MICROTUBULE-DEPENDENT CONTROL OF CELL-SHAPE AND PSEUDOPODIAL ACTIVITYIS INHIBITED BY THE ANTIBODY TO KINESIN MOTOR DOMAIN

One of the major functions of cytoplasmic microtubules is their involv ement in maintenance of asymmetric cell shape. Microtubules were consi dered to perform this function working as rigid structural elements. A t the same time, microtubules play a critical role in intracellular or ganelle transport, and this fact raises the possibility that the invol vement of microtubules in maintenance of cell shape may be mediated by directed transport of certain cellular components to a limited area o f the cell surface (e.g., to the leading edge) rather than by their fu nctioning as a mechanical support. To test this hypothesis we microinj ected cultured human fibroblasts with the antibody (called HD antibody ) raised against kinesin motor domain highly conserved among the diffe rent members of kinesin superfamily. As was shown before, this antibod y inhibits kinesin-dependent microtubule gliding in vitro and interfer es with a number of microtubule-dependent transport processes in livin g cells. Preimmune IgG fraction was used for control experiments. Inje ctions of fibroblasts with HD antibody but not with preimmune IgG sign ificantly reduced their asymmetry, resulting in loss of long processes and elongated cell shape. In addition, antibody injection suppressed pseudopodial activity at the leading edge of fibroblasts moving into a n experimentally made wound. Analysis of membrane organelle distributi on showed that kinesin antibody induced clustering of mitochondria in perinuclear region and their withdrawal from peripheral parts of the c ytoplasm. HD antibody does not affect either density or distribution o f cytoplasmic microtubules. The results of our experiments show that m any changes of phenotype induced in cells by microtubule-depolymerizin g agents can be mimicked by the inhibition of motor proteins, and ther efore microtubule functions in maintaining of the cell shape and polar ity are mediated by motor proteins rather than by being provided by ri gidity of tubulin polymer itself.