Calcium regulation of secretion in neuroendocrine cells

描述(申请人提供)：神经肽、生物胺和神经营养因子通过调节突触前和突触后功能来影响突触传递。这些神经调节剂的调节释放是通过钙离子依赖的致密核小泡(DCV)与质膜的融合来介导的。尽管调控DCV的胞吐类似于介导突触递质释放的突触小泡(SVS)的钙依赖性胞吐，但这些过程在速度、潜伏期、钙调节和位置上都不同。更全面地了解钙离子触发的DCV融合的分子机制将揭示两种囊泡融合途径的异同，这两种途径可以识别选择性抑制调节剂分泌的独特药物靶点，而不会抑制突触传递。蛋白CAPS(分泌物中的钙依赖激活蛋白)似乎是DCV所必需的，而不是SV胞吐所必需的。我们将阐明CAPS在调节DCV融合中的作用的分子机制，并确定该蛋白在神经系统中的生理作用。CAPS是一种与PIP2结合的蛋白，它与SNARE融合机制的关键成分Synaxin具有高亲和力相互作用。这些相互作用可能在DCV胞吐的融合前晚期调节CAPS的功能。CAPS还能与RabPhilin结合，这可能在一定程度上调节CAPS与DCV的相互作用。我们的具体目标将是：1.确定CAPS-Synaxin相互作用在DCV胞吐中的功能意义；2.确定CAPS在DCV胞吐中是否作为PIP2效应因子发挥作用；3.确定CAPS在DCV胞吐中选择性作用的基础以及这是否通过RabPhilin相互作用介导；以及4.确定CAPS在调节神经肽、生物胺和神经营养素分泌的神经传递通路中的一般作用。这项工作的结果将有助于了解神经传递途径，并有助于分泌囊泡与质膜融合的分子基础。

DESCRIPTION (provided by applicant): Neuropeptides, biogenic amines, and neurotrophins affect synaptic transmission by regulating pre- and postsynaptic function. The regulated release of these neuromodulators is mediated by the Ca2+-dependent fusion of dense-core vesicles (DCVs) with the plasma membrane. Although regulated DCV exocytosis is similar to the Ca2+-dependent exocytosis of synaptic vesicles (SVs) that mediate synaptic transmitter release, these processes differ in speed, latency, Ca2+ regulation and location. A fuller understanding of molecular mechanisms underlying Ca2+-triggered DCV fusion will reveal similarities and differences in the two vesicle fusion pathways that could identify unique drug targets for the selective inhibition of modulator secretion without inhibiting synaptic transmission. The protein CAPS (Ca2+-dependent activator protein in secretion) appears to be required for DCV but not SV exocytosis. We will elucidate the molecular mechanism of CAPS function in regulated DCV fusion and determine the physiological role of this protein in the nervous system. CAPS is a PIP2-binding protein that exhibits high affinity interactions with syntaxin, a key component of the SNARE fusion machinery. These interactions may mediate the function of CAPS at a late pre-fusion step in DCV exocytosis. CAPS also binds rabphilin, which may in part mediate CAPS interactions with DCVs. Our specific aims will be: 1. To determine the functional significance of CAPS-syntaxin interactions for DCV exocytosis; 2. To determine if CAPS functions as a PIP2 effector in DCV exocytosis; 3. To determine the basis for the selective role of CAPS in DCV exocytosis and whether this is mediated through rabphilin interactions; and 4. To determine the general role of CAPS in neural trafficking pathways that mediate neuropeptide, biogenic amine and neurotrophin secretion. The results from this work will contribute to understanding neural trafficking pathways and to the molecular basis for secretory vesicle fusion with the plasma membrane.