αA‐crystallin and αB‐crystallin, newly identified interaction proteins of protease‐activated receptor‐2, rescue astrocytes from C2‐ceramide‐ and staurosporine‐induced cell death

Abstract

Protease‐activated receptor‐2 (PAR‐2) is a G protein‐coupled receptor activated by trypsin and other trypsin‐like serine proteases. The widely expressed PAR‐2 is involved in inflammation response but the physiological/pathological roles of PAR‐2 in the nervous system are still uncertain. In the present study, we report novel PAR‐2 interaction proteins, αA‐crystallin and αB‐crystallin. These 20 kDa proteins have been implicated in neurodegenerative diseases like Alexander’s disease, Creutzfeldt‐Jacob disease, Alzheimer’s disease, and Parkinson’s disease. Results from yeast two‐hybrid assay using the cytoplasmic C‐tail of PAR‐2 as bait suggested that αA‐crystallin interacts with PAR‐2. We further demonstrate the in vitro and cellular in vivo interaction of C‐tail of PAR‐2 as well as of full‐length PAR‐2 with αA(αB)‐crystallins. We use pull‐down, co‐immunoprecipitation, and co‐localization assays. Analysis of αA‐crystallin deletion mutants showed that amino acids 120–130 and 136–154 of αA‐crystallin are required for the interaction with PAR‐2. Co‐immunoprecipitation experiments ruled out an interaction of αA(αB)‐crystallins with PAR‐1, PAR‐3, and PAR‐4. This demonstrates that αA(αB)‐crystallins are PAR‐2‐specific interaction proteins. Moreover, we investigated the functional role of PAR‐2 and α‐crystallins in astrocytes. Evidence is presented to show that PAR‐2 activation and increased expression of α‐crystallins reduced C2‐ceramide‐ and staurosporine‐induced cell death in astrocytes. Thus, both PAR‐2 and α‐crystallins are involved in cytoprotection in astrocytes.

Critical role for PAR1 in kallikrein 6‐mediated oligodendrogliopathy

“…Importantly, while the present studies indicate that PAR2 does not play an essential role in Klk6-mediated oligodendrogliopathy in vitro , we cannot exclude other regulatory roles. At least low levels of PAR2 expression were observed throughout oligodendrocyte development and taken with the anti-apoptotic and proliferative functions established for PAR2 in astrocytes (Li et al 2009; Wang et al 2002), future studies will be needed to fully dissect the potential functional roles of PAR2 in oligodendrocyte and white matter biology.…”

Crystallins and neuroinflammation: The glial side of the story

“…Indeed, overexpression of either αA- or αB-crystallin in cultured astrocytes prevented cell death induced by ceramide and staurosporine[28] or H2O2[29]. This anti-apoptotic function has been linked to the p38 MAPK signaling cascade, the activation of which has been shown to result from inflammation.…”

The roles of thrombin and protease-activated receptors in inflammation

“…Both have been shown to interact specifically with PAR2, but not PAR-1,-3, or -4. In vitro, activation of PAR2 and increased expression of these proteins protected astrocytes from C2-ceramide-and staurosporine-induced cell death, suggesting that both PAR2 and α-crystallin may be involved in cytoprotection of astrocytes [75]. The authors of this study suggested that PAR-2 activation by these proteins might be an important mechanism for protecting the brain against damage in chronic degenerative conditions.…”