title: Mimicking Cdk2 phosphorylation of Bcl-xL at Ser73 results in caspase activation and Bcl-xL cleavage.
abstract: Cisplatin is a widely used chemotherapeutic agent, yet its efficacy is limited by nephrotoxicity. The severity of nephrotoxicity is associated with the extent of kidney cell death. Previously, we found that cisplatin-induced kidney cell death was dependent on Cdk2 activation, and inhibition of Cdk2 protected cells from cisplatin-induced apoptosis. Using an in vitro kination assay, we showed that Cdk2 phosphorylated Bcl-xL, an anti-apoptotic member of Bcl-2 family proteins, at serine 73. We also found that this phosphorylated Bcl-xL participated in cell death, as a phosphomimetic mutant of Bcl-xL at the serine 73 site (S73D-Bcl-xL) activated caspases. We now find that S73D-Bcl-xL was cleaved at D61 and D76, which are putative caspase cleavage sites, to generate 15-kDa and 12-kDa fragments. Unlike full-length Bcl-xL, these cleavage products of Bcl-xL were previously reported to be pro-apoptotic. We sought to determine whether these Bcl-xL fragments were necessary for the induction of cell death by S73D-Bcl-xL. Mutation of these caspase cleavage sites prevented the formation of the 15-kDa and 12-kDa Bcl-xL cleavage products, but apoptosis still persisted in a S73D modified Bcl-xL. Our findings show that Cdk2 phosphorylation of Bcl-xL at Ser73, but not the Bcl-xL cleavage products, is necessary and sufficient to induce cell death.
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
authors.forename: N S
authors.initials: NS
authors.lastname: Seng
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA; Division of Nephrology, Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
authors.forename: J
authors.initials: J
authors.lastname: Megyesi
authors.affiliation: Division of Nephrology, Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, USA.
authors.forename: A
authors.initials: A
authors.lastname: Tarcsafalvi
authors.affiliation: Department of Physiology and Biophysics, University of Arkansas for Medical Sciences, Little Rock, AR, USA; Division of Nephrology, Department of Internal Medicine, University of Arkansas for Medical Sciences, Little Rock, AR, USA; Central Arkansas Veterans Healthcare System, Little Rock, AR, USA.
authors.forename: P M
authors.initials: PM
authors.lastname: Price