The pharmacology of T-kinin and des-Arg(11)-T-kinin in primary cultures of rat bladder smooth muscle cells

Bifunctional fusion proteins containing the sequence of the bradykinin homologue maximakinin: activities at the rat bradykinin B2 receptor

To support bradykinin (BK) B2 receptor (B2R) detection and therapeutic stimulation, we developed and characterized fusion proteins consisting of the BK homolog maximakinin (MK), or variants, positioned at the C-terminus of functional proteins (enhanced green fluorescent protein (EGFP), the peroxidase APEX2, or human serum albumin (HSA)). EGFP-MK loses its reactivity with anti-BK antibodies and molecular mass as it progresses in the endosomal tract of cells expressing rat B2Rs (immunoblots, epifluorescence microscopy). APEX2-(NG)15-MK is a bona fide agonist of the rat, but not of the human B2R (calcium and c-Fos signaling) and is compatible with the cytochemistry reagent TrueBlue (microscopy), a luminol-based reagent, or 3,3′,5,5′-tetramethylbenzidine (luminescence or colourimetric B2R detection, cell well plate format). APEX2-(NG)15-MK is a non-isotopic ligand suitable for drug discovery via binding competition. Affinity-purified secreted forms of HSA fused with peptides possessing the C-terminal MK or BK sequence failed to stimulate the rat B2R in the concentration range of 50–600 nmol/L. However, the non-secreted construction myc-HSA-MK is a B2R agonist, indicating that protein denaturation made the C-terminal sequence available for receptor binding. Fusion protein ligands of the B2R are stable but subjected to slow intracellular inactivation, strong species specificity, and possible steric hindrance between the receptor and large proteins.

Pharmacological and functional characterization of bradykinin B2 receptor in human prostate

The objective of this study was to pharmacologically characterize bradykinin receptors, a component of the kallikrein-kinin system, in normal human prostate cells. In primary cultured human prostate stromal cells, bradykinin, but not [des-Arg9]bradykinin or [des-Arg10]kallidin, produced calcium mobilization or inositol phosphates accumulation with potencies (pEC50) of 8.8+/-0.2 and 8.2+/-0.2, respectively. This was consistent with abundance of bradykinin B2 mRNA over bradykinin B1 mRNA in prostate stromal cells. Although the prostate epithelial cells (prostate epithelium, BPH-1, and PC-3) expressed mRNA for bradykinin B2 receptors (albeit in lesser amounts than stromal cells), bradykinin was not functionally efficacious in the epithelial cells. Increasing concentrations of D-arginyl-L-arginyl-L-prolyl-trans-4-hydroxy-L-prolylglycyl-3-(2-thienyl)-L-alanyl-L-seryl-D-1,2,3,4-tetrahhydro-3-isoquinolinecarbonyl-L-(2alpha,3beta,7alphabeta)-octahydro-1H-indole-2-carbonyl-L-arginine (HOE-140), a bradykinin B2-selective peptide antagonist, attenuated bradykinin concentration-response curves in human prostate stromal cells with apparent estimate of affinity similar to that for the human bradykinin B2 receptor. Bradykinin (10 nM) caused proliferation of prostate stromal cells and phosphorylated extracellular signal-regulated kinases (ERK-1 and ERK-2) that were blocked by HOE-140 (1 microM). This study demonstrated that, in primary cultures of normal human prostate stromal cells, bradykinin activates bradykinin B2 receptors that may play a significant role in proliferation via activation of ERK-1/2 pathways.