Molekulrn mechanismy apoptzy bunecn smrti

1
Molekulární mechanismy apoptózy(bunecné smrti)

• Ladislav Andera
• Ústav molekulární genetiky AV CR

2
Rozvrh a témata prednáek

• 6.5. Mechanism and regulation of cell death in
  non- vertebrates (C. elegans, D. melanogaster,
  plants etc.).
• 13.5. Role of the cell death in the homeostasis
  of organisms and diseases connected with
  aberrations in the cell death. CD with lectures
  and relevant literature.

3
Cell death in non-vertebrate organisms

• Yeasts (Saccharomyces cerevisiae)
• Worms (Caenorhabditis elegans)
• Flies (Drosophila melanogaster)
• Plants (e.g. Arabidopsis thaliana)

4
Death of a yeasta different world (?)

• There are no homologs of Bcl-2, DD, DED family
  proteins in yeasts
• BUT there are homologs of caspases (metacaspase
  YCA1), serine protease HrtA2/Omi (Nma111), Bax
  inhibitor BI-1 and conserved proteosomal pathway.
  
• In addition to caspase activation, there is
  chromatin condensation, release of cytochrome c
  from mitochondria and exposure of
  phosphatidylserine at the surface of dying yeast
  cells.
• Yeast death is induced by ROS, nutrient
  deprivation, aging, mating a-factor, UV or acid
  stress.
• Apoptosis/cell death in yeast is a mechanism that
  ensures survival of the fittest cells (removal
  of old cells with budding scars, cells with
  damaged DNA).

5
Yeast apoptosis inducers executors
6
Pheromone-induced PCD in yeasts
7
(No Transcript)
8
Summary of the yeast death

• In spite many differences there is apoptosis-like
  cell death in yeast. Yeast apoptosis depends on
  metacaspase YCA-1 and one of its major
  inducers/intermediates are ROS.
• Yeast apoptosis is induced by a number of signals
  (lack of nutrients, severe DNA damage, acid or
  oxidative environment, improperly triggered
  mating signals, etc.) and could be at least
  partially inhibited by overexpressed exogenous
  Bcl-2 or BclXL.
• Yeast apoptosis is a tool for yeast colony to
  remove aged or damaged cells or to ensure, under
  limited source of nutrients, survival of the
  fittest cells.

9
C. elegans co-founder of the apoptosis
research

• Nematode Caenorhabditis elegans was one of the
  first organisms to study apoptosis. During its
  development exactly 131 cells (out of 1090) die
  through apoptosis.
• In contrast (or analogy) to yeasts, death of
  these cells is for C. elegans beneficial (or
  crucial for its survival).
• Through screening of loss- or gain-of-function
  mutations that affect death of these (131) and
  other cells, R. Horvitz and his colleagues cloned
  responsible genes and named them ced (cell death
  abnormal).
• These genes (their products) represent
  prototypes of basic members of the apoptotic
  machinery. CED-3 is caspase, CED-4 is homolog of
  Apaf1 and CED-9, EGL-1 are homologs of Bcl-2, BH3
  sentinels.
• C.elegans also encodes homologs of the essential
  genes for phagocytosis/engulfement and in fact
  the mechanism of apoptosis and phagocytosis that
  is in principle valid in mammalian cells was as
  first described in C.elegans (R.Horvitz, X.Yuan,
  M.Hengartner).

10
The worm movie cell death during the development
WT C.elegans
Mutant C.elegans (CED-10 engulfement)
11
Paradigm of C.elegans apoptosis
12
C.elegans genes involved in cell death
13
Simple and spicy meal phagocytosis from
C.elegans to mammals
14
Summary of death in C.elegans

• Upstream signals (DNA damage, transcription)
  activate or induce BH3-only protein EGL-1 that
  sequesters Bcl-2 homolog CED-9 from its complex
  with CED-4/CED-3.
• Liberated CED-4/CED-3 (Apaf1/caspase) then
  becomes proteotically active and through cleavage
  of downstream targets initiates apoptosis. Though
  these proteins are attached to mitochondria,
  there is no requirement for cytochrome c (CED-4
  in contrast to its fly and vertebrates homologs
  does not contain WD40 domains).
• Apparently, phagocytic machinery is highly
  conserved from nematodes to mammals
  (phosphatidylserine exposure, engulfment
  signals).

15
FLYing death or dying cells in Drosophila

• Cell death apparatus in fruit fly Drosophila
  melanogaster represents more evolved, though also
  from C.elegans slightly different system.
• Similarly as in mammals there are initiator and
  effector caspases, Apaf1 homolog with WD40
  domains, IAP proteins and their inhibitors (IAP
  antagonists).
• In contrast to both nematodes and mammals, there
  is no obvious anti-apoptotic member of the Bcl-2
  family (like Ced-9) in the fruit fly.
• Interestingly, very important role in the
  regulation of apoptosis have anti-apoptotic
  proteins of the IAP family and their
  apoptosis-inducing inhibitors of RHG family.
• In addition to protein regulators of apoptosis,
  inhibitory or microRNAs (miRNA) are involved in
  fine tuning of the apoptosis machinery.

16
Components of Drosophila death factory
17
(No Transcript)
18
(No Transcript)
19
Regulation of cell death in Drosophila
20
MicroRNAs in regulation of cell death
21
Essential role of DIAP1 in regulation of apoptosis
22
Autophagic cell death in Drosophila

• Autophagic cell death plays an important role
  during Drosophila development.
• It is coordinated with the induction of apoptosis
  and there is interplay between autophagy and
  apoptosis in the destruction of salivary glands
  between prepupa and pupa stages.
• Mechanism of autophagy is conserved from yeast to
  mammals.

23
Recapitulation of death in Drosophila

• Cell death in fruit fly is significantly more
  advanced and regulated at multiple levels than
  apoptosis in C.elegans.
• In addition to multiple (initiator executor)
  caspases there are new players in the cell death
  match inhibitors of apoptosis (DIAPs) and their
  killers proteins of the IBM/RHG family (Reaper,
  Hid, Grim Sickle).
• Role of the Bcl-2 proteins (Debcl, Buffy) and
  cytochrome c in the induction and regulation of
  apoptosis is less defined.
• MicroRNAs (Bantam, Mir-2,13) can suppress
  apoptosis through inhibition of RHG proteins
  expression.
• Ecdysone-induced autophagic cell death also
  participates in the removal of unwanted cells
  (e.g. salivary glands) during Drosophila
  development.

24
(No Transcript)
25
Dying plants (or at least their cells)

• Cell death in plants is either physiological
  (embryogenesis- or senescence-related) or
  pathological (viral or bacterial infection
  hypersensitive response, HR)
• Generation of ROS (activation of NADPH oxidase)
  is one of the major death-inducing signals in
  plants (resembles death induction in yeasts).
• Metacaspases (caspase-like proteases, CLPs),
  serine proteases and nucleases are major
  effectors of plant cell death.
• Though Bcl-2-like proteins were not detected in
  plants, there two Bcl-related regulatory proteins
  expressed in plant cell Bax-inhibitor-1-like
  (BI-1) and BAR-like proteins.
• Autophagy-like cell death in which participate
  plant vacuoles could be of an importance
  especially embryogenesis-related cell death.

26
(No Transcript)
27
HR vs. PCD

• Hypersensitive response is one of the plant
  defense mechanisms that should prevent spreading
  of plant pathogens (e.g. Agrobacterium
  tumefaciens, tabacco mosaic virus).
• Developmentally regulated PCD ensures correct
  growth and function formation of trachea,
  senescence of old leaves, etc.).
• Both types of plant cell death feature activation
  of serine and caspase-like proteases, DNA
  cleavage and chromatin condensation, blebbing and
  destruction of vacuoles and destruction of
  organelles. In HR cell collapses but in PCD it
  forms ordinal, functional structures.

28
(No Transcript)
29
Signaling in plant cell death
30
Next lecture (13.5.2009)

• Death around and inside us or when something
  goes wrong with it.
• Zkouka
• od 18.5. vcetne
• písemný test publikacní esej
• Skupinové termíny ci individuální dohoda