Mitochondrial translocation of cofilin is an early step in apoptosis induction.
Increasing evidence suggests that movement of key proteins in or out of mitochondria during apoptosis is essential for the regulation of apoptosis. Here, we report identification of the actin-binding protein cofilin by a proteomic approach, as such a factor translocated from cytosol into mitochondria after induction of apoptosis. We found that after induction of apoptosis, cofilin was translocated to mitochondria before release of cytochrome c. Reduction of cofilin protein levels with small-interfering RNA (siRNA) resulted in inhibition of both cytochrome c release and apoptosis. Only dephosphorylated cofilin was translocated to mitochondria, and the cofilin S3D mutant, which mimicks the phosphorylated form, suppressed mitochondrial translocation and apoptosis. Translocation was achieved through exposure of an amino-terminal mitochondrial targeting signal in combination with carboxy-terminal sequences. When correctly targeted to mitochondria, cofilin induced massive apoptosis. The apoptosis-inducing ability of cofilin, but not its mitochondrial localization, was dependent on the functional actin-binding domain. Thus, domains involved in mitochondrial targeting and actin binding are indispensable for its pro-apoptotic function. Our data suggest that cofilin has an important function during the initiation phase of apoptosis.
Chua
Boon Tin
BT
Laboratory of Apoptosis Regulation, Institute of Molecular and Cell Biology, National Institute of Singapore, 30 Medical Drive, 117609, Singapore.
Volbracht
Christiane
C
Tan
Kuan Onn
KO
Li
Rong
R
Yu
Victor C
VC
Li
Peng
P
D051339:Actin Depolymerizing Factors; D000199:Actins / Q000378:metabolism; D000818:Animals; D017209:Apoptosis / Q000235:genetics*; D001665:Binding Sites / Q000235:genetics; D019556:COS Cells; D002460:Cell Line; D045304:Cytochromes c / Q000378:metabolism*; D006367:HeLa Cells; D006801:Humans; D008840:Microfilament Proteins / Q000172:deficiency* / Q000235:genetics / Q000378:metabolism*; D008928:Mitochondria / Q000378:metabolism*; D009154:Mutation / Q000235:genetics; D010766:Phosphorylation; D017434:Protein Structure, Tertiary / Q000502:physiology; D021381:Protein Transport / Q000235:genetics*; D034741:RNA, Small Interfering
D051339:Actin Depolymerizing Factors; D000199:Actins; D008840:Microfilament Proteins; D034741:RNA, Small Interfering; D045304:Cytochromes c