Mutations in the gene (GJA1) encoding
connexin43 (
Cx43) are responsible for several rare
genetic disorders, including non-syndromic skin-limited diseases. Here we used two different functional expression systems to characterize three
Cx43 mutations linked to
palmoplantar keratoderma and congenital alopecia-1,
erythrokeratodermia variabilis et progressiva, or inflammatory
linear verrucous epidermal nevus. In HeLa cells and Xenopus oocytes, we show that Cx43-G8V, Cx43-A44V and Cx43-E227D all formed functional gap junction channels with the same efficiency as wild-type
Cx43, with normal voltage gating and a unitary conductance of ~110 pS. In HeLa cells, all three mutations also localized to regions of cell-cell contact and displayed a punctate staining pattern. In addition, we show that Cx43-G8V, Cx43-A44V and Cx43-E227D significantly increase membrane current flow through formation of active hemichannels, a novel activity that was not displayed by wild-type
Cx43. The increased membrane current was inhibited by either 2 mM
calcium, or 5 µM
gadolinium, mediated by hemichannels with a unitary conductance of ~250 pS, and was not due to elevated
mutant protein expression. The three
Cx43 mutations all showed the same gain of function activity, suggesting that augmented hemichannel activity could play a role in skin-limited diseases caused by human
Cx43 mutations.