KCNK12 Membrane Protein Introduction

Introduction of KCNK12

Potassium channel subfamily K member 12 (KCNK12), also known as tandem pore domain halothane-inhibited potassium channel THIK-2 and K_2P12.1, is encoded by gene KCNK12. KCNK12 is classified into the two-pore-domain (K2P) family of K⁺-selective channels, a category of the eukaryotic mechanosensitive ion channel. Characterized by four transmembrane segments (M1-M4), an extracellular cap domain and a pseudo-tetrameric architecture around the central selectivity filter, human KCNK12 is mainly expressed in the kidney, especially in the proximal tubule (PT), thick ascending limb (TAL), and cortical collecting duct (CCD). Significantly, the cytoplasmic N-terminal region of KCNK12 possesses an arginine-rich motif which is recognized as a retention/retrieval signal and any mutation of this motif will induce migration of KCNK12 to the plasma membrane resulting in measurable currents.

Function of KCNK12 Membrane Protein

K2P family plays important roles in the generation of potassium leak current, contributing to the maintenance of resting membrane potential and functional phenotypes in many types of invertebrate and vertebrate neurons. However, KCNK12 belongs to the 'silent' channels of K2P family, which is not active upon heterologous expression, because of a unique combination of strong retention in the endoplasmic reticulum and low intrinsic channel activity at the plasma membrane. The mutant KCNK12-A155P located in the second membrane-spanning segment (M2) or deletion of a highly conserved 19-amino-acid region in its N terminus (THIK-2(Δ6-24) mutant) can recover its function and produce K⁺-selective currents. Similar to most members of K2P family, KCNK12 is also regulated by various physical factors and pharmacological agents, such as osmotic stress, pH, temperature, mechanical stimulation and natural ligands including polyunsaturated fatty acids (arachidonic acid (AA)), volatile anesthetics, neuroprotective drugs and antidepressants (fluoxetine), etc. Moreover, a wide range of neurotransmitters such as nitric oxide, serotonin, norepinephrine and substance P can also modulate the extracellular sensation of KCNK12. It is documented that KCNK12 can act as a novel DNA methylation marker with a strong association with pancreatic cancer. Furthermore, KCNK12 is detected in dorsal root ganglia and shows a close relation to inflammation and spontaneous pain behavior.

Fig.1 The transmembrane topology (left) and dendrogram of human K2P channels (right). (Enyedi, 2010)

Application of KCNK12 Membrane Protein in Literature

1. Theilig F., et al. Cellular localization of THIK-1 (K2P13.1) and THIK-2 (K2P12.1) K⁺ channels in the mammalian kidney. Cellular Physiology and Biochemistry. 2008, 21(1-3): 063-074. PubMed ID: 18209473
   
   

   In this article, the authors used immunocytochemical methods, in situ hybridization, and RT-PCR to identify the detailed cellular localization of THIK-1 (K(2P)13.1, KCNK13) and THIK-2 (K(2P)12.1, KCNK12) and they identified that THIK-1 and THIK-2 were mainly expressed in the proximal tubule (PT), thick ascending limb (TAL), and cortical collecting duct (CCD) in human kidney.

2. Blin S., et al. Tandem pore domain halothane-inhibited K⁺ channel subunits THIK1 and THIK2 assemble and form active channels. Journal of Biological Chemistry. 2014, 289(41): 28202-28212. PubMed ID: 25148687
   
   

   This article revealed that THIK1 and THIK2 can assemble to form active channels. Moreover, Tandem-THIK1-THIK2 can induce K⁺ currents of amplitude similar to Tandem-THIK1-THIK1 but with a noticeable difference in the current kinetics.

3. Renigunta V., et al. Breaking the silence: functional expression of the two-pore-domain potassium channel THIK-2. Pflügers Archiv-European Journal of Physiology. 2014, 466(9): 1735-1745. PubMed ID: 24297522
   
   

   This article demonstrated that deletion of a highly conserved 19-amino-acid region in its N terminus (THIK-2(Δ6-24) mutant) could lead to functional expression of the channel and produces K⁺-selective currents in Xenopus oocytes and mammalian cell lines.

4. Marsh B., et al. Leak K⁺ channel mRNAs in dorsal root ganglia: relation to inflammation and spontaneous pain behaviour. Molecular and Cellular Neuroscience. 2012, 49(3): 375-386. PubMed ID: 22273507
   
   

   The authors firstly demonstrated that THIK1, THIK2, and TWIK2 could express in dorsal root ganglia (DRGs), where K2P channels and their altered expression were associated with inflammation-induced spontaneous pain behavior (SFL).

5. Kisiel J.B., et al. New DNA methylation markers for pancreatic cancer: discovery, tissue validation, and pilot testing in pancreatic juice. Clinical cancer research. 2015, 21(19): 4473-4481. PubMed ID: 26023084
   
   

   The authors identified and validated several novel DNA methylation markers strongly associated with pancreatic cancer, including CD1D, KCNK12, CLEC11A, NDRG4, IKZF1, PKRCB, and KRAS.

KCNK12 Preparation Options

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Reference

1. Enyedi P and Czirják G. (2010). Molecular background of leak K⁺ currents: two-pore domain potassium channels. Physiological reviews. 90(2): 559-605.

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