3 - mechanisms behind gordons syndrome

Question 1

what is NCC

Answer 1

sodium (Na+) chloride (Cl-) co-transporter

Question 2

what is NKCC2

Answer 2

Na+ K+ Cl- co-transporter

Question 3

where is NCC found

Answer 3

apical membrane of the DCT

Question 4

function of NCC

Answer 4

symports Na+ and Cl- into the cell for Na+ reabsorption

responsible for reabsorption of 5-10% filtered NaCl

Question 5

where is NKCC2 found

Answer 5

thick ascending loop in LoH

Question 6

function of NKCC2

Answer 6

responsible for reabsorption of 15-20% filtered NaCl

Question 7

why are electroneutral cation chloride symporters important?

Answer 7

they define the final salt concentration in the urine
they effects the blood volume and therefore arterial pressure
they can be inhibited by thiazide-type or loop diuretics

Question 8

how much blood is filtered by the kidney

Answer 8

180 litres per day

Question 9

what happens when activated WNK kinase bind to SPAK

Answer 9

SPAK gets phosphorylated at thr243 and phospho-SPAK then binds to NCC

Question 10

what happens when phospho-SPAK binds to NCC

Answer 10

phospho-SPAK gets phosphorylated at thr60
becomes phospho-NCC (pNCC)
pNCC has increased intrinsic activity
causes influx of Na+

Question 11

what happens if you block NCC

Answer 11

you increase diuresis (urine production) by salt wasting

Question 12

where is SPAK expression localised to

Answer 12

the TAL and DCT

Question 13

effect of mutation in Thr60 of NCC

Answer 13

prevents Na+ uptake

Question 14

general function of protein kinases

Answer 14

modify other proteins via phosphorylation

Question 15

what is a kinome

Answer 15

all the protein kinase genes
500
2% of the genome

Question 16

why can SPAK and OSR1 both be activated by WNK

Answer 16

they have highly similar catalytic domains

Question 17

what leads to WNK signalling

Answer 17

hyperosmotic or hypotonic stress

Question 18

what regulates WNK-SPAK signalling

Answer 18

CUL3 - KLHL3 - E3 ligase complex

Question 19

3 main steps of ubiquitination

Answer 19

1 - activation
2 - conjugation
3- ligation

Question 20

outline process of ubiquitination

Answer 20

1 - Ub activated by E1 ubiquitin-activating enzyme (ATP dependent)

2 - E2 conjugating enzyme catalyses transfer of Ub from E1 to active site of E2 via trans-esterification

3 - E3 ubiquitin ligase catalyses final step of ubiquitination cascade

Question 21

mutations in which proteins can cause gordons syndrome

Answer 21

mutations in KLHL3 and CUL3

Question 22

what is CUL3

Answer 22

gene coding for protein Cullin-3 involved in ubiquitination

Question 23

if WNK1/4 are not ubiquitinated …

Answer 23

then they are not degraded in the proteasome
WNK accumulates in tubule of lumen cells
WNK signalling is increased

Question 24

effect of mutations in WNK1 and WNK4

Answer 24

makes them over-reactive

increases signalling

Question 25

result of increased WNK signalling

Answer 25

increased phosphorylation and activation of SPAK
over-activation of NCC and NKCC2
increased Na+ in blood

Question 26

difference between WNK1 and WNK4

Answer 26

WNK1 - expressed ubiquitously including brain and heart

WNK4 - has much shorter amino acid sequence, expressed mainly in kidneys

Question 27

explain the mutations that prevent WNK ubiquitylation

Answer 27

E3 ligase complex contains a
‘cullin ring’ composed of CUL3
and BTB protein KLHL3.

Mutations in these prevent
ligation (catalysed by the E3
complex)

no ligation –> no ubiquitylation