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Journal of Virology, April 2003, p. 5026-5029, Vol. 77, No. 8
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.8.5026-5029.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
Human Rhinovirus 2A Proteinase Cleavage Sites in Eukaryotic Initiation Factors (eIF) 4GI and eIF4GII Are Different
Alessandra Gradi,1,
Yuri V. Svitkin,1 Wolfgang Sommergruber,2 Hiroaki Imataka,1,
Shigenobu Morino,1,
Tim Skern,3 and Nahum Sonenberg1*
Department of Biochemistry and McGill Cancer Center, McGill University, Montreal, Quebec, Canada H3G 1Y6 ,1
Department of Exploratory Research, Boehringer Ingelheim,2
Institute of Medical Biochemistry, Division of Biochemistry, Vienna Bio Center, University of Vienna, Vienna, Austria3
Received 27 August 2002/
Accepted 30 January 2003

ABSTRACT
Several picornaviruses shut down host cellular protein synthesis
by proteolytic cleavage of the eukaryotic initiation factor
(eIF) 4GI and eIF4GII isoforms. Viral RNA translation is maintained
by a cap-independent mechanism. Here, we identify the human
rhinovirus 2 2A
pro cleavage site in eIF4GII in vitro as PLLNV
699*GSR;
this sequence lies seven amino acids C-terminal to the cleavage
site previously identified in eIF4GI (LSTR681*GPP).

TEXT
Picornaviruses, which include human rhinovirus (HRV), poliovirus
(PV), and coxsackievirus (CV) as well as the animal pathogen
foot-and-mouth disease virus, contain a single-stranded RNA
of positive polarity. Eukaryotic cellular mRNAs possess at their
5' ends a cap structure (m
7GpppX, where X is any nucleotide)
(
27), which is important for ribosomal recruitment mediated
by a cap-binding protein complex, eukaryotic initiation factor
(eIF) 4F. The genomic viral RNA lacks a 5'-terminal cap structure
(
9,
22), and virus translation proceeds by a cap-independent
mechanism, whereby ribosomes bind directly to an internal ribosome
entry site of the viral RNAs (
11,
23). The cap-binding protein
complex eIF4F is a three-subunit complex. The three subunits
are eIF4E, which interacts directly with the cap (
19,
21,
29),
eIF4A, an ATPase which in conjunction with eIF4B exhibits RNA
helicase activity (
25), and eIF4G (formerly p220 or eIF4

[
31]),
which is a large scaffolding protein that plays a key role in
the assembly of the mRNA-ribosome initiation complex. eIF4G
binds directly to the ribosome-associated eIF3, thus delivering
the small ribosomal subunit to the mRNA (
12,
18). We have cloned
and characterized a homologue of eIF4G, which we have termed
eIF4GII (
4), while the original eIF4G (
31) was renamed eIF4GI.
eIF4GII is 41% identical to eIF4GI, binds eIF4E, eIF3, and eIF4A,
and functionally complements eIF4GI (
4,
10).
Different picornavirus proteinases can cleave both isoforms of eIF4G, generating in each case their respective N- and C-terminal cleavage products, cpN and cpC (reviewed in references 2 and 28). The cpC of eIF4G retains the capacity to interact with internal ribosome entry sites as well as with eIF3 and eIF4A (15-17, 20, 24) and can therefore support cap-independent translation. Indeed, initiation of translation on HRV and PV RNA is stimulated under these conditions (7, 14, 32). However, as the eIF4G cpC lacks the eIF4E-binding site, it is unable to support cap-dependent translation of cellular mRNAs (reviewed in reference 8) or does this inefficiently (1).
We have previously shown, using PV1 and HRV14 as model systems (5, 30), that eIF4GII cleavage precisely coincides with the inhibition of host cellular protein synthesis, whereas the cleavage of eIF4GI occurs earlier. However, in HRV2-infected cells, eIF4GI and eIF4GII are cleaved at similar rates, coincident with the shutoff of host cell protein synthesis (26).
To begin to understand the differences in the kinetics of eIF4GI and eIF4GII cleavage, we set out to determine the in vitro HRV2 2Apro cleavage site in human eIF4GII and compare it to that previously determined for HRV2, CVB4, and PV1 2Apro on eIF4GI. First, we used HRV2 2Apro to cleave recombinant eIF4GII (4). After incubation of recombinant eIF4GII (20 µg for 30 h at 30°C) with the purified enzyme in vitro, we examined the status of eIF4GII by using antibodies against N- and C-terminal regions of the protein. The C-terminal fragment of endogenous or purified recombinant eIF4GII generated by in vitro cleavage ran at about 90 kDa, with mobility identical to that found in vivo in HRV16-infected cells (Fig. 1A, compare lanes 2 and 3 to lane 1) or in HRV2-infected cells (data not shown). Five cycles of N-terminal sequencing by automated Edman degradation of the recombinant eIF4GII cpC (Fig. 1A, lane 3) generated the following amino acids: glycine, serine, arginine, arginine, and serine. These amino acids correspond to the sequence V700GSRR704 on eIF4GII, indicating that HRV2 2Apro must cleave eIF4GII at Val699*Gly700 (Fig. 2). We attempted to determine the N-terminal sequence of the endogenous eIF4GII cpC isolated by immunoprecipitation from HRV16-infected cells but were unsuccessful, as the preparation contained a mixture of polypeptides.
To further substantiate our results, we introduced mutations
at the HRV2 2A
pro cleavage site in eIF4GII. Glutathione
S-transferase
(GST)-eIF4GII (amino acids [445 to 744])-FLAG fragments, containing
either a single point mutation (G700E) in or a 27-aa deletion
(

674-702) of the putative hinge region (Fig.
1B) were generated,
expressed in
Escherichia coli, and purified by glutathione-Sepharose
affinity chromatography. The purity and integrity of the proteins
were confirmed by sodium dodecyl sulfate-polyacrylamide gel
electrophoresis (SDS-PAGE) followed by Coomassie blue staining
(data not shown). Equal amounts of the fusion proteins (wild
type and two mutants) were incubated with the purified HRV2
2A
pro or buffer alone at 30°C for 1 h. Protein samples were
resolved by SDS-12.5% PAGE and analyzed by Western blotting
using antisera against either the FLAG or GST tag (Fig.
1C).
Both mutants were resistant to 2A
pro cleavage (lanes 2 and 3),
strongly supporting the conclusion that HRV2 2A
pro directly
cleaves eIF4GII between V
699 and G
700. Identical results were
obtained when the eIF4GII mutants were treated with purified
recombinant CVB4 2A
pro (data not shown), demonstrating that
this enzyme also recognizes the same site.
These results identify the cleavage site of HRV2 and CVB4 2Apro in eIF4GII as PLLNV699*700GS, lying 7 aa downstream of the cleavage site identified in eIF4GI as TLSTR641*642GP (13). As the two isoforms are cleaved equally well during infection by HRV2 (26) and HRV16 (data not shown), both eIF4G isoforms must exist in a cleavable form. Moreover, the binding to eIF4E, which is required for efficient cleavage, is not limiting for eIF4G cleavage. In contrast, during HRV14 and PV1 infection, eIF4GI is cleaved more rapidly than eIF4GII, indicating that the respective 2Apro poorly recognizes the eIF4GII cleavage site, compared to recognition of the eIF4GI site. The reason for this discrimination remains, however, unclear. An analysis of the cleavage sites recognized on the viral polyprotein and eIF4G isoforms by HRV2, -14, and -16 2Apro as well as that of PV1 2Apro (Fig. 3) does not indicate any particular pattern which could explain the discrimination. This suggests that the overall conformations of the two isoforms may be important.
Indeed, the experiments presented here provide evidence that
a significant conformational component in cleavage site recognition
is present. Efficient cleavage of the recombinant GST-eIF4GII
fragments was achieved in the absence of eIF4E (Fig.
1C). In
contrast, the cleavage of eIF4GII, as well as eIF4GI (
6), in
HeLa extracts could be prevented by the addition of the GST-4E-BP1
fusion protein, which can sequester the eIF4E in the extract
and prevent its binding to both eIF4G isoforms (data not shown).
Thus, although the cleavage site is present in eIF4GII, it is
no longer in a conformation which can be recognized by the enzyme.
Interestingly, this is not the case when fragments of eIF4GII
are used as in Fig.
2C, as efficient cleavage of recombinant
GST-eIF4GII by purified 2A
pro was observed in the absence of
eIF4E. Thus, the remainder of eIF4GII, as well as other factors
which may be bound to it, affects the conformation of the cleavage
site. Further experiments will be required to examine the nature
of these conformational changes and to elucidate in which way
they are responsible for the differential cleavage of the eIF4G
isoforms during HRV14 and PV infection.

ACKNOWLEDGMENTS
We thank Graham Belsham for critical reading of the manuscript
and for support and insights during the course of this work.
We are grateful to Colin Lister for exceptional technical assistance.
We are indebted to F. Hayden and R. Rueckert for HeLa-I cells
and HRV16, respectively.
This work was supported by a grant from the Canadian Institute of Health Research (CIHR) to N.S., who is the recipient of a CIHR Distinguished Scientist Award and a Howard Hughes Medical Institute International Scholarship. A.G. was supported by a fellowship of Istituto Superiore di Sanitá, Italy.

FOOTNOTES
* Corresponding author. Mailing address: Department of Biochemistry, McGill University, 3655 Promenade Sir William Osler, Montreal, Quebec, Canada H3G 1Y6. Phone: (514) 398-7274. Fax: (514) 398-1287. E-mail:
nahum.sonenberg{at}mcgill.ca.

Present address: Institute for Animal Health, Pirbright, Surrey GU24 ONF, United Kingdom. 
Present address: RIKEN Genomic Sciences Center, Tsurumi-ku, Yokohama 230-0045, Japan. 
Present address: Research Center Kyoto, Soraku-gun, Kyoto 619-0216, Japan. 

REFERENCES
1 - Ali, I. K., L. McKendrick, S. J. Morley, and R. J. Jackson. 2001. Truncated initiation factor eIF4G lacking an eIF4E binding site can support capped mRNA translation. EMBO J. 20:4233-4242.[CrossRef][Medline]
2 - Belsham, G. J., and R. J. Jackson. 2000. Translation initiation on picornavirus RNA, p. 869-900. In N. Sonenberg, J. W. B. Hershey, and M. Mathews (ed.), Translational control of gene expression. Cold Spring Harbor Laboratory Press, Cold Spring Harbor, N.Y.
3 - Byrd, M. P., M. Zamora, and R. E. Lloyd. 2002. Generation of multiple isoforms of eukaryotic translation initiation factor 4GI by use of alternate translation initiation codons. Mol. Cell. Biol. 22:4499-4511.[Abstract/Free Full Text]
4 - Gradi, A., H. Imataka, Y. V. Svitkin, E. Rom, B. Raught, S. Morino, and N. Sonenberg. 1998. A novel functional human eukaryotic translation initiation factor 4G. Mol. Cell. Biol. 18:334-342.[Abstract/Free Full Text]
5 - Gradi, A., Y. V. Svitkin, H. Imataka, and N. Sonenberg. 1998. Proteolysis of human eukaryotic translation initiation factor eIF4GII, but not eIF4GI, coincides with the shutoff of host protein synthesis after poliovirus infection. Proc. Natl. Acad. Sci. USA 95:11089-11094.[Abstract/Free Full Text]
6 - Haghighat, A., Y. Svitkin, I. Novoa, E. Kuechler, T. Skern, and N. Sonenberg. 1996. The eIF4G-eIF4E complex is the target for direct cleavage by the rhinovirus 2A proteinase. J. Virol. 70:8444-8450.[Abstract]
7 - Hambidge, S. J., and P. Sarnow. 1992. Translational enhancement of the poliovirus 5' noncoding region mediated by virus-encoded polypeptide 2A. Proc. Natl. Acad. Sci. USA 89:10272-10276.[Abstract/Free Full Text]
8 - Hellen, C. U., and P. Sarnow. 2001. Internal ribosome entry sites in eukaryotic mRNA molecules. Genes Dev. 15:1593-1612.[Free Full Text]
9 - Hewlett, M. J., J. K. Rose, and D. Baltimore. 1976. 5'-terminal structure of poliovirus polyribosomal RNA is pUp. Proc. Natl. Acad. Sci. USA 73:327-330.[Abstract/Free Full Text]
10 - Imataka, H., A. Gradi, and N. Sonenberg. 1998. A newly identified N-terminal amino acid stretch of human eIF4G binds poly(A) binding protein and functions in poly(A) dependent translation. EMBO J. 17:7480-7489.[CrossRef][Medline]
11 - Jang, S. K., H.-G. Kräusslich, M. J. H. Nicklin, G. M. Duke, A. C. Palmenberg, and E. Wimmer. 1988. A segment of the 5' nontranslated region of encephalomyocarditis virus RNA directs internal entry of ribosomes during in vitro translation. J. Virol. 62:2636-2643.[Abstract/Free Full Text]
12 - Lamphear, B. J., R. Kirchweger, T. Skern, and R. E. Rhoads. 1995. Mapping of functional domains in eukaryotic protein synthesis initiation factor 4G (eIF4G) with picornaviral proteases. Implications for cap-dependent and cap-independent translational initiation. J. Biol. Chem. 270:21975-21983.[Abstract/Free Full Text]
13 - Lamphear, B. J., R. Yan, F. Yang, D. Waters, H. D. Liebig, H. Klump, E. Kuechler, T. Skern, and R. E. Rhoads. 1993. Mapping the cleavage site in protein synthesis initiation factor eIF-4
of the 2A proteases from human coxsackievirus and rhinovirus. J. Biol. Chem. 268:19200-19203.[Abstract/Free Full Text]
14 - Liebig, H. D., E. Ziegler, R. Yan, K. Hartmuth, H. Klump, H. Kowalski, D. Blaas, W. Sommergruber, L. Frasel, B. Lamphear, R. E. Rhoads, E. Kuechler, and T. Skern. 1993. Purification of two picornaviral 2A proteinases: interaction with eIF-4
and influence on in vitro translation. Biochemistry 32:7581-7588.[CrossRef][Medline]
15 - Lomakin, I. B., C. U. Hellen, and T. V. Pestova. 2000. Physical association of eukaryotic initiation factor 4G (eIF4G) with eIF4A strongly enhances binding of eIF4G to the internal ribosomal entry site of encephalomyocarditis virus and is required for internal initiation of translation. Mol. Cell. Biol. 20:6019-6029.[Abstract/Free Full Text]
16 - Lopez de Quinto, S., E. Lafuente, and E. Martinez-Salas. 2001. IRES interaction with translation initiation factors: functional characterization of novel RNA contacts with eIF3, eIF4B, and eIF4GII. RNA 7:1213-1226.[Abstract]
17 - Lopez de Quinto, S., and E. Martinez-Salas. 2000. Interaction of the eIF4G initiation factor with the aphthovirus IRES is essential for internal translation initiation in vivo. RNA 6:1380-1392.[Abstract]
18 - Mader, S., H. Lee, A. Pause, and N. Sonenberg. 1995. The translation initiation factor eIF-4E binds to a common motif shared by the translation factor eIF-4
and the translational repressors 4E-binding proteins. Mol. Cell. Biol. 15:4990-4997.[Abstract]
19 - Marcotrigiano, J., A.-C. Gingras, N. Sonenberg, and S. K. Burley. 1997. Cocrystal structure of the messenger RNA 5' cap-binding protein (eIF4E) bound to 7-methyl-GDP. Cell 89:951-961.[CrossRef][Medline]
20 - Marcotrigiano, J., I. B. Lomakin, N. Sonenberg, T. V. Pestova, C. U. Hellen, and S. K. Burley. 2001. A conserved HEAT domain within eIF4G directs assembly of the translation initiation machinery. Mol. Cell 7:193-203.[CrossRef][Medline]
21 - Matsuo, H., H. Li, A. M. McGuire, C. M. Fletcher, A.-C. Gingras, N. Sonenberg, and G. Wagner. 1997. Structure of translation factor eIF4E bound to m7GDP and interaction with 4E-binding protein. Nat. Struct. Biol. 4:717-724.[CrossRef][Medline]
22 - Nomoto, A., Y. F. Lee, and E. Wimmer. 1976. The 5' end of poliovirus mRNA is not capped with m7G(5')ppp(5')Np. Proc. Natl. Acad. Sci. USA 73:375-380.[Abstract/Free Full Text]
23 - Pelletier, J., and N. Sonenberg. 1988. Internal initiation of translation of eukaryotic mRNA directed by a sequence derived from poliovirus RNA. Nature 334:320-325.[CrossRef][Medline]
24 - Pilipenko, E. V., T. V. Pestova, V. G. Kolupaeva, E. V. Khitrina, A. N. Poperechnaya, V. I. Agol, and C. U. Hellen. 2000. A cell cycle-dependent protein serves as a template-specific translation initiation factor. Genes Dev. 14:2028-2045.[Abstract/Free Full Text]
25 - Rozen, F., I. Edery, K. Meerovitch, T. E. Dever, W. C. Merrick, and N. Sonenberg. 1990. Bidirectional RNA helicase activity of eucaryotic translation initiation factors 4A and 4F. Mol. Cell. Biol. 10:1134-1144.[Abstract/Free Full Text]
26 - Seipelt, J., H. D. Liebig, W. Sommergruber, C. Gerner, and E. Kuechler. 2000. 2A proteinase of human rhinovirus cleaves cytokeratin 8 in infected HeLa cells. J. Biol. Chem. 275:20084-20089.[Abstract/Free Full Text]
27 - Shatkin, A. J. 1976. Capping of eucaryotic mRNAs. Cell 9:645-653.[CrossRef][Medline]
28 - Skern, T., B. Hampölz, A. Guarné, I. Fita, E. Bergmann, J. Petersen, and M. N. G. James. 2002. Structure and function of picornavirus proteinases, p. 199-212. In B. L. Semler and E. Wimmer (ed.), Molecular biology of picornaviruses. ASM Press, Washington, D.C.
29 - Sonenberg, N., K. M. Rupprecht, S. M. Hecht, and A. J. Shatkin. 1979. Eukaryotic mRNA cap binding protein: purification by affinity chromatography on Sepharose-coupled m7GDP. Proc. Natl. Acad. Sci. USA 76:4345-4349.[Abstract/Free Full Text]
30 - Svitkin, Y. V., A. Gradi, H. Imataka, S. Morino, and N. Sonenberg. 1999. Eukaryotic initiation factor 4GII (eIF4GII), but not eIF4GI, cleavage correlates with inhibition of host cell protein synthesis after human rhinovirus infection. J. Virol. 73:3467-3472.[Abstract/Free Full Text]
31 - Yan, R., W. Rychlik, D. Etchison, and R. E. Rhoads. 1992. Amino acid sequence of the human protein synthesis initiation factor eIF-4
. J. Biol. Chem. 267:23226-23231.[Abstract/Free Full Text]
32 - Ziegler, E., A. M. Borman, R. Kirchweger, T. Skern, and K. M. Kean. 1995. Foot-and-mouth disease virus Lb proteinase can stimulate rhinovirus and enterovirus IRES-driven translation and cleave several proteins of cellular and viral origin. J. Virol. 69:3465-3474.[Abstract]
Journal of Virology, April 2003, p. 5026-5029, Vol. 77, No. 8
0022-538X/03/$08.00+0 DOI: 10.1128/JVI.77.8.5026-5029.2003
Copyright © 2003, American Society for Microbiology. All Rights Reserved.
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