INHIBITION OF INSULIN-STIMULATED GLUCOSE-TRANSPORT IN 3T3-L1 CELLS BYCLOSTRIDIUM-DIFFICILE TOXIN-B, CLOSTRIDIUM-SORDELLII LETHAL TOXIN, AND CLOSTRIDIUM-BOTULINUM C2 TOXIN

The role of the actin cytoskeleton and/or GTPases of the Rho/Rac-famil y in glucose transport regulation was investigated in 3T3-L1 cells wit h clostridial toxins which depolymerize actin by inactivation of Rho/R ac (Clostridium difficile toxin B and Clostridium sordellii lethal tox in (LT)) or by direct ADP-ribosylation (Clostridium botulinum C2 toxin ). Toxin B and C2 reduced insulin-stimulated, but not basal, 2-deoxygl ucose (2-DOG) uptake rates in 3T3-L1 fibroblasts. In parallel, the tox ins produced morphological alterations of the cells reflecting disrupt ion of the actin cytoskeleton. Both toxins reduced the maximum respons e to insulin but failed to alter the half-maximally stimulating concen trations of insulin. In 3T3-L1 adipocytes, the lethal toxin reduced th e effect of insulin on 2-DOG uptake, whereas toxin B and C2 failed to affect glucose transport or cell morphology. When cells were exposed t o the toxins after treatment with insulin, both toxin B and the lethal toxin, in contrast to the phosphatidylinositol (PI) 3-kinase inhibito r wortmannin, failed to reduce the 2-DOG uptake rates. Thus, both tran slocation to the plasma membrane and internalization of glucose transp orters were inhibited by the toxins, whereas the PI 3-kinase inhibitor selectively affects translocation. The data suggest that the effects of the clostridial toxins on trafficking of glucose transporters are m ediated by the depolymerization of the actin cytoskeleton and are an i ndirect consequence of Rho or Rac inactivation. It is suggested that p athways signalling through Pac or Rho may play a modulatory role in gl ucose transport regulation through their effects on the actin network.