NEDD4L

NEDD4L Full Name

neural precursor cell expressed, developmentally down-regulated 4-like, E3 ubiquitin protein ligase

NEDD4L Introduction

NEDD4L (also called NEDD4-2) is a member of the NEDD4 family of HECT-domain E3 ubiquitin ligases that control the abundance of proteins at the plasma membrane by tagging them with ubiquitin, a modification that targets them for internalization and degradation. The ligase is best known for its regulation of the epithelial sodium channel ENaC: NEDD4L binds to PY motifs in the channel subunits and ubiquitinates them, reducing the number of channels at the cell surface and thereby limiting sodium reabsorption in the kidney and other epithelia. This function places NEDD4L at the center of blood pressure control, and both genetic variation in the human gene and experimental manipulation of the enzyme have been linked to hypertension and to disorders of sodium balance, including Liddle syndrome, in which mutations that delete ENaC's PY motifs render the channel resistant to NEDD4L and cause severe early-onset hypertension. NEDD4L is, however, a general regulator of membrane proteins: it ubiquitinates numerous ion channels, transporters, and receptors, as well as signaling proteins such as PTEN and members of the TGF-beta pathway. Through these diverse substrates, NEDD4L influences neuronal excitability, cardiac function, immune responses, and cancer, making it a molecule of wide-ranging physiological and pathological importance.

Figure 1. The structure of NEDD4L.

HECT-Domain Ligase Architecture and Substrate Selection
NEDD4L belongs to the NEDD4 family of HECT-domain E3 ligases, which differ from RING ligases in that they form a covalent intermediate with ubiquitin before transferring it to the substrate.
The protein contains an N-terminal C2 domain that mediates membrane association, multiple WW domains that recognize proline-rich PY motifs in substrates, and a C-terminal HECT domain that carries out the ubiquitin transfer reaction.
The NEDD4L gene is located on human chromosome 18, and alternative splicing generates isoforms with different substrate-binding properties and tissue distributions.
Substrate recognition is dictated largely by the WW domains, which bind short PY (PPxY) sequences; proteins lacking such motifs are generally poor substrates unless they are presented by adaptor proteins.
Because ubiquitination of plasma membrane proteins promotes their endocytosis and lysosomal degradation, NEDD4L acts as a master regulator of cell-surface protein abundance.
The activity and stability of NEDD4L itself are controlled by phosphorylation, ubiquitination, and interactions with accessory proteins, allowing cells to fine-tune the rate of substrate removal.
Mutations that alter the subcellular localization of NEDD4L can convert the ligase into a driver of disease, as seen in some inherited forms of epilepsy.

Sodium Homeostasis, Hypertension, and Broad Roles in Health and Disease
In the distal nephron and collecting duct of the kidney, NEDD4L-mediated ubiquitination of ENaC limits sodium reabsorption, and loss of this regulation increases sodium retention and elevates blood pressure.
Genetic studies have associated common NEDD4L variants with blood pressure variation and hypertension risk, and animal models with reduced NEDD4L expression are hypertensive.
In Liddle syndrome, mutations that delete or alter the PY motifs of ENaC prevent NEDD4L binding, producing constitutive channel activity and severe hypertension with low renin and aldosterone, a direct demonstration of the pathway's importance.
Beyond ENaC, NEDD4L ubiquitinates voltage-gated sodium channels in the brain, and rare NEDD4L mutations or altered expression have been linked to epilepsy and neuronal hyperexcitability.
The ligase also targets the tumor suppressor PTEN and TGF-beta receptors, and its deregulation in cancer can influence tumor cell survival, invasion, and drug responsiveness in a context-dependent manner.
Because of its central role in sodium balance, NEDD4L is being studied as a therapeutic target for hypertension, and strategies that modulate its activity could complement existing diuretic and antihypertensive treatments.

Alternate Names for NEDD4L

NEDD4L; neural precursor cell expressed, developmentally down-regulated 4-like, E3 ubiquitin protein ligase; RSP5; NEDD4-2; NEDD4.2; hNEDD4-2; E3 ubiquitin-protein ligase NEDD4-like; ubiquitin-protein ligase Rsp5;