Mammalian DCN-1-like Proteins Enhance Neddylation of CUL3, and Vary in Localization and Tissue-Specific Expression

by Ryan, Russell J.H.

The Squamous Cell Carcinoma-Related Oncogene (SCCRO/DCUN1D1), located at 3q26.3, is a candidate oncogene that is gene-amplified and overexpressed in squamous-cell carcinomas of the upper aerodigestive tract and lung. The SCCRO protein is a member of a phylogenically conserved protein family, the defective in cullin neddylation 1 like domain containing (Dcun1d) proteins, which have been shown to promote the covalent modification of cullin proteins by the ubiquitin-like protein Nedd8.

In this study, we sought to characterize the expression and molecular interactions of vertebrate Dcun1d proteins, in order to better understand the normal function of genes in this family. We demonstrate that the majority of SCCRO protein in cultured human epithelial cell lines is not found in stable complexes with known interactors, including cullins, UBC12, and CAND1, a regulator of cullinRING-finger ubiquitin ligases (CRLs). We show that SCCRO expression is not cell-cycle regulated in HeLa-S cells. We describe five highly conserved vertebrate Dcun1d genes, and show that the products of all five genes interact with cullins and with CAND1. We show that four of the five proteins enhance the neddylation of CUL3 in a dose-dependant fashion in-vitro. We demonstrate that the UBA domain-containing SCCRO and Dcun1d2 proteins are pan-cellular in localization, while other family members contain alternate N-terminal domains which mediate their exclusive localization to the nucleus (Dcun1d4 and Dcun1d5) or to cellular membranes (Dcun1d3). We demonstrate that expression of alternate Dcun1d1 transcipts is specifically regulated in mouse germ cells during spermatogenesis, and we present evidence for specific expression of Dcun1d2 in brain and muscle tissue. We conclude that spermatogenesis and myogenesis could serve as valuable model systems for future studies of the interaction between expression levels of vertebrate Dcun1d proteins and the activity of CRL complexes. Such work could be valuable in understanding how SCCRO overexpression contributes to cancer.