TABLE 1

Effect of mutation of human GIPR on its expression and ability to induce cAMP formation

Receptor expression was measured by flow cytometry using GIP-Alexa F 647 as label of GIPR. Results are expressed as percentage of expression value of the WT-GIPR and are the means ± S.E.M. of three or four individual experiments. F_mut (mutation factor) was calculated as EC₅₀ (mutated GIPR)/EC₅₀ (WT-GIPR), where EC₅₀ is the potency of GIP (based on four to nine determinations). E_max corresponds to efficacy of GIP to stimulate cAMP production. E_max values are expressed as percentage of GIP-stimulated cAMP production with the WT-GIPR.

GIP-R	Location	Receptor Expression	cAMP production
GIP-R	Location	Receptor Expression	EC₅₀	F_mut	E_max
		%	nM		%
WT		100	1.96 ± 0.32		100
Mutant R183A	TMH II	76.1 ± 4.6	149.7 ± 30.8***	76.4	84.2 ± 9.5
Mutant R190A	TMH II	84.9 ± 6.7	139.3 ± 16.8***	71.2	81.7 ± 7.1
Mutant Q220A	TMH III	110.2 ± 1.1	9.2 ± 4.3***	4.7	99.0 ± 7.0
Mutant T223A	TM III	116.9 ± 17.0	6.7 ± 2.6***	3.4	100.3 ± 5.1
Mutant Q224A	TM III	77.2 ± 7.6	11.0 ± 5.0***	5.6	117.0 ± 6.7
Mutant N230A	TM III	91.9 ± 0.7	12.7 ± 1.2***	6.5	98.1 ± 6.8
Mutant Y231A	TM III	102.5 ± 1.7	4.2 ± 0.9*	2.1	114.5 ± 15.2
Mutant Y231F	TM III	96.2 ± 8.1	7.9 ± 4.8**	4.0	101.2 ± 7.8
Mutant R300A	TM V	75.1 ± 6.5	82.3 ± 15.9***	42.0	85.8 ± 3.8
Mutant H353A	TM VI	96.5 ± 8.7	2.5 ± 1.7	1.3	130.9 ± 8.9
Mutant F357A	TM VI	77.0 ± 6.1	30.8 ± 9.3***	15.7	114.1 ± 11.7
Mutant Q384A	TM VII	115.3 ± 3.4	5.2 ± 1.4**	2.6	111.5 ± 23.0
Mutant Q384N	TM VII	109.4 ± 9.7	3.2 ± 1.6	1.6	115.8 ± 15.8
Mutant Y392A	TM VII	89.9 ± 3.9	9.5 ± 4.0***	4.8	106.8 ± 13.2
R1831.Q384A-GIPR	TMII-VII	12.0 ± 0.2	32.5 ± 12.3**	16.6	28.0 ± 10.2

↵* P < 0.05 evaluated by Student's t test compared with wild-type receptor value.
↵** P < 0.01 evaluated by Student's t test compared with wild-type receptor value.
↵*** P < 0.001 evaluated by Student's t test compared with wild-type receptor value.