CONCOMITANT DECREASE OF RESISTANCE AND MODIFICATIONS OF THE CYTOSKELETON AFTER ALL-TRANS-RETINOIC ACID AND PHORBOL ESTER TREATMENTS IN A NAVELBINE-RESISTANT BLADDER-CARCINOMA CELL-LINE

The bladder carcinoma cell line J82-NVB was selected for resistance to the new vinca alkaloid Navelbine. These cells possessed a non-MDR phe notype and were cross-resistant to vinca alkaloids and taxoids. Some m orphological differences between sensitive (J82) and resistant (J82-NV B) cells were observed. J82 cells had a heterogeneous population morph ology with both epithelial and spindle shaped cells, while J82-NVB cel ls were almost all of the epithelial type. Vimentin intermediate filam ents were less organized in J82-NVB than in J82 cells. Moreover, desmo somes were present in the membranes of J82-NVB cells but not in J82 ce lls. These findings suggest that J82 cells are poorly differentiated e pithelial cells while J82-NVB cells possess some characteristics of a more differentiated epithelial cell line. After a two-week treatment w ith all-trans retinoic acid, all the cells became spindle shaped, vime ntin filaments reappeared in the cytoplasm of J82-NVB cells and desmos omes disappeared from the membranes of these cells. These changes were accompanied by a decrease from 17 to 4.6 of the resistance factor of J82-NVB cells to Navelbine. This decrease in resistance was concomitan t with modifications of microtubules assembly regulation mechanisms. A fter Navelbine treatment, microtubule reassembly, occurred in resistan t but not in sensitive nor in retinoic acid treated cells. Okadaic aci d, a protein phosphatase inhibitor; inhibited microtubule reassembly i n resistant cells, and 2-aminopurine, a protein kinase inhibitor, indu ced microtubule reassembly in sensitive cells after Navelbine treatmen t. These findings show that microtubule reassembly after depolymerizat ion is regulated by the kinase/phosphatase systems. A treatment with p horbol myristate acetate (PMA), a protein kinase C (PKC) agonist, indu ced the same morphological modifications and resistance decrease as re tinoic acid treatment. A specific PKC inhibitor (Bisindolylmaleimide) prevented these PMA-induced morphological modifications and resistance decrease in J82-NVB cells, showing that these effects were mediated b y PKC. This study suggests that in part by acting on some properties o f the cytoskeleton, the differentiation modulator, retinoic acid, and the signal transduction modulator, phorbol myristate acetate, can decr ease the resistance of J82-NVB cells to microtubule poisons.