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Intracellular transport, assembly, and degradation of wild-type and disease-linked mutant gap junction proteins

J K VanSlyke1, S M Deschenes, L S Musil

  • 1Vollum Institute for Advanced Biomedical Research, Oregon Health Sciences University, Portland, Oregon 97201, USA.

Molecular Biology of the Cell
|June 10, 2000
PubMed

Insights

Mutations in connexin32 (Cx32) cause X-linked Charcot-Marie-Tooth disease (CMTX). This study reveals Cx32 mutants are rapidly degraded by cellular quality control, not aggregated, explaining disease mechanisms.

Area of Science:

  • Cell Biology
  • Neuroscience
  • Genetics

Background:

  • Over 130 mutations in connexin32 (Cx32) are linked to X-linked Charcot-Marie-Tooth disease (CMTX), a human peripheral neuropathy.
  • The cellular processing and disease mechanisms of Cx32 mutants remain largely unknown.

Purpose of the Study:

  • To investigate the intracellular transport, assembly, and degradation of three CMTX-linked Cx32 mutants.
  • To elucidate how cellular quality control mechanisms handle these abnormal Cx32 proteins.

Main Methods:

  • Stable expression of three CMTX-linked Cx32 mutants (E208K, E186K, R142W) in PC12 cells.
  • Analysis of intracellular transport using cell imaging.
  • Assessment of protein assembly, solubility, and degradation pathways (ER, lysosomes, proteasomes).

Main Results:

  • Each Cx32 mutant exhibited distinct intracellular trafficking patterns: retention in ER (E208K), perinuclear localization with lysosomal (R142W) or ER (E186K) trafficking.
  • All mutants were soluble but failed to form functional homomeric connexons.
  • Both mutant and wild-type Cx32 proteins were rapidly degraded (t½ < 3 h), partly in the ER via proteasome-sensitive pathways.

Conclusions:

  • CMTX-linked Cx32 mutants do not cause disease through aggregation but are efficiently cleared by cellular quality control.
  • Quality control mechanisms prevent abnormal Cx32 proteins from progressing through the secretory pathway, impacting peripheral nerve function.

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