Accompanying protein alterations in malignant cells with a microtubule-polymerizing drug-resistance phenotype and a primary resistance mechanism

Biochem Pharmacol. 2001 Dec 1;62(11):1469-80. doi: 10.1016/s0006-2952(01)00804-8.


Microtubules (MTs) are cytoskeletal components whose structural integrity is mandatory for the execution of many basic cell functions. Utilizing parental and drug-resistant ovarian carcinoma cell lines that have acquired point mutations in beta-tubulin and p53, we studied the level of expression and modification of proteins involved in apoptosis and MT integrity. Extending previous results, we demonstrated phosphorylation of pro-survival Bcl-x(L) in an epothilone-A resistant cell line, correlating it with drug sensitivity to tubulin-active compounds. Furthermore, Mcl-1 protein turned over more rapidly following exposure to tubulin-modifying agents, the stability of Mcl-1 protein paralleling the drug sensitivity profile of the paclitaxel or epothilone-A resistant cell lines. The observed decreases in Mcl-1 were not a consequence of G(2)M arrest, as determined by flow cytometry analysis, which showed prominent levels of Mcl-1 in the absence of any drug treatment in populations enriched in mitotic cells. We also observed that a paclitaxel-resistant cell line expressed Bax at a much lower level than the sensitive parental line [A2780(1A9)], consistent with its mutant p53 status. MT-associated protein-4 (MAP4), whose phosphorylation during specific phases of the cell cycle reduces its MT-polymerizing and -stabilizing capabilities, was phosphorylated in response to drug challenge without a change in expression. Phosphorylation of MAP4 correlated with sensitivity to tubulin-binding drugs and with a dissociation from MTs. We propose that the tubulin mutations, which result in a compromised paclitaxel:tubulin or epothilone:tubulin interaction and paclitaxel or epothilone resistance, indirectly inhibit downstream events that lead to cell death, and this, in turn, may contribute to the drug-resistance phenotype

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology
  • Drug Resistance, Neoplasm / genetics*
  • Female
  • Fluorescent Antibody Technique
  • Humans
  • Microtubule-Associated Proteins / metabolism
  • Microtubules
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins / metabolism*
  • Ovarian Neoplasms / pathology
  • Paclitaxel / pharmacology*
  • Phenotype
  • Phosphorylation
  • Protein Processing, Post-Translational / drug effects
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • Tubulin / drug effects
  • Tubulin / metabolism
  • Tumor Cells, Cultured
  • Vinblastine / pharmacology
  • bcl-2-Associated X Protein
  • bcl-X Protein


  • Antineoplastic Agents, Phytogenic
  • BAX protein, human
  • BCL2L1 protein, human
  • MAP4
  • Microtubule-Associated Proteins
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Tubulin
  • bcl-2-Associated X Protein
  • bcl-X Protein
  • Vinblastine
  • Paclitaxel