Defective Potassium Channel Kir2.1 Trafficking Underlies Andersen-Tawil Syndrome

Abstract

Andersen-Tawil syndrome is a skeletal and cardiac muscle disease with developmental features caused by mutations in the inward rectifier K ؉ channel gene KCNJ2. Patients harboring these mutations exhibit extremely variable expressivities. To explore whether these mutations can be correlated with a specific patient phenotype, we expressed both wild-type (WT) and mutant genes cloned into a bi-cistronic vector. Functional expression in human embryonic kidney 293 cells showed that none of the mutant channels express current when present alone. When co-expressed with WT channels, only construct V302M-WT yields inward current. Confocal microscopy fluorescence revealed three patterns of channel expression in the cell: 1) mutations D71V, N216H, R218Q, and pore mutations co-assemble and co-localize to the membrane with the WT and exert a dominant-negative effect on the WT channels; 2) mutation V302M leads to channels that lose their ability to co-assemble with WT and traffic to the cell surface; 3) deletions ⌬95-98 and ⌬314 -315 lead to channels that do not traffic to the membrane but retain their ability to co-assemble with WT channels. These data show that the Andersen-Tawil syndrome phenotype may occur through a dominant-negative effect as well as through haplo-insufficiency and reveal amino acids critical in trafficking and conductance of the inward rectifier K ؉ channels.

Mutations of KCNJ2 gene associated with Andersen–Tawil syndrome in Korean families

“…2c). Although the defective role of this mutation for the function of inward rectifying K + channel protein was not characterized, the C-terminal region has been suggested to be an essential motif of PIP 2 binding and channel trafficking (Huang et al 1998;Zhang et al 1999;Lopes et al 2002;Bendahhou et al 2003). In addition, a neighboring V302M mutation has also shown the defect of channel trafficking .…”

Evidence for Activity-Dependent Cortical Wiring: Formation of Interhemispheric Connections in Neonatal Mouse Visual Cortex Requires Projection Neuron Activity

“…Several mutant Kir2.1 channels (144 -146GYG3 AAA, D71V, and del314 -315SY) were used to determine whether decreased expression or activity of Kir2.1 causes abnormalities in cortical development. These mutant channels are well characterized and show strong dominant-negative effects in heterologous expression systems (such as Xenopus oocytes and mammalian cell lines) (Tristani-Firouzi et al, 2002;Bendahhou et al, 2003). The 144 -146GYG3 AAA and D71V Kir2.1 mutants have a channel pore mutation and a point mutation in the first transmembrane domain, respectively; both coassemble with wild-type channels on the cell surface, thus forming nonfunctional channels and suppression of channel activity.…”

Management and Treatment of Andersen-Tawil Syndrome (ATS)

“…Other mutations act by a mechanism of haploinsufficiency, probably affecting trafficking and assembly of second messengers via the interaction of abnormal amino acid positioning along the muscle membrane where the Kir2.1 channels are localized. 6,[22][23][24] Given the ubiquitous distribution of Kir2.1 channels and the complexity of their interactions with second messengers and other associated membrane components, including anchoring and modeling molecules, it would not be surprising that the effects on these channels would extend to other molecular targets affecting other tissues or organs, either directly or indirectly. It is likely, therefore, that a wider spectrum of phenotypic expressions of KCNJ2 mutations exists.…”