Two major apoptosis pathways have been defined in mammalian cells, the Fas/TNF-R1 death receptor pathway and the mitochondria pathway. The Bcl-2 family proteins consist of both anti-apoptosis and pro- apoptosis member...Two major apoptosis pathways have been defined in mammalian cells, the Fas/TNF-R1 death receptor pathway and the mitochondria pathway. The Bcl-2 family proteins consist of both anti-apoptosis and pro- apoptosis members that regulate apoptosis, mainly by controlling the release of cytochrome c and other mitochondrial apoptotic events. However, death signals mediated by Fas/TNF-R1 receptors can usually activate caspases directly, bypassing the need for mitochondria and escaping the regulation by Bcl-2 family proteins. Bid is a novel pro-apoptosis Bcl-2 family protein that is activated by caspase 8 in response to Fas/TNF-R1 death receptor signals. Activated Bid is translocated to mitochondria and induces cytochrome c release, which in turn activates downstream caspases. Such a connection between the two apoptosis pathways could be important for induction of apoptosis in certain types of cells and responsible for the pathogenesis of a number of human diseases.展开更多
Upon encountering the antigen (Ag), the immune system can either develop a specific immune response or enter a specific state of unresponsiveness, tolerance. The response of B cells to their specific Ag can be activat...Upon encountering the antigen (Ag), the immune system can either develop a specific immune response or enter a specific state of unresponsiveness, tolerance. The response of B cells to their specific Ag can be activation and proliferation, leading to the immune response, or anergy and activation-induced cell death (AICD), leading to tolerance. AICD in B lymphocytes is a highly regulated event initiated by crosslinking of the B cell receptor (BCR). BCR engagement initiates several signaling events such as activation of PLCr, Ras, and PI3K, which generally speaking, lead to survival. However, in the absence of survival signals (CD40 or IL-4R engagement), BCR crosslinking can also promote apoptotic signal transduction pathways such as activation of effector caspases, expression of pro-apoptotic genes, and inhibition of pro-survival genes. The complex interplay between survival and death signals determines the B cell fate and, consequently, the immune response.展开更多
文摘Two major apoptosis pathways have been defined in mammalian cells, the Fas/TNF-R1 death receptor pathway and the mitochondria pathway. The Bcl-2 family proteins consist of both anti-apoptosis and pro- apoptosis members that regulate apoptosis, mainly by controlling the release of cytochrome c and other mitochondrial apoptotic events. However, death signals mediated by Fas/TNF-R1 receptors can usually activate caspases directly, bypassing the need for mitochondria and escaping the regulation by Bcl-2 family proteins. Bid is a novel pro-apoptosis Bcl-2 family protein that is activated by caspase 8 in response to Fas/TNF-R1 death receptor signals. Activated Bid is translocated to mitochondria and induces cytochrome c release, which in turn activates downstream caspases. Such a connection between the two apoptosis pathways could be important for induction of apoptosis in certain types of cells and responsible for the pathogenesis of a number of human diseases.
文摘Upon encountering the antigen (Ag), the immune system can either develop a specific immune response or enter a specific state of unresponsiveness, tolerance. The response of B cells to their specific Ag can be activation and proliferation, leading to the immune response, or anergy and activation-induced cell death (AICD), leading to tolerance. AICD in B lymphocytes is a highly regulated event initiated by crosslinking of the B cell receptor (BCR). BCR engagement initiates several signaling events such as activation of PLCr, Ras, and PI3K, which generally speaking, lead to survival. However, in the absence of survival signals (CD40 or IL-4R engagement), BCR crosslinking can also promote apoptotic signal transduction pathways such as activation of effector caspases, expression of pro-apoptotic genes, and inhibition of pro-survival genes. The complex interplay between survival and death signals determines the B cell fate and, consequently, the immune response.
