Enzymes involved in DNA repair. Which are inactivated by caspase cleavage. DNA repair is a homeostatic activity that is inappropriate in an apoptotic cell.
PRIZED Horvitz, and Sulston share Physiology or Medicine Nobel （2002） “for their discoveries concerning genetic regulation of organ development and programmed cell death ”
Activation phase：
The cell responds to “death signals” that commit it to undergoing self-destruction.
Execution phase： The death sentence is carried out. Apoptosis cells are recognized by phagocytes because they carry exposed markers, called “eat me” signals. The best studied “eat me” signal is the presence of phosphatidylserine molecules in the outer leaflet of PM of apoptotic cells (by flop-flipase).
her-1.
保守性高，在哺乳动物中有相应同源物：
Ced-3=ICE, Ced-4=Apaf-1, Ced-9=Bcl-2.
Mammalian: CED3 is related to mammalian interleukin1ß–converting enzyme (ICE or
Apoptosis is carried out by a proteolytic system — caspase
Extracellular growth factors stimulate cell growth
Activation of cell-surface receptors
Activation of PI 3-kinase Activation of elF4E (translation initiation factor) and S6 kinase(phosphorylates ribosomal protein S6) Increasing protein synthesis and cell growth
Chapter 13
Cell apoptosis
1. Extracellular cotrol of cell division,
cell growth, and apoptosis
Mitogens stimulate G1-Cdk and G1/S-Cdk activities
1090 –131= 959(cells)
Fas (also called Apo-1 or CD95) is a member of the tumor necrosis factor receptor (TNFR) superfamily.
Bcl-2 Family(cytoplasmic factors):
Bad,Bid,and bax: promote apoptosis; Bcl-X, Bcl-w,and Bcl-2: prevent apoptosis.
线虫体细胞凋亡研究：PCD相关基因15个，分为四组：
1、与PCD有关的基因，负责PCD控制：ced-3、ced-4和ced-9。 2、与PCD过程吞噬作用有关：ced-1、ced-2、ced-5-8 和 ced-10。 3、核酸酶基因（nuc-1）, 控制DNA降解，但非PCD所必须。 4、影响特异细胞类型PCD的基因：ces-1、ces-2、cgl-1、和
Procaspases are activated by binding to adaptor proteins
The caspase cascade involved in apoptosis A. Procaspase activation by proteolytic cleavage. B. Caspase cascade
The target proteins of caspase are the following:
More than a dozen protein kinase, including FAK, PKC, and Raf1. FAK– disrupt cell adhesion for the apoptotic cell. Lamins. Cleavage of lamins leads to the disassembly of the nuclear lamina and shrinkage of the nucleus. Proteins required for cell structure. Such as IF, actin, and gelsilin. Cleavage and inactivation of these proteins lead to changes in cell shape. Induce cell display signals marked it for phagocytosis .
(1) Why called caspase? Active site: Cysteine Cleavage site: Asparatic acid Cysteine Asparatic acid specific protease
Aps-Xxx 天冬氨酸特异性的半光氨酸蛋白水解酶
Apoptosis can be divided into two phases：
How are procaspases activated to initiate the caspase cascade? The activation is triggered by adaptor proteins that bring multiple copies of specific procaspases. 3 groups of caspase:
A、Normal cell
B、Apoptosis: Apoptotic bodies
Biochemical characteristics of apoptosis :
180~200bp DNA ladder, Accumulation of tTG, PS flip-flop
Apoptosis induced by Cyto C
3.Molecular mechanisms of apoptosis
Early researches (MIT: Robert Horrid , 1986)
C. elegans:1090 cells, 131 cells death.
The Finding of CED3 mutant Without losing any of their
Molecular pathways of apoptosis
Two principle pathways Extrinsic pathway Intrinsic pathway
(1) Extrinsic pathway: Fas Signaling Pathway
Receptor-mediated pathway of apoptosis
cells to apoptosis.
CED3 gene play a crucial role in the process of apoptosis.
C elegans: a millimeter long, transparent body only a few cell types, from zygote to mature adult only in 3.5days.
How to activate caspases?
All caspases expressed as proenzymes— Procaspases
NH2-terminal prodomain: Highly variable
Procaspase
Large subunit (20kD) Small subunit (10kD)
1、apoptotic initiators: caspase-2, caspase-8, caspase-9 and caspase-10 2、apoptotic executioners: caspase-3, caspase-6 ，caspase-7 and 14 (morphology change) 3、inflammatory mediateors: caspase-1, and caspase-11
衰老
机体结构
细胞增殖
细胞分化
细胞凋亡
细胞信号转导
染色体
（DNA与蛋白质的相互作用）
A simplified model of one way that mitogens stimulate cell division
Human cells have a built-in limitation on the number of times they can divide
Lane 1．0 h 2． 1 h 2.0kbp 3． 2 h 4． 3 h 1.0 5． 4 h 6．Control 0.5 7．Marker
0.2
Contrast ofApoptosis and necrosis