Pro-apoptotic apoptosis protease-activating factor 1 (Apaf-1) has a cytoplasmic localization distinct from Bcl-2 or Bcl-x(L)

Hausmann, G; O&#39;Reilly, LA; van Driel, R; Beaumont, JC; Strasser, A; Adams, JM; Huang, DCS

Author(s): Hausmann, G; O'Reilly, LA; van Driel, R; Beaumont, JC; Strasser, A; Adams, JM; Huang, DCS;
Details: Publication Year 2000-05-01,Volume 149,Issue #3,Page 623-633
Journal Title: JOURNAL OF CELL BIOLOGY
Publication Type: Journal Article
Abstract: How Bcl-2 and its pro-survival relatives prevent activation of the caspases that mediate apoptosis is unknown, but they appear to act through the caspase activator apoptosis protease-activating factor 1 (Apaf-1). According to the apoptosome model, the Bcl-2-like proteins preclude Apaf-1 activity by sequestering the protein. To explore Apaf-1 function and to test this model, we generated monoclonal antibodies to Apaf-1 and used them to determine its localization within diverse cells by subcellular fractionation and confocal laser scanning microscopy. Whereas Bcl-2 and Bcl-x(L) were prominent on organelle membranes, endogenous Apaf-1 was cytosolic and did not colocalize with them, even when these pro-survival proteins were overexpressed or after apoptosis was induced. Immunogold electron microscopy confirmed that Apaf-1 was dispersed in the cytoplasm and not on mitochondria or other organelles. After the death stimuli, Bcl-2 and Bcl-x(L) precluded the release of the Apaf-1 cofactor cytochrome c from mitochondria and the formation of larger Apaf-1 complexes, which are steps that presage apoptosis. However, neither Bcl-2 nor Bcl-x, could prevent the in vitro activation of Apaf-1 induced by the addition of exogenous cytochrome c. Hence, rather than sequestering Apaf-1 as proposed by the apoptosome model, Bcl-2-like proteins probably regulate Apaf-1 indirectly by controlling upstream events critical for its activation.
Publisher: ROCKEFELLER UNIV PRESS
Keywords: CYTOCHROME-C; CELL-DEATH; CASPASE ACTIVATION; X-L; ENDOPLASMIC-RETICULUM; NUCLEAR-ENVELOPE; FAMILY MEMBERS; MITOCHONDRIA; COMPLEX; CED-4
Publisher's Version: https://doi.org/10.1083/jcb.149.3.623
Terms of Use/Rights Notice: Refer to copyright notice on published article.

Creation Date: 2000-05-01 12:00:00