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The MRTFs (myocardin-releated transcription factors) protein family consists of myocardin, MRTF-A (MKL1, MAL) and MRTF-B (MKL2). These proteins are included in the common family due to the presence of evolutionarily conserved domains which are responsible for homo- and heterodimerization with other members of the family as well as actin binding and transcription activation. Despite high structural homology, these factors present different characteristics in terms of localization. The expression of myocardin is limited to the myocardial cells and smooth muscle cells, exclusively, whereas MRTF-A and MRTF-B are commonly found in various cells and tissues. These proteins interact with MADS box transcription factors as well as serum response factors (SRF) thus being engaged into signal transduction, which results from cytoskeleton reorganisation, from cytoplasm to the nucleus. It has been concluded that these proteins both take part in muscle tissue differentiation as well as mediate the development of pathological conditions (vascular diseases, cancer and fibrosis).

Ezrin, radixin and moesin, forming the ERM protein family, act as molecular crosslinkers between actin filaments and proteins anchored in the cell membrane. By participating in a complex intracellular network of signal transduction pathways, ERM proteins play a key role in the regulation of adhesion and polarity of normal cells through interactions with membrane molecules, e.g. E-cadherin. Dynamic cytoskeletal transformations, in which the ERM and Rho GTPases are involved, lead to the formation of membrane-cytoplasmic structures, such as filopodia and lamellipodia, which are responsible for cellular motility. The interactions of ERM proteins with active Akt kinase cause the acquisition of antiapoptotic cellular features by downregulation of the proapoptotic protein Bad. ERM protein activity is regulated by phosphorylation/dephosphorylation reactions and linking phosphatidylinositols. The model of activation based on the molecular conformation changes by breaking the intramolecular bonds and exposing actin binding sites is essential for the proper functioning of the ERM proteins. Additionally, the connection types between the ERM and membrane proteins (direct or indirect by EBP50 and E3KARP) play an important role in transduction of signals from the extracellular matrix. Due to the wide range of ezrin, radixin and moesin cytophysiological features, detailed exploration of the ERM biochemistry will provide a series of answers to questions about ambiguous functions in many intracellular signal transduction pathways.

Muscle contraction and different forms of motility of nonmuscle cells depend on cyclic interactions between actin filaments and myosin motors. Calcium ions are the main intracellular signal, which induces activation of actin-myosin interactions. Depending on the cell type and the class of myosin, the molecular mechanisms of regulation are different and take place on two levels - actin filament and myosin. In striated muscle, the actin thin filament is regulated by the troponin-tropomyosin complex. In smooth muscle and nonmuscle cells, actin filaments are predominantly regulated by caldesmon. The control of myosin activity in these cells also depends on the myosin light chain phosphorylation and the phosphorylation of the heavy chain. Direct binding of calcium ions to the myosin light chains (which could be calmodulin molecules) was observed in myosin from molluscan muscle and in some unconventional myosins. Intensive world-wide studies allow us to understand details of the mechanisms of actin-myosin interactions. In this article, we present the contemporary view on these mechanisms.

Myosins are actin-based motor proteins that use energy derived from ATP hydrolysis to generate force and move along actin filaments. Myosin VI is a unique motor protein because it moves towards the "minus" end of actin filament, which is the opposite direction to all of the other myosins studied so far, and therefore is thought to have unique properties and cellular functions. Localization and functional studies indicate that myosin VI plays a role in a variety of different intracellular processes, such as endocytosis and secretion as well as cell division, differentiation, and cell migration. These various functions of myosin VI are mediated by interaction with a range of different binding partners. In this review, we describe the structure, kinetic properties and functions proposed for myosin VI, and present current hypotheses on the mechanisms of functioning of this unique protein in vivo.

Endocytosis is the way of uptaking and transporting substances from the immediate surroundings, as well as the way of removal and/or recycling of the plasma membrane components. For many years, it was thought that this process was not operating in plant cells in which high turgor pressure of the protoplast prevented invagination of the plasma membrane. Recent years, however, brought the evidence for intensive endocytosis in plants. So far, four types of endocytosis, among 5 known, have been identified in plants. Use of protein markers of different compartments of the endomembrane system, specific dyes, and the cytoskeleton inhibitors, made possible demonstration that, as opposed to animal and fungal systems, endocytosis in plant cells was dependent on actin and plant-specific myosins of VIII and XI classes. Although cell divisions in plants and animals differ considerably, they both are dependent on the proper endocytosis. It has been shown that during cytokinesis secretion and endocytosis act in concert, delivering polysaccharides directionally to the growing cell plate. What is more important, new cell walls are built from e.g. pectins transported by endocytosis from existing cell walls.

Wound healing is an important biological process of crucial value for organisms survival and retention of its proper functions. The recognition of molecular mechanisms of these phenomenon is still under investigation. The transition of mesenchymal fibroblasts to myofibroblasts is a key point in wound healing. The contraction ability of myofibroblast enables the shrinkage of a wound and closes its edges. Alpha smooth muscle actin (alpha-SMA), one of six actin isoforms, is a marker of compeletely differentiated myofibroblast. The regulation of differentiation process depends on many growth factors (especially TGF beta 1), the level of active thymosin beta 4, extracellular matrix proteins--including fibronectin, and also on specificity of microenvironment. Thymosin beta 4 is responsible for maintenance of pool of monomeric actin and actin filaments depolymerization. It can also act as a transcription factor, migration stimulator and immunomodulator, so this protein deserves for more attention in wound healing research field.

Rearrangements of actin cytoskeleton enable proper functioning of the cells under normal conditions, and also cellular adaptations to changes in the direct surroundings. Formins are actin binding proteins, responsible for actin nucleation and further elongation of microfilaments. The distinguishing feature of formins is the presence of conserved FH2 (formin homology domain 2) domain, as well as other domains typical for distinct formin classes. In animal cells formins are involved in cytokinesis and determination and maintenance of the cell shape and polarity, but also in the formation of filopodia, endocytosis and many other processes. The presence of proteins from the formin family in plant cells, and their involvement in the tip growth and cytokinesis, has been determined only recently. As the functional organization of plant and animal cells is different, one can assume that the range of putative functions of plant formins might also be diverse. One of such proposed functions for formins in plants is the role of linker protein within WMC continuum (cell wall-plasma membrane-cytoskeleton). Unfortunately, for that moment the state of knowledge about plant formins in comparison with animal or fungal ones is much poorer.

Amoeba proteus and smaller by an order of magnitude (and evolutionary younger) Acanthamoeba castellanii have been for many years model cells for studies of amoeboidal (crawling) type of movement, characteristic also for some of metazoan cells such as fibroblasts, granulocytes and macrophages. Amoeboidal migration is indispensable of organization and dynamics of actin-based cytoskeleton. While there is a number of data on molecular mechanisms of motility of A. castellanii, there is very little known about bases of migration of A. proteus. Noteworthy, a large A. proteus (length approximately 600 microm) have been from over a century an object for studies on biology and physiology of cellular migration. This review describes the current knowledge on molecular aspects of force generation required for migration of these two amoebae and attempts to compare the functioning and regulation of actin cytoskeleton in these free-living unicellular species.

Problems in successful cancer therapy result from an adaptive character and high plasticity in tumor cells behaviour. Their accommodation to a differentiated environment is preceded by an alteration in expression profile of several proteins. Three types of tumor cell migration were characterized so far: mezenchymal, ameboid and collective. In mezechymal and ameboid types of tumor cell migration, cells move individually. Collective type of migration to a bigger extend presents characteristics of the mezenchymal one. Diverse types of tumor cell locomotion differ with cell protrutions and signaling pathways that control those processes. Mezenchymal type of movement is regulated by Cdc42 kinase. Cells that move in this manner present elongated shape with distinctly exposed lamellipodium and adhere to ECM proteins. Cellular membrane blebbing of pseudopodial character appear in ameboid type of movement. This one is under Rho/ROCK signal transduction cascade control. Our review focuses on description of different movement types and mechanisms of their regulation.

Myosins, actin-dependent molecular motors are expressed in almost all eukaryotic cells where are engaged in a panoply of cellular processes such as muscle contraction, cell migration and adhesion, intracellular trafficking, cytokinesis, endocytosis and secretion. In recent years a number of reports has been published revealing nuclear localization of myosins as well as actin and actin-binding proteins. Namely, nuclear form of myosin IC (NMI), myosin VI, myosin XVIB and myosin XVIIIB were found in nucleus. NMI and myosin VI seem to be involved in gene transcription and possibly intranuclear transport. In this paper, current knowledge on the role of myosin motors in nucleus has been presented.

Actin is multifunctional protein occurring in all eukaryotic cells. It appears in cytoplasm and in nucleus. Organization and functions of nuclear actin are not well recognized to distinguish from cytoplasmic actin. Actin monomers are shuttling between cytoplasm and nucleus, integrating both of those compartments. Monomers, oligomers and short polimers are observed as the result of the limited space within the nucleus. Actin participates in nuclear structure organization, chromatin remodeling, transcription and signal transduction. Nuclear actin level, organization and functions are under control of ABPs (similarly as it takes place in cytoplasm), including some proteins appearing only in the nucleus.

Gc-globulin is a multifunctional glycoprotein with a molecular mass of 51-58 kDa. It is also called vitamin D-binding protein (DBP). The main function of Gc-globulin is to bind vitamin D and actin, which is released into the extracellular environment upon cell and tissue lysis. Gc-globulin appears to have important clinical significance. Some investigation have shown that a low concentration of Gc-globulin may be used as a prognostic factor in patients with fulminant hepatic failure, acetaminophen (paracetamol) overdose, multiple trauma or multiple organ dysfunction syndrome (MODS), or sepsis. Many studies suggest an association between Gc-globulin phenotypes and resistance or susceptibility to chronic obstructive pulmonary disease (COPD), thyroid diseases, diabetes, multiple sclerosis, and sarcoidosis.

Proteins of the Rho protein family (RhoA, Rac1, Cdc42) work as molecular switches in the regulation of many cellular processes. They are involved in cell migration, cell-cycle control, apoptosis, and the regulation of gene transcription. Rho proteins show their activity mainly in the cell's cytoskeleton by taking part in the reorganization of microfilaments and microtubules. In recent years, significant progress has been made in understanding the biochemical and genetic nature of many processes controlled by Rho proteins. Although there are still seveal unknowns and hypothesizes which require confirmation, newer and more precise experimental results allow us to better understand these processes. It has also been suggested to use Rho family proteins in the therapy of some diseases. The purpose of this study was to characterize the significance of Rho processes in the cellular cytoskeleton.

Alzheimer's disease is associated with the formation of extracellular senile plaques and intracellular neurofibrillary tangles. In the neurons of patients, all the morphological features of apoptosis, e.g. blebbing, formation of apoptotic bodies, and chromatin condensation, as well as cytoskeleton reorganization were observed. Actin filaments interact with proteins characteristic of Alzheimer's disease, such as apolipoprotein E, amyloid precursor protein, pressenilin, and tau protein. The degeneration of neurons is associated with the formation of Hirano bodies, which contain actin, cofilin, tubulin, tau protein, and proteins of the MAP family and APP. Actin rods are also observed in postmortal brains of patients with Alzheimer's disease. These 'rods' have been shown to play a role in Hirano body precursors.

Migration of crawling cells (amoebae and some kinds of the tissue cells) is a process related to the dynamic reorganization of actomyosin cytoskeleton. That reorganization engages actin polymerization and de-polymerization, branching of actin network and interaction of myosin II with actin filaments. All those cytoskeleton changes lead to the cell progression, contraction and shifting of the uropod and the cell adhesion. Numerous external stimuli, which activate various surface receptors and signal transduction pathways, can promote migration. Rho family proteins play an important role in the regulation of actin cytoskeleton organization. The most known members of this family are Rho, Rac and Cdc42 proteins, present in all mammalian tissue cells. These proteins control three different stages of cell migration: progression of the frontal edge, adhesion which stabilizes the frontal area, and de-adhesion and shifting of the uropod. Cdc42 and Rac control cell polarization, lamellipodium formation and expansion, organization of focal complexes. Rho protein regulates contractile activity of actomyosin cytoskeleton outside the frontal area, and thus contraction and de-adhesion of the uropod.