Pelizaeus-Merzbacher-like disease is caused not only by a loss of connexin47 function but also by a hemichannel dysfunction.
Autosomal recessive mutations in the GJA12/GJC2 gene encoding the gap junction protein connexin47 (C x 47) cause a form of Pelizaeus-Merzbacher-like disease (PMLD) with hypomyelination, nystagmus, impaired psychomotor development and progressive spasticity. We investigated the functional consequences of four C x 47 missense mutations (G149S, G236R, T265A, and T398I) and one C x 47 complex mutation (A98G_V99insT) by immunoblot analysis and immunocytochemistry in transfected communication-incompetent HeLa cells and in OLI-neu cells. All studied C x 47 mutants, except G236R, generated stable proteins in transfected HeLa cells and OLI-neu cells. The mutants T265A and A98G_V99insT were retained in the ER, T398I formed gap junctional plaques at the plasma membrane, and G149S showed both, structures at the plasma membrane and ER localization. Two-microelectrode voltage clamp analyses in Xenopus laevis oocytes injected with wild-type and mutant C x 47 cRNA revealed reduced hemichannel currents for G236R, T265A, and A98G_V99insT. In contrast, T398I revealed hemichannel currents comparable to wild-type. For C x 47 mutant T398I, our results indicate a defect in hemichannel function, whereas C x 47 mutants G149S, G236R, T265A, and A98G_V99insT are predicted to result in a loss of C x 47 hemichannel function. Thus, PMLD is likely to be caused by two different disease mechanisms: a loss of function and a dysfunction.
Diekmann
Simone
S
Department of Pediatrics and Pediatric Neurology, Georg August University, Göttingen, Germany.
Henneke
Marco
M
Burckhardt
Birgitta C
BC
Gärtner
Jutta
J
D000595:Amino Acid Sequence; D000818:Animals; D017630:Connexins / Q000235:genetics* / Q000502:physiology; D004566:Electrodes; D006367:HeLa Cells; D006801:Humans; D007150:Immunohistochemistry; D007473:Ion Channels / Q000737:chemistry / Q000235:genetics / Q000502:physiology*; D008969:Molecular Sequence Data; D020125:Mutation, Missense; D020371:Pelizaeus-Merzbacher Disease / Q000235:genetics*; D014982:Xenopus laevis
D017630:Connexins; D007473:Ion Channels; C427305:connexin 47