ASSOCIATION OF MITOGEN-ACTIVATED PROTEIN-KINASE WITH THE MICROTUBULE CYTOSKELETON

Using indirect immunofluorescence microscopy and biochemical technique s, we have determined that approximately one-third of the total mitoge n-activated protein kinase (MAPK) is associated with the microtubule c ytoskeleton in NIH 3T3 mouse fibroblasts. This population of enzyme ca n be separated from the soluble form that is found distributed through out the cytosol and is also present in the nucleus after mitogen stimu lation. The microtubule-associated enzyme pool constitutes half of all detectable MARK activity after mitogenic stimulation. These findings extend the known in vivo associations of MAPK with microtubules to inc lude the entire microtubule cytoskeleton of proliferating cells, and t hey suggest that a direct association of MARK with microtubules may be in part responsible for the observed correlations between MARK activi ties and cytoskeletal alteration.