Investigating the fundamental mechanisms of immune cell exocytosis

点击翻译按钮获取中文摘要

Vesicular exocytosis is a fundamental cellular process that plays an imperative role in both brain and immune system function. In the brain, synaptic vesicle exocytosis is the basis for interneuronal communication, enabling a diversity of functional and cognitive processes. In the immune system, specialized immune cells such as mast cells, natural killer (NK) cells and cytotoxic T-lymphocytes (CTLs) undergo secretory granule exocytosis, which facilitates the eradication of infected and malignant cells. Neurons and immune cells use paralogous sets of proteins to control Ca2+-dependent exocytosis. However, the functional machinery involved in immune cell exocytosis is much less characterized and understudied compared to the intensively studied neuronal exocytosis. My lab has developed extensive knowledge and expertise in studying both neuronal and immune cell exocytosis, which has led to a synergy in understanding common and distinct aspects between the two processes. For example, although SNARE proteins play essential roles in both types of exocytosis, each type appears to utilize different isoforms of SNARE proteins. Furthermore, neuronal and immune cell exocytosis also employ distinct proteins for inducing exocytosis, although common C2 domains seem to be used for the Ca2+ sensing action that is required. The long-term objective of the present research program is to elucidate the mechanisms of immune cell exocytosis and ultimately, to modify and enhance immune cell exocytosis to generate a more robust immune system. The short-term objective is to determine the key SNARE proteins and their regulators (or priming proteins) that mediate immune cell exocytosis and to investigate the underlying biochemical mechanisms of immune cell exocytotic regulation. Based on our recent studies, we propose the following hypotheses: 1) Syntaxin-3 and SNAP-23 are the key t-SNARE proteins involved in immune cell exocytosis. 2) Munc13-4 plays a dual role in secretory granule exocytosis by acting as a Ca2+ sensor for exocytosis and facilitating exocytotic priming along with Munc18-2. 3) The Ca2+ sensing function of Munc13-4 is mediated via its C2 domains, while the priming function of Munc13-4 and Munc18-2 is facilitated through interactions with the SNARE complexes containing syntaxin-3 and SNAP-23. We will explore these hypotheses by focusing on the following Specific Aims: Aim 1. What are the critical t-SNARE proteins for immune cell exocytosis? Aim 2. Can potential gain-of-function Munc13-4 and Munc18-2 mutants enhance exocytosis from immune cells as well as increase the cytotoxicity of NK cells? Aim 3. What is the biochemical basis for the regulatory functions of Munc13-4? Our research will provide fundamental insight into the mechanisms of granule exocytosis in immune cells. Importantly, the knowledge that would be obtained from this study has the potential to reveal novel strategies for improving the effectiveness of the immune system.