3. Cell biology represents the study of the normal
physiological processes that occur in the cell
including cell cycle, differentiation, apoptosis,
angiogenesis and growth factors.
Cell Biology
4. It is a series of distinct biochemical and physiological events
occurring during cell replication.
Time of cell cycle is variable:
Some adult cells don’t divide (i.e. reach to cell cycle
stop phase or G0): e.g. Nerve cells and eye lens
Cell cycle
5. 1) G1, Growing or Gap phase 1
2) S or Synthetic phase
3) G2, Growing or Gap phase 2
4) M or Mitosis phase
Stages of normal cell cycle
6. During this phase:
• Growth stimulatory and replication signals arrive
and accumulate within the cell.
• The cell grows in size and stores the materials
required for DNA replication.
• Cell checks everything OK for DNA replication.
G1 may be the longest phase of cell cycle.
G1, Growing or Gap phase 1
7. During S phase, cell replicates its DNA and doubles the
number of chromosomes.
DNA synthesis occur during S phase because:
1) Cell contains excess quantities of DNA polymerase than
during the other phases.
2) There is excess activity of enzymes that responsible for the
formation of the substrates for DNA synthesis i.e. enzymes
for formation of dATP, dGTP , dCTP and dTTP.
S or Synthetic phase
8. During this phase the cell prepare itself for mitosis.
Accumulates proteins that activate cell division.
Cell checks everything is OK for cell division
G2, Growing or Gap phase 2
9. During this phase the cell undergoes actual cell division into
two daughter cells.
It is the shortest phase of cell cycle.
Divided into six phases:
» Prophase
» Prometaphase
» Metaphase
» Anaphase
» Telophase
» Cytokinesis
M or Mitosis phase
10.
11. Cell cycle is regulated by a gene that produces protein
called cyclin.
Cyclin govern the transition from one phase of the cell cycle
to another through controlling a number of enzymes called
cycline-dependent protein kinases (cdpk).
These enzymes are activated by mitogenic growth factors.
Regulation of cell cycle
12. The sequential events of the cell cycle are directed by a
distinct cell cycle control system, which is similar to a clock
The clock has specific checkpoints where the cell cycle
stops until a go-ahead signal is received
For many cells, the G1 checkpoint seems to be the most
important one
Regulation of cell cycle
14. 1G
checkpoint1G
1G
0G
If a cell receives a go-ahead
thecheckpoint,1signal at the G
cell continues on in the cell cycle.
If a cell does not receive a go-
checkpoint,1ahead signal at the G
the cell exits the cell cycle and
dividingstate.-a non,0goes into G
15. During cancer development there is no control on the cell
cycle and lead to continuous uncontrolled cell division
without repairing of DNA leading to DNA mutation.
On time these mutations lead to more and more aggressive
tumors.
So, some strategies in cancer therapy depend on the use of
chemicals that interfere with cell cycle progression.
Cell cycle and cancer
16. It means the specialization of unspecialized embryonic cells
into specific cells to perform specific function.
N.B.: Normal cells are called differentiated cells but cancer
cells are called dedifferentiated cells.
Stem cells: these cells that can be differentiated into more
than one type of cells.
Application of stem cells:
• Gene therapy.
• Tissue transplantation.
Differentiation
17. It is also called programmed cell death
Apoptosis is a normal physiological process
occurring in damaged cells.
The term “apoptosis” is a Greek word = “Falling off”
of leaves from a tree
Apoptosis
18. Biomedical Importance:
• It serves as the mechanism that eliminate the damaged cells
when they are no longer needed.
• It plays an important role in embryogenesis and normal
tissue homeostasis.
• It is involved in certain pathological conditions such as
malignancy and AIDS.
19. • General Mechanism:
• Apoptosis is a multi-step process involve fur distinct phases:
1) Initiation phase: it start by an apoptotic stimulus, and is subject to very
complex regulation.
2) Effector phase: It occurs when pro-apoptotic signals override the anti-
apoptotic signals (the cell becomes committed to die).
3) Degradation phase: include the following:
• Shrinkage of plasma membrane and cytoplasmic organelles
• Nuclear chromatin condensation.
4) Engulfment phase: apoptotic bodies are rapidly ingested by neighboring
cells, without inflammation
N.B.: Defects in the regulation at any of these phases may ultimately
result in disease.
20. • Biochemistry of Apoptosis:
• Ultimately, apoptosis is the net result of the balance
between pro- and anti-apoptotic stimuli.
• The most important regulatory mechanisms of apoptosis in
mammalian cells belong to the following categories:
1) Death receptors.
2) Caspases
3) Mitochondria
4) The Bcl-2 family of proto-oncogenes
5) Certain tumor-suppressor genes
21. Site: may be membrane-bound or in a soluble form.
Function: act as sensors to extracellular apoptotic stimuli.
Mechanism: when apoptotic stimuli bind to specific death
receptor it lead to intracellular proteolytic cascade by
agroup of enzymes called “caspases” resulting in cellular
death within hours.
Examples: The prototypical death receptors include Fas
and tumor necrosis factor receptors (TNF-Rs).
1- Death Receptors
22. They belong to the family of cysteine proteases
Site and Function: They exist in the cytoplasm as
proenzymes (less active), but once activated, play important
roles in the initiation and effector phases of apoptosis.
2- Caspases
Structure: Each caspase consists of
a structurally related molecule with a
prodomain, and a large (~20 kD) and
small (~10kD) subunit that combine
to form tetramers after activation.
23. Classification:
• More than 13 caspase member are known,11 of which have
human counterparts.
• They are classified according to their substrate
specificity and function into:
1) Upstream enzymes [caspases 8, 9,10], that serve to initiate
and amplify the death signal
2) CED-3-like [caspases 2, 3, 6, 7], that are involved in the rapid
cleavage of vital cellular components, e.g, nuclear membrane
3) ICE-like [caspases 1, 4, 5 and 13], that are less involved in
cell death.
24. Mechanism:
• Like the clotting cascade, the caspase cascade proceeds in
an auto-catalytic manner, leading to intense amplification of
the initial apoptotic stimuli.
• This cascade is regulated by various cofactors (e.g., apoptotic
protease activating factor-1 and inhibitors) at the post-
translation level, by protein-protein interactions
25. It plays a central role in apoptosis
Mechanism: disruption of mitochondrial membrane lead to
matrix swelling and loss of mitochondrial transmembrane
potential leading to:
1. Release of specific proteins, such as cytochrome c, which
activates procaspase-9 thus activating the caspase cascade
2. Disruption of electron transport (an early feature of apoptosis)
3. Modification of cellular oxidation-reduction potential.
3- Mitochondria
26. Classification: Many proto-oncogenes are involved in
maintaining cell survival and proliferation.
It could promote:
A. Cell survival e.g. Bcl-2 (anti-apoptotic)
B. Cell death e.g. Bax (apoptotic)
Bcl-2
It is a membrane-associated protein located at the
mitochondrial and peri-nuclear membranes
Its role is to promote cell survival and proliferation.
4- Proto-Oncogenes (Bcl-2 Family )
27. • p53 is one of the most important tumor-suppressor genes
• It can induce cell death in response to DNA damage.
Defect: Mutations causing its loss of function are associated with
many human cancers.
Mechanism: activated p53 lead to cycle arrest causing either:
1) Allow DNA repair (if failed….)
2) Cell death
by initiating apoptotic signals
5- Tumor-Suppressor Genes (p53)
28. • The cell is also subjected to many other apoptosis
modifiers including:
1) Various cytokines (e.g., IL-4, IL-2, IL-10),
2) Circulating or membrane-bound molecules which are
capable of triggering specific ligand-receptor
interactions (e.g., Fas ligand/Fas, TNF-α /TNF-RI),
Nitric oxide
6- Other Apoptosis Modifiers
29. Nitric oxide:
• It is a potent pro-inflammatory molecule with a role in various
pathological conditions, such as joint damage in rheumatoid arthritis
and osteoarthritis, as well as in diseases associated with vascular
dysfunction. It has dual action:
• Pro-apoptotic activity: where it increased the mitochondrial
membrane potential releasing cytochrome c that subsequently
activates caspase-3.
• Anti-apoptotic activity : where induces the S-nitrosylation of
caspases, thereby preventing their activation and promoting
resistance to Fas-mediated apoptosis.
30. • Difference between apoptosis and necrosis
Cellular
Modification
Apoptosis Necrosis
Cellular role Active Passive
Distribution Dispersed Contiguous
Morphology Decreased
volume of
the cell
Increased
volume of the
cell
Cellular
membrane
Preserved Loss of
integrity
Induction Slow
(hours)
Rapid
(seconds–
minutes)
Cell removal Rapid Slow
Tissue
inflammation
Absent Present
31. • Angiogenesis is the formation of new blood vessels from pre-
existing ones.
• Vasculogenesis is development of blood vessels from in situ
differentiating endothelial cells.
Angiogenesis
32. Steps of angiogenesis:
1. Local basement membrane degradation of the parent vessel
2. Locomotion of endothelial cells away from the parent vessel in the
direction of an angiogenic stimulus
3. Elongation of endothelial cells to form a capillary sprout
4. Endothelial cell proliferation in the parent venule and in the capillary sprout
5. Lumen formation
6. Anastomosis of two hollow sprouts to form a capillary loop,
7. Onset of blood flow
8. Production of new basement membrane.
33. Regulation of angiogenesis:
• Angiogenesis is a complex process regulated by a balance
between angiogenic and antiangiogenic factors
1. Angiogenic factors
• Includes variety of cytokines and growth factors such as:
• Vascular endothelial growth factor (VEGF):
• It is a key regulator of both physiological and pathological
angiogenesis.
• Its biological effect is mediated through 3 receptor tyrosine
kinases; VEGFR-1, VEGFR-2 and VEGFR-3. Also, a soluble
form of VEGFR-1 (sVEGF-R1) had been identified.
34. 2. Anti-angiogenic factors: such as
• Thrombospondin and Pigment epithelium derived growth
factor (PEDF)
• PEDF is the most recently discovered antiangiogenesis factor.
• It can significantly reduce tumor neoangiogenesis and tumor
growth in animal models with HCC and lewis lung carcinoma.
35. Angiogenesis in physiological and pathological
conditions:
• Physiologically, it is essential for embryonic development,
menstrual cycle, and wound repair.
• Pathologically: Unregulated angiogenesis is seen in
several pathological conditions including: psoriasis,
nephropathy, cancer, retinopathy, rheumatoid arthritis,
obesity, infectious diseases, etc.
• Angiogenesis can be considered as a therapeutic target
in the treatment of some diseases.
36. Therapeutic angiogenesis:
• Stimulation of angiogenesis can be used in ttt of:
1) Myocardial ischaemia
2) Cerebral ischaemia
3) Peripheral ischaemia (peripheral arterial occlusive
disease)
4) Wound healing and fracture repair
5) Reconstructive surgery: Skin flaps
6) Induction of collateral vessel formation
37. • Inhibition of angiogenesis can be used in:
1) Inhibition of tumor growth and metastasis.
2) Treatment of ocular neovascularization.
3) Treatment of haemangioma
4) Treatment of rheumatoid arthritis
5) Treatment of atherosclerotic plaque
neovascularization
38. Targets of angiogenesis inhibitors:
1) Inhibition of exogenous or endogenous angiogenic
growth factors or their receptors.
2) Inhibition of endothelial cell growth and survival.
3) Some inhibitors target the basement membrane and
extracellular matrix.
4) Inhibition of angiogenic signalling pathway.
39. FDA approved angiogenesis based treatments:
1) Avastin
• It is the first approved angiogenesis based anticancer agent
• It is a recombinant humanized monoclonal antibody directed
against VEGF.
• In combination with 5FU it is significantly effective against
metastatic colon cancer
40.
41. FDA approved angiogenesis based treatments:
2) Regranex gel
The active ingredient is becaplermin (a recombinant
human platelet-derived growth factor, PDGF)
It is approved by FDA for topical administration in
treatment of diabetic neuropathic foot ulcers.
42. • Growth factors are polypeptides exert a mitogenic response
on their target cells.
• They affect many different types of cells e.g. blood cells,
nervous system, mesenchymal tissues and epithelial tissues.
• Types: Growth factors act like hormones:
• Endocrine manner: pass in circulation to their target cells.
• Paracrine manner: affect neighboring cells.
• Autocrine manner: affect their secreting cells
Growth factors
43. • Clinical implication of growth factors:
• They are implicated in pathogenesis, diagnosis and prognosis of
many diseases including:
1. Diabetes mellitus: in certain types there is absence of insulin as
a growth factor and as a hormone that stimulates the secretion of
other growth factors as IGF-I.
2. Cancer aggression.
3. Chronic inflammatory diseases: due to defective control on
angiogenesis through growth factors.
4. Neurogenerative diseases: due to defective nerve growth factor
and pro-apoptotic cytokines.
44. • Examples of growth factors:
Growth Factor Source Function
Epidermal growth factor
(EGF)
Mouse salivary gland Stimutates growth of many
epidermal and epithelial cells
Erythropoietin Kidney Regulates development of
early erythropoietic cells
Fibroblast growth factors
(FGFs) (at least nine family
members)
Many different cells Promote proliferation of many
cells
lnterleukin (IL-1) Conditioned media Stimulates production of IL-2
by T cells
lnterleukin-2 (IL-2) Conditioned media Stimulates growth of T cells
Nerve growth factor (NGF) Mouse salivary gland Tropic effect on sympathetic
and certain sensory neurons
Platelet-derived growth factor
(PDGF)
Platelets Stimulates growth of
mesenchymal and glial cells
Transforming growth factor
(TGF)
Conditioned media of
transformed or tumor cells
Similar to EGF
Transforming growth factor
(TGF)
Kidney, platelets Exerts both stimulatory and
inhibitory effects on certain
cells.
