Regulation of the Human Ether-a-go-go Related Gene Potassium Channel by Neural Precursor Cell Expressed Developmentally Down-regulated Protein 4-2 Interacting Proteins
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Dysfunction of the human ether-a-go-go related gene (hERG)-encoded rapidly activating delayed rectifier K+ channel is a major cause of long QT syndrome (LQTS) due to its critical role in the repolarization of cardiac action potentials. The density of hERG channels on the cell surface, as a key determinant of its regular function, is balanced by channel trafficking to and internalization from the plasma membrane. We have shown that the E3 ubiquitin (Ub) ligase, Nedd4-2 (neural precursor cell expressed developmentally down-regulated protein 4-2), regulates hERG channel degradation by targeting the PY motif in the C-terminus of hERG channels. Interestingly, although a PY motif exists in both the immature (intracellular) and mature (cell-surface) channels, Nedd4-2 selectively degrades the mature hERG proteins. Moreover, Nedd4-2 is modulated by various proteins, such as protein kinase C (PKC). In this work, I investigated the hypotheses that the selective degradation of the 155-kDa hERG channel by Nedd4-2 is achieved by additional Nedd4 family interacting proteins (Ndfips) and that PKC signalling regulates hERG expression and function through Nedd4-2. Using whole-cell patch-clamp, Western blot, and immunocytochemistry, I demonstrated that Nedd4-2 is directed to specific cellular compartments by Ndfip1 and Ndfip2. Ndfip1 is primarily localized in the Golgi apparatus where it recruits Nedd4-2 to target mature hERG proteins for degradation during channel trafficking to the plasma membrane. Ndfip2 mainly recruits Nedd4-2 to the multivesicular bodies (MVBs), which may impair MVBs function and impede the degradation of internalized hERG proteins. On the other hand, PKA and PKC activations increase hERG proteins on the plasma membrane by distinct mechanisms. While it is possible that PKA enhances hERG protein synthesis, PKC attenuates hERG channel degradation by inactivating Nedd4-2 via phosphorylation. These findings extend our understanding of hERG channel regulation by Nedd4-2 and provide information useful for rescuing impaired hERG function in LQTS.