Role for Bcl-xL as an inhibitor of cytosolic cytochrome C accumulation in DNA damage-induced apoptosis

Role for Bcl-x_L as an inhibitor of cytosolic cytochrome C accumulation in DNA damage-induced apoptosis

^*Division of Cancer Pharmacology, Dana Farber Cancer Institute, Harvard Medical School, 44 Binney Street, Boston, MA 02115; ^§Department of Radiation and Cellular Oncology, University of Chicago, Chicago, IL 60637; ^†Oncology Research Program, Preclinical Research, Novartis Pharmaceuticals Corporation, East Hanover, NJ 07936; and ^‡Manitoba Institute of Cell Biology, University of Manitoba, Winnipeg, Manitoba, Canada R3E0V9

Abstract

Cytochrome C is a mitochondrial protein that induces apoptosis when released into the cytosol or when added to cell-free extracts. Here we show that cells that overexpress the Bcl-2-related protein Bcl-x_L fail to accumulate cytosolic cytochrome C or undergo apoptosis in response to genotoxic stress. Coimmunoprecipitation studies demonstrate that Bcl-x_L associates with cytochrome C. Cytochrome C binds directly and specifically to Bcl-x_L and not to the proapoptotic Bcl-x_s protein. The results also demonstrate that Bcl-x_s blocks binding of cytochrome C to Bcl-x_L. Our findings support a role for Bcl-x_L in protecting cells from apoptosis by inhibiting the availability of cytochrome C in the cytosol.

Footnotes

↵ ¶ To whom reprint requests should be addressed.
Sidney Udenfriend, Roche Institute of Molecular Biology, Nutley, NJ
ABBREVIATIONS:

IR,

ionizing radiation;

PARP,

poly(ADP ribose) polymerase;

CDDP,

cisplatinum;

GST,

glutathione S-transferase