Calbindin-D(28k) in nerve cell nuclei

Calbindin-D(28k) is a member of the large EF-hand family of calcium- binding proteins, that is believed to function, in part, as a cytosolic calcium buffer. Recent studies have demonstrated that cells containing Calbindin-D(28k) are protected from degeneration caused by conditions that elevate intracellular calcium concentrations. Since its initial discovery in 1966, Calbindin-D(28k) has been localized in the cytoplasm of many neuronal populations, but its nuclear localization has been uncertain. Using light and electron microscopic immunohistochemistry, and nuclear fractionation methods, we demonstrate localization of Calbindin-D(28k) not only in the cytoplasm, but also in the nucleus of rodent midbrain dopaminergic neurons and cerebellar Purkinje cells. The Calbindin-D(28k) immunoreactive staining intensity in the nucleus was routinely equal or greater than that in the cytoplasm. Since calcium signals are propagated to the nucleus, where they can regulate gene expression, the existence of nuclear Calbindin-D(28κ) has important implications for cellular function.