Cell contact-dependent functional selectivity of ß2-adrenergic receptor ligands in stimulating cAMP accumulation and extracellular signal-regulated kinase phosphorylation.

Activation of ß(2)-adrenegic receptor (ß(2)-AR) leads to an increase in intracellular cAMP and activation of ERK. These two signals are activated by the interaction of the receptor with different transducer partners. We showed that the intrinsic activities of ß(2)-AR ligands for stimulating cAMP production and ERK phosphorylation responses in HEK-293 cells were not correlated. The lack of correlation resulted mainly from the discrepancy between the intrinsic activities of two groups of ligands for these two responses: The first group consisted of clenbuterol, cimaterol, procaterol, and terbutaline which acted as full agonists for cAMP production but displayed very weak effect on ERK phosphorylation. The second group comprised adrenaline and noradrenaline which displayed higher intrinsic activity for the ERK phosphorylation than for the cAMP response. Thus, both groups behaved as functionally selective ligands. The functional selectivity of the first group was observable only in adherent cells when confluence was approximately 100%. When cell-cell contact was minimized either by decreasing the density of the adherent cells or by bringing the cells into suspension, the first group of ligands gained the ability to stimulate ERK phosphorylation without a change in their effect on cAMP production. In contrast, selectivity of the second group was independent of the adherence state of the cells. Our results show that the inherent "bias" of ligands in coupling a G protein-coupled receptor to different transducers may not always be revealed as functional selectivity when there is a "cross-talk" between the signaling pathways activated by the same receptor.

Determination of factor V Leiden mutation and R2 polymorphism in cis position.

FVA4070G (R2 polymorphism) influences plasma factor V (FV) concentration and was associated with mild activated protein C resistance. This polymorphism was reported to have a trans inheritance with FV Leiden (FVL) mutation. The aim of this study is to investigate the inheritance of R2 polymorphism in the homozygous FVL carriers. In this study, 99 patients with thrombosis and 7 individuals without a history of thrombosis all of which homozygous for FVL were included. Of 99 patients, 1 was heterozygous for FV A4070G. Additionally, 6 polymorphisms in the FV gene were analyzed for the heterozygous R2 patient and her family. When the allelic distribution was classified, 8 different haplotypes were obtained. In contrast to the literature, it was shown that R2 polymorphism could be inherited in cis position with FVL and also the family members could have co-inheritance of the FVL and R2 on the same chromosome as proband.