TOPIC B CELL TALK: Communication networks inside and outside cell Flashcards
1
Q
What is paracrine signalling?
A
- Local signalling
2
Q
What is endocrine signalling?
A
- Long distance–> hormone related
- Released from tissue that is FAR from target cell
3
Q
What are the three different types of effector proteinsproduced from signalling pathways and what are their actions?
A
- Metabolic enzyme (altered metabolism)
- Cytoskeletal protein (altered shape or movement)
- Transcriptional regulator( altered gene expression)
4
Q
What are the two features of signalling?
A
- SPECIFICTY `
2. AMPLIFICATION
5
Q
What is specificity?
A
- Signal molecule that fits binding site on complementary receptor (others don’t fit)
6
Q
What is amplification?
A
- Enzymes activate OTHER enzymes
- no. of affected molecules INCREASES geometrically in enzyme cascade
7
Q
What occurs in negative feedback?
A
- Build up of product turns off original activator
8
Q
What is positive feedback?
A
- build up of product amplifies pathway
9
Q
What type of signal transduction is FAST acting?
A
- Altered protein function (proteins already synthesised and ready to go)
e. g. insulin INCREASING GLUT receptors in membrane
10
Q
Which type of signal transduction is SLOW acting?
A
- Altered protein synthesis (and expression)
e. g. If cell wants to synthesise more receptors
11
Q
What are the three different classes of hormone?
A
- Polypeptide/protein hormones e.g. Insulin
- Amine –> Adrenaline
- Steroid–> Estrogens/testosterone (passes through cell membrane freely)
12
Q
What 4 things is cell communication required for?
A
- Regulation of development
- Organization into tissues
- Control of growth, death, and division
- Coordination of diverse cellular activities
13
Q
What is the biggest class of hormones?
A
- Polypeptide/protein
e.g. insulin/glucagon
leptin, GH, TRH LH Growth factors
14
Q
Why are polypeptide/portein hormones stored in secretory vesicles for up to 1 day vand what form are they in?
A
- Because otherwise it could be degraded
- Stored as a PROHORMONE (inactive form)
15
Q
What is the lifetime of protein hormones circulating in the blood freely?
A
- Minutes before they are degraded
16
Q
What is the secretion of polypeptide/protein hormones regulated by?
A
- Other hormones
- metabolites
- CNS
17
Q
What is the formation of mature insulin from immature insulin?
A
- Preproinsulin—(signal sequence chopped off)—-> Proinsulin—(c peptide chopped off)—-> Mature insulin
18
Q
What chains does insulin have and what are they joined together by?
A
- Alpha and beta chain
- Joined together by disulfide bonds
19
Q
What is insulin synthesised by?
A
- The beta cells of pancreas as PROHORMONE
20
Q
What are peptide.amine hormones derived from and what are they ?
A
- Tyrosine
- Adrenaline and NA
- T3 and T4
21
Q
Where are NA and A secreted from?
A
- Adrenal medulla
22
Q
If NA and A are secreted freely in the blood, how long will they last for?
A
- Seconds (so short lifetime)
23
Q
What are the 3 different types of cell surface receptors?
A
- Ion-channel coupled receptors
- G-protein coupled receptors (activated by GTP binding)
- Enzyme coupled receptors (variable) –> Receptors itself is enzyme
- can have catalytic domains OR associated with enzyme close to membrane
24
Q
Where does the signalling molecule bind to in nuclear receptors?
A
- Ligand binding domain (distinct from other domains)
25
In nuclear receptor pathways, what MAY NEED TO occur before gene transcription can happen?
-may need to have coavticator proteins binding (can become part of transcription activating domain)
26
What happens in nuclear receptor pathways when the ligand binds?
- there is conformational change q
27
What other important domain is part of the intracellular receptor?
- DNA-binding domain
28
What are the two pathways that can be active once G protein coupled receptor is activated?
`1. Cyclic AMP pathway (second messengers)
| 2. Inositol phospholipid pathway
29
What features are common to all G protein coupled receptors? -
- Cell surface receptors
- 7 transmembrane segments
- signalling molecule can activate MULTIPLE GcPRS
- ALL use G proteins to relay a signal
30
What is the structure of a G protein? (and subunits)
- Trimeric G protein complex
| - Has alpha, beta and gamma subunits - in some types may only have 1 or 3 subunits
31
What can the alpha subunit bind on a G protein?
- GDP (inactive form)
| - GRP active form
32
What do the phospholipid tails on the alpha and beta subunits of the G prtoein do?
- Anchor subunits into membrane
33
What are the 7 steps of the activation of a G protein? (Last step: when is switch turned off?)
1. Ligand binds to G protein coupled receptor
2. RECEPTOR changes conformation, interacts with inactive GDP bound G protein
3. Causes G protein to EJECT GDP and replace with GTP
4. This exchange causes conformational change
5. G protein: binding GTP releases receptor
6. It interacts with one or more effectors ---> active protein--> delivers message
7. Switch is turned off WHEN G PROTEIN HYDROLYSES its own bound GTP--> GDP (after time)
34
What happens in G protein coupled receptors when GTP is bound to the alpha unit?
- It DISSOCIATES from Beta or gamma units so they can activate another complex/pathway)
35
What is the role of a second messenger?
- Internal messenger that activates secondary pathways in cell e.g. cAMP--> activates PKA and self transcription
36
What occurs in the universal (not individual cell type) Inostiol Phospholipid pathway?
Signal molecules comes in from EXTRACELLULAR source and activates receptor--> induces conformational change--> activates G protein complex (beta and gamma subunits)---> Activates protein (phospholipase C--this cleaves phospholipid)---> Activated phospholipase C acts on INOSITOL PHOSPHOLIPID (IP2) in membrane and cleaves it from DAG (diacylglycerol) in membranre---> this FORMS IP3 (secondary messenger)
- IP3 binds to ligand gated ion channel--> Casues Ca2+ efflux from ER ---> Ca2+ activates PROTEIN KINASE C (PKC) ---> then activates other processes (cellular) like gene trancription and muscular contraction
37
What does PKC (protein kinase C) need to be activated in the insosital phospholipid pahtway?
Needs BOTH DAG (diacylglycerol) and and Ca2+ to be activated
38
What occurs in the cyclic AMP pathway of G protein coupled receptors?
Membrane bound recpetor: Adenylyl Cyclase converts ATP--> cyclic AMP
- Only alpha subunit involved
- cAMP then activated in signalling molecule in cell (second messenger)
- Inactive PKA (4 subunits--2 catalytic and 2 regulatory)
- cAMP binds to regulatory subunits of PKA---> these regulatory subunits then released from catalytic domains ---> activated PKA
39
What is an example of the cAMP pathway and what occurs?
ADRENALINE INDUCING GLYCOGEN BREAKDOWN
- Adrenaline binds and activated GPCR (sdrenergic) activates activated adenylyl cyclase and alpha subunit of protein
- ATP ---> cAMP --> active PKA --> activates enzymes specific to glycogen breakdown
- then via ATP it forms active glycogen phosphorylase
40
In activation of gene trasncription via adrenaline through cAMP pathway, what is the pathway from active PKA?
- Active PKA moves into nucleus (via pore) and binds to transcription regulaotrs--> leads to gene trasncription
41
Does active PKA have different cellular responsed based on cell type?
- YES!!
42
What are G protein coupled receptors as drug targets?-
Adrenergic receptors (beta blockers) --> to decrease HR and contractility)
43
What is a treatment of cardiac aryhtmia and angina?
- Inhibiting Beta adrengergic recpetor (GPCR) action
44
What does the drug inderal (proprananol) do?
- Acts as a Beta 1 agonist
| - competitively INHIBITS GPCR binding to NA--> slows heart contraction
45
What leads to cortisol secretion and what type of receptor pathay does this use?
ACTH
| - ACTH is a GPCR
46
What is cushing syndromec and what is it associated with?
- Chronic exposure to EXCESS glucocorticoids (steroids)
- decreased growth in kids
- Increased weight, hpertension, diabetes
- osteoperosis, muscle weakness
47
What are potential causes in cushings syndrome?
- Genetic Mutations in signalling pathway
48
What can lead to changes in the level of cortisol secreted?
- Mutations in any step of the pathway (cAMP signalling)
- Pathway is overactive (cancer also has this overactive effect)
- GPCR mutation
49
What are the two types of activating mutations that occur in cushings syndrome?
- Loss of function mutation (turns off protein) and gain of function (protein may be overactive)
50
What occurs in mutation in regulatory protein?-
- May not be able to turn off signalling pathway
51
What occurs with a mutation in an enzyme that needs to be activated
Pathway may be blocked
52
What are the key molecules in the phosphatidylnosol pathway?
- GPCR--> G protein--> inositol phospholipid --> inositol 1,4,5 triphosphate--> PKC
53
What are the key signalling molecules in the cAMP pathway?
- GPCR activation -->G protein activation--> Adenylate cyclase activation--> ATP--> cAMP--> PKA activation
54
Which two factors are responsible for directly activating Protein Kinase C (PKC)?
- Diacylglycerol (DAG) and Ca2+
55
What activates protein kinase A (PKA)
- Cyclic AMP (cAMP)
56
What does a loss of function mutation lead to?
- Leads to INHIBITION of signalling pathway (symptoms like hormone deficiency)
57
What does a gain of function mutation lead to?
Overactive pathway (symptoms similar to excess hormone or signalling molecule)
58
Where can a loss or gain of function mutation occur?
- ANY of the proteins involved in in GPCR signalling OR second messenger pathways
59
What is cushings syndrome a result of ?
INCREASED cortisol secretion (adrenal cortex) OVERTIME
60
How is cortisol normally produced and secreted?
- CRH (corticotropin releasing hormone) in hypothalamus goes into hypophyseal system into ANTERIOR pituitary and acts on a GPCR to allow ACTH to be produced --> released into blood stream --> adrenal gland ACTH stimulates adrenal cortex cells to release and produce CORTISOL!
61
What type of mutation occurs in cushings syndrome and which parts can be affected?
- Gain of function mutation
- overactive pathway
- Alpha subunit of trimeric G protein
- PKA
- GCPR
62
What are two gene mutation that lead to overactive /overexpressed receptor or G proteins or the catalytic subunit of PKA?
- Primary Bilateral Macronodular Adrenal Hyperplasia (PBMAH)
- Adrenal adenoma (tumors on adrenals gland)
63
What are the gene mutations associated with primary pigmented Nodular Adrenocortical Disease (PPNAD)?
-Mutations in the catalytic or regulatory sub-units of PKA
64
Which type of mutation can central hypothyroidism be and what does it lead to?
- Loss of function mutation
- mutation in Thyrotropin Releasing Hormone Receptor (TRHR) in anterior pituitary
- Mutation causes inositol pathway to be INHIBITED
- so thyrotropic cells can't be stimulated from the TRH released from hypothalamus
- SO NO production of TSH and no secretion of thyroid hormones
65
What is the correct order for the release of thyroid hormones?
- TRH released from HYPOTHALAMUS
- TSH released from anterior pituitary
- T 3 and T4 released from thyroid
66
A loss of function mutation in cAMP PDE would result in?
- Increased cAMP signalling due to inability to regulate duration of cAMP activation
67
What does GEF (guanine nucleotide exchange factor) do?
- Activates GTPase
- Stimulates the release of GDP
- GTP quickly binds--> GTPase activated--> GTP exchanged for GDP
68
What does GAP do?
- Gtpase Activsting Protein
- hydrolyses GTP--> GDP
- GDP remains tightly bound
69
Which 3 are the most commonly phosphorylated as part of the enzyme coupled receptpr pathways?
- Serine
- Threonine
- tyrosine
70
Which part of the RTK is the part that is catalytic and can phosphorylate other molecules when activated?
- Tyrosine kianse domain
71
What does the insulin rercepotr exist in membranes as?
Dimeric form
72
In general, what to RTK's lead to when activated?
- cell growth
- cell division
- proliferation/cell survival
73
What do RTK's prevent/inhibit?
- Apoptosis
74
How do receptor tyrosine kinases work?
- Receptor in membrane is monomer
- Ligand binds---> forms DIMER with a receptor of SAME family --> they can activate EACH OTHER (autophosphorylation) --> both receptors are activated
- Then receptors can activate multiple pathways in the cell
75
What do the phosphorylation points in the tail of the receptor (RTK pathway) provide?
- Binding sites for different adapter molecules
76
Which domains do proteins that are binding to ECF receptors have to have?
- SH2
SH3
PTB
PH
77
What does SH2 recognise?
- Phosphorylates tyrosine residues
78
What does SH3 do?
- Can bind to proline rich regions
79
What does PTB recognise?
- (Phospho Tyrosine Binding domain)
| - Recognises Phosphorylated tyrosine residues
80
What does PH recognise?
- Hyperphosphorylated inositide molecules
81
What are adaptor proteins?
- Act like bridges from one protein kinase to another
| - can form a bridge between molecules that don't have their own SH2 or PTB domains e.g. Grb2
82
What are scaffold proteins and what do they allow/reduce?
- bring together multiple interacting signals/proteins so they can activate each other
- CAUSES RAPID ACTIVATION
- REDUCES other signal molecules from other pathways from interfering
83
In cancer, what part of the RTK are looked at?
- The phosphorylation sites
| - Usually in cancer the phosphorylation sites can be overactive
84
What does PI3K do and what is it activated by?
- - Recruited and activated by RTKs
- Phosphorylates inositol phospholipids in plasma membrane
- Becomes the docking site for intracellular signalling proteins (Akt) and activates them
85
What is Akt also known as and what does it do?
- PKB (protein kinase B)
| - Promotes growth and survival (inhibits BAD--> BAD encourages apoptosis)
86
What is BcI2? (pro or anti apoptotic)
- Pro apaptotic
87
What is Bad? (pro or anti apaptotic)
- anti apoptotic
88
What occurs in terms of Bad and BcI2 when Akt (PKB) is active ?
- It phsophorylates Bad
- Bad and BcI2 dissociate
- So BcI2 is CTIVATED AND APOPTOSIS IS INHIBITED (SURVIVAL SIGNALS)
- So Phosphorylation INIHBITS Bad
89
What do tyrosine associated kinase receptors associate with?
- Proteins that have tyrosine kinase activity (not the tyrosine kinases)
- e.g. CYTOKINE RECEPTORS
90
Which two families of proteins are important for tyrosine associated receptors?-
1. Src (SARC) kinase family (associate with receptors)
2. Janus Kinase family e.g. JAK 1, 2, TYK 2
(signalling family receptors--> growth hormone receptors
91
How are cytokine receptors formed?
- Pre assembled with JAK protein on tail (has kinase function)
- JAKs are Phosphoryltors --> they autophospohrylate each other --> JAKS phosphorylate cytokine receptor
- STAT 1 and 2 recruited for transcription
92
What do epidermal growth factors activate?
- Receptor Tyrosine Kinases
93
Which protein domains bind phosphorylated tyrosine residues?
- PTB and SH2 (depends on individual affinity for which one actually binds)
94
Janus Kinases activates which family of proteins?
- STATs (src is also important)
95
What do nuclear receptors allow for?
- Transcription to be regulated!
| - Reproduction, homeostasis, integrated metabolism
96
What is the biggest class of hormones that bind to nuclear receptors?
- Steroids
| but also vitamin D and thyroid-less large
97
What type of receptor does cortisol use?
- A nuclear receptor becasue it is lipophillic
98
What receptor can be targeted in cushings syndrome?
- Glucocorticoid receptor (GR)
99
What does the drug Mifepristore (RU486) do?
- It is a GR and PR (progesterone receptor) antagonist (prevents signalling and activation)
- Active in abortion
- trialled in depression
100
Where are steroid hormoens synthesised?
- Adrenal, Overies and testes
101
What can congenital adrenal hyperplasia result from?
- Defficiencies in 1-hydroxylase
- 11 beta hydroxylase
- or 17 alpha hydroxylase or C17-20 lyase
102
What are DNA binding sites called?
- Hormone Response Elements (HREs)
103
Steroid hormones bind to HREs as.....
HOMO DIMERS (GR, ER, PR, AR)
104
RXR-NRs (Retinoid X receptors) bind to HREs as:
- Heterodimers (e.g. RAR, PPAR )
105
What do the estorgen receptors exist as?
- Homodiemrs
| - ER alhpa and ER beta receptors form the homodimer
106
What is ERalpha important for?
- Mediating estradiol effect (femaile reporoduction ,
| mammary gland function, bone, CV system, brain
107
What is ER beta im,portant for?
- OVARY, bone, breast, brain ,
| - different expression patterns
108
What occurs in a ER alpha deficiency?
- Resistant to estorgens (high estrogen blood levels)
- Continued growth
- Estrogen important for male and femalse bone formation
109
What is CML and which pathway is an issue here?
- Chronic Myelopid Leukemia (excess white blood cells)
- overflow of immature leukocytes into bloodstream
- OVERACTIVE INTRACELLULAR SIGNALLING PATHWAY (cell growth and survival)
- oncogenic tyrosine kinase (BCR-ABL)
110
What is the action of BCR-ABL in the overactive signalling pathway of CML?
- This oncogenic tyrosine kinase phosphorylates kinases in the cell proliferation pathway (Ras/MAPk, PI3K/Akt, JAK/STAT)
- This leads to uncontrolled cell growth
111
What is a possible treatment of CML in terms of the oncogene BCR-ABL?
- Gleevic (inhibitor)
112
What is the action of Gleevic and what is it used as
| ?
- binds to BCR-ABL binding site (so ATP can't bind) and so no phosphorylation
- Used as a possible treatment for CML
113
What is the action of TKIs (Tyrosine kinase inhibitors) ?
- Competitive inhibition of ATP and upstream or downstream substrate
114
How do mAbs (monoclonal antibodies) work (in context of CML treatment)
- They bind competitively with receptors ligand binding site (so can't be activated or dimerise) (inhibit cell surface receptors)
115
What is HER2, which family is it from, which protooncogene is it encoded by and what is a special feature of it?
- Human Epidermal Growth Factor receptor 2
- From the EGFR family
- Encoded by proto oncogene ERBB2
- Special feature: Can form heterodimers with other EGFR family members
- Associated with breast cancer (aggressive)
116
What does the HER2/EGFR do when active?
- Activates the MAPK and PI3K pathways
| - these pathways lead to cell growth and proliferation
117
What is Heceptin and what action does it have?
- Monoclonal antibody
- Specific to HER2
- binds to HER2 so it can't activate the intracellular signalling pathway
- Is a treatment for HER2 positive breast cancer
