Dihydrocytochalasin B (H2CB) does not inhibit sugar uptake in BALB/c 3T3 cells. Excess H2CB does not affect inhibition of sugar uptake by cytochalasin B (CB), indicating that it does not compete with CB for binding to high-affinity sites. As in the case of CB, H2CB inhibits cytokinesis and changes the morphology of the cells. These results demonstrate that the effects of CB on sugar transport and on cell motility and morphology involve separate and independent sites. Comparison of the effects of H2CB, CB, and cytochalasin D (CD) indicates that treatment of cells with any one of the compounds results in the same series of morphological changes; the cells undergo zeiosis and elongation at 2-4 microM CB and become arborized and rounded up at 10-50 microM CB. H2CB is slightly less potent than CB, whereas CD is five to eight times more potent than CB in causing a given state of morphological change. These results indicate that the cytochalasin-induced changes in cell morphology are mediated by a specific site(s) which can distinguish the subtle differences in the structures of the three compounds. Competitive binding studies indicate that excess H2CB displaces essentially all of the high-affinity bound [3H]CB, but, at less than 5 x 10(-5) M H2CB is not so efficient as unlabeled CB in the displacement reaction. In contrast, excess CD displaces up to 40% of the bound [3H]CB. These results suggest that three different classes of high-affinity CB binding sites exist in 3T3 cells: sites related to sugar transport, sites related to cell motility and morphology, and sites with undetermined function.

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