NEDD4: The founding member of a family of ubiquitin-protein ligases

Abstract

Ubiquitination plays a crucial role in regulating proteins post-translationally. The focus of this review is on NEDD4, the founding member of the NEDD4 family of ubiquitin ligases that is evolutionarily conserved in eukaryotes. Many potential substrates of NEDD4 have been identified and NEDD4 has been shown to play a critical role in the regulation of a number of membrane receptors, endocytic machinery components and the tumour suppressor PTEN. In this review we will discuss the diverse pathways in which NEDD4 is involved, and the patho-physiological significance of this important ubiquitin ligase.

Keywords: IGF signalling; NEDD4 family; PTEN; Ubiquitin; Ubiquitin protein ligases.

Figure 1.. (A) Schematic structure of the NEDD4 protein

Schematic of the modular structure of the human NEDD4 protein. The C2 calcium/phospholipid binding domain mediates NEDD4 binding to membranes, and is also involved in substrate recognition. The WW domains are protein-protein interaction domains that bind to conserved PY motifs in substrates and regulatory proteins. The catalytic ubiquitin ligase domain binds the E2 conjugation enzyme and forms a thioester bond with ubiquitin before transferring ubiquitin to the substrate. (B) Phylogenetic relationship of NEDD4 proteins from various species. NEDD4 sequences were obtained from the NCBI protein database as follows; S. pombe (Schizosaccharomyces pombe Pub3; NP_595793.1), S. cerevisiae (Saccharomyces cerevisiae Rsp5p; AAC03223.1), mosquito (Anopheles gambiae; XP_003436401.1), Drosophila [Drosophila melanogaster; NP_996116.1), Xenopus (Xenopus laevis; NP_001084258.1), zebrafish (Danio rerio; NP_001029358.1), chicken (Gallus gallus; XP_413791.3), mouse (Mus musculus; NP_035020.2), rat (Rattus norvegicus; NP_037118.1), monkey (Macaca fascicularis; XP_005559683.1), chimpanzee (Pan troglodytes; XP_523083.3),and human (Homo sapiens; NP_006145.2 ). Sequences were aligned using NCBI COBALT (Constraint Based Multiple Protein Alignment Tool) http://www.stva.ncbi.nlm.nih.gov/tools/cobalt/re_cobalt.cgi (Papadopoulos and Agarwala, 2007) and the minimum-evolution Phylogenetic Tree output displayed. The individual domains on the NEDD4 schematics were identified using NCBI Conserved Domain Database search http://www.ncbi.nlm.nih.gov/Structure/bwrpsb/bwrpsb.cgi (Marchler-Bauer et al., 2011) and are drawn roughly to scale. The scale bar indicates evolutionary distance (Grishin, 1995).

Figure 2.. The proposed role of NEDD4 in IGF-1R signaling

Stimulation of the IGF-1R with IGF-1 ligand results in auto-phosphorylation of the receptor, leading to phosphorylation of insulin receptor substrate 1 (IRS1) and the activation of the PI3K pathway that ultimately results in cellular growth and proliferation. PTEN has recently been shown to be a protein phosphatase for IRS-1, and NEDD4 antagonizes this phosphatase activity (Shi et al., 2014). IGF-1 signalling stimulates the ubiquitination of pAKT by NEDD4 to promote the peri-nuclear trafficking of pAKT (Fan et al., 2013). The adaptor protein Grb10 negatively regulates IGF-1 signalling by binding the IGF-1R, and in vivo data indicates that NEDD4 down-regulates Grb10 expression (Cao et al., 2008). IGF-1R is also targeted by ubiquitin ligases such as MDM2 and c-Cbl for endocytosis and degradation.