Interaction of CSR1 with XIAP reverses inhibition of caspases and accelerates cell death.
Cellular Stress Response 1 (CSR1) is a tumor suppressor gene that is located at 8p21, a region that is frequently deleted in prostate cancer as well as a variety of human malignancies. Previous studies have indicated that the expression of CSR1 induces cell death. In this study, we found that CSR1 interacts with X-linked Inhibitor of Apoptosis Protein (XIAP), using yeast two-hybrid screening analyses. XIAP overexpression has been found in many human cancers, and forced expression of XIAP blocks apoptosis. Both in vitro and in vivo analyses indicated that the C-terminus of CSR1 binds XIAP with high affinity. Through a series of in vitro recombinant protein-binding analyses, the XIAP-binding motif in CSR1 was determined to include amino acids 513 to 572. Targeted knock-down of XIAP enhanced CSR1-induced cell death, while overexpression of XIAP antagonized CSR1 activity. The binding of CSR1 with XIAP enhanced caspase-9 and caspase-3 protease activities, and CSR1-induced cell death was dramatically reduced on expression of a mutant CSR1 that does not bind XIAP. However, a XIAP mutant that does not interact with caspase-9 had no impact on CSR1-induced cell death. These results suggest that cell death is induced when CSR1 binds XIAP, preventing the interaction of XIAP with caspases. Thus, this study may have elucidated a novel mechanism by which tumor suppressors induce cell death.
Department of Pathology, University of Pittsburgh School of Medicine, Pittsburgh, Pennsylvania 15261, USA.
Zhong-Liang
ZL
Zheng
Lang-Zhu
LZ
Tan
Yan P
YP
Yu
George
G
Michalopoulos
Jian-Hua
JH
Luo
D020816:Amino Acid Motifs; D053148:Caspase 3 / Q000378:metabolism*; D053453:Caspase 9 / Q000378:metabolism*; D016923:Cell Death / Q000528:radiation effects; D045744:Cell Line, Tumor; D004789:Enzyme Activation / Q000528:radiation effects; D055785:Gene Knockdown Techniques; D006360:Heat-Shock Proteins / Q000737:chemistry / Q000378:metabolism*; D006801:Humans; D008297:Male; D011485:Protein Binding / Q000528:radiation effects; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D051117:Scavenger Receptors, Class A / Q000737:chemistry / Q000378:metabolism*; D014466:Ultraviolet Rays; D051636:X-Linked Inhibitor of Apoptosis Protein / Q000378:metabolism*
D006360:Heat-Shock Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; C112525:SCARA3 protein, human; D051117:Scavenger Receptors, Class A; D051636:X-Linked Inhibitor of Apoptosis Protein; C496866:XIAP protein, human; D053148:Caspase 3; D053453:Caspase 9