The Golgi PMR1 P-type ATPase of Caenorhabditis elegans - Identification ofthe gene and demonstration of calcium and manganese transport

In recent years, it has been well established that the Ca2+ concentration i n the lumen of intracellular organelles is a key determinant of cell functi on. Despite the fact that essential functions of the Golgi apparatus depend on the Ca2+ and Mn2+ concentration in its lumen, little is known on the tr ansport system responsible for ion accumulation. The Gels ion pump PMR1 has been functionally studied only in yeast, In humans, mutations in the ortho logous gene ATP2C1 cause Hailey-Hailey disease. We report here the identifi cation of the PMR1 homologue in the model organism Caenorhabditis elegans a nd after ectopic expression the direct study of its ion transport in permea bilized COS-1 cells. The C. elegans genome is predicted to contain a single PMR1 orthologue on chromosome I. We found evidence for alternative splicin g in the 5'-untranslated region, but no indication for the generation of di fferent protein isoforms. C. elegans PMR1 overexpressed in COS-1 cells tran sports Ca2+ and Mn2+ with high affinity into the Golgi apparatus in a thaps igargin-insensitive manner. Part of the accumulated Ca2+ can be released by inositol 1,4,5-trisphosphate, in agreement with the idea that the Gels app aratus is an inositol 1,4,5-trisphosphate-sensitive Ca2+ store.