The peptides identified by mass spectrometry analysis are underlined with adouble line. to determine their colocalization in the retina. The effect of CaBP5 on dopamine release and neurite outgrowth of PC12 cells was analyzed using ELISA and fluorescent labeling. == Results. == Using affinity chromatography, the authors identified Munc181 and myosin VI as interacting partners for CaBP5. Munc181 was also identified using the yeast two-hybrid system. Colocalization and coimmunoprecipitation of CaBP5 with these two proteins in retinal tissue further established their physiological interactions. Furthermore, CaBP5 expression in NGF-stimulated PC12 cells stimulates neurite outgrowth and dopamine exocytosis. == Conclusions. == This study shows that CaBP5 interacts with Munc181 and myosin VI, two proteins involved in the synaptic vesicle cycle. Together with the effect of CaBP5 in stimulating neurite outgrowth and vesicle exocytosis in PC12 cells, these results suggest that CaBP5 plays a role in neurotransmitter release. Asubfamily of neuronal Ca2+-binding proteins is highly similar to calmodulin (CaBP18), and CaBP5 is a member of that subfamily.13CaBP4 function has been well characterized. It is localized at the photoreceptor synaptic terminals and is essential for photoreceptor synaptic function through enhanced activation of Cav1.4 L-type voltage-gated Ca2+channels and transmitter release.4,5Mutations in theCabp4gene have been shown in patients with autosomal recessive incomplete congenital stationary night blindness and cone-rod synaptic disorder.68In contrast, the specific function of CaBP5 in vivo has not yet been clearly established. In mice, CaBP5 is expressed in rod bipolar cells, in type 5 ON-cone bipolar cells, and in type 3 OFF-cone bipolar cells.3,9,10In both KRAS G12C inhibitor 16 human and monkey retina, CaBP5 is also expressed in rod bipolar cells and both ON and OFF cone bipolar cells.11Like CaBP1, CaBP2, and CaBP4, CaBP5 has been observed in cochlear inner hair cells.12We previously generated and characterized CaBP5 knockout mice to investigate the function of CaBP5 in the retina. No evidence of morphologic changes and no significant differences in the amplitude of the ERG responses were observed in CaBP5 knockout mice compared with wild-type mice. However, the sensitivity of retinal ganglion cell light responses was reduced by 50% inCabp5/mice, suggestive of a role for CaBP5 in the normal transmission of light signals throughout the retinal circuitry. In transfected HEK293T cells, CaBP5 has a small effect in suppressing calcium-dependent inactivation of Cav1.2 and Cav1.3.12,13 To gain further insight into the function of CaBP5 in the retina, we investigated CaBP5 interaction with other retinal proteins using affinity chromatography and yeast two-hybrid screening of a retina cDNA library. We identified Munc181 and myosin VI, which are involved in synaptic vesicle cycling KRAS G12C inhibitor 16 and trafficking. A physiological interaction between these proteins is corroborated by our findings that CaBP5 also stimulates dopamine vesicle exocytosis and neurite outgrowth of PC12 cells. == Materials and Methods == == Antibodies == Commercially available antibodies were alkaline phosphatase-conjugated antimouse and antirabbit (Promega Corp., Madison, WI), rabbit antimyosin VI (Proteus Biosciences, Inc, Ramona, CA), mouse antiMunc181 (BD Biosciences, San Jose, CA; for immunohistochemistry and Western blot analysis experiments), rabbit antisyntaxin-3 (Synaptic Systems, Gttingen, Germany), and Alexa Fluor 555 goat antimouse and Alexa Fluor 488 goat antirabbit (Invitrogen, Carlsbad, CA). == CaBP5 Affinity Chromatography == The full-length bovine 6His-tagged CaBP53was coupled to CNBr-activated gel filtration media (Sepharose; GE Healthcare, Piscataway, NJ) according to the manufacturer’s protocol. Bovine retinas obtained from In Vision BioResources (Seattle, WA) Mouse monoclonal to Cyclin E2 were homogenized in 50 mM Hepes, pH 7.4, 100 mM NaCl, 5 mM MgCl2,0.5 mM dithiothreitol (DTT), 10 mM dodecyl–maltoside, and a KRAS G12C inhibitor 16 cocktail of inhibitor of proteases (Sigma, St. Louis, MO) with or without 1 mM CaCl2using a glass-glass homogenizer. The homogenate was centrifuged at 40,000gfor 20 minutes at 4C. The supernatant was loaded on the CaBP5-gel filtration media (Sepharose; GE Healthcare), and the column was washed with the homogenization buffer containing 150 mM NaCl..
