Protease‐activated receptor dependent and independent signaling by kallikreins 1 and 6 in CNS neuron and astroglial cell lines

Abstract

While protease-activated receptors (PARs) are known to mediate signaling events in CNS, contributing both to normal function and pathogenesis, the endogenous activators of CNS PARs are poorly characterized. In this study, we test the hypothesis that kallikreins (KLKs) represent an important pool of endogenous activators of CNS PARs. Specifically, KLK1 and KLK6 were examined for their ability to evoke intracellular Ca 2+ flux in a PAR-dependent fashion in NSC34 neurons and Neu7 astrocytes. Both KLKs were also examined for their ability to activate mitogen-activated protein kinases (extracellular signal-regulated kinases, C-Jun N-terminal kinases, and p38) and protein kinase B (AKT) intracellular signaling cascades. Cumulatively, these studies show that KLK6, but not KLK1, signals through PARs. KLK6 evoked intracellular Ca 2+ flux was mediated by PAR1 in neurons and both PAR1and PAR2 in astrocytes. Importantly, both KLK1 and KLK6 altered the activation state of mitogen-activated protein kinases and AKT, suggestive of important roles for each in CNS neuron and glial differentiation, and survival. The cellular specificity of CNS-KLK activity was underscored by observations that both proteases promoted AKT activation in astrocytes, but inhibited such signaling in neurons. PAR1 and bradykinin receptor inhibitors were used to demonstrate that KLK1-mediated activation of extracellular signal-regulated kinases in neurons occurred in a non-PAR, bradykinin 2 (B2) receptor-dependent fashion, while similar signaling by KLK6 was mediated by the combined activation of PAR1 and B2. Cumulatively results indicate KLK6, but not KLK1 is an activator of CNS PARs, and that both KLKs are poised to signal in a B2 receptor-dependent fashion to regulate multiple signal transduction pathways relevant to CNS physiologic function and dysfunction.

Kallikrein-related peptidases: proteolysis and signaling in cancer, the new frontier

“…Inspired by these observations, a recent study has investigated the hypothesis that KLKs 1 and 6 are physiological regulators of PAR signaling in neurons and astrocytes ( Vandell et al, 2008). The authors found that KLK6 could evoke PAR 1 -dependent signaling responses in neurons and astrocytes, whereas activation of PAR 2 occurred only in the case of astrocytes, which express low levels of PAR 1 .…”

PAR1 and PAR2 Couple to Overlapping and Distinct Sets of G Proteins and Linked Signaling Pathways to Differentially Regulate Cell Physiology

“…However, to confirm the physiological relevance of these observations, we deemed it necessary to determine whether these differences in PAR/G protein coupling and signaling are maintained in cells that endogenously express these proteins. For this purpose, we obtained Neu7 astrocytes, a cell line reported to express both native PAR1 and PAR2 (Vandell et al, 2008).…”

Activation of membrane-bound proteins and receptor systems: a link between tissue kallikrein and the KLK-related peptidases

“…Interestingly, using murine whole splenocyte preparations and the human Jurkat T cell line it has been shown that KLK6 via PAR1 promotes pro-survival and inhibits pro-apoptotic mechanisms, leading to vigorous splenic T cell survival in the presence of the cell death inducing agents, camptothecin, dexamethasone, staurosporine and Fas-ligand (Scarisbrick et al, 2011). This KLK can also initiate intracellular signalling in neurons via PAR1 and in astrocytes through both PAR1 and PAR2 (Vandell et al, 2008) and has recently been reported to serve as a molecular trigger via PAR1 of processes involved in development of astrogliosis (Scarisbrick et al, 2012a). In addition, use of function blocking antibodies and pharmacological approaches demonstrated that KLK4 activates PAR1 but not PAR2 in colon cancer cells with PAR1 signalling promoting migration of these cells via ERK1/2 (Gratio et al, 2010).…”