Molecular and Cellular Biology, May 2009, p. 2899-2912, Vol. 29, No. 10
0270-7306/09/$08.00+0 doi:10.1128/MCB.01774-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
The hnRNA-Binding Proteins hnRNP L and PTB Are Required for Efficient Translation of the Cat-1 Arginine/Lysine Transporter mRNA during Amino Acid Starvation
,
Mithu Majumder,1
Ibrahim Yaman,2
Francesca Gaccioli,1
Vladimir V. Zeenko,1
Chuanping Wang,1
Mark G. Caprara,3
Richard C. Venema,4
Anton A. Komar,5
Martin D. Snider,6 and
Maria Hatzoglou1*
Departments of Nutrition,1
RNA Biology,3
Biochemistry, School of Medicine, Case Western Reserve University, Cleveland, Ohio,6
TÜB
TAK Marmara Research Center, Food Institute, Gebze/Kocaeli, Turkey,2
Vascular Biology Center, Medical College of Georgia, Augusta, Georgia,4
Center for Gene Regulation in Health and Disease and Department of Biological, Geological and Environmental Sciences, Cleveland State University, Cleveland, Ohio5
Received 19 November 2008/ Returned for modification 6 January 2009/ Accepted 27 February 2009
The response to amino acid starvation involves the global decrease of protein synthesis and an increase in the translation of some mRNAs that contain an internal ribosome entry site (IRES). It was previously shown that translation of the mRNA for the arginine/lysine amino acid transporter Cat-1 increases during amino acid starvation via a mechanism that utilizes an IRES in the 5' untranslated region of the Cat-1 mRNA. It is shown here that polypyrimidine tract binding protein (PTB) and an hnRNA binding protein, heterogeneous nuclear ribonucleoprotein L (hnRNP L), promote the efficient translation of Cat-1 mRNA during amino acid starvation. Association of both proteins with Cat-1 mRNA increased during starvation with kinetics that paralleled that of IRES activation, although the levels and subcellular distribution of the proteins were unchanged. The sequence CUUUCU within the Cat-1 IRES was important for PTB binding and for the induction of translation during amino acid starvation. Binding of hnRNP L to the IRES or the Cat-1 mRNA in vivo was independent of PTB binding but was not sufficient to increase IRES activity or Cat-1 mRNA translation during amino acid starvation. In contrast, binding of PTB to the Cat-1 mRNA in vivo required hnRNP L. A wider role of hnRNP L in mRNA translation was suggested by the decrease of global protein synthesis in cells with reduced hnRNP L levels. It is proposed that PTB and hnRNP L are positive regulators of Cat-1 mRNA translation via the IRES under stress conditions that cause a global decrease of protein synthesis.
* Corresponding author. Mailing address: Department of Nutrition, School of Medicine, Case Western Reserve University, 10900 Euclid Avenue, Cleveland, OH 44106-4954. Phone: (216) 368-3012. Fax: (216) 368-6644. E-mail: mxh8{at}case.edu
Published ahead of print on 9 March 2009.
Supplemental material for this article may be found at http://mcb.asm.org/.
Molecular and Cellular Biology, May 2009, p. 2899-2912, Vol. 29, No. 10
0270-7306/09/$08.00+0 doi:10.1128/MCB.01774-08
Copyright © 2009, American Society for Microbiology. All Rights Reserved.
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