hRpn13/ADRM1/GP110 is a novel proteasome subunit that binds the deubiquitinating enzyme, UCH37

Abstract

The 26S proteasome catalyzes the degradation of most proteins in mammalian cells. To better define its composition and associated regulatory proteins, we developed affinity methods to rapidly purify 26S proteasomes from mammalian cells. By this approach, we discovered a novel 46-kDa (407 residues) subunit of its 19S regulatory complex (previously termed ADRM1 or GP110). As its N-terminal half can be incorporated into the 26S proteasome and is homologous to Rpn13, a 156-residue subunit of the 19S complex in budding yeast, we renamed it human Rpn13 (hRpn13). The C-terminal half of hRpn13 binds directly to the proteasome-associated deubiquitinating enzyme, UCH37, and enhances its isopeptidase activity. Knockdown of hRpn13 in 293T cells increases the cellular levels of ubiquitin conjugates and decreases the degradation of short-lived proteins. Surprisingly, an overproduction of hRpn13 also reduced their degradation. Furthermore, transfection of the C-terminal half of hRpn13 slows proteolysis and induces cell death, probably by acting as a dominant-negative form. Thus in human 26S proteasomes, hRpn13 appears to be important for the binding of UCH37 to the 19S complex and for efficient proteolysis.

Regulation of NF-κB activity and inducible nitric oxide synthase by regulatory particle non-ATPase subunit 13 (Rpn13)

“…Deletion of ADRM1 by siRNA does not lead to global accumulation of ubiquitinated cellular proteins or changes in proteasome expression, suggesting that ADRM1 must have a specialized role in proteasome function (8). Shorty after the above report, three independent groups confirmed that ADRM1 is a novel 19S proteasome cap-associated protein, but they further revealed a unique role for ADRM1 in protein degradation (7,9,10). These groups found that ADRM1 interacts with the carboxyl-terminal tail of ubiquitin C-terminal hydrolase UCH37 and recruits it to the proteasome.…”

“…One such protein is adhesion regulating molecule (ADRM1), which is recently identified as a novel proteasome-associated protein, which recruits the deubiquitinating enzyme UCH37 to the 26S proteasome (7)(8)(9)(10). Before this discovery, ADRM1 had been described as a heavily glycosylated membrane protein, which regulates cell adhesion (11).…”

“…UCH37 is the principal deubiquitinating enzyme associated with mammalian proteasomes. The N-terminal one-third of ADRM1 is 41% similar to Rpn13, which is a subunit of the 19S regulatory complex in yeast and, therefore, ADRM1 has been renamed Rpn13 (7,9,10). We will use the term Rpn13 henceforth.…”

hRpn13, a newly identified component of the 19S particle, regulates proliferation, differentiation, and function in the human osteoblast-like cell line MG63

“…hRpn13, a component of the 19S regulatory subparticle of the 26S proteasome, is a major ubiquitin receptor [7], facilitating the docking of ubiquitinated proteins to the proteasome complex which ultimately leads to the degradation of the tagged protein. Interestingly, hRpn13 can also accelerate the deubiquitination process by recruiting the deubiquitinating enzyme UCH37 to the proteasome [22]. UCH37 is recently associated with the 19S regulatory particle that possesses robust deubiquitinating activity [14,26].…”

“…The 19S portion is responsible for stimulating 20S to degrade proteins [9,10]. hRpn13 is a component of the 19S particle, serves as a receptor for both ubiquitin and the deubiquitinating enzyme UCH37, and can also enhance the activity of UCH37 [16,22]. Therefore, it can be inferred that hRpn13 has bi-directional roles in modulating UPP activity.…”