Kallikrein activates bradykinin B₂ receptors in absence of kininogen

Abstract

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 culture medium, we cultured and maintained cells in medium entirely free of animal proteins. We compared the responses of stably transfected CHO cells that express human B 2 receptors (CHO-B 2 ) and cells that co-express 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 or baseline levels. 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. Next, we tested an ACE inhibitor for enhanced BK receptor activation in the absence of kinin release and synthesized an ACE-resistant BK analogue as a control for these experiments. Enalaprilat (1μM) 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.

Tissue kallikrein in cardiovascular, cerebrovascular and renal diseases and skin wound healing

“…This novel finding is consistent with our reports that tissue kallikrein induced contraction of isolated rat uterus in the absence of kinin formation, and elicited cardioprotection by direct kinin B2 receptor activation in kininogen-deficient Brown Norway rats (Chao et al, 1981. Moreover, ACE inhibition has been shown to potentiate the effect of kallikrein on kinin B2 receptor activation, implicating that tissue kallikrein could contribute to the therapeutic effects of ACE inhibition in addition to kinin formation (Biyashev et al, 2006). However, contraction of the isolated jugular vein by tissue kallikrein appears to be dependent on blood vesselderived kininogen and kinin B2 receptor activation (Houle et al, 2003).…”

“…Interestingly, tissue kallikrein was recently shown to directly activate kinin B2 receptor independent of kininogen and kinin release in cultured CHO cells (Hecquet et al, 2000;Biyashev et al, 2006). This novel finding is consistent with our reports that tissue kallikrein induced contraction of isolated rat uterus in the absence of kinin formation, and elicited cardioprotection by direct kinin B2 receptor activation in kininogen-deficient Brown Norway rats (Chao et al, 1981.…”

10 Kallikrein-Kinin Cascade: Bioregulation by Human Tissue Kallikrein 1 (hK1, KLK1)

“…Furthermore, hK1 activates the bradykinin B 2 receptor (B 2 R), suggesting that B 2 R may function as a novel serine protease-activated receptor (Hecquet et al, 2000). Moreover, when activating B 2 R, hK1 induces its redistribution on the plasma membrane (Hecquet et al, 2002) by a mechanism that seems to be independent of kinin release (Biyashev et al, 2006).…”

Cellular expression of plasma prekallikrein in human tissues

“…It is reasonable to assume that the PPK synthesised in these cells may subserve special local functions at or near the cellular site of its synthesis. Recently, a novel function of PK was described that provides experimental evidence of direct activation of the kinin B 2 receptor, independent of kinin release (Hecquet et al, 2000(Hecquet et al, , 2002Biyashev et al, 2006). The proteolytic activity of PK is compulsory for this receptor activation, but the mechanism of action seems to be different from that of the known proteinase-activated receptors (Dery et al, 1998).…”