Trafficking Of BK Channels To The Nuclear Membrane

Nucleus contains the genetic information of a cell individual,it is the place of gene expression and the control center of life activities.The nuclear envelope(NE)has a double-lipid bilayer and is made up of an outer nuclear membrane(ONM)and an inner nuclear membrane(INM).The ONM is in contact with the endoplasmic reticulum(ER),INM is in contact with the nucleoplasm.ONM and INM are connected by nuclear pore complexes(NPC).Nuclear membrane is not only important for maintaining nuclear coordination,the lacuna(perinuclear space)formed by NE is also an important calcium ion pool.Perinuclear calcium pool is a significant source of nuclear calcium signal,which can regulate gene transcription by regulating nuclear calcium signal.Recent studies have shown that transmembrane proteins,including ion channels,express in the INM and regulate gene transcription and other important physiological processes,such as IP3R,RyR,KATP and BK channels.However,it is still unclear how the ion channels pass through the NPC to the INM.According to the diffusion-retention theory,nuclear membrane proteins are synthesized from ribosomes on ER and spread to the ONM through the membrane system on ER.After the proteins reach the ONM,they pass through the NPC through the nuclear localization sequence(NLS)or other mechanisms to reach the INM,and anchor in the nuclear lamina or chromatin to play a role.Many studies have shown that the proteins of LBR,LEM and SUN families reach the INM mainly through the diffusion-retention mechanism.These proteins have some common characteristics,which are consistent with the diffusion-retention theory.Firstly,LBR and other endomembrane proteins are specially located in the INM,so they do not need to transport away from the ER through vesicles,and their diffusion on the continuous membrane structure of ER is enough to reach the target location.Mechanism to enrich on nuclear membrane has remained enigmatic.Secondly,they are all intrinsic components of nuclear membrane structure.They can stabilize nuclear membrane structure and regulate chromatin localization by anchoring and binding with with cytoskeleton.Therefore,the binding ability with nuclear lamina is the intrinsic feature feature of these nuclear membrane proteins.However,other types of membrane proteins may have different characteristics from LBR,such as ion channels.First of all,ion channels are often widely located in the membrane structure which is discontinuous with ER,such as the cytoplasmic membrane.They depend on the vesicle transport mechanism to leave the ER and be transported to the target location.This mechanism of leaving the ER may cause the dynamic process of diffusion to the nuclear membrane to become complex.On the other hand,as a membrane protein,ion channel does not have the same affinity as LBR.Based on these properties,whether the ion channels are also enriched on the nuclear membrane through the diffusion-retention pathway needs to be studied.Our previous study found that BK channels are located in the nuclear membrane of cells,so we explored the nuclear membrane location of BK channels.We use fluorescence recovery after photobleaching(FRAP)experiment to find that BK channels on the nuclear membrane have high mobility,which shows that the location of BK channels in nuclear membrane do not depend on the anchoring of nuclear membrane.By constructing a series of truncated BK channels,we found that the S0S1 connection sequence of BK channels promote its enrichment in nuclear membrane,and this process involves vesicle transport mechanism.In addition,we found a bipartite NLS in the cytoplasm of BK channels,which helps BK channels to pass through the NPC and promote its enrichment in the nuclear nuclear membrane.These results show that BK channels are enriched on the nuclear membrane by dynamic mechanisms such as vesicle transport and NPC transport.