Meltrin β (ADAM19) mediates ectodomain shedding of Neuregulin β1 in the Golgi apparatus:: fluorescence correlation spectroscopic observation of the dynamics of ectodomain shedding in living cells

Membrane-anchored Neuregulin beta 1 sheds its ectodomain as soluble factors. Two proteases that belong to a disintegrin and metalloprotease (ADAM) family are known to cleave Neuregulin beta 1. One is tumor necrosis factor-alpha converting enzyme (TACE/ADAM17). The other is Meltrin beta (ADAM19). Against our expectation that shedding by ADAM proteases occurs at the cell surface, here we found that Meltrin beta mediates the ectodomain shedding of Neuregulin beta 1 in the Golgi apparatus. Meltrin beta was localized in and around the Golgi apparatus in developing sensory neurons. Subcellular fractionation revealed that Meltrin beta generated soluble Neuregulin beta 1 in Golgi-enriched fractions while TACE-cleaved Neuregulin beta 1 was recovered in lighter fractions. To examine whether Meltrin beta-mediated ectodomain shedding occurs in the Golgi apparatus in living cells, we took advantage of different diffusion properties of cleavage products from those of membrane-anchored precursor proteins. Fluorescence correlation spectroscopy (FCS) is the most sensitive method to determine milli similar to submillisecond diffusion in vivo. Protease-active Meltrin beta caused a shift in autocorrelation function in FCS of green fluorescent protein (GFP)-tagged Neuregulin beta 1 in the Golgi apparatus, suggesting a conversion of Neuregulin beta 1 molecules from membrane-anchored to soluble forms in that organelle. The Golgi apparatus is a site of processing Neuregulin beta 1 by Meltrin beta.