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Irina Kalatskaya, Steffen Schüssler, Cornelia Seidl, Marianne Jochum, Alexander Faussner

C-Terminal fusion of eGFP to the bradykinin B₂ receptor strongly affects down-regulation but not receptor internalization or signaling

Keywords: bradykinin B2 receptor, endocytosis, G protein-coupled receptor, green fluorescent protein

A functional comparison was made between the wild-type bradykinin B₂ receptor (B₂wt) and the chimera B₂eGFP (enhanced green-fluorescent protein fused to the C-terminus of B₂wt), both stably expressed in HEK 293 cells. There was almost no difference in terms of ligand-inducible receptor phosphorylation and internalization, signal transduction (accumulation of inositol phosphates) or expression and affinity. However, stimulation for up to 8 h with 10 ?M bradykinin (BK) resulted in a strong decrease in surface receptors (by 60% within 5 h) in B₂wt, but not in B₂eGFP. When the expression levels of both constructs where comparably reduced using a weaker promoter, long-term stimulation resulted in a reduction in surface receptors for B₂wt_low to less than 20% within 1 h, whereas the chimera B₂eGFP_low still displayed 50% binding activity after 2 h. A 1-h incubation in the absence of BK resulted in a recovery of 60% of the binding in B₂wt_low after 1-h stimulation with BK, but of only 20% after 7-h stimulation. In contrast, B₂eGFP_low levels were restored to more than 70%, even after 7-h stimulation. These data indicate that although the fusion of eGFP to B₂wt does not affect its ligand-induced internalization, it strongly reduces the down-regulation, most likely by promoting receptor recycling over degradation.

Biological Chemistry, Walter de Gruyter

Print ISSN: 1431-6730
Volume: 387, 05/2006
Pages: 603 - 610

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