Kallikrein activates bradykinin B 2 receptors in absence of kininogen

• Published in: American journal of physiology. Heart and circulatory physiology 2006-03, Vol.290 (3), p.H1244-H1250
• Main Authors: Biyashev, Dauren, Tan, Fulong, Chen, Zhenlong, Zhang, Kai, Deddish, Peter A., Erdös, Ervin G., Hecquet, Claudie
• Format: Article
• Language: English
• ISSN: 0363-6135; 1522-1539
• DOI: 10.1152/ajpheart.00934.2005

Kallikreins cleave plasma kininogens to release the bioactive peptides bradykinin (BK) or kallidin (Lys-BK). These peptides then activate widely disseminated B 2 receptors with consequences that may be either noxious or beneficial. We used cultured cells to show that kallikrein can bypass kinin release to activate BK B 2 receptors directly. To exclude intermediate kinin release or kininogen uptake from the cultured medium, we cultured and maintained cells in medium entirely free of animal proteins. We compared the responses of stably transfected Chinese hamster ovary (CHO) cells that express human B 2 receptors (CHO B 2 ) and cells that coexpress angiotensin I-converting enzyme (ACE) as well (CHO AB). We found that BK (1 nM or more) and tissue kallikrein (1–10 nM) both significantly increased release of arachidonic acid beyond unstimulated baseline level. An enzyme-linked immunoassay for kinin established that kallikrein did not release a kinin from CHO cells. We confirmed the absence of kininogen mRNA with RT-PCR to rule out kininogen synthesis by CHO cells. We next tested an ACE inhibitor for enhanced BK receptor activation in the absence of kinin release and synthesized an ACE-resistant BK analog as a control for these experiments. Enalaprilat (1 μM) potentiated kallikrein (100 nM) in CHO AB cells but was ineffective in CHO B 2 cells that do not bear ACE. We concluded that kallikrein activated B 2 receptors without releasing a kinin. Furthermore, inhibition of ACE enhanced the receptor activation by kallikrein, an action that may contribute to the manifold therapeutic effects of ACE inhibitors.