Volume 271, Number 36, Issue of September 6, 1996 pp. 21699-21702
©1996 by The American Society for Biochemistry and Molecular Biology, Inc.

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COMMUNICATION:
An Interleukin-1 Converting Enzyme-like Protease Is a Key Component of Fas-mediated Apoptosis

(Received for publication, May 7, 1996, and in revised form, June 18, 1996)

From the Department of Biochemistry, University of Alberta, Edmonton, AB T6G 2H7, Canada

Cytotoxic T lymphocytes (CTLs) are able to kill target cells bearing foreign antigen through two distinct mechanisms: granule- and Fas-mediated cytotoxicity. The exact events involved in the induction of target cell apoptosis remain elusive, but research indicates a role for members of the interleukin-1 converting enzyme (ICE)/Ced-3 family of cysteine proteases. The exact nature of the protease(s) involved is yet to be determined. Here we use activity assays and peptide inhibitors of ICE/Ced-3 proteases to study their role in Fas-mediated killing. We find that while certain inhibitors block DNA fragmentation and chromium release, others do not. Most notably, potent inhibitors of CPP32 and ICE could not inhibit DNA fragmentation during all cases of Fas-mediated cytotoxicity although an ``ICE'' inhibitor could suppress ⁵¹Cr release. Additionally, we find that CPP32 is not cleaved in all target cells during Fas killing. Although ICE activity (as measured by a fluorogenic substrate) is present in cell lysates from anti-Fas-treated cells, we found no pro-IL-1-cleaving activity in these lysates. Taken together, our results suggest that an alternate pathway to DNA fragmentation exists, which does not involve CPP32 activity, and that CPP32 and ICE activities are not essential to Fas-mediated killing.

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