Mouse Receptor Interacting Protein 3 Does Not Contain a Caspase-Recruiting or a Death Domain but Induces Apoptosis and Activates NF-κB

Abstract

The death domain-containing receptor superfamily and their respective downstream mediators control whether or not cells initiate apoptosis or activate NF-κB, events critical for proper immune system function. A screen for upstream activators of NF-κB identified a novel serine-threonine kinase capable of activating NF-κB and inducing apoptosis. Based upon domain organization and sequence similarity, this novel kinase, named mRIP3 (mouse receptor interacting protein 3), appears to be a new RIP family member. RIP, RIP2, and mRIP3 contain an N-terminal kinase domain that share 30 to 40% homology. In contrast to the C-terminal death domain found in RIP or the C-terminal caspase-recruiting domain found in RIP2, the C-terminal tail of mRIP3 contains neither motif and is unique. Despite this feature, overexpression of the mRIP3 C terminus is sufficient to induce apoptosis, suggesting that mRIP3 uses a novel mechanism to induce death. mRIP3 also induced NF-κB activity which was inhibited by overexpression of either dominant-negative NIK or dominant-negative TRAF2. In vitro kinase assays demonstrate that mRIP3 is catalytically active and has autophosphorylation site(s) in the C-terminal domain, but the mRIP3 catalytic activity is not required for mRIP3 induced apoptosis and NF-κB activation. Unlike RIP and RIP2, mRIP3 mRNA is expressed in a subset of adult tissues and is thus likely to be a tissue-specific regulator of apoptosis and NF-κB activity. While the lack of a dominant-negative mutant precludes linking mRIP3 to a known upstream regulator, characterizing the expression pattern and the in vitro functions of mRIP3 provides insight into the mechanism(s) by which cells modulate the balance between survival and death in a cell-type-specific manner.

ACKNOWLEDGMENTS

We thank J. M. Kyriakis for the RIP constructs used in this study.

This research was supported in part by National Institutes of Health grants AI42798 (M.A.H.) and CA67891 and CA73023 (D.B.D.) and in part by the Project Development Program, Research and Sponsored Programs, Indiana University at Indianapolis (M.A.H.).

ADDENDUM IN PROOF

Two independent groups (P. W. Yu et al., Curr. Biol.9:539–542, 1999; X. Sun et al., J. Biol. Chem.274:16871–16875, 1999) have recently reported cloning of human RIP3.