Polypyrimidine tract-binding proteins are cleaved by caspase-3 during apoptosis.
The polypyrimidine tract-binding protein (PTB), an RNA-binding protein, is required for efficient translation of some mRNAs containing internal ribosomal entry sites (IRESs). Here we provide evidence that the addition of apoptosis-inducing agents to cells results in the cleavage of PTB isoforms 1, 2, and 4 by caspase-3. This cleavage of PTB separated the N-terminal region, containing NLS-RRM1, from the C-terminal region, containing RRM2-3-4. Our data indicate that there are three noncanonical caspase-3 target sites in PTBs, namely Ile-Val-Pro-Asp(7)Ile, Leu-Tyr-Thr-Asp(139)Ser, and Ala-Ala-Val-Asp(172)Ala. The C-terminal PTB fragments localized to the cytoplasm, as opposed to the nucleus where most intact PTBs are found. Moreover, these C-terminal PTB fragments inhibited translation of polioviral mRNA, which contains an IRES element requiring PTB for its activation. This suggests that translation of some IRES-containing mRNAs is regulated by proteolytic cleavage of PTB during apoptosis.
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Sung Hoon
SH
National Research Laboratory, Department of Life Science, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San31, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea.
Shin
Sejeong
S
Jang
Sung Key
SK
D000595:Amino Acid Sequence; D017209:Apoptosis; D001665:Binding Sites; D015153:Blotting, Western; D053148:Caspase 3; D020169:Caspases / Q000378:metabolism*; D002460:Cell Line; D003593:Cytoplasm / Q000378:metabolism; D000939:Epitopes; D049452:Green Fluorescent Proteins; D006367:HeLa Cells; D006801:Humans; D019169:Jurkat Cells; D008164:Luminescent Proteins / Q000378:metabolism; D008856:Microscopy, Fluorescence; D008969:Molecular Sequence Data; D010957:Plasmids / Q000378:metabolism; D017955:Poliovirus / Q000378:metabolism; D038941:Polypyrimidine Tract-Binding Protein; D011485:Protein Binding; D014176:Protein Biosynthesis; D017434:Protein Structure, Tertiary; D012333:RNA, Messenger / Q000378:metabolism; D016601:RNA-Binding Proteins / Q000378:metabolism*; D011994:Recombinant Proteins / Q000378:metabolism; D012261:Ribonucleoproteins / Q000378:metabolism*; D017386:Sequence Homology, Amino Acid; D014158:Transcription, Genetic; D014162:Transfection
D000939:Epitopes; D008164:Luminescent Proteins; D012333:RNA, Messenger; D016601:RNA-Binding Proteins; D011994:Recombinant Proteins; D012261:Ribonucleoproteins; D038941:Polypyrimidine Tract-Binding Protein; D049452:Green Fluorescent Proteins; C505407:CASP3 protein, human; D053148:Caspase 3; D020169:Caspases