effect seems to be related to the abolishment by troponin of the potentiating effect of tropomyosin on caldesmon-induced inhibition of actomyosin ATPase activity.

A 35-kilodalton fragment from gizzard smooth muscle caldesmon that induces F-actin bundles

Specific thrombin proteolysis of native 120-kDa gizzard caldesmon gave rise to a major cleavage into an N-terminal 90-kDa and a C-terminal 35-kDa fragment. Fluorescent labeling, cosedimentation, passage through an affinity column, and carbodiimide crosslinking with actin revealed that the 35-kDa purified segment of the molecule contains the actin and the calcium-calmodulin binding regions. Electron microscopic analysis of its actin complex demonstrated that the 35-kDa segment possesses the bundling properties of the intact molecule. Thus, a possible pathway for the expression of the caldesmon regulatory function during smooth muscle contraction would be a conformational change twisting the helicoïdal structure of the actin filament, which occurs when the 35-kDa caldesmon portion binds to it.

Identification of a 15 kilodalton actin binding region on gizzard caldesmon probed by chemical cross-linking

Fluorescent labeling, limited proteolysis, amino acid sequence determinations, affinity chromatography and specific chemical crosslinking were used to determine the smallest fragment of gizzard caldesmon that interacts with actin. The time course of cleavage with thrombin or submaxillaris arginase-C protease indicates that 90kDa and 35kDa fragments are the two major pieces of the 120kDa native protein. Amino acid sequence determination indicates that the 90kDa fragment is the N-terminal portion of the molecule. Further degradation gave rise to a 15kDa product whose N-terminal amino acid sequence was determined within the first 28 amino acids. Carbodiimide crosslinking with actin revealed that the 15kDa part of the molecule is probably not involved in the actin binding process but may participate in a twisting of the F-actin filament and be responsible of the caldesmon regulatory function during smooth muscle contraction.