The Bmi-1 oncoprotein interacts with dinG and MPh2: the role of RING finger domains

Abstract

Experimentally-induced mutations in the C 3 HC 4 RING ®nger domain of the Bmi-1 oncoprotein block its ability to induce lymphomas in mice. In this report, the role of the Bmi-1 RING ®nger in mediating protein-protein interactions is examined using the yeast two-hybrid system. Bmi-1 interacts directly with the RING ®nger protein dinG/RING1B. Heterodimerization of the two proteins requires the intact RING ®nger structures of both Bmi-1 and dinG. Although the RING ®nger domains are necessary for dimerization, they are not su cient for this process as residues outside the C 3 HC 4 motif are also required. Thus, binding speci®city may be partly conferred by residues outside the RING motif. Both Bmi-1 and dinG interact with the Polyhomeotic protein MPh2 through binding domains apart from the RING ®nger. The data suggest a model whereby Bmi-1, dinG, and MPh2 form a stable heterotrimeric complex in which each protein contributes to the binding of the others.

The polycomb protein MPc3 interacts with AF9, an MLL fusion partner in t(9;11)(p22;q23) acute leukemias

“…However, characterization of both¯y and mammalian PcG proteins indicates that the individual PcG proteins contain one or more domains that mediate binding to other PcG proteins. Thus multiple protein ± protein contacts appear to be made within a PcG complex serving to stabilize the structure through mutual interactions (Alkema et al, 1997a;Gunster et al, 1997;Peterson et al, 1997;Schoorlemmer et al, 1997;Hashimoto et al, 1998;Hemenway et al, 1998). These ®ndings are consistent with the long-standing observation that single PcG gene mutations produce a relatively mild phenotype while multiple mutations act synergistically to produce severe developmental anomalies.…”

“…Several PcG proteins have been described that have the capacity to simultaneously bind multiple other PcG proteins (Hashimoto et al, 1998;Hemenway et al, 1998;Satijn and Otte, 1999). Data presented here indicate that MPc3 can simultaneously bind both RING1B and AF9 to form a trimeric complex.…”

“…Data suggest that PcG proteins assemble as large multiprotein complexes stabilized by mutually interacting binding partners (Hashimoto et al, 1998;Hemenway et al, 1998;Satijn and Otte, 1999). The C-box at the extreme carboxy-terminus of MPc3 is responsible for interactions with the proteins RING1A and RING1B (Hemenway et al, 2000), a characteristic that is shared with other Pc proteins.…”

Differential expression of polycomb repression complex 1 (PRC1) members in the developing mouse brain reveals multiple complexes

“…With the exception of Ring1a and mPh2, interactions between subgroup I members M33, Ring1a, Rnf2, and mPh2 have been shown in vitro (Schoorlemmer et al, 1997;Hemenway et al, 1998;Satijn and Otte 1999b) and are likely to occur in the regions of overlapping expression. Interactions for subgroup II members have been shown in vitro only for Bmi1 and Cbx4 , as well as Cbx8 and Mel18 (Bardos et al, 2000).…”

Mmip-2, a novel RING finger protein that interacts with mad members of the Myc oncoprotein network

“…Although the RING ®nger has now been determined to be necessary for protein : protein interactions in a variety of cases (Kim et al, 1996;Bellon et al, 1997;Jensen et al, 1998), other bona ®de in vivo interactions do not require this motif. These include the associations between the RING ®nger-containing proteins Bmi-1 and dinG/RING1B and the Polyhomeotic protein Mph2 (Hemenway et al, 1998), the small nuclear RING ®nger protein SNURF and the androgen receptor (Moilanen et al, 1998), and the formation of a ternary complex between cyclinH-cdk7 and the MAT1 RING ®nger protein (Tassan et al, 1995). However, while the RING ®nger of Mmip-2 is dispensable for its interaction with mad family members, it seems reasonable to believe that it may function to bind other targets, perhaps as part of a higher order complex in association with mad proteins.…”