SignalSilence^® KLHL12 siRNA I #9410

Cullins are proteins that function as molecular scaffolds for modular ubiquitin ligases typified by the SCF (Skp1-CUL1-F-box) complex (1-3). The substrate selectivity of these E3 ligases is dictated by a specificity module that binds cullins. In the SCF complex, this module is composed of Skp1, which binds directly to CUL1, and a member of the F-box family of proteins such as Skp2 (1-4). CUL3 has been shown to be required for embryonic development in mammals and Caenorhabditis elegans (5-7) but until recently, its substrate specificity adaptor had yet to be elucidated. It is now recognized that substrate adaptors for CUL3-based ubiquitin ligase complexes contain a conserved BTB/POZ (Pox virus and Zinc finger) domain. This domain, which was initially identified in the Drosophila transcriptional repressors broad complex, tramtrack, and bric-a-brac is present in more than 190 human proteins. BTB proteins contain a variety of putative protein-protein interaction domains, including MATH domains, zinc finger repeats, and kelch repeats (8).

There are several lines of evidence suggesting that Kelch-like 12 protein (KLHL12) is a substrate-specific adaptor for the CUL3-based ubiquitin ligase complex. Analysis of the amino acid sequence of KLHL12 reveals an amino-terminal BTB motif, a central linker region, and a carboxy-terminal kelch domain composed of kelch repeats. Furthermore, KLHL12 has been shown to negatively regulate Wnt signaling by binding Disheveled and targeting it for ubiquitin-dependent proteasomal degradation (9). More recently, KLHL12 was shown to drive the assembly of large COPII vesicles by promoting the monoubiquitination of the COPII component Sec31. As a result, CUL3-KLHL12-dependent ubiquitination is essential for collagen export, a step that is required for integrin-dependent mouse embryonic stem cell division (10) .