Receptor-mediated uptake of an extracellular Bcl-xL fusion protein inhibits apoptosis
- Biochemistry Section, Surgical Neurology Branch, National Institute of Neurological Disorders and Stroke, National Institutes of Health, Bethesda, MD 20892
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Communicated by R. John Collier, Harvard Medical School, Boston, MA (received for review February 5, 1999)
Abstract
Bcl-xL, a member of the Bcl-2 family, inhibits many pathways of apoptosis when overexpressed in the cell cytosol. We examined the capacity of Bcl-xL fusion proteins to bind cells from the outside and block apoptosis. Full-length Bcl-xL protein at micromolar concentrations did not affect apoptosis when added to cell media. To increase uptake by cells, Bcl-xL was fused to the receptor-binding domain of diphtheria toxin (DTR). The Bcl-xL–DTR fusion protein blocked apoptosis induced by staurosporine, γ-irradiation, and poliovirus in a variety of cell types when added to media. The potency of inhibition of poliovirus-induced apoptosis by Bcl-xL–DTR was greater than that of strong caspase inhibitors. Brefeldin A, an inhibitor of vesicular traffic between the endoplasmic reticulum and Golgi apparatus, prevented the Bcl-xL–DTR blockade of apoptosis induced by staurosporine, suggesting that Bcl-xL–DTR must be endocytosed and reach intracellular compartments for activity. Many diseases are caused by overexpression or underexpression of Bcl-xL homologues. Extracellular delivery of Bcl-2 family member proteins may have a wide range of uses in promoting or preventing cell death.
Footnotes
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↵ * To whom reprint requests should be addressed at: National Institutes of Health, Building 10, Room 5D-37, MSC 1414, 10 Center Drive, Bethesda, MD 20892-1414. E-mail: youle{at}helix.nih.gov.
- ABBREVIATIONS:
- DT,
- diphtheria toxin;
- DTR,
- DT receptor-binding domain;
- PARP,
- poly(ADP-ribose) polymerase;
- STS,
- staurosporine
- Copyright © 1999, The National Academy of Sciences
