Apoptosis

, Volume 18, Issue 10, pp 1163–1174

Gamma-secretase inhibition attenuates oxaliplatin-induced apoptosis through increased Mcl-1 and/or Bcl-xL in human colon cancer cells

Authors

  • Cindy R. Timme
    • Department of Experimental TherapeuticsMoffitt Cancer Center
    • Cancer Biology Ph.D. Program, Department of Oncologic SciencesUniversity of South Florida
  • Mike Gruidl
    • Department of Experimental TherapeuticsMoffitt Cancer Center
    • Gibbs Cancer Center
Original Paper

DOI: 10.1007/s10495-013-0883-x

Cite this article as:
Timme, C.R., Gruidl, M. & Yeatman, T.J. Apoptosis (2013) 18: 1163. doi:10.1007/s10495-013-0883-x

Abstract

The Notch signaling pathway plays a significant role in differentiation, proliferation, apoptosis, and stem cell processes. It is essential for maintenance of the normal colon crypt and has been implicated in colorectal cancer oncogenesis. Downregulation of the Notch pathway through gamma-secretase inhibitors (GSIs) has been shown to induce apoptosis and enhance response to chemotherapy in a variety of malignancies. In this study, we analyzed the effect of MRK-003 (Merck), a potent inhibitor of gamma-secretase, on oxaliplatin-induced apoptosis in colon cancer. Unexpectedly, gamma-secretase inhibition reduced oxaliplatin-induced apoptosis while GSI treatment alone was shown to have no effect on growth or apoptosis. We determined that the underlying mechanism of action involved an increase in protein levels of the anti-apoptotic Bcl-2 family members Mcl-1 and/or Bcl-xL which resulted in reduced Bax and Bak activation. Blocking of Mcl-1 and/or Bcl-xL through siRNA or the small molecule inhibitor obatoclax restored the apoptotic potential of cells treated with both oxaliplatin and MRK-003. Moreover, obatoclax synergized with MRK-003 alone to induce apoptosis. Our findings warrant caution when treating colon cancer with the combination of GSIs and chemotherapy, whereas other drug combinations, such as GSIs plus obatoclax, should be explored.

Keywords

Gamma-secretase inhibitorOxaliplatinMcl-1Bcl-xLColon

Supplementary material

10495_2013_883_MOESM1_ESM.pptx (58 kb)
Effects of Alternative GSIs on HCT-116 and SW480 Colon Cancer Cell Lines. HCT-116 and SW480 cells were treated with 15 μM (HCT-116) or 30 μM (SW480) oxaliplatin (Oxa) for 48 h in the absence or presence of 25 μM DAPT (A), 5 μM (HCT-116) or 10 μM (SW480) GSI-XII (B), or 2 μM GSI-XX (C). Apoptosis rates were measured by flow cytometry following active caspase-3 reactivity. Represented data are mean ± SEM of two independent experiments. Supplementary material 1 (PPTX 58 kb)
10495_2013_883_MOESM2_ESM.pptx (43 kb)
Effects of MRK-003 on Oxaliplatin-Induced Apoptosis in HT-29, HCT-15, and Colo205 Colon Cancer Cell Lines. HT-29, HCT-15, and Colo205 were treated with either 30 (HCT-15) or 50 μM (HT-29 and Colo205) Oxa in the absence or presence of 5 μM (HT-29) or 10 μM MRK-003 (HCT-15 and Colo205) for 48 h. Apoptosis rates were measured by flow cytometry following active caspase-3 reactivity. Represented data are mean ± SEM of at least two independent experiments. Supplementary material 2 (PPTX 43 kb)

Copyright information

© Springer Science+Business Media New York 2013