Transcript 细胞凋亡与衰老

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)
PRIZED Horvitz, and Sulston share Physiology or Medicine Nobel
（2002）
“for their discoveries concerning genetic regulation
of organ development and programmed cell death”
衰老
机体结构
细胞增殖
细胞分化
细胞信号转导
染色体
（DNA与蛋白质的相互作用）
细胞凋亡
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
The cell division is cotrolled not only by extracellular mitogens but
also by intracellular mechanisms that can limit cell proliferation.
Cell-cycle arrest
or apoptosis
induced by
excessive
stimulation of
mitogenic
pathways.
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
2.Apoptosis, Programmed cell death
Biological functions of apoptosis
细胞凋亡是多细胞生物在发育过程中，一种由基因控制
的主动的细胞生理性自杀行为。
 In development, homeostasis, tumor
surveillance, and the function of the immune
system.
Morphological and biochemical
characteristics of apoptosis
 Morphologi changes:
Early : Chromosome condensation, cell body shrink
Later : Blebbing and Nucleus and cytoplasm fragment—
Apoptotic bodies
At last: Phagocytosed
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
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
Apoptosis
Necrosis
Death by apoptosis is a neat, orderly process
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
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.
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
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
(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：
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).
How to activate caspases?
All caspases expressed as proenzymes— Procaspases
NH2-terminal prodomain: Highly variable
Procaspase
Large subunit (20kD)
Small subunit (10kD)
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:
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
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 .
The inhibitor of CAD (Caspase-activated Dnase,
an endonuclease). Cleavage of CAD inhibitor lead to
activation of CAD, once activated, CAD translocates
from the cytosol to the nucleus severing DNA into
fragments.
Enzymes involved in DNA repair. Which are
inactivated by caspase cleavage. DNA repair is a
homeostatic activity that is inappropriate in an
apoptotic cell.
Molecular pathways of apoptosis
Two principle pathways
Extrinsic
pathway
Intrinsic
pathway
(1) Extrinsic pathway:
Fas Signaling
Pathway
Receptor-mediated pathway of
apoptosis
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.
Internal stimuli: DNA damage, high Ca2+ ,
Oxidative stress
(2) Intrinsic pathway:
Mitochondrial
pathway
The mitochondria-mediated
pathway of apoptosis
Various types ofcellular stress
Bcl-2 family: Bad or Bax to become
inserted into OM of Mit
Release of cytochrome c from I-O
space of Mit.
Form a multisubunit complex; and
Caspase Cascade,…
Activation of caspase2 is required for
permeabilization of
mitochondria, release
of cytochrome c, and
apoptosis
Pathways to cell death in C. elegans and mammals