Noxa/Mcl-1 balance regulates susceptibility of cells to camptothecin-induced apoptosis

Neoplasia. 2007 Oct;9(10):871-81. doi: 10.1593/neo.07589.


Although camptothecin (CPT) has been reported to induce apoptosis in various cancer cells, the molecular details of this regulation remain largely unknown. In this study, we demonstrate that BH3-only protein Noxa is upregulated during CPT-induced apoptosis, which is independent of p53. In addition, we show that phosphatidylinositol 3-kinase (PI3K)/Akt signaling pathway is responsible for Noxa's induction. Luciferase assay and cAMP response element binding protein (CREB) knockdown experiments further demonstrate that CREB is involved in the transcriptional upregulation of Noxa. Moreover, blocking Noxa expression using specific small interfering ribonucleic acid (siRNA) significantly reduces the apoptosis in response to CPT, indicating that Noxa is an essential mediator for CPT-induced apoptosis. Interestingly, antiapoptotic Mcl-1 was also upregulated through PI3K/Akt signaling pathway upon CPT treatment. Using immunoprecipitation assay, Noxa was found to interact with Mcl-1 in the presence or absence of CPT. Knockdown of Mcl-1 expression by short hairpin ribonucleic acid (shRNA) was shown to potentiate CPT-induced apoptosis. Consistently, ectopic overexpression of Mcl-1 rescued cells from apoptosis induced by CPT. Cells coexpressing Noxa and Mcl-1 at different ratio correlates well with the extent of apoptosis, suggesting that the balance between Noxa and Mcl-1 may determine the susceptibility of HeLa cells to CPT-induced apoptosis.

Keywords: CREB; Mcl-1; Noxa; apoptosis; camptothecin.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents, Phytogenic / pharmacology*
  • Apoptosis / drug effects*
  • Apoptosis / physiology
  • Blotting, Western
  • CREB-Binding Protein / drug effects
  • CREB-Binding Protein / metabolism
  • Camptothecin / pharmacology*
  • Drug Resistance, Neoplasm / genetics*
  • Gene Expression / drug effects
  • HeLa Cells
  • Humans
  • Immunoprecipitation
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins / metabolism*
  • Phosphatidylinositol 3-Kinases / drug effects
  • Phosphatidylinositol 3-Kinases / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism*
  • RNA, Small Interfering
  • Reverse Transcriptase Polymerase Chain Reaction
  • Signal Transduction / drug effects
  • Up-Regulation


  • Antineoplastic Agents, Phytogenic
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Neoplasm Proteins
  • PMAIP1 protein, human
  • Proto-Oncogene Proteins c-bcl-2
  • RNA, Small Interfering
  • CREB-Binding Protein
  • Phosphatidylinositol 3-Kinases
  • Camptothecin