Analysis of CAPS2 gene function

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CAPS protein regulates exocytosis of catecholamine- or neuropeptide-containing dense-core vesicles (DCVs) at secretion sites such as nerve terminals. However, large amounts of CAPS protein are localized in the cell soma, and the role of somal CAPS protein remains unclear. We showed that somal CAPS1 plays an important role in dense-core vesicle (DCV) trafficking in the trans-Golgi network. The anti-CAPS1 antibody appeared to pull down membrane fractions, including many Golgi-associated proteins such as ADP-ribosylation factor (ARF) small GTPases. Biochemical analyses of the protein-protein interaction showed that CAPS1 interacted specifically with the class II ARF4/ARF5, but not with other classes of ARFs, via the pleckstrin homology (PH) domain in a GDP-bound ARF form-specific manner. The PH domain of CAPS1 showed high affinity for the Golgi membrane, thereby recruiting ARF4/ARF5 to the Golgi complex. These findings implicate a functional role for CAPS1 protein in regulating DCV trafficking in the trans-Golgi network.