A Connexin50 Mutant, CX50fs, That Causes Cataracts Is Unstable, but Is Rescued by a Proteasomal Inhibitor

Minogue, Peter J.; Beyer, Eric C.; Berthoud, Viviana M.

doi:10.1074/jbc.m113.452847

Cited by 22 publications

(27 citation statements)

References 48 publications

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“…We suspect that the Cx40 protein is partially mis-folded or is slow to assume its proper folding, therefore it is susceptible to “quality control”. Our findings regarding these Cx40 mutants parallel the conclusions drawn from our recent studies of a Cx50 frame-shift mutant containing an abnormal carboxyl-terminus that increases its susceptibility to the proteasome [31]. …”

Section: Discussionsupporting

confidence: 87%

“…The ubiquitin-proteasome system has previously been implicated in the ER-associated degradation of wild type and mutant connexins [25, 31–33]. The simplest explanation for the faster degradation of G38D is that most of the protein undergoes proteasomal degradation before it can reach the plasma membrane and form gap junction plaques (probably in early compartments of the secretory pathway).…”

Section: Discussionmentioning

confidence: 99%

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Degradation of a connexin40 mutant linked to atrial fibrillation is accelerated

Gemel

Simon

Patel

et al. 2014

Journal of Molecular and Cellular Cardiology

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Several Cx40 mutants have been identified in patients with atrial fibrillation (AF). We have been working to identify physiological or cell biological abnormalities of several these human mutants that might explain how they contribute to disease pathogenesis. Wild type (wt) Cx40 or four different mutants (P88S, G38D, V85I, and L229M) were expressed by transfection of communication-deficient HeLa cells or HL-1 cardiomyocytes. Biophysical channel properties and the sub-cellular localization and protein levels of Cx40 were characterized. Wild type Cx40 and all mutants except P88S formed gap junction plaques and induced significant gap junctional conductances. The functional mutants showed only modest alterations of single channel conductances or gating by trans-junctional voltage as compared to wtCx40. However, immunoblotting indicated that the steady state levels of G38D, V85I, and L229M were reduced relative to wtCx40; most strikingly, G38D was only 20 − 31% of wild type levels. After inhibition of protein synthesis with cycloheximide, G38D (and to a lesser extent the other mutants) disappeared much faster than wtCx40. Treatment with the proteasomal inhibitor, epoxomicin, greatly increased levels of G38D and restored the abundance of gap junctions and the extent of intercellular dye transfer. Thus, G38D, V85I, and L229M are functional mutants of Cx40 with small alterations of physiological properties, but accelerated degradation by the proteasome. These findings suggest a novel mechanism (protein instability) for the pathogenesis of AF due to a connexin mutation and a novel approach to therapy (protease inhibition).

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Section: Discussionsupporting

confidence: 87%

Section: Discussionmentioning

confidence: 99%

Degradation of a connexin40 mutant linked to atrial fibrillation is accelerated

Gemel

Simon

Patel

et al. 2014

Journal of Molecular and Cellular Cardiology

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“…Some connexin mutants that do not traffic properly are not degraded by the proteasome. Chloroquine treatment of HeLa cells transfected with CMTX-associated Cx32 mutants that are retained in the Golgi led to intracellular accumulation of Cx32-positive granules that partially co-localized with a lysosomal-associated membrane protein [98]. Thus, at least some of the mutants may be routed directly to the lysosome for degradation resembling the by-pass pathway described by Qin et al [72].…”

Section: Degradation Of Disease-linked Mutant Connexinsmentioning

confidence: 82%

“…Proteasomal inhibition increased the levels of mutant Cx32 protein, but did not alter their cytoplasmic distribution [73]. In contrast, trafficking to the plasma membrane and function of an autosomal recessive cataract‐linked Cx50 mutant, Cx50fs, which undergoes proteasomal degradation, were rescued by proteasomal inhibition [96]. These effects were independent of Akt protein kinase activity [96].…”

Section: Degradation Of Disease‐linked Mutant Connexinsmentioning

confidence: 99%

Degradation of connexins and gap junctions

2014

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Connexin proteins are short-lived within the cell, whether present in the secretory pathway or in gap junction plaques. Their levels can be modulated by their rate of degradation. Connexins, at different stages of assembly, are degraded through the proteasomal, endo-/lysosomal, and phago-/lysosomal pathways. In this review, we summarize the current knowledge about connexin and gap junction degradation including the signals and protein-protein interactions that participate in their targeting for degradation.

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“…CIP75 mediates the proteasomal degradation of Cx43 via ERAD by facilitating the interaction of Cx43 with the proteasome [27,29]. Notably, this interaction does not require prior ubiquitination of Cx43 [26,30], as is typically found on proteins targeted for proteasomal degradation, such as Cx32 and Cx50 [31,32]. …”

Section: Introductionmentioning

confidence: 99%

Degradation of gap junction connexins is regulated by the interaction with Cx43-interacting protein of 75 kDa (CIP75)

Kopanic

Schlingmann

Koval

et al. 2015

Biochemical Journal

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Connexins are a family of transmembrane proteins that form gap junction channels. These proteins undergo both proteasomal and lysosomal degradation, mechanisms that serve to regulate connexin levels. Our previous work described CIP75 [connexin43 (Cx43)-interacting protein of 75 kDa], a protein involved in proteasomal degradation, as a novel Cx43-interacting protein. We have discovered two additional connexins, connexin40 (Cx40) and connexin45 (Cx45), that interact with CIP75. Nuclear magnetic resonance (NMR) analyses identified the direct interaction of the CIP75 UBA domain with the carboxyl-terminal (CT) domains of Cx40 and Cx45. Reduction in CIP75 by shRNA in HeLa cells expressing Cx40 or Cx45 resulted in increased levels of the connexins. Furthermore, treatment with trafficking inhibitors confirmed that both connexins undergo endoplasmic reticulum-associated degradation (ERAD), and that CIP75 preferentially interacts with the connexin proteins bound for proteasomal degradation from the ER. In addition, we have also discovered that CIP75 interacts with ER-localized Cx32 in a process that is likely mediated by Cx32 ubiquitination. Thus, we have identified novel interacting connexin proteins of CIP75, indicating a role for CIP75 in regulating the levels of connexins in general, through proteasomal degradation.

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A Connexin50 Mutant, CX50fs, That Causes Cataracts Is Unstable, but Is Rescued by a Proteasomal Inhibitor

Cited by 22 publications

References 48 publications

Degradation of a connexin40 mutant linked to atrial fibrillation is accelerated

Degradation of a connexin40 mutant linked to atrial fibrillation is accelerated

Degradation of connexins and gap junctions

Degradation of gap junction connexins is regulated by the interaction with Cx43-interacting protein of 75 kDa (CIP75)

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