Oculodentodigital dysplasia (
ODDD) is a dominantly inherited human disorder associated with different symptoms like craniofacial anomalies,
syndactyly and heart dysfunction.
ODDD is caused by mutations in the GJA1 gene encoding the
gap junction protein connexin43 (
Cx43). Here, we have characterized four
Cx43 mutations (I31M, G138R, G143S and H194P) after stable expression in HeLa cells. In patients, the I31M and G138R mutations showed all phenotypic characteristics of
ODDD, whereas G143S did not result in facial abnormalities and H194P mutated patients exhibited no
syndactylies. In transfected HeLa cells, these mutations led to lack of the P2 phosphorylation state of the
Cx43 protein, complete inhibition of gap junctional coupling measured by
neurobiotin transfer and increased hemichannel activity. In addition, altered trafficking and delayed degradation were found in these mutants by immunofluorescence and pulse-chase analyses. In G138R and G143S mutants, the increased hemichannel activity correlated with an increased half-time of the
Cx43 protein. However, the I31M mutated
protein showed no extended half-time. Thus, the increased hemichannel activity may be directly caused by an altered conformation of the mutated channel forming
protein. We hypothesize that increased hemichannel activity may aggravate the phenotypic abnormalities in
ODDD patients who are deficient in
Cx43 gap junction channels.