Abstract
The voltage-dependent potassium channel Kv1.3 participates in the immune response. Kv1.3 is essential in different cellular functions, such as proliferation, activation and apoptosis. Because aberrant expression of Kv1.3 is linked to autoimmune diseases, fine-tuning its function is crucial for leukocyte physiology. Regulatory KCNE subunits are expressed in the immune system, and KCNE4 specifically tightly regulates Kv1.3. KCNE4 modulates Kv1.3 currents slowing activation, accelerating inactivation and retaining the channel at the endoplasmic reticulum (ER), thereby altering its membrane localization. In addition, KCNE4 genomic variants are associated with immune pathologies. Therefore, an in-depth knowledge of KCNE4 function is extremely relevant for understanding immune system physiology. We demonstrate that KCNE4 dimerizes, which is unique among KCNE regulatory peptide family members. Furthermore, the juxtamembrane tetraleucine carboxyl-terminal domain of KCNE4 is a structural platform in which Kv1.3, Ca2+/calmodulin (CaM) and dimerizing KCNE4 compete for multiple interaction partners. CaM-dependent KCNE4 dimerization controls KCNE4 membrane targeting and modulates its interaction with Kv1.3. KCNE4, which is highly retained at the ER, contains an important ER retention motif near the tetraleucine motif. Upon escaping the ER in a CaM-dependent pattern, KCNE4 follows a COP-II-dependent forward trafficking mechanism. Therefore, CaM, an essential signaling molecule that controls the dimerization and membrane targeting of KCNE4, modulates the KCNE4-dependent regulation of Kv1.3, which in turn fine-tunes leukocyte physiology.
Highlights
The voltage-dependent potassium channel Kv1.3 participates in the immune response
KCNEs are present in the immune system, and their expression is regulated by several insults, highlighting the importance of this peptide family in leukocytes[8,9]
The fact that several dileucine-rich domains participate in protein–protein interactions and that the tetraleucine signature of KCNE4 facilitates the association with CaM and Kv1.3 points to whether this element could be involved in further interactions regulated by CaM
Summary
The voltage-dependent potassium channel Kv1.3 participates in the immune response. Kv1.3 is essential in different cellular functions, such as proliferation, activation and apoptosis. The juxtamembrane tetraleucine carboxyl-terminal domain of KCNE4 is a structural platform in which Kv1.3, Ca2+/calmodulin (CaM) and dimerizing KCNE4 compete for multiple interaction partners. CaM-dependent KCNE4 dimerization controls KCNE4 membrane targeting and modulates its interaction with Kv1.3. CaM, an essential signaling molecule that controls the dimerization and membrane targeting of KCNE4, modulates the KCNE4-dependent regulation of Kv1.3, which in turn fine-tunes leukocyte physiology. KCNE4 interacts with Ca2+/CaM through a tetraleucine domain in the juxtamembrane of the KCNE4 C-terminus[15]. The tetraleucine motif hub forms a competing mechanism that directs the KCNE4 association with either CaM or Kv1.3, tuning the membrane targeting of the channel. The evidence suggests that the CaM interaction, and the molecular determinants involved, is an important intracellular signaling mechanism of ion channel function
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