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Cytochalasins are fungal metabolites that have the ability to bind to actin filaments and block polymerization and the elongation of actin. As a result of the inhibition of actin polymerization, cytochalasins can change cellular morphology, inhibit cellular processes such as cell division, and even cause cells to undergo apoptosis (Haidle and Myers, 2004)[1]. Cytochalasins have the ability to permeate cell membranes, prevent cellular translocation and cause cells to enucleate (Cooper, 1987)[2]. Cytochalasins can also have an effect on other aspects on biological processes unrelated to actin polymerization. For example, cytochalasin A and cytochalasin B can also inhibit the transport of monosaccharides across the cell membrane (Cooper, 1987), cytochalasin H has been found to regulate plant growth (Cox et al., 1983)[3], cytochalasin D inhibits protein synthesis (Ornelles et al., 1986)[4] and cytochalasin E prevents angiogenesis (Udagawa et al., 2000)[5].

Contents

Binding to actin filaments

Cytochalasins are known to bind to the barbed, fast growing plus ends of microfilaments, which then blocks both the assembly and disassembly of individual actin monomers from the bound end. Once bound, cytochalasin essentially caps the end of the new actin filament. One cytochalasin will bind to one actin filament (Cooper, 1987). Studies done with Cytochalasin D (CD) have found that the formation of CD-actin dimers, contain ATP bound actin (Goddette and Frieden, 1986)[6]. These CD-actin dimers are reduced to CD-actin monomers as a result of ATP hydrolysis. The resulting CD-actin monomer can bind ATP-actin monomer to reform the CD-actin dimer (Cooper, 1987). CD is very effective; only low concentrations (0.2 μM) are needed to prevent membrane ruffling and disrupt treadmilling (Yahara et al., 1982). Yahara et al. (1982)[7] found that higher concentrations (2-20 μM) of CD were needed to remove stress fibers. Yahara et al. (1982) analyzed the effects of many different cytochalasins had on actin filaments.

Uses and applications of cytochalasins

Actin microfilaments have been widely studied using cytochalasins. Due to their chemical nature, cytochalasins can help researchers understand the importance of actin in various biological processes. The use of cytochalasins has allowed researchers to better understand actin polymerization, cell motility, ruffling, cell division, contraction, and cell stiffness. The use of cytochalasins has been so important to understanding cytoskeletal movement and many other biological processes, researchers have created two synthetic cytochalasins (Haidle and Myers, 2004).[8]

Cytochalasin has found practical application in thromboelastometry (TEM) whole blood assays for the assessment of fibrinogen and fibrin polymerization disorders in the FIBTEM assay on ROTEM. This test is based on the principle that cytochalasin D very effectively inhibits platelet function by inhibition oft the contractile elements.[9] The platelet inhibition is more effective than when platelets are blocked by GPIIb/IIIa antagonists.[10] In vitro and clinical data indicate that the clot strength in FIBTEM increases in a fibrinogen concentration-dependent manner independent of platelet count.[11] Therefore fibrinogen deficiency or fibrin polymerization disorders can be rapidly detected.

References

  1. ^ Haidle, Andrew and Myers, Andrew (2004). An enantioselective, modular, and general route to the cytochalasins: Synthesis of L-696,474 and cytochalasin B. Proc. Natl. Acad. Sci. USA 101, 12048-12053.
  2. ^ Cooper, John A. (1987). Effects of Cytochalasin and Phalloidin on Actin. J. Cell Biol. 105, 1473-1478.
  3. ^ Cox, R. H., Cutler, H. G., Hurd, R. E. & Cole, R. J. (1983) J. Agric. Food Chem. 31, 405–408.
  4. ^ Ornelles et al. (1986) Cytochalasin releases mRNA from the cytoskeletal framework and inhibits protein synthesis. Mol. Cell Biol. 6, 1650-1662.
  5. ^ Udagawa, T., Yuan, J., Panigrahy, D., Chang, Y.-H., Shah, J. & D’Amato, R. J. (2000) J. Pharmacol. Exp. Ther. 294, 421–427.
  6. ^ Goddette and Frieden (1987) Actin polymerization: the mechanism of action of cytochalasin D. J. Biol. Chem. 261, 15974-15980.
  7. ^ Yahara et al. (1982). Correlation between Effects of 24 Different Cytochalasins on Cellular Structures and Cellular Events and Those on Actin In Vitro. J. Cell Biol. 92, 69-78.
  8. ^ Natural Product Synthesis Special Feature: An enantioselective, modular, and general route to the cytochalasins: Synthesis of L-696,474 and cytochalasin B - Haidle and Myers 101 (33): 12048 - Proceedings of the National Academy of Sciences
  9. ^ May JA, Ratan H, Glenn JR, Lösche W, Spangenberg P, Heptinstall S. GPIIb-IIa antagonists cause rapid disaggregation of platelets pretreated with cytochalasin D. Evidence that the stability of platelet aggregates depends on normal cytoskeletal assembly. Platelets.1998;9:227-32.
  10. ^ Lang T, Toller W, Gütl M, Mahla E, Metzler H, Rehak P, März W, Halwachs-Baumann G. Different effects of abciximab and cytochalasin D on clot strength in thrombelastography. J Thromb Haemost 2004;2:147-53.
  11. ^ Lang T, Johanning K, Metzler H, Piepenbrock S, Solomon C, Rahe-Meyer N, Tanaka KA. The effects of fibrinogen levels on thromboelastometric variables in the presence of thrombocytopenia. Anesth Analg 2009;108:751-8.

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