CrmA-inhibitable Cleavage of the 70-kDa Protein Component of the U1 Small Nuclear Ribonucleoprotein during Fas- and Tumor Necrosis Factor-induced Apoptosis

doi:10.1074/jbc.270.32.18738

CrmA-inhibitable Cleavage of the 70-kDa Protein Component of the U1 Small Nuclear Ribonucleoprotein during Fas- and Tumor Necrosis Factor-induced Apoptosis (*)

From theDepartment of Pathology and Graduate Program in Cellular and Molecular Biology, University of Michigan Medical School, Ann Arbor, Michigan 48109

** Established Investigator of the American Heart Association. To whom correspondence should be addressed:
Dept. of Pathology, University of Michigan Medical School, 1301 Catherine St., Box 0602, Ann Arbor, MI 48109.
Tel.: 313-747-2921; Fax: 313-764-4308; vishva.dixit{at}med.umich.edu.

Abstract

Fas and the type I tumor necrosis factor receptor (TNF-R) are two cell surface receptors that, when stimulated with ligand or cross-linking antibody, trigger apoptotic cell death by a mechanism that has yet to be elucidated. The CrmA protein is a serpin family protease inhibitor that can inhibit interleukin-1β converting enzyme (ICE) and ICE-like proteases. We showed previously that expression of CrmA potently blocks apoptosis induced by activation of either Fas or TNF-R, implicating protease involvement in these death pathways (Tewari, M., and Dixit, V. M.(1995) J. Biol. Chem. 270, 3255-3260). Here we report that the 70-kDa component of the U1 small ribonucleoprotein (U1-70 kDa) is a proteolytic substrate rapidly cleaved during both Fas- and TNF-R-induced apoptosis. This cleavage was inhibited by expression of CrmA but not by expression of an inactive point mutant of CrmA, confirming the involvement of an ICE-like protease. These data for the first time identify U1-70 kDa as a death substrate cleaved during Fas- and TNF-R-induced apoptosis and emphasize the importance of protease activation in the cell death pathway.

Footnotes

↵^§ Supported by a Young Scientist MD/PhD Scholarship from the Life and Health Insurance Medical Research Fund; Fellow of the Medical Scientist Training Program.
↵^¶ Supported by United States Public Health Service Award HL07517.
↵* This work was funded by National Institutes of Health Grant CA64803 (to V. M. D.). The costs of publication of this article were defrayed in part by the payment of page charges. This article must therefore by hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵¹ The abbreviations used are:

PCD

programmed cell death

TNF-R

tumor necrosis factor receptor

ICE

interleukin-1β-converting enzyme

PBS

phosphate-buffered saline

U1-70 kDa

70-kDa protein component of the U1 small ribonucleoprotein

PARP

poly(ADP-ribose) polymerase.
↵²M. Tewari and V. M. Dixit, unpublished observations.
- Received June 5, 1995.