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Journal of Virology, July 2000, p. 6459-6468, Vol. 74, No. 14
Department of Microbiology and Immunology,
The University of Texas Medical Branch at Galveston, Galveston,
Texas 77555-1019,1 and Department of
Medicine, The University of North Carolina at Chapel Hill, Chapel
Hill, North Carolina 275142
Received 13 January 2000/Accepted 24 April 2000
Glyceraldehyde 3-phosphate dehydrogenase (GAPDH), a cellular enzyme
involved in glycolysis, binds specifically to several viral RNAs, but
the functional significance of this interaction is uncertain. Both
GAPDH and polypyrimidine tract binding protein (PTB) bind to
overlapping sites in stem-loop IIIa of the internal ribosome entry site
(IRES) of Hepatitis A virus (HAV), a picornavirus. Since
the binding of GAPDH destabilizes the RNA secondary structure, we
reasoned that GAPDH may suppress the ability of the IRES to direct
cap-independent translation, making its effects antagonistic to the
translation-enhancing activity of PTB (D. E. Schultz, C. C. Hardin, and S. M. Lemon, J. Biol. Chem. 271:14134-14142,
1996). To test this hypothesis, we constructed plasmids containing a dicistronic transcriptional unit in which the HAV IRES was placed between an upstream GAPDH-coding sequence and a downstream
Renilla luciferase (RLuc) sequence. Transfection with this
plasmid results in overexpression of GAPDH and in RLuc production as a
measure of IRES activity. RLuc activity was compared with that from a control, null-expression plasmid that was identical except for a
frameshift mutation within the 5' GAPDH coding sequence. In transfection experiments, GAPDH overexpression significantly suppressed HAV IRES activity in BSC-1 and FRhK-4 cells but not in Huh-7 cells, which have a significantly greater cytoplasmic abundance of PTB. GAPDH
suppression of HAV translation was greater with the wild-type HAV IRES
than with the IRES from a cell culture-adapted virus (HM175/P16) that
has reproducibly higher basal translational activity in BSC-1 cells.
Stem-loop IIIa RNA from the latter IRES had significantly lower
affinity for GAPDH in filter binding experiments. Thus, the binding of
GAPDH to the IRES of HAV suppresses cap-independent viral translation
in vivo in African green monkey kidney cells. The enhanced replication
capacity of cell culture-adapted HAV in such cells may be due in part
to reduced affinity of the viral IRES for GAPDH.
0022-538X/00/$04.00+0
Copyright © 2000, American Society for Microbiology. All rights reserved.
Functional Significance of the Interaction of
Hepatitis A Virus RNA with Glyceraldehyde 3-Phosphate Dehydrogenase
(GAPDH): Opposing Effects of GAPDH and Polypyrimidine Tract Binding
Protein on Internal Ribosome Entry Site Function
and
*
Corresponding author. Mailing address: Department of
Microbiology and Immunology, The University of Texas Medical Branch at Galveston, 301 University Blvd., Galveston, TX 77555-1019. Phone: (409)
772-2354. Fax: (409) 772-3757. E-mail: smlemon{at}utmb.edu.
Present address: Qiagen, Inc., Valencia, CA 91355.
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