Cell Signaling plays a significant role when it comes to human body functioning and regulation

1. The Progress of Cell Signaling

2. Schedule
Week Date Content
2
20230904
20230906
Cell communication and Signaling
GPCR-overview
3
20230911
20230913
GPCR-signaling
G protein and small G protein
4
20230918
20230920
RTK
GPCR and RTK crosstalk
5
20230925
20230927
Cytokine receptor
Ion channel
6
20231002
20231004
Nuclear receptor
MAPK pathway
7
20231009
20231011
PI3K and mTOR pathway
Protein modification
8
20231016
20231018
Ca2+ signal
cAMP signal
9
20231023
20231025
Drug development topics

3. Reference Books and Link
• Biochemistry of Signal Transduction and Regulation. 3d ed. Gerhard Krauss,
2003
• Molecular Biology of the Cell, Bruce Alberts et.al., by Garland Science, Fifth
Edition 2008
• Molecular Cell Biology, Harvey Lodish et al，by W. H. Freeman and
Company，Fifth Edition 2003
• Biochemistrry, Lehninger
• The cell, Albert
• Cell, Lewis
• 细胞信号转导，孙大业主编

4. Course Requirements
• Attendance: 10%
• Oral presentation: 30%
• Closed-book exam: 60%
Type Single-choice
(15 items, 2 points each)
True or False
(20 items, 1 point each)
Definition
(10 items, 5 points each)
Total
Point 30 20 50 100

5. Cells and the body
Cell Communication and Cell Signaling
Cells are the basic units of life. Together, they form tissues that
themselves form organs, and eventually entire organisms.

6. How a cell singals?
Each cells is
programmed to
respond to specific
stimulations of
extracellular signals.
Different signaling
cause different cell
activity and decide the
cell fate.

7. Cell communication
All forms of communication between cells requires two
essential components:
1. a signaling cell that produces an instructive signal,
2. a responding cell that receives, acts on, and is
changed by the instructive signal.

8. Four main forms of cell communication
1) Gap junction 2) Contact signaling by plasma
membrane bound molecules
3) Chemical signaling 4) Exosome. ..

9. 1) Gap junction
Ø Cells must be in direct contact
Ø Directly cell content exchange in both side of small
molecules (<1.5 kDa, inorganic ion or water soluble
small molecules, e.g. Ca2+, cAMP)
Ø Fast and reversible

10. e.g. Protein channel connecting the cytoplasm of two adjacent cells

11. 2) Contact signaling by plasma membrane
bound molecules
Ø Cell-cell recognition by
interaction with molecules on cell
surface
Ø Also called contact-dependent
signaling or juxtacrine interaction
Ø e.g. immune response, cell
apoptosis
(major histocompatibility complex)

12. 3) Chemical signaling
Different forms for chemical signaling
transmission:
Ø Autocrine
Ø Paracrine
Ø Endocrine
Ø Chemical synapse signaling
l Most chemical molecules are hydrophilic and only
some of them are hydrophobic.
l They can be proteins, peptides, amino acids and
other products.
l It can be both local or distal response.

13. 3) Chemical signaling
Ø Autocrine
Autocrine signaling is a form of cell signaling in which a
cell secretes a chemical messenger that binds to the
receptors on that same cell, leading to changes in the cell.

14. 3) Chemical signaling
Ø Paracrine
Tissue fluid
Secretory
cell
Adjacent
target cell
local signaling
Messenger molecules
e.g. cytokines, growth factors, neurotransmitters

16. 3) Chemical signaling
Ø Endocrine
Ø Slow, long-distance, long-term
Ø Blood transport, broad distribution
Ø Low ligand concentration
Ø Receptor high affinity
Endocrine cell Blood
vessel
Hormone travels in
bloodstream to target cells
Target cell
Hormonal signaling: e.g. Insulin,
Thyroxine, Adrenaline…

17. 3) Chemical signaling
Ø Chemical synapse signaling
Ø Fast
Ø Local ligand
Neurotransmitter
e.g. acetylcholine,
serotonin, glutamate,
dopamine, γ-aminobutyric
acid (GABA)…

18. Postsynaptic activity
Receptor “A” activity
Receptor “B” activity
Receptor “A”
Receptor “B”

20. 4) Exosome
Nano-sized biovesicles released into surrounding body fluids upon
fusion of multivesicular bodies and the plasma membrane
Protein,
lipid,
mRNA,
miRNA,
et.al inside Intercellular communication by exosomes plays
a critical role in the regulation of cellular and
physiological processes.

21. migrasome (迁移体)
When cell migrate, the long fibrillar structures leaved behind are
retraction fibers, where small vesicles grow up, which is call
migrasome (Prof. Yu Li, Tsinghua University).
The production of migrasomes is highly correlated with the
migration of cells.
Cell Research volume 25, 24–38 (2015)
Cell Research (2022) 0:1 – 4

22. Front. Cell Dev. Biol., 16 June 2020

23. Cell communication
1) Gap junction
2) Contact signaling by plasma membrane bound
molecules
3) Chemical signaling
Ø Paracrine
Ø Endocrine
Ø Autocrine
Ø Chemical synapse signaling
4) Exosome, migrasome…

24. ü Signal transduction is the
mechanism by which a cell
receives, acts on, and alters its
behavior in response to
extracellular signal.
ü Signal transduction
pathway is the intracellular
processes that allow that
signal to be transduced from
the outer cell membrane of the
responding cell to the nucleus
where it effects a new program
of gene expression and cell
behavior.
From another
cell
inside
(cytosol)
outside
Cell response
From the cell
itself

25. Three stages of cell signaling
1) Reception: ligand molecules are recognized by
receptor protein bound within a cell membrane. (Initiation)
2) Transduction: the interaction of receptor and ligand
leads to receptor conformation change, results in receptor
interacting with other intra-cellular molecules.
(Amplification/modulation)
3) Response stage is usually a cellular activity, as enzyme
catalysis, or the rearrangement of cytoskeleton (movement),
or specific gene activity. (Excution)

26. Overview of signal transduction pathways

27. From the cell
itself
From another
cell
inside
(cytosol)
outside
From the
environment
Light , Temperature,
Pressure, Taste, Smell,
Virus, Drug…
Signal transduction is
essential for cell
communication;
it is also important for
the sensory and response
to the environment.

28. Cell signaling
Ø Extracellular signal
Ø Receptor
Ø Second messenger
Ø Signaling modulation or
Molecular switch
Ø Examples of receptor-induced
signaling pathway
Ø Characters of signaling
transduction

29. Ø Extracellular signal
1) Lipid-soluble or water-soluble hormones
2) Nitric oxide (NO) and carbon monoxide (CO) as
cellular messengers
3) Cell surface receptors
4) Others
**Slow effect - alters gene expression
Intracellular Receptors
– Steroid Hormones, Thyroid Hormones, Retinoids and Vitamin D
**Fast effect - alters protein function
Nitric Oxide----Directly activates Enzymes
Or signaling molecules (Ligand)
Light , Temperature,
Pressure, Taste, Smell,
Virus, Drug…

30. ØLigands
- Agonist
- Antagonist
Agonists are drugs or naturally occurring substances that
activate physiologic receptors, whereas antagonists are
drugs that block those receptors.
- Allosteric modulator: increases or decreases the strength
of the agonist-induced receptor response in a binding site
different from agonist
positive allosteric modulator, negative allosteric
modulator

31. Ø Characters of ligand binding to receptor
ü Specificity
ü High affinity
ü Saturation
ü Reversible
ü Affinity is controlled by receptor modification

32. Ø Receptor
ü Cell membrane receptor
• Ion channels
• G protein-coupled receptors (GPCR)
• Enzyme-Linked receptors
• Integrin
• others
ü Intracellular receptor
• Cytoplasmic receptor
• Nuclear receptor
Also refered as first messenger

34. Ø Ion channel
Ion channels are pore-
forming membrane proteins
which permit ions to cross
membrane including
plasma membrane and
organelle membrane.

35. Ø Ion channel

36. Ø G protein-coupled receptors
Ø Seven-helix transmembrane;
Ø N-terminal in the extracellular side and C-terminal in cytosol
Ø C-terminal: Ser- and Thr-rich
Ø GPCR phosphorylation can induce the desensitization and
recruiment of β-arrestin

37. Ø GPCRs: the most complex family of receptors
>800 members

38. Ø Enzyme-Linked Receptors
Six subfamilies:
① Receptor Tyrosine Kinases
② Tyrosine Kinase Associated Receptors
③ Receptor-like Tyrosine Phosphatases
④ Receptor Serine/Threonine Kinases
⑤ Receptor Guanylyl Cyclases
⑥ Histidine-Kinase Associated Receptors

39. Ø Receptor tyrosine kinases (RTKs)
Receptor tyrosine kinases recognize soluble or membrane bound
peptide/protein hormones that act as growth factors.
ØLigands
e.g. Vascular Endothelial Growth Factor (VEGF) family;
Platelet-derived Growth Factor (PDGF) family;
Transforming Growth Factor-b (TGF-b) family;
Neurotrophins;
Epithelial growth factor (EGF);
Fibroblast growth factor (FGF) family;
Insulin

40. Ø General Structure and Activation of RTKs
• RTKs generally exist as monomers with poorly active kinases.
• Binding of two ligands to the extracellular domains of two RTKs
forms or stabilizes an activated dimeric receptor.
• One kinase phosphorylates the other on a tyrosine residue in the
activation loop—autophosphorlation or tranphosphorylation,
resulting in kinase activation and dowstream signaling.

41. Ø Nuclear Receptors
Nuclear receptors are a class of proteins found within cells that are responsible
for sensing steroid and thyroid hormones and certain other molecules. In
response, these receptors work with other proteins to regulate the expression of
specific genes, thereby controlling the development, homeostasis, and
metabolism of the organism.

42. Receptor, first messenger
Second messenger
Cell signaling
Second messengers are intracellular
signaling molecules released by the
cell in response to exposure to extra
cellular signaling molecules-
the first messengers.
Second messengers trigger physiological changes at cellular level such
as proliferation, differentiation, migration, survival, apoptosis and
depolarization.

43. Small molecules and ions as
second messengers
p The extracellular signal molecule that binds to the receptor
is a pathway’s “first messenger”.
p Second messengers are small, nonprotein, water-soluble
molecules or ions that spread throughout a cell by
diffusion.
p Cyclic AMP and calcium ions are common second
messengers.
p Second messengers participate in pathways initiated by G
protein-coupled receptors and receptor tyrosine kinases

44. The intracellular “second messengers” are characterized by a
series of properties that make them particularly suitable as
elements of signal transduction:
- Intracellular messenger substances can be formed and
degraded again in specific enzyme reactions. Via enzymatic
pathways, large amounts of messenger substances can be
rapidly created and inactivated again.
- Messenger substances such as Ca2+ may be stored in special
storage organelles, from which they can be rapidly released by a
signal.
- Messenger substances may be produced in a location-specific
manner, and they may also be removed or inactivated according
to their location. It is therefore possible for the cell to create
signals that are spatially and temporally limited.
Ø Properties of second messenger

45. Low-molecular-weight messenger substances; Diffusible signal molecules
- Hydrophobic character:
diacylglycerol or
phosphatidylinositol
phosphates
- hydrophilic,
cytosolic:
cAMP, cGMP,
inositol
phosphates,
Ca2+
Ø Second messenger

46. Receptor, first messenger
Second messenger
Cell signaling
Kinases
Signaling modulation or
Molecular switch
Ø Protein phosphorylation
and dephosphorylation
Ø GTPase switch proteins

47. Protein phosphorylation and dephosphorylation
ü Protein kinases transfer
phosphates from ATP to
protein, a process called
phosphorylation.
ü Phosphorylation can flip
a protein from “active”
to “inactive” or vis-versa.
ü In many pathways, the
signal is transmitted by a
cascade of protein
phosphorylations.
Receptor
Signaling
molecule
Activated relay molecule
Inactive
protein kinase
3
Inactive
protein kinase
1
Inactive
protein kinase
2
Active
protein kinase
1
Active
protein kinase
2
Active
protein kinase
3
ADP
P
P
Pi
Pi
Pi
PP
PP
PP
ATP
ATP
ATP
ADP
ADP
Active
protein
Cellular
response
P
Inactive
protein
Ø Signaling modulation or Molecular switch

48. guanosine triphosphatases (GTPase, 鸟苷酸三磷酸酶)
Ø Signaling modulation or Molecular switch
G protein acts as a molecular switch
during signal transduction. After
binding to GDP, the G protein is in
an inactive state. After GTP replaces
GDP, G protein activates and
transmits signals
Guaninenucleotide exchange factor,
GEF, 鸟苷酸交换因子
GTPase activating protein, GAP,
鸟苷酸三磷酸酶激活蛋白

49. Ø Examples of receptor-induced signaling pathway
l GPCR signaling
- cAMP pathway
- Phosphatidylinositol pathway
l RTK signaling
- MAPK pathway
- PI3K/Akt pathway

50. Ø GPCR-coupled adenylyl cyclase-cAMP system
- Gs-coupled GPCRs,
cAMP↑
- Gi/o-coupled GPCRs,
cAMP↓

51. Ø GPCR Phosphatidylinositol (磷脂酰肌醇) Pathway
Ø IP3/Ca2+ and DAG/PKC pathway
- Gq-coupled GPCRs

52. Ø The Effectors of GPCRs
β-arrestin

53. Ø RTK signaling
MAPK (Mitogen-activated
Protein Kinase) Cascades
PI3K/Akt
pathway

54. Ø RTK signaling
- MAP kinase pathways
Activated Ras induces a kinase
signal cascade that
culminates in activation of
MAP kinase.
MAP kinase is a
serine/threonine kinase that
can translocate into the
nucleus and phosphorylation
of many different proteins,
including transcription
factors that regulate gene
expression.

55. Ø RTK signaling
- PI3K/Akt pathways

56. Insulin receptor induced PI3K Signaling
Berridge MJ. Cell Signalling Biology. 2014. doi:10.1042/csb0001002
IRS: insulin receptor substrate

57. Ø Insulin and glucagon work together to maintain a
stable blood glucose level
胰高血糖素

58. Summery of four classes of receptors and signaling

59. Ø Character of signaling transduction
ü Convergence; Divergence;
Converge on Ras Divergence

60. Ø Character of signaling transduction
ü Cascade response; Crosstalk
Cascade response
GPCR and RTK
signaling Crosstalk

61. Ø Conserved regulation:
- e.g. similar regulation through phosphorylation and
dephosphrylation in Ser, Thr and Tyr; conserved in evolution
among species
Ø Character of signaling transduction
IR
PI3K
PTEN
FOXO
FOXO
apoptosis
C. elegans
Humans

62. Summary
Ø Extracellular signal (Ligand)
Ø Receptor (membrane and intracellular receptor)
Ø Second messenger (e.g. cAMP, IP3, Ca2+….)
Ø Signaling modulation or Molecular switch
(Phosphorylation, GTPase)
Ø Examples of receptor-induced signaling pathway
(GPCR: cAMP; IP3-Ca2+; DAG-PKC
RTK: MAPK, PI3K/Akt pathway)
Ø Characters of signaling transduction
(Convergence; Divergence; Cascade response;
Crosstalk; Conserved regulation)
Cell signaling

63. Evolution and properties of cell
signaling cascades
Past:
Enumerate
components
Now:
Modules
Design Logic
Cross-talk
Specificity
Affinity
Cooperativity
Sensitization
Amplification
Integration
A signal transduction pathway is a series of steps by which a signal
on a cell’s surface is converted into a specific cellular response

64. Cell signaling in Eukaryotes
p Eukaryotic signaling systems are much more elaborate
than those in yeasts or bacteria (Prokaryotes).
p Flies, worms and mammals all use essentially similar
machinery for cell communication.
p In plants, as in animals, cells are in constant
communication with one another. Plants use different
signaling molecules and receptors than animals.
p More than 1500 genes encode different receptor
proteins in human.

65. Overview: the cellular internet
p Cell signaling is essential for life of unicellular and
multicellular organisms.
p Cells can communicate to the cell(s) next to them or
cells from much further away in another part of the body.
p How do cells send and receive a signal?
p Once cells receive the signal, how does this lead to
changes inside the cell (response)?

66. Significance of cell signaling
üFor normal functioning coordination of every signaling
pathway is necessary
ü Defect can be in any component of signaling ultimately
leading to the disease development.
ü Cell signaling has been identified in Cancer,
Cardiovascular diseases (hypertension, heart disease, etc.…),
Alzheimer's disease, and many other disorders.
üCell Signaling – an important area of research for drug
discovery

67. Future of cell signaling
ü With advances in separations methodology, mass spectrometry,
and hybridization, the complex protein interactions in cellular
signaling networks should become clear.
ü Future cell signaling studies would involve integration of
genomic, transcriptomic, proteomic, and metabolomic data that
will provide complete picture of cellular mechanisms and their
responses.

71. Schedule
Week Date Content
2
20230904
20230906
Cell communication and Signaling
GPCR-overview
3
20230911
20230913
GPCR-signaling
G protein and small G protein
4
20230918
20230920
RTK
GPCR and RTK crosstalk
5
20230925
20230927
Cytokine receptor
Ion channel
6
20231002
20231004
Nuclear receptor
MAPK pathway
7
20231009
20231011
PI3K and mTOR pathway
Protein modification
8
20231016
20231018
Ca2+ signal
cAMP signal
9
20231023
20231025
Drug development topics

72. The end!