Overexpression of p21waf1 Decreases G2-M Arrest and Apoptosis Induced by Paclitaxel in Human Sarcoma Cells Lacking Both p53 and Functional Rb Protein

  1. WeiWei Li,
  2. Jianguo Fan,
  3. Debabrata Banerjee and
  4. Joseph R. Bertino
  1. Laboratory of Molecular Pharmacology, Sloan-Kettering Institute, Memorial Sloan-Kettering Cancer Center, New York, New York

    Abstract

    We examined the effect of overexpression of p21waf1 on cytotoxicity of paclitaxel, a microtubule stabilizer, using a tetracycline-inducible expression system in human sarcoma cells (SaOs-2) that lack both functional retinoblastoma protein and p53. Under normal growth conditions, p21waf1 is not detectable in SaOs-2 cells. Upon p21waf1 induction by tetracycline withdrawal, we observed a reduced apoptotic response to paclitaxel with a 3- to 6-fold increase in IC50 values compared with that of cells not induced by p21waf1. We also observed a 5-fold increase in the IC50 value when cytotoxicity to vincristine, another microtubule-disrupting agent, was assessed, whereas we observed a marked decrease in the IC50 value after p21waf1 induction in response to etoposide, a topoisomerase II inhibitor. After treatment with paclitaxel, less accumulation of G2-M was observed in p21waf1-induced cells compared with non-p21waf1-induced cells (57% versus 74%). p21waf1 induction also inhibited the increased cyclin B1-associated kinase activity induced by paclitaxel. Overexpression of p21waf1 in SaOs-2 cells lacking both p53 and functional retinoblastoma protein may decrease the G2-M arrest induced by paclitaxel due to suppression of the S-G2 checkpoint, resulting in a decreased apoptotic response of cells to paclitaxel.

    Footnotes

    • Send reprint requests to: Dr. Joseph R. Bertino, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, New York 10021. E-mail: bertinoj{at}mskcc.org

    • This work was supported by United States Public Health Service Grant PO1-CA47179. J.R.B. is an American Cancer Society Professor of Medicine and Pharmacology.

    • Abbreviations:
      CDK
      cyclin-dependent kinase
      pRb
      retinoblastoma protein
      VP-16
      etoposide
      VCR
      vincristine
      CDDP
      cisplatin [cis-dichlorodiammineplatinum(II)]
      TC
      tetracycline
      SRB
      sulforhodamine B
      FACS
      fluorescence-activated cell sorter
      PAGE
      polyacrylamide gel electrophoresis
      • Received January 15, 1999.
      • Accepted March 15, 1999.
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    1. Molecular Pharmacology June 1, 1999 vol. 55 no. 6 1088-1093
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