PMR1/SPCA Ca2+ pumps and the role of the Golgi apparatus as a Ca2+ store

Besides the well-known sarco/endoplasmic-reticulum Ca2+-transport ATPases (SERCA), animal cells contain a much less characterized P-type Ca2+-transport ATPase: the PMR1/SPCA Ca2+/Mn2+-transport ATPase. SPCA is mainly targeted to the Golgi apparatus. Phylogenetic analysis indicates that it might be more closely related to a putative ancestral Ca2+ pump than SERCA. SPCA supplies the Golgi apparatus, and possibly other more distal compartments of the secretory pathway, with the Ca2+ and Mn2+ necessary for the production and processing of secretory proteins. In the lactating mammary gland, SPCA appears to be the primary pump responsible for supplementing the milk with high (60–100 mM) Ca2+. It could also play a role in detoxification of cells overloaded with Mn2+. Mutations in the human gene encoding the SPCA pump (ATP2C1) result in Hailey–Hailey disease, a keratinocyte disorder characterized by incomplete cell adhesion. Recent observations show that the Golgi apparatus can function as a Ca2+ store, which can be involved in setting up cytosolic Ca2+ oscillations.