INTERNALIZATION AND RESENSITIZATION MECHANISMS OF THE HISTAMINE TYPE 2 RECEPTOR

FERNANDEZ N; MONCZOR F; NOTCOVICH C; BALDI A; DAVIO C; SHAYO C

Delfos, Grecia

Congreso; 35th Annual Meeting of the EHRS; 2006

EHRS

We have previously reported that the magnitude and duration of H2R agonist-evoked response are key features in biological processes such as cellular differentiation (Biochem. Biophys. Res. Commun., 314:798, 2004). Thus, in COS-7 cells the termination of the signal is dependent upon GRK2 and GRK3 induced phosphorylation of the H2R (Mol. Pharmacol., 60:1049, 2001). Once a GPCR is phosphorylated it may suffer either internalization and degradation or recycling to the membrane following dephosphorylation. Further receptor dephosphorylation may occur without internalization. Given the relevance of such mechanisms in the desensitization/resensitization process of  receptor-evoked responses, we sought to establish H2R trafficking following selective agonist treatment. Confocal microscopy and binding assays performed in H2R transfected COS-7 cells showed that the number of H2R sites in the membrane was reduced by 50% after 60 min agonist stimulation but it was fully recovered 60 min after stimuli withdrawal. Furthermore, cAMP accumulation evoked by H2R stimulation with a selective agonist for 60 min was reduced by 90% but it was partially recovered (50%) when the stimulus was removed. Arrestin and dynamin are two important proteins involved in GPCRs internalization. Cotransfection studies with negative dominants for these two proteins showed that although the number of H2R sites in the membrane remained unaltered following agonist stimulation, the receptor response resulted abolished and failed to recover after the stimulus was removed. Present findings support that although internalization is not necessary for H2R desensitization it is relevant for active sites recycling to the membrane. In addition results show that arrestin and dynamin are involved in H2R endocytosis and recycling.