Interaction of Calcium-dependent Activator Protein for Secretion 1 (CAPS1) with the Class II ADP-ribosylation Factor Small GTPases Is Required for Dense-core Vesicle Trafficking in the trans-Golgi Network

Abstract

Ca2؉ -dependent activator protein for secretion (CAPS) 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. The present study shows that somal CAPS1 plays an important role in 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 domain in a GDP-bound ARF form-specific manner. The pleckstrin homology domain of CAPS1 showed high affinity for the Golgi membrane, thereby recruiting ARF4/ARF5 to the Golgi complex. Knockdown of either CAPS1 or ARF4/ARF5 expression caused accumulation of chromogranin, a DCV marker protein, in the Golgi, thereby reducing its DCV secretion. In addition, the overexpression of CAPS1 binding-deficient ARF5 mutants induced aberrant chromogranin accumulation in the Golgi and consequently reduced its DCV secretion. These findings implicate a functional role for CAPS1 protein in the soma, a major subcellular localization site of CAPS1 in many cell types, in regulating DCV trafficking in the trans-Golgi network; this activity occurs via protein-protein interaction with ARF4/ARF5 in a GDP-dependent manner.

CAPS1 Deficiency Perturbs Dense-Core Vesicle Trafficking and Golgi Structure and Reduces Presynaptic Release Probability in the Mouse Brain

“…Similar experiments on CAPS2 also suggest a role for the CAPS family in the TGN-DCV pathway (Sadakata et al, 2012). However, the cellular and biochemical functions of CAPS1 in the brain remain unclear, because Caps1 knock-out mice die shortly after birth (Speidel et al, 2005).…”

“…The Ca 2ϩ -dependent activator protein for secretion (CAPS) family is involved in dense-core vesicle (DCV) release (Walent et al, 1992;Ann et al, 1997;Berwin et al, 1998;Tandon et al, 1998;Renden et al, 2001;Grishanin et al, 2004;Liu et al, 2008;Sadakata et al, 2010). In mammals, there are two family members, CAPS1 (Berwin et al, 1998) and CAPS2 (Speidel et al, 2003;Sadakata et al, 2004Sadakata et al, , 2007a.…”

“…In mammals, there are two family members, CAPS1 (Berwin et al, 1998) and CAPS2 (Speidel et al, 2003;Sadakata et al, 2004Sadakata et al, , 2007a. Previous studies have shown that CAPS1 deficiency affects the secretion of catecholamines [e.g., norepinephrine (Berwin et al, 1998;Tandon et al, 1998)], neuropeptides [e.g., neuropeptide Y (Fujita et al, 2007)], and peptide hormones [e.g., insulin (Speidel et al, 2008)].…”

“…Our previous studies showed that CAPS1 interacts with the Golgi membrane and the class II ADP ribosylation factor (ARF) small GTPases (ARF4 and ARF5) and that CAPS1 knockdown (KD) and ARF-binding mutations result in abnormal morphology of the trans-Golgi network (TGN) and a decrease in the number of DCVs, suggesting that CAPS1 has a functional role in the trafficking pathway between TGN and DCVs (Sadakata et al, 2010). Similar experiments on CAPS2 also suggest a role for the CAPS family in the TGN-DCV pathway (Sadakata et al, 2012).…”

Reduced axonal localization of a Caps2 splice variant impairs axonal release of BDNF and causes autistic-like behavior in mice

“…Together, these findings represent a unique mouse model of a molecular mechanism linking BDNFmediated coordination of brain development to autism-related behaviors and patient genotype. -dependent activator protein for secretion 2 (CAPS2 or CADPS2) is a member of the CAPS protein family that regulates the trafficking of dense-core vesicles by binding both phosphoinositides and dense-core vesicles (1)(2)(3)(4)(5). We initially identified mouse Caps2 as a potent factor promoting the release of brain-derived neurotrophic factor (BDNF) during cerebellar development (6,7).…”