L17 - Cytokines and prostaglandins

Question 1

Function of cytokines and cells that secrete them?

Answer 1

Mediators/ Co-ordinator of body’s defense responses

Secreted mostly by immune cells

Question 2

Describe the modalities of cytokine transport? (i.e. short or long distance?)

Answer 2

Usually act as local hormones, some endocrine functions:
 Autocrine: acts on same cell
 Paracrine: nearby cell
 Endocrine: transported in circulation/bloodstream&raquo_space; distant cell

Question 3

Define pleiotropy and synergy and redundancy of cytokines?

Answer 3

same cytokine may produce different effects on different cell types (pleiotropy)

Two cytokines may enhance each other’s effect (synergy)

Many cytokines produce same effect on same cell (redundancy)

Question 4

Describe the structure of cytokine receptors?

Answer 4

multisubunit, diff. cytokine receptors have diff. subunits

Heterodimer:
α subunit = specific, for binding the cytokine (extracellular)
β subunit = produces intracellular signals.

Question 5

Describe the 2 modes of action of α subunit of cytokine receptors?

Answer 5

1. Soluble a subunit&raquo_space; bind to cytokine and antagonize: Prevent interaction between cytokine and its receptor
2. Trans-signalling: soluble α-subunit:cytokine complex binds with β-subunit expressed in another cell
   (if both cells dont have both a and B subunits)

Question 6

Describe the specificity of a and B subunits of cytokine receptors to produce antagonism?

Answer 6

Different cytokine receptors have diff. a subunit but same B subunit

i.e. cytokine A use up both a and B subunits of receptor, then cytokine B cannot bind = Cytokine A is antagonistic to Cytokine B

Question 7

Describe the intracellular signalling events in B subunit of cytokine receptors?

Answer 7

1 cytokine binds across 2 B subunits

> > 2 B subunits cluster and each JAK kinase is brought together
2 JAK kinases cross phosphorylate
Recruit and phosphorylate transcription factor STAT
STAT translocation into nucleus
Gene trasncription for immune response

Question 8

Describe the downstream reaction in macrophages to signal liver cells after activation by pathogen.

Answer 8

1) Macrophage receptors (i.e. LPS, Mannose, Glycan receptors) bind to pathogen
2) Release of cytokines: IL-6

3) IL-6 activates synthesis of acute phase proteins in Liver
a) C-reactive protein binds phosphorylcholine on bacterial&raquo_space; activates complement to opsonization
b) Mannose-binding protein binds mannose residues on bacterial&raquo_space; activate compliment lysis and opsonization

Question 9

Source of prostaglandins?

Answer 9

Synthesized from arachidonic acid liberated from phospholipids

Question 10

List mechanisms for synthesis of Arachidonic acid from Phospholipids??

Answer 10

1) Phospholipase A2 (most common) = directly break bond, liberate AA from PL
2) Phospholipase C (PL > DAG), DAG lipase pathway (DAG > AA)
3) Phospholipase D (PL > Phosphatidic acid) > Phospholipase A2 (Phospatidic acid > AA)

Question 11

Reaction to form Prostaglandin-H from Phospholipids? Which organelle is involved?

Answer 11

All occur at ER

PL –[cPLA2]–> Arachidonic acid

AA –[COX 1 or 2]–> Prostaglandin-G

PG-G –[Peroxidase]–> Prostaglandin-H

same protein has both cyclooxygenase + peroxidase domains

Question 12

What is the precursor to all cell-type specific Prostaglandins?

Answer 12

PG-H

Question 13

Difference in the functions of COX-1 and COX-2?

Answer 13

COX - 1 = in all cells for normal physiological functions

COX -2 = Expressed by inflammatory signals for inflammatory reaction (e.g. bacterial LPS, IL-2)

Question 14

Which enzyme is expressed in platelets to process PG-H? Function?

Answer 14

platelets: TxA2

vasoconstriction, platelet aggregation

Question 15

Which enzyme is expressed in BV endothelium to process PG-H? Function?

Answer 15

PGI2

> > vasodilation, platelet declumping

Question 16

Which enzyme is expressed in uterus to process PG-H? Function?

Answer 16

PGF2α

contraction of uterine smooth muscle&raquo_space; Parturition

Question 17

Which enzyme is expressed in Mast cells to process PG-H? Function?

Answer 17

PGD2

chemotaxis, allergy

Question 18

Which enzyme is expressed in Almost all nucleated cells to process PG-H? Function?

Answer 18

PGE2

fever, pain, ovulation

Question 19

Explain which is better: Non-specific or COX-2 inhibitors?

Answer 19

Specific COX-2 inhibitor&raquo_space; suppress COX-2 = suppress inflammatory rxn

No effect on COX1 =normal physiological functions not suppressed

(suppresses some normal physiological functions of COX-2)

Question 20

Arachidonic acid can be metabolised to which 2 inflammatory mediators?

Answer 20

Prostaglandin-H

Leukotrienes

Question 21

Describe the Leukotriene formation pathway?

Answer 21

1) Receptor stimulation induces action of cPLA2 and 5-Lipoxygenase
2) Phospholipid –[cPLA2]–> AA
3) FLAP*** presents AA to 5-Lipoxygenase instead of COX
4) AA –[5-LO]–> LTA4

i) LTA4 react to form LTB4
ii) LTA4 react with Glutathione to form LTC4&raquo_space; LT transporter for export

Question 22

Cell-surface receptors for PG and LT are interchangable. T or F?

Answer 22

False

Specific for each LT or PG

Many diff. types of receptors

Question 23

Brief summary of intracellular signalling cascade from PG or LT receptor signalling?

Answer 23

Change in intracellular Ca2+ level,

Change in cAMP level

Activation of protein kinases, etc