HSP27 Inhibitory Activity against Caspase-3 Cleavage and Activation by Caspase-9 Is Enhanced by Chaperone O-GlcNAc Modification in Vitro

One of the O-GlcNAc modifications is the protectionof cells againsta variety of stressors that result in cell death. Previous experimentshave focused on the overall ability of O-GlcNAc to prevent proteinaggregation under stress as well as its ability to affect stress-responsesignaling pathways. Less attention has been paid to the potentialrole for O-GlcNAc in the direct inhibition of a major cell-death pathway,apoptosis. Apoptosis involves the sequential activation of caspaseproteases, including the transfer of cell-stress information frominitiator caspase-9 to effector caspase-3. Cells have multiple mechanismsto slow the apoptotic cascade, including heat shock protein HSP27,which can directly inhibit the activation of caspase-3 by caspase-9.We have previously shown that O-GlcNAc modification increases thechaperone activity of HSP27 against amyloid aggregation, raising thequestion as to whether this modification may play important rolesin other facets of HSP27 biology. Here, we use protein chemistry togenerate different versions of O-GlcNAc modified HSP27 and demonstratethat the modification enhances this antiapoptotic function of thechaperone, at least in an in vitro context. Theseresults provide additional molecular insight into how O-GlcNAc functionsas a mediator of cellular stress with important implications for humandiseases like cancer and neurodegeneration.

Automated summary

O-GlcNAc modification protects cells against stress-induced cell death by directly inhibiting the apoptotic pathway. The modified chaperone, HSP27, exhibits enhanced antiapoptotic function in an in vitro context. These findings provide molecular insights into how O-GlcNAc serves as a mediator of cellular stress and have important implications for human diseases like cancer and neurodegeneration.