Cell signaling - WordPress.com · · 2017-02-022017-02-02 · What is the important of cell...

Cell signaling

Assistant Prof. Dr. Panida Khunkaewla ([email protected])School of Chemistry, Suranaree University of Technology

109700: Graduate BiochemistryTerm 2/2016

What is the important of cell signaling ?

Cells need to communicate with its environment then it can make appropriate responses .

General

circulation

Endocrine

glandDistant

target cells

Neurosecretory

cell Distant

target cells

Local

circulation

Intracrine

Autocrine

Paracrine

Endocrine

neuroendocrine

Chemical Signaling

Adapted from S.S. Nussey and S.A. Whitehead, Endocrinology: An integrated approach, BIOS Scientific Publishers 2001

http://www.garlandscience.com/about.asp

Koolman, Color Atlas of Biochemistry, 2nd edition © 2005 Thieme

Cell signaling

Nelson & Cox, Fig. 12-1, Lehninger Principles of Biochemistry, 4th ed., 2005

Four features of the signal transducing system

The two-component signaling mechanism in bacterial chemotaxis


A Model Signal Transduction Pathway

W.K. Purves, D. Sadava, G.H.Orians , and O. C.Heller, Life: The Science of Biology, 7th ed, 2004

Nelson & Cox, Lehninger Principles of Biochemistry, 4th ed., 2005

9

Hormone


Tropic hormones

Overview of hormone functions

Location for receptors



Six general types of signal transducers1

2

3 4

5

6

1. Signaling via gated ion channel

“Allow ion to pass through the membrane e.gCa+, Na+ and K+ ion”

Voltage-gate channel

Ligand-gated channel


The voltage-gated Na+ and K+

channels of neuronal membranes carry the action of potential along the exon as a wave of depolarization (Na+ influx) followed by repolarization (K+ efflux).


Stages of acethylcholine receptor

2. Signaling via cell surface enzymes1. Signaling enzymes which are cell-surface receptors:

1.1 Receptor tyrosine kinases1.2 Receptor serine/threonine kinases1.3 Receptor tyrosine phosphatase (RTP)1.4 Receptor guanylyl cyclase

2. Signaling enzymes anchored on the cytosolic face of the plasma membrane:

2.1 Non-receptor tyrosine kinases2.2 Ras (Small G protein)

1.1 Receptor Tyrosine Kinases (RTKs)“Part of the receptor on the cytoplasmic side serves as an enzyme which catalyzes the

transfer of phosphate groups from ATP to the amino acid Tyrosine on a substrate protein”

Seven subfamilies of receptor tyrosine kinases

SIGNALING LIGAND RECEPTORS SOME RESPONSESEpidermal growth factor (EGF) EGF receptor stimulates proliferation of various cell types

Insulin Insulin receptor stimulates carbohydrate utilization and protein synthesis

Insulin-like growth factors (IGF-1 and IGF-2)

IGF receptor-1 stimulate cell growth and survival

Nerve growth factor (NGF) Trk A stimulates survival and growth of some neurons

Platelet-derived growth factors (PDGF AA, BB, AB)

PDGF receptors (α and β) stimulate survival, growth, and proliferation of various cell types

Macrophage-colony-stimulating (M-CSF)

M-CSF receptor factor stimulates monocyte/macrophage proliferation and differentiation

Fibroblast growth factors (FGF-1 to FGF-24)

FGF receptors (FGF-R1-FGF- R4, plus multiple isoforms of each)

stimulate proliferation of various cell types; inhibit differentiation of some precursor cells; inductive signals in development

Vascular endothelial growth factor (VEGF)

VEGF receptor stimulates angiogenesis

Ephrins (A and B types) Eph receptors (A and B types) stimulate angiogenesis; guide cell and axon migration

Some signal proteins that act via RTKs

Two signal molecule binds to two nearby Tyrosine-Kinase Receptors, causing them to forming a dimer.

The formation of a dimer activated the Tyrosine-Kinase portion of each polypeptide.

The activated Tyrosine-Kinases phosphorylate the Tyrosine residues on the protein.

The activated receptor protein is now recognized by specific relay proteins they bind to the phosphorylated tyrosines,

which leads a conformation change.

The activated relay protein can then trigger a cellular response.

One activated Tyrosine-Kinase dimer can activate over ten different relay proteins, which triggers a different response.

The ability of one ligand binding event to elicit so many response pathways is a key difference between these receptors

and G-protein-linked receptors.

Abnormal Tyrosine-Kinases that aggregate without the binding of a ligand have been linked with some forms of cancer.

Activation of a Tyrosine-kinase receptors

1.2 Receptor serine/threonine kinases (RSTKs)“There are two classes of these receptor serine/threonine kinases, type I and type II, which are

structurally similar.”

Each member of the TGF-superfamily binds to a characteristic combination of type-I and type-II receptors, both of which are required for signaling.

The ligand first binds to and activates a type-II receptor homodimer, which recruits, phosphorylates, and activates a type-I receptor homodimer, forming an active tetrameric receptor complex.

Nature Reviews Molecular Cell Biology;2003:4, 700-711

Protein phosphatases“Protein phosphatases can be classified as protein tyrosine phosphatases (PTPs) or

serine/threonine phosphatases (PPs)”

The soluble PTPs and RPTPs have diverse structures, yet their catalytic domains are remarkably well conserved and have nearly identical three-dimensional configurations.

1.3 Receptor Tyrosine phosphatases (RTPTs)

“RTPTs remove phosphate groups from specific tyrosine residues”

Cell-surface proteins with a single TM region and intracellular phosphotyrosine phosphatase activity. Many family members exhibit constitutive activity in heterologous expression, dephosphorylating

intracellular targets such as Src tyrosine kinase (SRC) to activate signaling cascades. Family members bind components of the extracellular matrix or cell-surface proteins indicating a role in

intercellular communication.

www.lookfordiagnosis.com

1.4 Receptor guanylyl cyclase“Catalyze the synthesis of cGMP”

PPi

Most of the actions of cGMP in animals are believed to be mediated by cGMP-dependent protein kinase ( protein kinase G or PKG)

PKG is ativated by cGMP, phosphorylates Ser and Thr residues in target proteins

Two types (isozymes) of guanylyl cyclase that participate in signal transduction


2.1 Non-receptor tyrosine kinases

Can be subdivided in 10 families (Src-A and Src-B are shown as one "Src" family). Most of them contain SH2 and SH3 domains which plays an important role in the regulation of kinase activity. Several were originally discovered as transforming genes of a viral genome, hence names like Src or Abl, derived

from Rous sarcoma virus or Abelson murine leukaemia virus. The acronym in between brackets indicates the family member of which the domain architecture is illustrated.

http://www.cellbiol.net/ste/rpimages.php

2.2 Small G Protein

Monomeric G proteins with molecular weight of 20-40 kDa.

Like heteromeric G proteins, their activity depends on the binding of GTP.

More than 100 small G proteins have been identified.

They are classified into five families: Ras, Rho, Rab, Ran and Arf.

GDP GDP GEF

GTPGTP GAP

GDP GTP

Cycling of the Ras protein between active and inactive states.

GEF = guanine nucleotide exchange factor GAP = GTPase-activating protein

Protein Kinase Cascades


RAS and Cancer

Mutations of the Ras proto-oncogenes are found in about 25% of all human tumors.

Most mutations result in the abrogation of the normal GTPase activity of Ras.

The Ras mutants can still bind to GAP, but cannot catalyze GTP hydrolysis.

As a result, they remain in the active state for a much longer period.

Malignant transformation may arise from the unregulated stimulation of Ras signaling pathways, which either stimulate cell growth or inhibit apoptosis.

3. Signaling via G Protein–Coupled Receptors and Second Messengers

Structure of G protein coupled receptor

7-helix receptors


43 kDa

37 kDa

7.5-10 kDa

G Protein coupled Receptor


Self inactivation of Gs


Transduction of the epinephrine signal: the adrenergic pathway


Epinephrine and its synthetic analogs


Toxins produced by bacteria that cause cholera



4. Signal via Hydrophobic molecules

A Cytoplasmic Receptor


5. Integrin signaling Normal cells cannot grow in suspension (as cancer cells do), but need to attach to a surface that

resembles the extracellular matrix (ECM) in a tissue. Cells have transmembrane proteins called integrins that anchor them to materials in the ECM

(fibronectin, collagen, proteoglycans, etc). Interaction of integrins with an extracellular ligand generates a variety of signals, some essential for cell

growth and differentiation.

The interaction of the cell with the ECM is donethrough focal adhesions containing clustered integrins,cytoplasmic proteins and actin stress fibers.

The tyrosine kinase Src is localized to focal adhesions. Src phosphorylates the focal adhesion kinase (FAK) Phosphorylated FAK is bound by SH2 proteins like

Grb2-Sos, activating the MAP kinase cascade.

6. Intracellular signaling


44

Secondary messengers1. Cyclic AMP2. Inositol-1,4,5 trisphosphate and diacylglycerol3. Ca2+


Formation of Cyclic AMP (cAMP)

PKA is a principle target of cAMPW.K. Purves, D. Sadava, G.H.Orians , and O. C.Heller, Life: The Science of Biology, 7th ed, 2004

Nelson & Cox,, Lehninger Principles of Biochemistry, 4th ed., 2005

Activation of cAMP-dependent protein kinase (PKA)


Two Second Messengers Are Derived from Phosphatidylinositols

Diacylglycerol (DAC)

Inositoltrisphosphate (IP3)

49


The IP3 and DAG Second Messenger System


51

Phospholipase C catalyses PIP2 into IP3 and DAG

•Murray K.R., Granner K.D., Mayes A.P., Rodwell W. V. 26th edition. Harper’s Illustrated Biochemistry,2003


Hormone-activated phospholipase C and IP3

Figure 15-61 Five parallel intracellular signaling pathways activated by G-protein-linked receptors, receptor tyrosine kinases, or bothIn this schematic example, the five kinases (shaded yellow) at the end of each pathway phosphorylate target proteins (shaded red), some of which are phosphorylated by more than one of the kinases. The specific phospholipase C activated by the two types of receptors is different: G-protein linked receptors activate PLC-, whereas receptor tyrosine kinases activate PLC- (not shown).

Adaptor proteinsMany signaling pathways require the formation of large protein complexes

that are held together by adaptor proteins. These proteins contain several specialized domains that act as docking sites for other proteins (e.g. SH2 domains bind to phosphotyrosines; SH3 domains bind to proline-rich sequences).

Domain organization of proteins that associate with phosphorylated tyrosine kinase-containing receptors.

http://www.cellbiol.net/ste/rpimages.php

Pathways leading to cell death

Susan L. Fink, and Brad T. Cookson Infect. Immun. 2005;73:1907-1916

Term CharacteristicsProgrammed cell death Dependent on genetically encoded signals or activities within the dying cell; a sequence of

potentially modifiable events leading to the death of the cell

Apoptosis Mediated by a subset of caspases morphology includes nuclear and cytoplasmic condensation and formation of membrane-bound cellular fragments or apoptotic bodies; not inflammatory

Autophagy Degradation of cellular components within the dying cell in autophagic vacuoles; not inflammatory

Oncosis Prelethal pathway leading to cell death accompanied by cellular and organelle swelling and increased membrane permeability; proinflammatory

Pyroptosis. Proinflammatory pathway resulting from caspase-1 activity leading to membrane breakdown andproinflammatory cytokine processing

Necrosis Postmortem observation of dead cells that have come into equilibrium with their environment

Relevant terms for describing dead and dying cells

Susan L. Fink, and Brad T. Cookson Infect. Immun. 2005;73:1907-1916

Tiago Nunes et al. Biomed Res Int. 2014;2014:218493. doi: 10.1155/2014/218493. Epub 2014 Jul 14.

Three major pathways of cell death

http://www.ncbi.nlm.nih.gov/pubmed/?term=Cell+Death+and+Inflammatory+Bowel+Diseases:+Apoptosis,+Necrosis,+and+Autophagy+in+the+Intestinal+Epithelium

NecrosisFeature

Definition Cell death along with degradation of tissue by hydrolytic enzymes

Causative agents Hypoxia, toxin

Morphology Inflammatory reaction present Death of many adjacent cells Cell swelling initially Membrane disruption Phagocytosis of cell debris by macrophages

Molecular change Lysosome breakdown with liberation of hydrolytic enzymes

Cell death by ATP depletion, membrane damage, free radical injury

Billions of cells in our body die by apoptosis everyday.

Apoptosis is essential during development

morphogenesis

neurons

T lymphocytes

Apoptosis is used as a control against cancer development

Importance of Apoptosis

Development of mouse paw

Apoptosis pathways

Adapted from Elmore S. Toxicologic Pathology,2007;35:495-516,

Caspaseindependent

Evgeny V. Mymrikov et al. Physiol Rev 2011;91:1123-1159

The intrinsic pathway is based on the cytochrome c-dependent activation of caspases.

Different signals (such as γ-irradiation, oxidative stress, or antineoplastic agents) lead to liberation of cytochrome c from mitochondria.

In the cytosol, cytochrome c interacts with apoptotic protease activating factor-1 (Apaf-1), procaspase-9, and dATP forming the so-called apoptosome.

Formation of the apoptosome leads to activation of procaspase-9, which in turn cleaves procaspase-3, the main caspase effector during apoptosis.

Intrinsic pathway

Extrinsic pathway

http://biology-forums.com/index.php?action=gallery;sa=view;id=385

Caspases“Special proteases which are involved in cleavage and processing of more than 300 different cellular proteins”

Feature

Definition Programmed and coordinated cell death

Causative agents Physiological and pathological processes

Morphology No Inflammatory reaction Death of single cell

Cell shrinkage Cytoplasmic blebs on membrane Chromatin condensation Phagocytosis of apoptotic bodies by

macrophages

Molecular change Lysosome and other organelle intact Genetic activation by proto-oncogenes and

oncosupressor genes and cytotoxic T cell mediated target cell killing

Apoptosis

Autophagy or Autophagocytosis‘eating of self’,

Autophagy is a self-degradative process that is important for balancing sources of energy atcritical times in development and in response to nutrient stress.

Autophagy also plays a housekeeping role in removing misfolded or aggregated proteins,clearing damaged organelles, such as mitochondria, endoplasmic reticulum and peroxisomes,as well as eliminating intracellular pathogens.

Autophagy is generally thought of as a survival mechanism, although its deregulation hasbeen linked to non-apoptotic cell death.

Autophagy can be either non-selective or selective in the removal of specific organelles,ribosomes and protein aggregates, although the mechanisms regulating aspects of selectiveautophagy are not fully worked out.

Macroautophagy“It is the main pathway, used primarily to eradicate damaged cell organelles or unused proteins”

Involves the sequestration of cytosolic proteinsand organelles within double-membranestructures termed autophagosomes and theirsubsequent degradation via lysosomal hydrolases.Atg12 ubiquitin- like system activity takes placeduring elongation of the phagophore mediatingLC3 lipidation (LC3-II) and its localization to theautophagosome membrane. Fusion of theautophagosome and the lysosome is driven byintraorganelle acidification. Ultimately,autophagosome and lysosome fusion leads to(a) the degradation of cytosolic components with

ulterior generation of amino acids and fattyacids to be recycled for cellular survival.

(b) the removal of potential damaging proteinsand organelles. Under certain conditionsautophagy might induce cell death to destroyimpaired/damaged cells.Rodriguez-Rocha H. et. al. DNA damage and Autophagy. Mutat Res. 2011 June 3; 711(1-2): 158–166.

Microautophagy

During microautophagy, invaginations at the surface of the lysosome or late endosomes trap cytosolic material,including proteins, and are then internalized after membrane scission and degraded in the lumen of the organelle. Cytosolicmaterial can be sequestered 'in bulk' or selectively with the help of a cytosolic chaperone that recognizes the substrates.

“Involves the direct engulfment of cytoplasmic material into the lysosome”

Sahu R. et. al. Developmental Cell 2011 20, 131-139DOI: (10.1016/j.devcel.2010.12.003)

Chaperone-mediated autophagy“Involves the recognition by the hsc70-containing complex.”

(a) Recognition of substrate proteins by hsc70/co-chaperones; (b) binding of substrate–chaperone complex to LAMP-2A; (c)unfolding of the substrate; (d) LAMP-2A multimerization, substrate translocation, and subsequent degradation; (e) disassemblyof LAMP-2A multimer/translocon. Regulation of the levels of LAMP-2A at the lysosomal membrane is achieved through (1) denovo synthesis, and (2) degradation in specialized microdomains at the lysosomal membrane.

Kaushik S. ana Cuervo M. Trends in Cell Biology 2012 22, 407-417

Types of Autophagy“Cytosolic proteins can enter the lysosome for degradation by at least three autophagic pathways”

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