Role of Caspase-8 in Yersinia virulence and host defense

描述（由申请人提供）：宿主对细菌感染的免疫防御需要激活保守的信号通路，从而上调炎症介质的产生以清除感染。许多细菌病原体抑制这些信号通路以逃避宿主的免疫防御。这类病原体包括致病性耶尔森菌，它利用YopJ毒力因子阻断NF-？B和MAPK信号。对阻断免疫信号通路的病原体如何介导免疫防御仍知之甚少。NF - ?B阻断感染的巨噬细胞导致细胞凋亡、焦亡和坏死。令人惊讶的是，增加假结核耶尔森菌或鼠疫耶尔森菌的细胞毒性导致细菌的毒力急剧下降，这表明耶尔森菌感染诱导细胞死亡可能是宿主的一种防御机制。我们的中心假设是，细胞死亡是由耶尔森菌阻断NF- ？B和MAPK导致促炎细胞死亡，提醒未感染的邻近细胞感染的存在。然而，yopj诱导细胞死亡的机制和细胞死亡在免疫防御感染中的确切作用尚不清楚。在耶尔森菌感染期间，多种半胱天冬酶被激活，但目前还不知道耶尔森菌诱导的细胞死亡所需的特定因子。我们的初步数据表明，caspase -8在耶尔森菌诱导的细胞死亡和宿主对体内耶尔森菌感染的防御中是必需的。此外，caspase-8在响应耶尔森菌的caspase-1加工中是必需的，但在响应其他caspase-1激活刺激时则不需要。caspase- 8依赖性caspase-1激活是一种使凋亡的caspase激活焦亡细胞死亡的新途径。然而，caspase-8依赖性caspase-1激活的分子机制尚不清楚。这是一个重要的问题，因为它可能对许多阻断关键先天免疫信号通路的病原体起作用，并在导致caspase-8激活的病理刺激的背景下起作用。我们提出了两个特定的目标来解决我们知识中的这一重要空白。首先，我们将定义caspase-8依赖性caspase-1激活的分子基础，并剖析不同的细胞死亡途径对耶尔森菌诱导的细胞死亡的相对贡献。其次，我们将定义caspase-8在免疫防御耶尔森菌感染中的作用。

DESCRIPTION (provided by applicant): Host immune defense against bacterial infection requires activation of conserved signaling pathways that upregulate production of inflammatory mediators to clear infection. Many bacterial pathogens inhibit these signaling pathways in order to evade host immune defenses. Such pathogens include the pathogenic Yersiniae which utilize the YopJ virulence factor to block NF-?B and MAPK signaling. How immune defense is mediated against pathogens that block immune signaling pathways remains poorly understood. NF-?B blockade in infected macrophages leads to cell death with characteristics of apoptosis, pyroptosis, and necrosis. Surprisingly, increasing cytotoxicity of Y. pseudotuberculosis or Y. pestis results in dramatically decreased virulence of the bacteria, suggesting that induction of cell death in response to Yersinia infection may be a host defense mechanism. Our central hypothesis is that cell death triggered in response to Yersinia blockade of NF- ?B and MAPK leads to pro-inflammatory cell death that alerts uninfected neighboring cells to the presence of infection. However, the mechanisms of YopJ-induced cell death and the precise role of cell death in immune defense against infection remain unclear. Multiple caspases are activated during Yersinia infection, but no specific factor(s) are yet known that are required for Yersinia-induced cell death. Our preliminary data demonstrate that caspsase-8 is required for Yersinia-induced cell death, and for host defense in response to Yersinia infection in vivo. Furthermore, caspase-8 is required for caspase-1 processing in response to Yersinia, but not in response to other caspase-1 activating stimuli. Caspase-8-dependent caspase-1 activation is a novel pathway that enables an apoptotic caspase to activate a pyroptotic cell death. However, the molecular mechanism of caspase-8-dependent caspase-1 activation remains unknown. This is an important problem as it likely functions in response to many pathogens that block critical innate immune signaling pathways and in the context of pathological stimuli that lead to caspase-8 activation We propose two Specific Aims to address this important gap in our knowledge. First we will define the molecular basis of caspase-8-dependent activation of caspase-1, and dissect the relative contribution of distinct cell death pathways to Yersinia-induced cell death. Second, we will define the role of caspase-8 in immune defense against Yersinia infection.