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.