Dynamics and functions of microtubules during myogenic differentiation and cell cycle progression
The common theme of our lab’s research is the function of microtubules in directed cell motility. Mostmicrotubules in proliferating cells are highly dynamic, that is, assembly of microtubulesfrom tubulin subunits and disassembly of microtubule polymers into subunits, occurs within a matter of minutes. However, differentiating and migrating cells in culture or within vertebrate organisms selectively stabilize a subset of microtubules.For example, migratingfibroblasts use the polarization of stabilized microtubules as a determinants of persistent motility in that direction.
Meanwhile, since several cytoplasmic enzymes are capable of post-translationally modifying the tubulin subunits found within microtubule polymers. These post-translational modifications confer one or more chemical marks along the length of microtubules in the stable subpopulation. The selective stabilization of microtubules that face the leading edge of migrating fibroblasts has been studied rather extensively; our work has endeavored to elucidate the functional consequences of their post-translational modification by acetylation. We have exploited motile fibroblasts in which the acetylation modification can be augmented by means of genetic or chemical inhibitors of the tubulin deacetylation enzyme, HDAC6, which is a member of the histone deacetylase family.Fibroblasts with hyper-acetylated microtubules are reduced in their motility; this occurs because the cells are prevented from polarizing their contents and are inhibited in the de-adhesion they need to allow cell translocation as well as in the bi-directional transport of Golgi vesicles that permits efficient extension of the leading edge membrane of the motile cell.
Sparked by thedemonstration that connexins contribute to cell polarization and interact with microtubules in the process, our lab also recently begun studies of gap junctions, which mediate cell-to-cell communication. These studies are nicely pertinent to our ongoing studies of the mechanisms by which direct current electric fields and other physical forces induce directional motility. As a part of our studies of gap junctional proteins, we discovered that the subunit proteins of gap junctions, called connexins, are also subject to post-translational acetylation. We are currently investigating the role of acetylation in gap junction assembly, trafficking, and disassembly.
Studies of acetylated proteins and their functions in motile cells are especially relevant to human health, as histone deacetylase inhibitors are now in use as clinical therapies to combat human cancers and inflammatory diseases. These inhibitors cause hyper-acetylation of microtubules, as well as other cytoplasmic proteins, including connexins, in addition to the histones and chromatin-associated proteins for which they were developed. Further, histone deacetylase inhibitors often cause dose-limiting thrombocytopenia, arguing for an exploration of the role of acetylated microtubules in platelet development and function. Thus, our studies on the sequelae of the hyper-acetylation of cytoplasmic proteins may inform the clinical use of histone deacetylase inhibitors, including an understanding of both desirable and undesirable off-target effects. The ability of microtubule hyper-acetylation to reduce cell migration may help in the development of metastasis inhibitors, especially for sarcomas, which develop from fibroblasts and other mesodermal cells.
- Finkelstein, E.I., Chao, P.H., Hung, C.T., and Bulinski, J.C. (2007) Electric field-induced polarization of charged cell surface proteins does not determine the direction of galvanotaxis. Cell Motil Cytoskeleton 64: 833-846. Article
- Patel-Hett, S., Richardson, J.L., Schulze, H., Drabek, K., Isaac, N.A., Hoffmeister, K., Shivdasani, R.A., Bulinski, J.C., Galjart, N., Hartwig, J.H., and Italiano, J.E., Jr. (2008) Visualization of microtubule growth in living platelets reveals a dynamic marginal band with multiple microtubules. Blood 111: 4605-4616. Article
- Soucek, K., Kamaid, A., Phung, A.D., Kubala, L., Bulinski, J.C., Harper, R.W., and Eiserich, J.P. (2006) Normal and prostate cancer cells display distinct molecular profiles of alpha-tubulin posttranslational modifications. Prostate 66: 954-965. Article
- Tran, A.D., Marmo, T.P., Salam, A.A., Che, S., Finkelstein, E., Kabarriti, R., Xenias, H.S., Mazitschek, R., Hubbert, C., Kawaguchi, Y., Sheetz, M.P., Yao, T.P., and Bulinski, J.C. (2007) HDAC6 deacetylation of tubulin modulates dynamics of cellular adhesions. J Cell Sci 120: 1469-1479. Article