MRIT, a novel death-effector domain-containing protein, interacts with caspases and BclX _L and initiates cell death

Abstract

Activation of the cascade of proteolytic caspases has been identified as the final common pathway of apoptosis in diverse biological systems. We have isolated a gene, termed MRIT, that possesses overall sequence homology to FLICE (MACH), a large prodomain caspase that links the aggregated complex of the death domain receptors of the tumor necrosis factor receptor family to downstream caspases. However, unlike FLICE, the C-terminal domain of MRIT lacks the caspase catalytic consensus sequence QAC(R͞Q)G. Nonetheless MRIT activates caspase-dependent death. Using yeast two-hybrid assays, we demonstrate that MRIT associates with caspases possessing large and small prodomains (FLICE, and CPP32͞YAMA), as well as with the adaptor molecule FADD. In addition, MRIT simultaneously and independently interacts with BclX L and FLICE in mammalian cells. Thus, MRIT is a mammalian protein that interacts simultaneously with both caspases and a Bcl-2 family member.

Modulation of the NF-κB pathway by virally encoded Death Effector Domains-containing proteins

“…Both MC159L and E8 lack such an ability (Bertin et al, 1997;Hu et al, 1997a;Thome et al, 1997 and our unpublished results). However, like ORF-K13, the DEDs-containing prodomains of Caspase 8 and MRIT/cFLIP have been reported to induce apoptosis when over-expressed in mammalian cells Han et al, 1997;Shu et al, 1997). We have recently discovered that the prodomains of Caspase 8 and MRIT/cFLIP, like ORF-K13, can also activate the NF-kB pathway (manuscript in preparation).…”

“…The expression constructs for the death receptors, RIP, Caspase 8, CrmA, MRIT, E8 and MC159L have been described previously Han et al, 1997;Hu et al, 1997a). Constructs encoding ORF-K13 (GenBank U90534) were prepared by PCR ampli®cation of the desired coding sequence from a human genomic DNA sample containing KSHV/HHV8 (human herpesvirus 8) genomic DNA which was obtained from Dr Tim Rose (University of Washington, Seattle, WA, USA).…”

“…Caspase 8 is the apical caspase of the caspase cascade and possesses an N-terminal prodomain consisting of two homologous Death E ector Domains (DEDs) Fernandes-Alnemri et al, 1996;Muzio et al, 1996). DEDs-containing prodomains are also found in two additional cellular proteins; Caspase 10 (Mch4, FLICE2) (FernandesAlnemri et al, 1996;Vincenz and Dixit, 1997), and MRIT (c-FLIP, Casper, I-FLICE, FLAME, CASH, CLARP) (Goltsev et al, 1997;Han et al, 1997;Hu et al, 1997b;Inohara et al, 1997;Irmler et al, 1997;Shu et al, 1997;Srinivasula et al, 1997). Recently, several viruses were also found to encode proteins with homology to the DEDs (Bertin et al, 1997;Hu et al, 1997a;Thome et al, 1997).…”

The opposing roles of the Akt and c-Myc signalling pathways in survival from CD95-mediated apoptosis

“…However, there is no obvious molecular mechanism linking anti-apoptotic Bcl-2 family members with the classical type 1 CD95/ FADD/caspase-8 pathway. Although it has been suggested that Bcl-2 and Bcl-X L directly (Boise and Thompson, 1997) or indirectly (Chinnaiyan et al, 1997;Han et al, 1997;Ng et al, 1997;Hu et al, 1998) bind caspase-8 and so modulate its activation (Medema et al, 1998), a recent report indicates that, in a system in which Bcl-X L e ectively suppresses CD95-induced apoptosis, Bcl-X L neither interacts with caspase-8 nor inhibits its recruitment or activation (Medema et al, 1998). This ®nding seems to leave little room for a role for Bad as an intermediary modulating activation of caspase-8 by FADD.…”

c-FLICE inhibitory protein expression inhibits T-cell activation

“…1,2 Cellular FLICE-inhibitory protein (c-FLIP) specifically regulates the DR apoptotic process. [3][4][5][6][7][8][9] c-FLIP is expressed in both a long-form (c-FLIP L ) and a short-form (c-FLIP S ) due to alternative splicing. The DEDs of c-FLIP L and c-FLIP S interact with the DEDs of FADD and procaspasse-8.…”