Limits...
An atrial-fibrillation-linked connexin40 mutant is retained in the endoplasmic reticulum and impairs the function of atrial gap-junction channels.

Sun Y, Tong X, Chen H, Huang T, Shao Q, Huang W, Laird DW, Bai D - Dis Model Mech (2014)

Bottom Line: When the Q49X mutant was co-expressed with Cx40 or Cx43, the mutant substantially reduced the gap-junction plaque formation of Cx40 and Cx43.Electrophysiological studies revealed no electrical coupling of cell pairs expressing the mutant alone and a significant decrease in the coupling conductance when the mutant was co-expressed with Cx40 or Cx43.Further colocalization experiments with the organelle residential proteins indicate that Q49X was retained in the endoplasmic reticulum.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, The University of Western Ontario, London, ON N6A 5C1, Canada.

ABSTRACT
Connexin40 (Cx40)-containing gap-junction channels are expressed in the atrial myocardium and provide a low-resistance passage for rapid impulse propagation. A germline mutation in the GJA5 gene, which encodes Cx40, resulting in a truncated Cx40 (Q49X) was identified in a large Chinese family with lone (idiopathic) atrial fibrillation (AF). This mutation co-segregated with seven AF probands in an autosomal-dominant way over generations. To test the hypothesis that this Cx40 mutant affects the distribution and function of atrial gap junctions, we studied the Q49X mutant in gap-junction-deficient HeLa and N2A cells. The Q49X mutant, unlike wild-type Cx40, was typically localized in the cytoplasm and failed to form gap-junction plaques at cell-cell interfaces. When the Q49X mutant was co-expressed with Cx40 or Cx43, the mutant substantially reduced the gap-junction plaque formation of Cx40 and Cx43. Electrophysiological studies revealed no electrical coupling of cell pairs expressing the mutant alone and a significant decrease in the coupling conductance when the mutant was co-expressed with Cx40 or Cx43. Further colocalization experiments with the organelle residential proteins indicate that Q49X was retained in the endoplasmic reticulum. These findings provide evidence that the Q49X mutant is capable of impairing gap-junction distribution and function of key atrial connexins, which might play a role in the predisposition to and onset of AF.

Show MeSH

Related in: MedlinePlus

Known lone-AF-linked Cx40 mutants. Composite model of Cx40 denoting the locations of mutations associated with AF. AF-linked somatic (yellow circles) and germline (red circles) Cx40 mutations are illustrated. All of the AF-linked germline Cx40 mutants are autosomal-dominantly inherited. The Q49X mutant was predicted to be a loss-of-function mutant because it retains only the N-terminus, first transmembrane domain and a small part of the first extracellular domain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC4007407&req=5

f1-0070561: Known lone-AF-linked Cx40 mutants. Composite model of Cx40 denoting the locations of mutations associated with AF. AF-linked somatic (yellow circles) and germline (red circles) Cx40 mutations are illustrated. All of the AF-linked germline Cx40 mutants are autosomal-dominantly inherited. The Q49X mutant was predicted to be a loss-of-function mutant because it retains only the N-terminus, first transmembrane domain and a small part of the first extracellular domain.

Mentions: In the present study, we characterized the Q49X AF-linked mutant, which consists of only the N-terminus, first transmembrane domain and a small part of the first extracellular loop of Cx40 (Fig. 1). Our results indicate that the Q49X mutant was not localized to cell-cell junctions but was retained within the endoplasmic reticulum (ER). Interestingly, the Q49X mutant also displayed dominant-negative effects on the formation of functional gap junctions composed of Cx40 or Cx43. These findings in mammalian cell lines are consistent with the idea that the truncated Cx40 mutant could impair the overall gap-junction function in the atria and possibly play a role in the pathogenesis of AF.


An atrial-fibrillation-linked connexin40 mutant is retained in the endoplasmic reticulum and impairs the function of atrial gap-junction channels.

Sun Y, Tong X, Chen H, Huang T, Shao Q, Huang W, Laird DW, Bai D - Dis Model Mech (2014)

Known lone-AF-linked Cx40 mutants. Composite model of Cx40 denoting the locations of mutations associated with AF. AF-linked somatic (yellow circles) and germline (red circles) Cx40 mutations are illustrated. All of the AF-linked germline Cx40 mutants are autosomal-dominantly inherited. The Q49X mutant was predicted to be a loss-of-function mutant because it retains only the N-terminus, first transmembrane domain and a small part of the first extracellular domain.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4007407&req=5

f1-0070561: Known lone-AF-linked Cx40 mutants. Composite model of Cx40 denoting the locations of mutations associated with AF. AF-linked somatic (yellow circles) and germline (red circles) Cx40 mutations are illustrated. All of the AF-linked germline Cx40 mutants are autosomal-dominantly inherited. The Q49X mutant was predicted to be a loss-of-function mutant because it retains only the N-terminus, first transmembrane domain and a small part of the first extracellular domain.
Mentions: In the present study, we characterized the Q49X AF-linked mutant, which consists of only the N-terminus, first transmembrane domain and a small part of the first extracellular loop of Cx40 (Fig. 1). Our results indicate that the Q49X mutant was not localized to cell-cell junctions but was retained within the endoplasmic reticulum (ER). Interestingly, the Q49X mutant also displayed dominant-negative effects on the formation of functional gap junctions composed of Cx40 or Cx43. These findings in mammalian cell lines are consistent with the idea that the truncated Cx40 mutant could impair the overall gap-junction function in the atria and possibly play a role in the pathogenesis of AF.

Bottom Line: When the Q49X mutant was co-expressed with Cx40 or Cx43, the mutant substantially reduced the gap-junction plaque formation of Cx40 and Cx43.Electrophysiological studies revealed no electrical coupling of cell pairs expressing the mutant alone and a significant decrease in the coupling conductance when the mutant was co-expressed with Cx40 or Cx43.Further colocalization experiments with the organelle residential proteins indicate that Q49X was retained in the endoplasmic reticulum.

View Article: PubMed Central - PubMed

Affiliation: Department of Physiology and Pharmacology, The University of Western Ontario, London, ON N6A 5C1, Canada.

ABSTRACT
Connexin40 (Cx40)-containing gap-junction channels are expressed in the atrial myocardium and provide a low-resistance passage for rapid impulse propagation. A germline mutation in the GJA5 gene, which encodes Cx40, resulting in a truncated Cx40 (Q49X) was identified in a large Chinese family with lone (idiopathic) atrial fibrillation (AF). This mutation co-segregated with seven AF probands in an autosomal-dominant way over generations. To test the hypothesis that this Cx40 mutant affects the distribution and function of atrial gap junctions, we studied the Q49X mutant in gap-junction-deficient HeLa and N2A cells. The Q49X mutant, unlike wild-type Cx40, was typically localized in the cytoplasm and failed to form gap-junction plaques at cell-cell interfaces. When the Q49X mutant was co-expressed with Cx40 or Cx43, the mutant substantially reduced the gap-junction plaque formation of Cx40 and Cx43. Electrophysiological studies revealed no electrical coupling of cell pairs expressing the mutant alone and a significant decrease in the coupling conductance when the mutant was co-expressed with Cx40 or Cx43. Further colocalization experiments with the organelle residential proteins indicate that Q49X was retained in the endoplasmic reticulum. These findings provide evidence that the Q49X mutant is capable of impairing gap-junction distribution and function of key atrial connexins, which might play a role in the predisposition to and onset of AF.

Show MeSH
Related in: MedlinePlus