REGULATION OF BCL XL BY CASPASES

程序性细胞死亡的失调是许多人类疾病的核心。 细胞死亡不足会导致癌症和一些自身免疫性疾病，而过度的细胞死亡会导致许多神经系统疾病和艾滋病。 Bcl-2是一种细胞凋亡抑制剂，其过表达是滤泡性淋巴瘤患者特有的染色体易位所致。Bcl-2家族成员Bcl-XL的过表达常见于艾滋病患者的卡波西肉瘤病变。在肿瘤发展的晚期，一个或多个Bcl-2家族成员的上调是常见的。 然而，Bcl-2家族成员调节程序性细胞死亡的分子机制才刚刚开始被理解。 同样，通过未知的机制，Bcl-XL和Bcl-2阻止半胱氨酸蛋白酶的激活，半胱氨酸蛋白酶家族是凋亡性细胞死亡的关键促进剂。 最近，Bcl-2家族成员被发现作为caspase底物。 半胱天冬酶在靠近N-末端的环结构域中切割Bcl-XL和Bcl-2，这导致BH 4同源结构域的损失，BH 4同源结构域是抑制细胞死亡所需的结构域。 因此，半胱天冬酶对Bcl-XL和Bcl-2的切割将这些蛋白质从细胞死亡的有效抑制剂转化为细胞死亡的有效诱导剂。然而，除了在Bcl-XL切割位点的P1位置的普遍保守的天冬氨酸外，这些位点不类似于任何其他已知的半胱天冬酶切割位点。 实验提出，以确定是否翻译后修饰的细胞激酶/磷酸酶的Bcl-XL切割位点调制这些网站的半胱天冬酶的识别。 将在神经元和肿瘤细胞系中研究磷酸化的作用和在凋亡过程中调节BcI-XL功能的负责激酶。 切割的Bcl-XL的促死亡活性所需的蛋白质结构域将通过广泛的诱变来确定。 将进行生化和功能分析，以探索这种促凋亡活性背后的分子机制。 这些研究预计将显着推进我们对程序性细胞死亡的分子过程的理解，这些过程影响着广泛的人类疾病。

Dysregulation of programmed cell death is central to a number of human diseases. Insufficient cell death leads to cancer and some autoimmune diseases while excessive cell death contributes to a number of neurological disorders and AIDS. Overexpression of Bcl-2, an inhibitor of apoptosis, results from the chromosomal translocations characteristic of follicular lymphoma patients. Overexpression of a Bcl-2 family member, Bcl-XL, is frequently found in the Kaposi's sarcoma lesions of AIDS patients. Upregulation of one or more Bcl-2 family members in the late stage of tumor development is a common occurrence. However, the molecular mechanisms by which Bcl-2 family members regulate programmed cell death are only beginning to be understood. Again by unknown mechanisms Bcl-XL and Bcl-2 prevent the activation of caspases, a family of cysteine proteases that are key facilitators of apoptotic cell death. Recently, Bcl-2 family members were found to serve as caspase substrates. Caspases cleave Bcl-XL and Bcl-2 in the loop domain near the N-terminus which results in loss of the BH4 homology domain, a domain that is required for inhibition of cell death. As a result, cleavage of Bcl-XL and Bcl-2 by caspases converts these proteins from potent inhibitors of cell death to potent inducers of cell death. However, except for the universally conserved aspartate at the P1 position of the Bcl-XL cleavage sites, these sites do not resemble any other known caspase cleavage sites. Experiments are proposed to determine if posttranslational modification of the Bcl-XL cleavage sites by cellular kinases/phosphatases modulates the recognition of these site by caspases. The role of phosphorylation and the responsible kinases that regulate BcI-XL function during apoptosis will be studied in neurons and tumor cell lines. The protein domains required for the pro-death activity of cleaved Bcl-XL will be determined by extensive mutagenesis. Biochemical and functional analyses will be performed to explore the molecular mechanism behind this pro-apoptotic activity. These studies are expected to significantly advance our understanding of the molecular processes of programmed cell death which impact on a wide range of human disorders.