European Review for Medical and Pharmacological Sciences 2009; 13: 13-21 Cytoskeleton structure and dynamic behaviour: quick excursus from basic molecular mechanisms to some implications in cancer chemotherapy C. ALBERTI L.D. of Surgical Semeiotics, University of Parma (Italy) Abstract. – Novel nanoscale microscopic duced tumor cell implantation within surgical technologies are driving dramatic advances in wounds may be prevented by perioperative ad- the knowledge of cytoskeleton structure and dy- ministration of microtubule/actin inhibitors. namics. Cytoskeleton, that is organized into mi- Even though, among the different cancer thera- crotubules, actin meshwork and intermediate fil- py strategies, the chemotherapy could appear to aments, besides providing cells with important be conceptually outclassed because of its low mechanical properties, allows, within the cell, cancer cell-selectivity in comparison with novel not only the molecule cargo transport, but also molecular mechanism-based agents. However the charged particle/biophoton transmission, so "combo-strategies", that combine the chemo- that the cell signaling might be considered as therapeutic high killing potential with new mole- consisting of both molecule/chemically- and cule targeted agents, may be an effective cura- charged particle/physically-addressed systems. tive measure. Some anticytoskeleton agents are Molecular motors that drive molecule cargo under evaluation for their applications in tumor translocation along the cytoskeletal highway, ei- chemotherapy; benomyl, griseofulvin, sulfon- ther through endocytic or secretory-exocytic amides, that are used as antimycotic and antimi- mechanisms, include kinesin and cytoplasmic crobial drugs, appear to have a powerful antitu- dynein, traveling on microtubule, and myosin mor potential by targeting microtubule assembly family members, traveling along actin mesh- dinamics, together with exhibiting, in compari- work. The membrane-bound organelles and pro- son with taxane and Vinca alkaloids, a more lim- tein complexes are sorted with high specificity ited toxicity. An exciting challenge for the next to their various destinations. In the field of high- future will be to properly define the cytoskeleton ly structured cell signaling machinery, the endo- structure and dynamic behaviour to design more cytosis appears to play an important role with effective drugs for cancer chemotherapy. following specific changes in gene expression. In the opposite direction, the exocytosis in- Key Words: volves many intracellular steps toward the vesi- Cytoskeleton, Intracellular signal trafficomics, Cy- cle fusion with the plasma membrane. Insights toskeleton inhibitors, Chemotherapy, Prostate cancer. into cytoskeletal structure and dynamics are providing important progress in identifying proper targets for cancer therapy. Taxane and Vinca alkaloids, by stabilizing the polymerized microtubules, are able to suppress their dynam- ic behaviour with subsequent cell death. Epith- elones, by acting in same way, are emerging as a Introduction new class of anticancer drugs, moreover their toxicity resulting unaffected also towards tax- Recent developments of microscopic tech- ane-resistant cancer cells. Even the alkylating nologies (atomic force microscopy, confocal agent nitrogen mustard exerts some cytotoxic laser-scanning microscopy, fluorescence reso- effects at the level of the microtubule, whereas nance energy transfer microscopy, small angle azaspiracid-1 induces cytoskeletal actin disorga- nization without affecting microtubule architec- X-ray diffraction microscopy, etc), that are able ture. Regarding the influences of extracellular to explore cytoskeletal structure and dynamics at mechanical forces on changes in cell adhesion nanometer scale, have induced tremendous gene expression, the iatrogenic pressure-in- progress in understanding single-molecular Corresponding Author: Contardo Alberti, MD; mobile: +39.331.9823032 13 C. Alberti events which promote the cytoskeleton dynamic actin meshwork (Figure 1). From here, in the re- behaviour, thus also providing idea-of-principle verse direction, microtubules, with their minus that targeting the microtubule/actin elements ends, converge on their organizing center1-4. may be a fruitful chance for an effective cancer Cortical actin meshwork is composed of actin therapy. plus end filaments that are oriented toward the plasma membrane and, in the opposite direction, Cytoskeleton Structure and Dynamics of actin minus end filaments reaching to intersect Three different cytoskeletal structures – micro- with microtubule cytoskeleton4,5. tubules, actin meshwork and intermediate fila- Intermediate filaments assemble into exten- ments – besides providing cells with proper me- sive cytoskeletal nanofibrillar complex which is chanical forces, contribute to ensure intracellular able to connect both cell surface/desmosomes signaling efficiency and specificity. and membranous organelles with the nuclear Microtubules are composed of several individ- surface and nucleoplasm, together with provid- ual polarized protofilaments consisting of α/β ing cells with important elasto-mechanical prop- tubulin dimers, whose addition or loss can induce erties. In fact, intermediate filaments are very growing or shortening of their ends. This dynam- flexible polymers (vimentin, desmin, keratin- ic behaviour – microtubule dynamic instability – epiplakin) that, on the one hand, act as tracks for is important for mediating the movements of car- the transduction of mechanical perturbation (me- go-carrying motors to reach their final destina- chanical stress) from the cell periphery to the tion at intracellular specific sites as well as for nucleus and, on the other hand, interact with promoting the alignment of sister chromatids, membranous organelles, such as Golgi appara- through tension at the kinetochores, on the mitot- tus, lysosomes, mitochondria and vesicles, as ic spindle during metaphase, and, subsequently, well as with other cytoskeleton components such during anaphase, their segregation into the as microtubules, actin meshwork and their asso- nascent daughter cells. Micro-tubules originate ciate motor proteins, thus playing important key from an organizing center (MTOC) near the nu- roles in organizing organelles in the cytoplasm, cleus, faning out, with their plus ends, toward the providing them with proper motility and anchor- cell cortex, where they intersect with cortical age sites1,6-8. A A M km A dm M M A M mtoc M Figure 1. Cartoon illustration of cell cortex N actin filaments (A)/cell interior microtubules (M) together with their plus-end(+)minus-end(-) and kinesin (km)/cytoplasmic dynein (dm) mi- A crotubule-based motors. Cell nucleus (N), micro- tubule-organizing center (mtoc). 14 Cytoskeleton targeted chemotherapy Molecular Cargo Transport and Delivery proteins are exported. This process requires spe- Intracellular cargo transport – transport of or- cific endoplasmic reticulum-derived vesicles and ganelles, secretory vesicles and protein complex- proper cytoskeletal structures for various cargo es – needs specific microtubule- and actin-based proteins sorted from endoplasmic reticulum14-19. molecular motors together with polarized micro- The Golgi apparatus activity is directed, on the tubule/actin rail-tracks along which the cargoes one hand, to post-translationally modify both go on. Molecular motors that drive cargo translo- protein and lipid cargoes, by modulating, cation along the cytoskeleton highway include through a glycosilation process, their stability kinesin and cytoplasmic dynein, traveling on mi- and function, and, on the other hand, to send crotubule, and myosin, traveling along actin them to the plasma membrane or toward other meshwork, both of them managing the transit cell compartments20-24. manoeuvres through a complex cytoskeletal net- In the field of highly structured cell signal work8-11. Cargoes carried by kinesin motors are transmission machinery, that is able to translate transferred to the plus ends of microtubules, that cell responses to external agents into specific are oriented toward the cell cortex and, subse- changes in gene expression, the endocytosis – quently, upon reaching the peripheral actin mesh- endocytic organelle-mediated process – appears work, they are translocated, by myosin Va motor, to play an active role in signal amplification, to the plus ends of F-actin filaments toward the propagation and spatial-temporal transduction plasma membrane. In the opposite direction (e.g., control. By the way, some downstream signal in endocytosis process), cargoes are transported cascades are carried-out by receptor-ligand com- by myosin Vl motors, that walk toward the minus plex internalization and endosome specific com- ends of F-actin filaments, into the cell interior, partmentalization, the molecular signal traffick- and, subsequently, upon reaching actin-micro- ing among various endocytic organelles requir- tubule intersections, they are transferred, by cyto- ing, anyhow, a suitable actin/microtubule-depen- plasmic dynein motors, toward the minus ends of dent motility25-27. microtubules, which are located, near the cell nu- In the opposite direction, the exocytosis is me- cleus, in the MTOC11,12. diated by exosomes, that are endosomal-derived All motor proteins – kinesin, cytoplasmic membrane vesicles shipping extracellular mole- dynein and myosin – are able to hydrolyze ATP, cule-messages. Exocytic process involves multi- adenosine triphosphate, to ADP, hence