F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria

Tian You Ling, Fu Yi, Tong D Lu, Xiao Li Wang, Xiaojing Sun, Monte S. Willis, Li Qun Wu, Win Kuang Shen, John P. Adelman, Hon Chi Lee

Research output: Contribution to journalArticle

Abstract

Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1F complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.

Original languageEnglish (US)
Pages (from-to)4160-4168
Number of pages9
JournalJournal of Biological Chemistry
Volume294
Issue number11
DOIs
StatePublished - Jan 1 2019

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Small-Conductance Calcium-Activated Potassium Channels
F-Box Proteins
Medical problems
Proteasome Endopeptidase Complex
Diabetes Mellitus
Ubiquitin
Down-Regulation
Proteolysis
Transfection
Muscle
Proteins
Complementary DNA
Degradation
Ubiquitin-Protein Ligases
HEK293 Cells
Vascular Smooth Muscle
Atrial Fibrillation
Muscle Cells
Small Interfering RNA
Smooth Muscle Myocytes

ASJC Scopus subject areas

  • Biochemistry
  • Molecular Biology
  • Cell Biology

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F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria. / Ling, Tian You; Yi, Fu; Lu, Tong D; Wang, Xiao Li; Sun, Xiaojing; Willis, Monte S.; Wu, Li Qun; Shen, Win Kuang; Adelman, John P.; Lee, Hon Chi.

In: Journal of Biological Chemistry, Vol. 294, No. 11, 01.01.2019, p. 4160-4168.

Research output: Contribution to journalArticle

Ling, Tian You ; Yi, Fu ; Lu, Tong D ; Wang, Xiao Li ; Sun, Xiaojing ; Willis, Monte S. ; Wu, Li Qun ; Shen, Win Kuang ; Adelman, John P. ; Lee, Hon Chi. / F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria. In: Journal of Biological Chemistry. 2019 ; Vol. 294, No. 11. pp. 4160-4168.
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abstract = "Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1F complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.",
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T1 - F-box protein-32 down-regulates small-conductance calcium-activated potassium channel 2 in diabetic mouse atria

AU - Ling, Tian You

AU - Yi, Fu

AU - Lu, Tong D

AU - Wang, Xiao Li

AU - Sun, Xiaojing

AU - Willis, Monte S.

AU - Wu, Li Qun

AU - Shen, Win Kuang

AU - Adelman, John P.

AU - Lee, Hon Chi

PY - 2019/1/1

Y1 - 2019/1/1

N2 - Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1F complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.

AB - Diabetes mellitus (DM) is an independent risk factor for atrial fibrillation, but the underlying ionic mechanism for this association remains unclear. We recently reported that expression of the small-conductance calcium-activated potassium channel 2 (SK2, encoded by KCCN2) in atria from diabetic mice is significantly down-regulated, resulting in reduced SK currents in atrial myocytes from these mice. We also reported that the level of SK2 mRNA expression is not reduced in DM atria but that the ubiquitin-proteasome system (UPS), a major mechanism of intracellular protein degradation, is activated in vascular smooth muscle cells in DM. This suggests a possible role of the UPS in reduced SK currents. To test this possibility, we examined the role of the UPS in atrial SK2 down-regulation in DM. We found that a muscle-specific E3 ligase, F-box protein 32 (FBXO-32, also called atrogin-1), was significantly up-regulated in diabetic mouse atria. Enhanced FBXO-32 expression in atrial cells significantly reduced SK2 protein expression, and siRNA-mediated FBXO-32 knockdown increased SK2 protein expression. Furthermore, co-transfection of SK2 with FBXO-32 complementary DNA in HEK293 cells significantly reduced SK2 expression, whereas co-transfection with atrogin-1F complementary DNA (a nonfunctional FBXO-32 variant in which the F-box domain is deleted) did not have any effects on SK2. These results indicate that FBXO-32 contributes to SK2 down-regulation and that the F-box domain is essential for FBXO-32 function. In conclusion, DM-induced SK2 channel down-regulation appears to be due to an FBXO-32-dependent increase in UPS-mediated SK2 protein degradation.

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