earticle

영어

Gonadotropin receptors are members of the seven transmembrane (TM) receptor families. Several point mutations in TM II, III, V and VI have been identified in the luteinizing hormone receptor (LHR) gene, leading to constitutive activation and inactivation of the receptor. In eelLHR, we generated 3 types of constitutive activating mutations (M410T, L469R and D590Y) and 2 types of constitutive inactivating mutations (D383N and Y546F) to investigate how they work on hormone-receptor interaction and receptor activation system on eel. To assess the functional effects of 5 receptor mutations directly, wt and mutant eel- LHRs were transiently expressed in CHO-K1 cells, and basal and recombinant eel LH-stimulated cAMP and IP-1 accumulations were measured. Rec-eelLH (0.076～1,200 ng/mL) produced a concentration-dependent increase in cAMP production in wt eelLHR expressing cells with an EC50 of 160 ng/mL and basal cAMP level of 2.6 nM. In contrast, the L469R activation mutant had most elevated (16.88 fold higher than wt) basal cAMP production (basal cAMP level=43.9 nM). Compared with the wt eelLHR, all the activation mutant receptors produced higher basal levels of cAMP (18.4 nM for D590Y and 7.9 nM for M410T). However, eelLH-stimulated (0.076～1,200 ng/mL) basal cAMP levels in the constitutive inactivation mutants D383N and Y546F did not obviously altered from that in wt eelLHR. D383N mutation increased the EC50 value to 185 ng/mL (inhibited receptor activity to 86%), while Y546F mutation increased that to 170 ng/mL which implies that receptor activity was inhibited to 94% only. As seen in IC50 values in IP-1 accumulation, activity for M410T mutant was 19% higher than that for wt receptor, but other activation mutants did not show any difference in IP-1 production. In case of inactivation mutants, there were no significant differences in IP-1 production and only 7% decreased activity was identified in D383N mutant. In summary, we have demonstrated 3 mutations that are responsible for constitutive activation of eelLHR. Although predicted 2 inactivation mutations led to slightly diminished activation of receptor, those could not impair signal transduction of eelLHR.