title: Increased expression of stefin B in the nucleus of T98G astrocytoma cells delays caspase activation.
abstract: Stefin B (cystatin B) is an endogenous inhibitor of cysteine proteinases localized in the nucleus and the cytosol. Loss-of-function mutations in the stefin B gene (CSTB) gene were reported in patients with Unverricht-Lundborg disease (EPM1). Our previous results showed that thymocytes isolated from stefin B-deficient mice are more sensitive to apoptosis induced by the protein kinase C (PKC) inhibitor staurosporin (STS) than the wild-type control cells. We have also shown that the increased expression of stefin B in the nucleus of T98G astrocytoma cells delayed cell cycle progression through the S phase. In the present study we examined if the nuclear or cytosolic functions of stefin B are responsible for the accelerated induction of apoptosis observed in the cells from stefin B-deficient mice. We have shown that the overexpression of stefin B in the nucleus, but not in the cytosol of astrocytoma T98G cells, delayed caspase-3 and -7 activation. Pretreatment of cells with the pan-caspase inhibitor z-Val-Ala-Asp(OMe)-fluoromethylketone completely inhibited caspase activation, while treatment with the inhibitor of calpains- and papain-like cathepsins (2S,3S)-trans-epoxysuccinyl-leucylamido-3-methyl-butane ethyl ester did not prevent caspase activation. We concluded that the delay of caspase activation in T98G cells overexpressing stefin B in the nucleus is independent of cathepsin inhibition.
authors.affiliation: Department of Biochemistry, Molecular and Structural Biology, Jožef Stefan Institute Ljubljana, Slovenia ; Liaoning Cancer Hospital and Institute Shenyang, Liaoning, PR China.
authors.forename: Tao
authors.initials: T
authors.lastname: Sun
authors.forename: Vito
authors.initials: V
authors.lastname: Turk
authors.forename: Boris
authors.initials: B
authors.lastname: Turk
authors.forename: Nataša
authors.initials: N
authors.lastname: Kopitar-Jerala