Polypyrimidine Tract-binding Proteins Are Cleaved by Caspase-3 during Apoptosis

doi:10.1074/jbc.M203887200

Polypyrimidine Tract-binding Proteins Are Cleaved by Caspase-3 during Apoptosis*

From the ^§National Research Laboratory and the ^¶National Creative Research Center for Biomolecular Interaction, Department of Life Science, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San31, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea

Abstract

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-Asp⁷↓Ile, Leu-Tyr-Thr-Asp¹³⁹↓Ser, and Ala-Ala-Val-Asp¹⁷²↓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.

Footnotes

↵* This work was supported in part by the G7, National Research Laboratory, and Molecular Medicine Research Group Programs of the Ministry of Science and Technology and by a grant from the Korea Science and Engineering Foundation through the Protein Network Research Center.The costs of publication of this article were defrayed in part by the payment of page charges. The article must therefore be hereby marked “advertisement” in accordance with 18 U.S.C. Section 1734 solely to indicate this fact.
↵‡ To whom correspondence should be addressed: Dept. of Life Science, Division of Molecular and Life Sciences, Pohang University of Science and Technology, San31, Hyoja-Dong, Pohang, Kyungbuk 790-784, Korea. Tel.: 82-54-279-2298; Fax: 82-54-279-8009; E-mail: sungkey@postech.ac.kr.
Published, JBC Papers in Press, May 9, 2002, DOI 10.1074/jbc.M203887200
Abbreviations:

hnRNP

heterogeneous nuclear ribonucleoprotein

PTB

polypyrimidine tract-binding protein

IRES

internal ribosomal entry site

TNF

tumor necrosis factor

TRAIL

tumor necrosis factor-related apoptosis-inducing ligand

NLS

nuclear localization signal

RRM

RNA recognition motif

GFP

green fluorescence protein

EGFP

enhanced GFP

RFP

red fluorescence protein

aa

amino acids

CHAPS

3-[(3-cholamidopropyl)dimethylammonio]-1-propanesulfonic acid

TRITC

tetramethylrhodamine isothiocyanate

Z

benxyloxycarbonyl

fmk

fluoromethyl ketone

mAb

monoclonal antibody

PARP

poly(ADP-ribose) polymerase

DAPI

4,6-diamidino-2-phenylindole
- Received April 22, 2002.
The American Society for Biochemistry and Molecular Biology, Inc.