Cleavage of Bax-alpha and Bcl-x(L) during carboplatin-mediated apoptosis in squamous cell carcinoma cell line

Oral Oncol. 2000 May;36(3):277-85. doi: 10.1016/s1368-8375(00)00010-5.


Although carboplatin (CBDCA) has been used for the treatment of several types of tumors, the complete response rate has been limited, probably because of inherent or CBDCA-induced resistance. As a first step to overcome these problems, we tried to elucidate the mechanisms of CBDCA-mediated cytotoxicity in the squamous cell carcinoma cell line MIT7. The treatment of cells with CBDCA resulted in apoptosis in a dose-dependent manner, as assessed by the propidium iodide staining method and DNA degradation in a nucleosomal pattern. The induction of apoptosis was accompanied by the decline of mitochondrial membrane potential (Deltapsi(m) ) at 12 h following CBDCA stimulation. Variant forms of p18 Bax-alpha and p16 Bcl-x(L) were generated with the down-regulation of both Bax-alpha (p21) and Bcl-x(L) (p31) at 36 and 48 h following CBDCA stimulation, suggesting that the modulation of Bcl-2 family proteins Bax-alpha and Bcl-x(L) play some role in CBDCA-mediated apoptosis. The activation of caspase-3 and -8 occurred at 12 and 24 h following the stimulation, respectively. The pretreatment of cells with pan-caspase inhibitor Z-VAD-fmk markedly prevented CBDCA-mediated cytotoxicity/apoptosis and the modulation of Bcl-2 family proteins (generation of p18 Bax-alpha and p16 Bcl-x(L) ) with only slight prevention of decline of Deltapsi(m). Taken together, these results may suggest that activation of several caspases, including caspase-3 and -8, plays some role in CBDCA-mediated apoptosis, probably through the modification of Bcl-2 family proteins, Bax-alpha and Bcl-x(L). Moreover, caspase activation may occur downstream of membrane depolarization.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / pharmacology*
  • Apoptosis / drug effects*
  • Carboplatin / pharmacology*
  • Carcinoma, Squamous Cell / drug therapy*
  • Carcinoma, Squamous Cell / enzymology
  • Carcinoma, Squamous Cell / metabolism
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases / metabolism
  • Dose-Response Relationship, Drug
  • Drug Resistance, Neoplasm / genetics
  • Enzyme Activation
  • Gene Expression Regulation, Neoplastic / drug effects*
  • Humans
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins c-bcl-2 / genetics*
  • Tumor Cells, Cultured / drug effects
  • bcl-2-Associated X Protein
  • bcl-X Protein


  • Antineoplastic Agents
  • BAX protein, human
  • BCL2L1 protein, human
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • bcl-2-Associated X Protein
  • bcl-X Protein
  • Carboplatin
  • CASP3 protein, human
  • CASP8 protein, human
  • CASP9 protein, human
  • Caspase 3
  • Caspase 8
  • Caspase 9
  • Caspases