Encyclopedia of Signaling Molecules

2018 Edition
| Editors: Sangdun Choi


Reference work entry
DOI: https://doi.org/10.1007/978-3-319-67199-4_101705


Historical Background

Nedd4 family-interacting protein 1 (Ndfip1) was first identified in a far-western screen searching for proteins that interact with the WW domains of the Nedd4 ubiquitin ligase (Jolliffe et al. 2000). It was initially named Nedd4 WW domain-binding protein 5 (N4WBP5). Following this discovery, a closely related mammalian protein was identified (named N4WBP5A, now called Ndfip2) and further characterized as belonging to a small group of evolutionarily conserved proteins (Harvey et al. 2002), with a single homologue in yeast [Bsd2p (Hettema et al., 2004)] and Drosophila melanogaster [dNdfip (Dalton et al. 2011); Fig. 1]. Both Ndfip1 and 2 are ubiquitously expressed and interact with several members of the Nedd4 family of ubiquitin ligases (Harvey et al. 2002; Shearwin-Whyatt et al. 2004). Ndfip1 mostly localizes to the Golgi, whereas Ndfip2 localizes to late endosomes and Golgi (Harvey et al. 2002; Shearwin-Whyatt et al. 2004). Ndfips all contain three transmembrane domains, plus several proline-rich motifs (PY motifs), which enable the binding to WW domain-containing proteins (Fig. 1). Specifically, Ndfips are best known for their ability to bind to the Nedd4 family of ubiquitin ligases, thereby regulating their subcellular localization (Beck et al. 2015) and activation (Mund and Pelham 2009), as well as functioning as adaptors to mediate the interaction between the ligase and non-PY-containing substrates (Foot et al. 2008). This latter function facilitates the ubiquitination of substrates and promoting their appropriate trafficking within the cell.
NDFIP1 and NDFIP2, Fig. 1

Primary structure of Ndfip family members is evolutionarily conserved. All Ndfip family members contain three transmembrane domains and either one (yeast, Drosophila) or two (mammals) PY motifs to enable binding to WW domain-containing substrates. There are two homologues in mammals (Ndfip1 and Ndfip2) but only one in Drosophila and yeast

Ndfips and Immunity

Not long after their initial characterization, an Ndfip1 knockout mouse was generated (Oliver et al. 2006), which paved the way for the discovery of the involvement of Ndfip1 in a number of novel mechanisms. These mice developed a severe inflammatory phenotype of the skin and lung, reminiscent of that of the Itch knockout mouse (Perry et al. 1998). Upon further analysis, it was determined that these mice had a complex dysregulation of T cell activation. Ndfip1 regulates the activity of the Nedd4 family ubiquitin ligase Itch in T cells, and thus in the absence of Ndfip1, Itch remains in an inactive state, preventing the downregulation of JunB (Fig. 2). This accumulation of JunB in activated T cells promotes T helper (Th) 2 maturation and proliferation, leading to inflammatory disease (Oliver et al. 2006). These mice also have fewer inducible regulatory T cells due to the accumulation of JunB, resulting in the production of IL-4 and IL-5 and the suppression of Foxp3 (Oliver et al. 2006; Beal et al. 2012). Ndfip1 has further been shown to be required for controlling the regulatory circuit that controls T cell activation through regulating IL-2 and CD25 levels to prevent T cells from becoming activated in the absence of costimulation by CD28 (Ramos-Hernandez et al. 2013). Additionally, Ndfip1 controls erroneous T cell activation by causing CD4+ T cells to exit the cell cycle prematurely and preventing differentiation into IL-4-producing cells (Altin et al. 2014). Ndfip1 has also been implicated in RIG-I-like receptor-mediated immune signaling, by controlling the levels of another Nedd4 family member Smurf1, which in turn regulates the degradation of the mitochondrial antiviral signaling protein MAVS (Wang et al. 2012). Recently, Ndfip1, along with the ubiquitin ligase Nedd4-2, has been shown to be involved as a negative regulatory axis in IgE-dependent mast cell activation (Yip et al. 2016). Combined, these studies indicate an essential role of Ndfip1 in immune cell function.
NDFIP1 and NDFIP2, Fig. 2

Ndfip1 is required for Itch-mediated regulation of JunB. Under normal conditions, activation of T cells leads to the binding of Itch to Ndfip1, which changes Itch conformation and allows phosphorylation by JNK. Phosphorylated Itch can then ubiquitinate JunB, leading to its degradation. In Ndfip1 −/− mice, Itch remains in a closed conformation, inhibiting phosphorylation by JNK and therefore preventing the ubiquitination of JunB. The resulting accumulation of JunB causes an increase in specific cytokine expression, resulting in a hyperactivated T cell phenotype

Ndfips and Brain Injury

As well as its essential role in controlling the immune system, Ndfip1 has also been implicated in neuronal cell survival following traumatic brain injury. During an initial screen for genes expressed in the cortex following injury, Ndfip1 was found to be upregulated in the cells surrounding the site of injury, and this was confirmed in vitro, where overexpression of Ndfip1-protected cultured cortical neurons from growth factor starvation induced cell death (Sang et al. 2006). This has been attributed in part to the role of Ndfip1 in the nuclear import of PTEN, which is required for the activation of Akt and the promotion of cell survival signaling pathways (Howitt et al. 2012; Goh et al. 2014; Mund and Pelham 2010) (Fig. 3). Ndfip1 also controls PTEN levels in the cell by targeting it to a subset of extracellular vesicles called exosomes, which are released from the multivesicular body (MVB) into the extracellular space (Putz et al. 2012).
NDFIP1 and NDFIP2, Fig. 3

Ndfip1 regulates PTEN nuclear import to promote neuronal survival following traumatic brain injury. PTEN normally acts by inhibiting the activation of Akt by PI3K. Following traumatic brain injury, Ndfip1 is upregulated to bind to PTEN and shuttle it into the nucleus where it is sequestered away from PI3K, allowing Akt to be activated and thus triggering cell survival pathways. Alternatively, Ndfip1 may target PTEN into MVBs for release in exosomes

Ndfips and Metabolism

In their role as adaptor proteins for Nedd4 family members, Ndfips control different metabolic processes to maintain body homeostasis. This was first discovered in yeast, where Bsd2p controls the divalent metal ion transporter Smf1p through the recruitment of the Nedd4 ubiquitin ligase Rsp5p (Hettema et al. 2004; Liu and Culotta 1999). This regulatory mechanism is conserved in mammals where both Ndfip1 and Ndfip2 control the regulation of the Smf1 homologue DMT1 via the recruitment of Nedd4 family members WWP2 and Nedd4-2, which is important for maintaining iron homeostasis in the mouse (Foot et al. 2008, 2011, 2016; Howitt et al. 2009)(Fig. 4). A similar role has been shown for the human ether-a-go-go-related gene (hERG) potassium channel, where both Ndfip1 and Ndfip2 recruit Nedd4-2 to subcellular compartments to facilitate the ubiquitination and subsequent degradation of hERG before it reaches the plasma membrane (Kang et al. 2015).
NDFIP1 and NDFIP2, Fig. 4

Ndfips act as adaptors to mediate the ubiquitination of transmembrane proteins. For target proteins that do not contain PY motifs (such as DMT1), Ndfips act as adaptors to recruit the Nedd4 family of ubiquitin ligases (shown as Nedd4) to enable ubiquitination and subsequent degradation either by the proteasome or through the endosomal pathway to the lysosome

Ndfip1 has also been implicated in pancreatic function through its role in regulating JunB (Beck et al. 2015). In pancreatic β cells, expression of Ndfip1 resulted in ER stress due to both the degradation of JunB (a potent inhibitor of ER stress) and the inhibition of the unfolded protein response that serves to protect cells against ER stress. This then prevents insulin secretion, induces caspase activity, and leads to β cell death (Beck et al. 2015).


Ndfips are highly conserved proteins that primarily regulate the function of the Nedd4 family of ubiquitin ligases in their role in regulating substrates through ubiquitination. Generation of knockout mouse models has revealed the importance of these proteins both in maintaining normal homeostasis in physiological systems such as the immune system and iron regulation and during injury or disease as shown in the brain’s response to traumatic brain injury. Given their ubiquitous expression pattern, it is likely that these proteins have as yet undiscovered roles in other tissues or systems.

See Also


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Copyright information

© Springer International Publishing AG 2018

Authors and Affiliations

  1. 1.Centre for Cancer BiologyUniversity of South AustraliaAdelaideAustralia