Mark Boldin

Involvement of MACH, a Novel MORT1/FADD-Interacting Protease, in Fas/APO-1- and TNF Receptor–Induced Cell Death

Fas/APO-1 and p55 tumor necrosis factor (TNF) receptor (p55-R) activate cellular mechanisms that result in cell death. Upon activation of these receptors, Fas/APO-1 binds a protein called MORT1 (or FADD) and p55-R binds a protein called TRADD. MORT1 and TRADD can also bind to each other. We have cloned a novel protein, MACH, that binds to MORT1. This protein exists in multiple isoforms, some of which contain a region that has proteolytic activity and shows marked sequence homology to proteases of the ICE/CED-3 family. Cellular expression of the proteolytic MACH isoforms results in cell death. Expression of MACH isoforms that contain an incomplete ICE/CED-3 region provides effective protection against the cytotoxicity induced by Fas/APO-1 or p55-R triggering. These findings suggest that MACH is the most upstream enzymatic component in the Fas/APO-1- and p55-R-induced cell death signaling cascades.

A protein related to a proteasomal subunit binds to the intracellular domain of the p55 TNF receptor upstream to its ‘death domain’

A novel protein that binds specifically to the intracellular domain of the p55 tumor necrosis factor (TNF) receptor was cloned by two‐hybrid screening of a HeLa cell cDNA library. Data bank searches revealed high sequence similarity of the protein (55.11) to yeast, nematode and plant proteins, whose functions are yet unknown. Significant similarity was also found between 55.11 and SEN3, the yeast equivalent of the p112 subunit of the 26S proteasome. Deletion analysis showed that the protein binds to the p55 receptor upstream to the region involved in induction of cell death.

THE YEAST TWO-HYBRID SCREENING TECHNIQUE AND ITS USE IN THE STUDY OF PROTEIN-PROTEIN INTERACTIONS IN APOPTOSIS

The yeast two-hybrid technique provides a general approach for cloning cDNAs merely by exploiting the ability of their encoded proteins to bind to a protein of interest. The technique therefore offered a useful access to the analysis of the mechanisms of cell death at the initial stage of their study, when only a few of the proteins involved and very little about their mode of action were known. Conversely, the knowledge of cell death mechanisms gained by this technique provided a useful insight into both the potential and the limitations of this technique.