Microtubular and cytoskeletal networks have been implicated in a variety of cellular functions including secretion, axoplasmic transport, cell shape, motility, and mitosis. In addition, drugs such as vinblastine and vincristine that interact with tubulin and microtubule (MT) systems, are effective antimitotic agents and have been employed as chemotherapeutic agents to treat several forms of cancer in man. Thus, understanding the factors that regulate MT and cytoskeletal elements will provide important insights into cellular regulation and potentially result in the development of more effective methods for treating human disease. Calcium ions play a major role in regulating the polymerization of microtubules and their relationship to the cytoskeleton. In addition, the calcium binding protein, calmodulin, has been shown to mediate some of the effects of calcium on tubulin dynamics. While calcium plays an important role in this system, little is known concerning the molecular mechanism mediating the effects of calcium on MT function. Our laboratory has identified and characterized a calcium-calmodulin protein kinase in membrane and cytosolic fractions of brain tissue that phosphorylates tubulin and microtubule associated proteins (MAPs) as major substrates. This calmodulin kinase is distinct from the previously described cyclic AMP magnesium kinases associated with MT. Preliminary results indicate that this kinase is associated with tubulin in the form of a complex, suggesting that the tubulin associated calmodulin kinase (TACK) may represent a biochemical system that mediates some of the effects of calcium on MT dynamics. Experiments in this proposal are directed at purifying and completely characterizing TACK and determining in in vitro and in vivo systems if TACK plays a role in mediating the effects of calcium on MT. The tau proteins represent a major group of MT associated proteins that have been shown to bind calmodulin. Preliminary work in this laboratory has demonstrated that the major calmodulin binding protein in the tau complex is homologous with the major calmodulin binding subunit of TACK. Experiments will be conducted to determine if the tau proteins represent a MT associated calmodulin kinase system that is structurally and functionally equivalent to TACK. The effects on TACK of several compounds, including chemotherapeutic agents, that regulate MT function will be determined. The proposed studies may provide an insight into the molecular basis for the regulation of MT dynamics by calcium, and provide a functional identity to the tau proteins.
| Taft, W C; Tennes-Rees, K A; Blair, R E et al. (1988) Cerebral ischemia decreases endogenous calcium-dependent protein phosphorylation in gerbil brain. Brain Res 447:159-63 |
