Hurpin Is a Selective Inhibitor of Lysosomal Cathepsin L and Protects Keratinocytes from Ultraviolet-Induced Apoptosis
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- 作者：Thomas Welss ; Jiuru Sun ; James A. Irving ; Rainer Blum ; A. Ian Smith ; James C. Whisstock ; Robert N. Pike ; Anna von Mikecz ; Thomas Ruzicka ; Phillip I. Bird ; and Harry F. Abts
- 刊名：Biochemistry
- 出版年：2003
- 出版时间：June 24, 2003
- 年：2003
- 卷：42
- 期：24
- 页码：7381 - 7389
- 全文大小：426K
- 年卷期：v.42,no.24(June 24, 2003)
- ISSN：1520-4995
文摘
Hurpin (headpin/PI13/serpinB13) is an intracellular, differentially spliced member of the serpinsuperfamily that has been linked to differentiation and apoptosis of human keratinocytes. It is transientlydownregulated by UV light and overexpressed in psoriatic skin lesions. Although it has all of the featuresof an inhibitory serpin, a productive interaction between hurpin and a proteinase has not yet been reported.Here we demonstrate that hurpin is a potent and selective inhibitor of the archetypal lysosomal cysteineproteinase cathepsin L (catL). Recombinant hurpin inhibits human catL with a stoichiometry of inhibition(SI) of 1.7 and a rate constant kassoc of (4.6 ± 0.14) × 105 M-1 s-1. It inefficiently inhibits catV and doesnot inhibit papain, catB, or catK. To investigate the inhibitory mechanism, we determined the P1-P1'bond in the reactive center loop cleaved by catL (356Thr-357Ser) and expressed variants in which theproximal hinge, P1 residue, or differentially spliced CD loop was mutated. The results of assays usingthese proteins suggest that inhibition of catL by hurpin occurs via the conventional serpin inhibitorymechanism and that the CD loop plays no role in the process. Finally, it was found that the majority ofhurpin is cytosolic and that its overexpression in human keratinocytes confers resistance to UV-inducedapoptosis. Given that lysosomal disruption, release of catL, and catL-mediated caspase activation areknown to occur in response to cellular stress, we propose that a physiological role of hurpin is to protectepithelial cells from ectopic catL.