Worm Breeder's Gazette 14(1): 94 (October 1, 1995)

These abstracts should not be cited in bibliographies. Material contained herein should be treated as personal communication and should be cited as such only with the consent of the author.

Baculovirus p35 protein is a substrate for and inhibitor of the C. elegans cell-death protease CED-3

Ding Xue, Bob Horvitz

HHMI, Dept. Biology, MIT, Cambridge, MA 02139

      Baculovirus protein p35 inhibits programmed cell death in such
diverse species as nematodes, insects and mammals  (1, 2), which suggests
that p35 may function by interacting with an evolutionarily conserved
component of a pathway for cell death.  Two such conserved components are
the cell-death effectors represented by the C. elegans protein CED-3 and
the mammalian cysteine protease interleukin-1B-converting enzyme (ICE)
and the cell-death inhibitors represented by the C. elegans protein CED-9
and the product of the mammalian proto-oncogene bcl-2  (3) .  We examined
the interaction of p35 with CED-3, which like the pro-form of ICE can
autocleave to generate a cysteine protease (4).  We found that recombinant
p35 protein purified from bacteria efficiently inhibited CED-3 protease
activity in vitro.  Furthermore, 35S-methionine-labeled p35 protein
synthesized in vitro was cleaved by purified CED-3 protease to generate
two products of 10K and 25K.  We determined by microsequencing analysis
that CED-3 cleaves p35 between aspartate 87 and glycine 88.  These results
suggest that p35 may prevent programmed cell death in C. elegans by
directly inhibiting CED-3 activity.
      Three observations indicate that the CED-3 cleavage site in p35 is
important for the activity of p35 in inhibiting cell death in C. elegans.
1) A p35 mutation (D87E) that greatly reduced p35 activity in vitro as a
CED-3 substrate and inhibitor abolished p35 activity in vivo in protecting
against cell death in C. elegans.  2) Introduction of a second p35
mutation (K127G) that created a new but weak CED-3 cleavage site
(aspartate-glycine) partially restored the ability of p35 to protect
against cell death.  3) Introduction of the CED-3 cleavage site in p35
into the cowpox virus protein crmA, which inhibits mammalian apoptosis
(5)  but not programmed cell death in C. elegans, caused crmA to block
CED-3-mediated cell death.  These results indicate that the CED-3 cleavage
site in p35 can confer to certain proteins the ability to protect against
programmed cell death and suggest that p35 may block cell death in C.
elegans by acting as a competitive inhibitor of the CED-3 protease.
      We found that p35 was also cleaved by four vertebrate cysteine
protease activities of the CED-3 family -- mouse ICE, human NEDD-2/ICH-1,
human CPP32/Yama and chicken S/M extract.  All four proteases most likely
cleaved at the same site, since their cleavage products co-migrated and
since a D87A substitution in p35 completely prevented the cleavage
reactions.  This result suggests that p35 may in general prevent
programmed cell death by directly inhibiting activities of such cysteine

1.  A. Sugimoto, P. D. Friesen, J. H. Rothman, EMBO J 13, 2023-8 (1994).
2.  H. Steller, Science 267, 1445-1449 (1995).
3.  M. O. Hengartner, H. R. Horvitz, Philos Trans R Soc Lond B Biol Sci
    345, 243-246 (1994).
4.  D. Xue, H. R. Horvitz, 10th C. elegans Meeting Abstract, 554 (1995).
5.  M. Miura, H. Zhu, R. Rotello, E. A. Hartwieg, J. Yuan, Cell 75, 653-60