Atypical protein kinase C in cell motility

Cell motility is defined as cell movement in the three-dimensional space leading to repositioning of the cell. Atypical protein kinase C (aPKC, including ζ and λ/ι) are a subfamily of PKC. Different from classic PKC and novel PKC, the activation of atypical PKC is not dependent on diacylglycerol or calcium. PKCζ can be activated by lipid components, such as phosphatidylinositols, phosphatidic acid, arachidonic acid, and ceramide. Both phosphatidylinositol (3,4,5)-trisphosphate and PDK1 are necessary for the complete and stable activation of PKCζ. Atypical PKC is involved in the regulation of cell polarization, directional sensing, formation of filopodia, and cell motility. It is essential for migration and invasion of multiple cancer cell types. Particularly, atypical PKC has been found in the regulation of the motility of hematopoietic cells. It also participates in the regulation of proteolytic activity of podosomes and invadopodia. It has been found that atypical PKC can work coordinately with other PKC subfamily members and other signaling pathways. Research on the roles of atypical PKC in cell motility may lead to new therapeutic strategies for cancer and other diseases.     

Espins and the actin cytoskeleton of hair cell stereocilia and sensory cell microvilli

The espins are novel actin-bundling proteins that are produced in multiple isoforms from a single gene. They are present at high concentration in the parallel actin bundle of hair cell stereocilia and are the target of deafness mutations in mice and humans. Espins are also enriched in the microvilli of taste receptor cells, solitary chemoreceptor cells, vomeronasal sensory neurons and Merkel cells, suggesting that espins play important roles in the microvillar projections of vertebrate sensory cells. Espins are potent actin-bundling proteins that are not inhibited by Ca2+. In cells, they efficiently elongate parallel actin bundles and, thereby, help determine the steadystate length of microvilli and stereocilia. Espins bind actin monomer via their WH2 domain and can assemble actin bundles in cells. Certain espin isoforms can also bind phosphatidylinositol 4,5-bisphosphate, profilins or SH3 proteins. These biological activities distinguish espins from other actin-bundling proteins and may make them well-suited to sensory cells.     

Association of intermediate filaments with other cell organelles in carcinoid tumor of the colon

Summary Carcinoid tumor of the colon was studied in electron microscope. In cytoplasm, prominent intermediate-sized filaments were seen frequently attaching to nucleus and mitochondria. Direct contacts of intermediate filaments with secretory granules were not observed.Acknowledgments. The skilful technical assistance of Ms Tuire Koro is gratefully acknowledged. — This study was supported by grants from the Finnish Medical Research Council, Finnish Culture Foundation and J.K. Paasikivi Foundation for Cancer Research.     

Stimulation of olfactory ensheathing cell motility enhances olfactory axon growth

Axons of primary olfactory neurons are intimately associated with olfactory ensheathing cells (OECs) from the olfactory epithelium until the final targeting of axons within the olfactory bulb. However, little is understood about the nature and role of interactions between OECs and axons during development of the olfactory nerve pathway. We have used high resolution time-lapse microscopy to examine the growth and interactions of olfactory axons and OECs in vitro. Transgenic mice expressing fluorescent reporters in primary olfactory axons (OMP-ZsGreen) and ensheathing cells (S100ß-DsRed) enabled us to selectively analyse these cell types in explants of olfactory epithelium. We reveal here that rather than providing only a permissive substrate for axon growth, OECs play an active role in modulating the growth of pioneer olfactory axons. We show that the interactions between OECs and axons were dependent on lamellipodial waves on the shaft of OEC processes. The motility of OECs was mediated by GDNF, which stimulated cell migration and increased the apparent motility of the axons, whereas loss of OECs via laser ablation of the cells inhibited olfactory axon outgrowth. These results demonstrate that the migration of OECs strongly regulates the motility of axons and that stimulation of OEC motility enhances axon extension and growth cone activity.     

Association of intermediate filaments with other cell organelles in carcinoid tumor of the colon.

Carcinoid tumor of the colon was studied in electron microscope. In cytoplasm, prominent intermediate-sized filaments were seen frequently attaching to nucleus and mitochondria. Direct contacts of intermediate filaments with secretory granules were not observed.     

Cofilin activity during insulin-like growth factor I-stimulated neuroblastoma cell motility

Insulin-like growth factor I (IGF-I) is a potent stimulator of neuroblastoma cell motility. Cell motility requires lamellipodium extension at the leading edge of the cell through organized actin polymerization, and IGF-I stimulates lamellipodial elaboration in human neuroblastoma cells. Rac is a Rho GTPase that stimulates lamellipodial formation via the regulation of actin polymerization. In this study, we show that IGF-I-stimulated phosphatidylinositol 3-kinase (PI-3K) activity promotes rac activation and subsequent activation of the down- stream effectors LIM kinase and cofilin. Overexpression of wild-type LIM kinase and wild-type Xenopus ADF/cofilin (XAC) suppresses IGF-I-stimulated motility in SH-SY5Y cells, while expression of dominant negative LIM kinase and constitutively active XAC increases SH-SY5Y motility in the absence of IGF-I stimulation. These results suggest that regulation by cofilin of actin depolymerization is important in the process of neuroblastoma cell motility, and IGF-I regulates cofilin activity in part through PI-3K, rac, and LIM kinase.Received 18 October 2004; received after revision 3 December 2004; accepted 16 December 2004     

Control of sperm motility and fertility: Diverse factors and common mechanisms

Spermatozoa generated in the testis are immature and incompetent for fertilization. During their journey toward the egg, the sperm acquire fertility and achieving fertilization. These sperm modifications to ensure fertilization are induced by many female or male extra-sperm factors: for example, sperm motility-activating factors from the egg jelly, sperm attractants from the eggs, and decapacitation factors from the seminal plasma. The factors controlling sperm fertility are myriad and species specific; they may be peptides, sugar chains, or small organic compounds. Nevertheless, the fundamental mechanisms underlying fertilization must be common among all animals; increase in [Ca²⁺]_i triggers all the steps in the process of fertilization, and cAMP plays important roles in many steps. Elucidating the dynamic functional and morphological changes in sperm cells is important for understanding the regulation of fertilization. Here, we introduce the diversity and generality of the control of sperm fertility. Received 28 April 2008; received after revision 13 June 2008; accepted 17 June 2008     

Functions of actin in endocytosis

Endocytosis is a fundamental eukaryotic process required for remodelling plasma-membrane lipids and protein to ensure appropriate membrane composition. Increasing evidence from a number of cell types reveals that actin plays an active, and often essential, role at key endocytic stages. Much of our current mechanistic understanding of the endocytic process has come from studies in budding yeast and has been facilitated by yeast’s genetic amenability and by technological advances in live cell imaging. While endocytosis in metazoans is likely to be subject to a greater array of regulatory signals, recent reports indicate that spatiotemporal aspects of vesicle formation requiring actin are likely to be conserved across eukaryotic evolution. In this review we focus on the ‘modular’ model of endocytosis in yeast before highlighting comparisons with other cell types. Our discussion is limited to endocytosis involving clathrin as other types of endocytosis have not been demonstrated in yeast.     

Contractile filaments in cells of regenerating tendon

Summary An extensive cytoplasmic fibrillar system has been observed in fibroblast-like cells of regenerating tendon. It consists of bundles of actin filaments, which often show a cross-striated appearance due to electron dense bodies occurring throughout their length. The functional role of this contractile apparatus seems to be related to the process of movement and orientation of the newly formed cells and to the retraction of the regenerating tendon.Work was supported by grant C. N. R. n. 75.01224.04–115.5479 from Consiglio Nazionale delle Ricerche, Italy.The authors are grateful to Dr G. F. Bottazzo, Dept. Immunology, Middlesex Hospital, London, for carrying out the absorption experiments with purified actin and to Miss M. Rita Nicotra, Miss Laura M. Vassallo and Mr Mario Termine for their technical assistance.     

Are intermediate filaments of vertebrate smooth muscle cells and tonofilaments of epithelial cells identical cell structures?

Summary In epithelial and smooth muscle cells of the urinary bladder of the frog, a class of filaments exists which is partly disintegrated by glycerol treatment and very resistant to potassium solutions of high ionic strength.We are indebted to Miss M. Schlatter for her technical assistance. This work was supported by the Deutsche Forschungsgemeinschaft (He 686/2).     

The biology of interleukin-1: emerging concepts in the regulation of the actin cytoskeleton and cell junction dynamics

Interleukin (IL)-1 is a proinflammatory cytokine with important roles in innate immunity, as well as in normal tissue homeostasis. Interestingly, recent studies have also shown IL-1 to function in the dynamics of the actin cytoskeleton and cell junctions. For example, treatment of different epithelia with IL-1α often results in the restructuring of the actin network and cell junctions, thereby leading to junction disassembly. In this review, we highlight new and interesting findings that show IL-1 to be a critical player of restructuring events in the seminiferous epithelium of the testis during spermatogenesis.     

Isolation of filaments of the chick lens

Summary A preparation of intermediate filaments isolated from the chicken lens is enriched with a 50,000 dalton polypeptide.This study was supported by research grant EY 01417 of the National Institutes of Health, Bethesda, Maryland, USA.     

Isolation of filaments of the chick lens

A preparation of intermediate filaments isolated from the chicken lens is enriched with a 50,000 dalton polypeptide.     

Molecular mechanism of actomyosin-based motility

Sophisticated molecular genetic, biochemical and biophysical studies have been used to probe the molecular mechanism of actomyosin-based motility. Recent solution measurements, high-resolution structures of recombinant myosin motor domains, and lower resolution structures of the complex formed by filamentous actin and the myosin motor domain provide detailed insights into the mechanism of chemomechanical coupling in the actomyosin system. They show how small conformational changes are amplified by a lever-arm mechanism to a working stroke of several nanometres, explain the mechanism that governs the directionality of actin-based movement, and reveal a communication pathway between the nucleotide binding pocket and the actin-binding region that explains the reciprocal relationship between actin and nucleotide affinity. Here we focus on the interacting elements in the actomyosin system and the communication pathways in the myosin motor domain that respond to actin binding.Received 12 January 2005; received after revision 4 March 2005; accepted 23 March 2005     

E-cadherin and plakoglobin recruit plakophilin3 to the cell border to initiate desmosome assembly

A decrease in the levels of the desmosomal plaque protein, plakophilin3 (PKP3), leads to a decrease in desmosome size and cell-cell adhesion. To test the hypothesis that PKP3 is required for desmosome formation, the recruitment of desmosomal components to the cell surface was studied in the PKP3 knockdown clones. The PKP3 knockdown clones showed decreased cell border staining for multiple desmosomal proteins, when compared to vector controls, and did not form desmosomes in a calcium switch assay. Further analysis demonstrated that PKP3, plakoglobin (PG) and E-cadherin are present at the cell border at low concentrations of calcium. Loss of either PG or E-cadherin led to a decrease in the levels of PKP3 and other desmosomal proteins at the cell border. The results reported here are consistent with the model that PG and E-cadherin recruit PKP3 to the cell border to initiate desmosome formation.     

Tachykinins in regulation of gastric motility and secretion

The tachykinins constitute a family of neuropeptides with a common C-terminal amino acid sequence. The best known tachykinin is substance P. Tachykinins are found in the nerve plexuses and nerve fibers in the stomach of all species examined. The circular muscle layer is densely innervated, whereas the longitudinal layer and the mucosa are less intensively innervated. Tachykinins are also found in a significant number of afferent neurons with cell bodies in the dorsal root ganglia. Release of tachykinin can be demonstrated in response to both electrical stimulation of the vagus nerves and application of capsaicin. In the stomach all three known tachykinin receptors seem to be present. Although species variations exist, NK-2 receptors are generally present on the musculature, NK-1 receptors on both neurons and muscles, and NK-3 receptors on neurons only. Tachykinins stimulate motility in all parts of the stomach, but tachykinins also appear to inhibit motility in certain situations. Also, motility initiated centrally, mediated through the vagus nerves, is influenced by tachykinins. The precise role of tachykinin in the various motor programs in the stomach is not clear. Gastric acid secretion is influenced by tachykinins in several species. Tachykinins do not seem to act as neurotransmitters directly on parietal cells, but may have a modulatory function. The importance of tachykinins for the regulation of pepsinogen and hormone secretion from the stomach remains unclear. Received 24 August 1999; received after revision 1 December 1999; accepted 3 December 1999