Caspase 3 Cleavage of the Ste20-Related Kinase SLK Releases and Activates an Apoptosis-Inducing Kinase Domain and an Actin-Disassembling Region

Abstract

We have demonstrated that a novel Ste20-related kinase, designated SLK, mediates apoptosis and actin stress fiber dissolution through distinct domains generated by caspase 3 cleavage. Overexpression of SLK in C2C12 myoblasts stimulated the disassembly of actin stress fibers and focal adhesions and induced apoptosis, as determined by annexin V binding and terminal deoxynucleotidyltransferase-mediated dUTP-biotin nick end labeling analysis. SLK was cleaved by caspase 3 in vitro and in vivo during c-Myc-, tumor necrosis factor alpha, and UV-induced apoptosis. Furthermore, cleavage of SLK released two domains with distinct activities: an activated N-terminal kinase domain that promoted apoptosis and cytoskeletal rearrangements and a C-terminus domain that disassembled actin stress fibers. Moreover, our analysis has identified a novel conserved region (termed the AT1-46 homology domain) that efficiently promotes stress fiber disassembly. Finally, transient transfection of SLK also activated the c-Jun N-terminal kinase signaling pathway. Our results suggest that caspase-activated SLK represents a novel effector of cytoskeletal remodeling and apoptosis.

ACKNOWLEDGMENTS

We thank Catherine Neville and Robert Korneluk for sequencing cDNAs, Linda Penn for kindly providing Rat1-Myc/ER cells, and Katsuyuki Tamai for raising rabbit anti-SLK antibodies. We are grateful to Sarang Kulkarni for microinjections.

L.A.S. is supported by a postdoctoral fellowship from the Medical Research Council of Canada. M.A.R. is a Research Scientist of the Medical Research Council of Canada and a member of the Genetics Disease Network of Excellence. This work was supported by a grant from the Medical Research Council of Canada to M.A.R.