Microtubule-dependent multilobular organization of the nucleus in sensitive and multidrug-resistant L0 leukemia cells

The relationship between the nuclear morphology and the microtubular organization of L100 and L1000 cells, two vincristine-induced multidrug resistant human acute lymphocytic leukemia cell lines, was examined and compared to that of L0 parental cells. The L0 parental cells contained a round nucleus and the microtubules were evenly distributed throughout the cytoplasm. In contrast, the microtubules of the L100 and L1000 cells were localized between the lobular structures of a multi-lobulated nucleus. Disassembly of microtubules in L100 and L100 cells by colchicine resulted in the loss of the multilobulated morphology of the nucleus. While the total cellular content of tubulin of L0 and L100 cells was similar, the content of microtubules of L100 cells was only 55% of that observed in L0 cells. Two, 28 kDa (pI 6.9) and 31 kDa (pI 4.4), microtubule associated proteins were found to be overexpressed in L100 and L1000 cells. The results indicate that the multilobulated nuclear morphology of L100 and L1000 cells is dependent upon the unique and intact organization of the microtubules; the distinct organization of the microtubules and the multilobular nuclear morphology of the two resistant cell lines may be due to the differential expression of specific microtubule-associated proteins.