Browsing by Subject "actin"

Sort by: Order: Results:

Now showing items 1-11 of 11
  • Ju, Meihua; Ioannidou, Sofia; Munro, Peter; Rämö, Olli; Vihinen, Helena; Jokitalo, Eija; Shima, David T. (2020)
    Fenestrae are transcellular plasma membrane pores that mediate blood-tissue exchange in specialised vascular endothelia. The composition and biogenesis of the fenestra remain enigmatic. We isolated and characterised the protein composition of large patches of fenestrated plasma membrane, termed sieve plates. Loss-of-function experiments demonstrated that two components of the sieve plate, moesin and annexin II, were positive and negative regulators of fenestra formation, respectively. Biochemical analyses showed that moesin is involved in the formation of an actin-fodrin submembrane cytoskeleton that was essential for fenestra formation. The link between the fodrin cytoskeleton and the plasma membrane involved the fenestral pore protein PV-1 and Na,K-ATPase, which is a key regulator of signalling during fenestra formation both in vitro and in vivo. These findings provide a conceptual framework for fenestra biogenesis, linking the dynamic changes in plasma membrane remodelling to the formation of a submembrane cytoskeletal signalling complex.
  • Acheva, Anna; Kärki, Tytti; Schaible, Niccole; Krishnan, Ramaswamy; Tojkander, Sari (2021)
    In postmenopausal women, a major risk factor for the development of breast cancer is obesity. In particular, the adipose tissue-derived adipokine leptin has been strongly linked to tumor cell proliferation, migration, and metastasis, but the underlying mechanisms remain unclear. Here we show that treatment of normal mammary epithelial cells with leptin induces EMT-like features characterized by higher cellular migration speeds, loss of structural ordering of 3D-mammo spheres, and enhancement of epithelial traction forces. Mechanistically, leptin triggers the phosphorylation of myosin light chain kinase-2 (MLC-2) through the interdependent activity of leptin receptor and Ca2+ channels. These data provide evidence that leptin-activated leptin receptors, in co-operation with mechanosensitive Ca2+ channels, play a role in the development of breast carcinomas through the regulation of actomyosin dynamics.
  • Pawlowski, Rafal; Rajakylä, Eeva; Vartiainen, Maria K.; Treisman, Richard (2010)
  • Rajakylä, Eeva Kaisa; Lehtimäki, Jaakko I.; Acheva, Anna; Schaible, Niccole; Lappalainen, Pekka; Krishnan, Ramaswamy; Tojkander, Sari (2020)
    Summary Defects in the maintenance of intercellular junctions are associated with loss of epithelial barrier function and consequent pathological conditions, including invasive cancers. Epithelial integrity is dependent on actomyosin bundles at adherens junctions, but the origin of these junctional bundles is incompletely understood. Here we show that peripheral actomyosin bundles can be generated from a specific actin stress fiber subtype, transverse arcs, through their lateral fusion at cell-cell contacts. Importantly, we find that assembly and maintenance of peripheral actomyosin bundles are dependent on the mechanosensitive CaMKK2/AMPK signaling pathway and that inhibition of this route leads to disruption of tension-maintaining actomyosin bundles and re-growth of stress fiber precursors. This results in redistribution of cellular forces, defects in monolayer integrity, and loss of epithelial identity. These data provide evidence that the mechanosensitive CaMKK2/AMPK pathway is critical for the maintenance of peripheral actomyosin bundles and thus dictates cell-cell junctions through cellular force distribution.
  • Kyheröinen, Salla (Helsingfors universitet, 2016)
    Actin is known as abundant cytoplasmic protein, which functions as a component of the cytoskeleton and in cell motility together with motor protein myosins. However, actin is also present in the nucleus, where it has been shown to take part in the control of gene expression, both independently and as part of chromatin remodeling complexes. An important aspect in the study of nuclear actin is to identify other nuclear proteins interacting with actin and to confirm these interactions in biochemical experiments. Through these interactions actin can be linked to various nuclear processes. The aim of this master’s thesis study was to express and purify five nuclear proteins that have been suggested to bind actin and to study the binding in detail both with actin filaments and monomers. The proteins of interest include four actin-related proteins (ARPs) Arp4, Arp5, Arp6 and Arp8 as well as RNA polymerase II subunit Rpb8. Out of the proteins selected for this study, the expression and purification of Arp4 and Rpb8 was successful. Neither one did bind monomeric actin with high affinity, but interestingly Rpb8 did bind actin filaments. On the other hand, Rpb8 did not have any effect on actin polymerization. These results provide new insights into nuclear actin function. It has been suggested earlier that Arp4 would form a heterocomplex with actin, but the results of this study do not support this. The binding between Rpb8 and actin in RNA polymerase II complex has not been extensively studied before, so the results provide new information about the function of actin in the polymerase complex.
  • Heuser, Vanina D.; Mansuri, Naziha; Mogg, Jasper; Kurki, Samu; Repo, Heli; Kronqvist, Pauliina; Carpen, Olli; Gardberg, Maria (2018)
    Basal-like breast cancer is an aggressive form of breast cancer with limited treatment options. The subgroup can be identified immunohistochemically, by lack of hormone receptor expression combined with expression of basal markers such as CK5/6 and/or epidermal growth factor receptor (EGFR). In vitro, several regulators of the actin cytoskeleton are essential for efficient invasion of basal-like breast cancer cell lines. Whether these proteins are expressed in vivo determines the applicability of these findings in clinical settings. The actin-regulating formin protein FHOD1 participates in invasion of the triple-negative breast cancer cell line MDA-MB-231. Here, we measure the expression of FHOD1 protein in clinical triple-negative breast cancers by using immunohistochemistry and further characterize the expression of another formin protein, INF2. We report that basal-like breast cancers frequently overexpress formin proteins FHOD1 and INF2. In cell studies using basal-like breast cancer cell lines, we show that knockdown of FHOD1 or INF2 interferes with very similar processes: maintenance of cell shape, migration, invasion, and proliferation. Inhibition of EGFR, PI3K, or mitogen-activated protein kinase activity does not alter the expression of FHOD1 and INF2 in these cell lines. We conclude that the experimental studies on these formins have implications in the clinical behavior of basal-like breast cancer.
  • Koskinen, Mikko; Hotulainen, Pirta (2014)
  • Jiu, Yaming; Kumari, Reena; Fenix, Aidan M.; Schaible, Niccole; Liu, Xiaonan; Varjosalo, Markku; Krishnan, Ramaswamy; Burnette, Dylan T.; Lappalainen, Pekka (2019)
    Summary Cell adhesion, morphogenesis, mechanosensing, and muscle contraction rely on contractile actomyosin bundles, where the force is produced through sliding of bipolar myosin II filaments along actin filaments. The assembly of contractile actomyosin bundles involves registered alignment of myosin II filaments and their subsequent fusion into large stacks. However, mechanisms underlying the assembly of myosin II stacks and their physiological functions have remained elusive. Here, we identified myosin-18B, an unconventional myosin, as a stable component of contractile stress fibers. Myosin-18B co-localized with myosin II motor domains in stress fibers and was enriched at the ends of myosin II stacks. Importantly, myosin-18B deletion resulted in drastic defects in the concatenation and persistent association of myosin II filaments with each other and thus led to severely impaired assembly of myosin II stacks. Consequently, lack of myosin-18B resulted in defective maturation of actomyosin bundles from their precursors in osteosarcoma cells. Moreover, myosin-18B knockout cells displayed abnormal morphogenesis, migration, and ability to exert forces to the environment. These results reveal a critical role for myosin-18B in myosin II stack assembly and provide evidence that myosin II stacks are important for a variety of vital processes in cells.
  • Sokolova, Maria; Moore, Henna M.; Prajapati, Bina; Dopie, Joseph; Meriläinen, Leena; Honkanen, Mikko; Matos, Rita Cerejeira; Poukkula, Minna; Hietakangas, Ville; Vartiainen, Maria K. (2018)
    Actin has been linked to processes spanning the whole gene expression cascade, from regulating specific transcription factors, such as myocardin-related transcription factor (Mrtf), to chromatin remodelling and RNA polymerase (Pol) function. However, whether actin controls transcription of only specific genes or has a global role in gene expression has remained elusive. Our genome-wide analysis reveals, for the first time, that actin interacts with essentially all transcribed genes in Drosophila ovaries. Actin co-occupies majority of gene promoters together with Pol II, and on highly expressed genes these two proteins also associate with gene bodies. Mechanistically, actin is required for Pol II recruitment to gene bodies and manipulation of nuclear transport factors for actin leads to decreased expression of egg shell genes. Collectively, these results uncover a global role for actin in transcription, and demonstrate the in vivo importance of balanced nucleo-cytoplasmic shuttling of actin in transcriptional control of a developmental process.
  • Kyyrönen, Marika (Helsingfors universitet, 2010)
    Suomalaisen perinnöllisen gelsoliiniamyloidoosin syntymekanismit ovat vielä epäselviä. Tässä tutkimuksessa pyrittiin selvittämään, mitkä muut syyt voisivat johtaa gelsoliiniamyloidoosissa ilmenevien oireiden syntyyn amyloidisäikeiden muodostumisen lisäksi. Potilaasta eristettyjä sileälihassoluja kasvatettiin ja niistä eristettiin proteiinit. Näiden solujen proteiiniekspressiota verrattiin kontrollisileälihassolujen proteiiniekspressioon. Ekspressio erot selvitettiin SDS-PAGE-analyysillä ja Coomassie-värjäyksellä sekä anti-FAF-, alfa-aktiini- ja beeta-aktiini-vasta-ainevärjäyksillä. Proteiinit tunnistettiin massaspektrometrillä. Tässä tutkimuksessa tunnistetut kaikki viisi proteiinia (alfa-aktiini, anneksiini A1, anneksiini A2, anneksiini V ja vimentiini), joiden ekspressiot erosivat gelsoliiniamyloidoosia sairastavan potilaan- ja kontrolli-sileälihassolujen välillä, ovat yhteyksissä solun tukirankaan ja erityisesti aktiinisäikeiden muokkaukseen. Lisäksi solut värjätiin alfa-aktiinivasta-aineella. Aktiinitukiranka oli rikkonainen verrattuna kontrollisolujen aktiinitukirankaan. Tämän tutkimuksen perusteella voidaan siis olettaa gelsoliiniamyloidoosin oireiden johtuvan amyloidin kertymisen lisäksi viallisesta aktiinitukirangan homeostasiasta. Amyloidin muodostuminen on kuitenkin yksi tärkeimmistä oireiden syistä. Koska gelsoliiniamyloidoosiin ei ole vielä olemassa spesifistä hoitoa, olisi sellainen tärkeää löytää. Siksi tässä tutkimuksessa selvitettiin ryhmämme kehittämän amyloidi-inhibiittori kykyä estää amyloidisäikeiden muodostuminen Tioflaviini-T-mittauksilla (ThT). Inhibiittori osoittautui tehokkaaksi amyloidisäikeiden muodostumisen estäjäksi. Amyloidi-inhibiittori voisikin olla tulevaisuudessa lääke gelsoliiniamyloidoosiin.
  • Tolonen, Mari (Helsingin yliopisto, 2019)
    Epithelial cells form a barrier between the tissue and the external environment. Epithelial morphogenesis refers to the shaping of epithelial layers and is a key step in the development of organisms. The actin cytoskeleton provides the cell its form and during epithelial morphogenesis, produces force to shape the cells. To achieve this, the actin cytoskeleton is organized into protrusive and contractile networks. In a living cell, these actin networks are dynamic, as the filaments are constantly undergoing assembly and disassembly. Actin-binding proteins regulate the turnover of actin filaments, but in epithelial morphogenesis, the regulatory role of most of these proteins is still relatively unknown. In all multicellular organisms, actin disassembly is controlled by ADF/cofilin. ADF/cofilin activity is furthermore enhanced by other actin-binding proteins, one of which is cyclase-associated protein (CAP). CAP promotes actin turnover by accelerating ADF/cofilin mediated actin disassembly and in recycling actin monomers to sites of actin polymerization. Unlike ADF/cofilin that regulates actin disassembly throughout the whole cell, CAP could be subject to more specific spatial regulation, as loss of CAP leads to F-actin accumulation on the apical side of epithelial cells. However, the role of CAP in morphogenetic cell rearrangements remains poorly known. In addition, the in vivo role of the biochemical functions of CAP has not been elucidated. The aim of this master’s thesis is to describe the role of CAP in regulating the actin cytoskeleton in the follicular epithelium of the fruit fly Drosophila melanogaster. For this purpose, chimeric mutant flies with homozygous CAP loss of function mutation were generated. Subsequently, the effect of the CAP loss of function was observed in follicle cell populations undergoing morphogenetic changes. In addition, CAP loss of function was rescued with different transgenes producing mutant CAP proteins to identify the protein domains of CAP with in vivo significance. In addition, a Drosophila CAP specific antibody was purified to be used in immunostaining. The ovaries were imaged using confocal microscopy. In this thesis, it is shown that CAP loss of function caused accumulation of filamentous actin in all observed follicular cell populations. Surprisingly, the actin turnover was rescued by all of the used CAP rescue transgenes, but the mutant transgenes exhibited phenotypes resembling the CAP loss of function in other epithelial tissues. Moreover, CAP loss of function caused defects in the follicle cell movement and cell spreading. The loss of function also caused expression changes in other actin-binding proteins. The findings of these thesis support the current knowledge of CAP importance for functional actin turnover in the follicle cells, even though the protein domain necessary for in vivo function could not be deciphered. Moreover, this project provides indication that CAP has an indispensable role in dynamic morphogenetic processes in the epithelium. Together with other actin-binding proteins, CAP could regulate epithelial actin turnover in spatially directed manner, providing force for epithelial cell adhesions or protrusions.