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Journal of Virology, August 2004, p. 8301-8311, Vol. 78, No. 15
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.15.8301-8311.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.

Dileucine and YXXL Motifs in the Cytoplasmic Tail of the Bovine Leukemia Virus Transmembrane Envelope Protein Affect Protein Expression on the Cell Surface

Sinisa Novakovic,1 Earl T. Sawai,1,2 and Kathryn Radke1,3*

Graduate Group in Microbiology,1 Departments of Medical Pathology,2 Animal Science, University of California, Davis, Davis, California 956163

Received 19 December 2003/ Accepted 12 March 2004

Several retroviruses downmodulate the cell surface expression of envelope (Env) proteins through peptide sequences located in the cytoplasmic tail of the transmembrane (TM) subunit. We investigated whether cell surface expression of a chimeric protein containing the cytoplasmic domain of the TM protein (CTM) of bovine leukemia virus (BLV) was regulated by two membrane-proximal dileucine motifs or by tyrosine Y487 or Y498 in YXXL motifs. A chimeric protein composed of the extracellular and membrane-spanning portions of human CD8-{alpha} plus a wild-type (wt) BLV CTM was detectable on the surface of only 40% of the cells in which it was transiently expressed. Replacement of either dileucine pair with alanines increased the level of surface display of chimeric proteins. Nearly all cells became surface positive when both dileucine motifs were altered simultaneously and when either an N-terminal segment containing both dileucine motifs or a C-terminal segment containing all YXXL motifs was deleted. In contrast, replacement of Y487 or Y498 with alanine or phenylalanine enabled only small increases in surface display compared with wt levels. Chimeric proteins had similar stabilities but were downmodulated from the cell surface at three different rates. Point mutants segregated into each of the three groups of proteins categorized according to these different rates. Interestingly, Y487 mutants were downmodulated less efficiently than Y498 mutants, which behaved like wt. CD8-CTM chimeric proteins were phosphorylated on serine residues, but the native BLV Env protein was not phosphorylated either in transfected cells or in a lymphoid cell line constitutively producing BLV. Thus, both dileucine and YXXL motifs within the BLV CTM contribute to downmodulation of a protein containing this domain. Interactions with other proteins may influence surface exposure of Env protein complexes in virus-infected cells, assisting in viral evasion of adaptive immunity.

* Corresponding author. Mailing address: Department of Animal Science, University of California, Davis, One Shields Ave., Davis, CA 95616-8521. Phone: (530) 752-9025. Fax: (530) 752-0175. E-mail: KLRadke{at}ucdavis.edu.

Journal of Virology, August 2004, p. 8301-8311, Vol. 78, No. 15
0022-538X/04/$08.00+0     DOI: 10.1128/JVI.78.15.8301-8311.2004
Copyright © 2004, American Society for Microbiology. All Rights Reserved.



This article has been cited by other articles:

  • Pery, E., Rajendran, K. S., Brazier, A. J., Gabuzda, D. (2009). Regulation of APOBEC3 Proteins by a Novel YXXL Motif in Human Immunodeficiency Virus Type 1 Vif and Simian Immunodeficiency Virus SIVagm Vif. J. Virol. 83: 2374-2381 [Abstract] [Full Text]  
  • Song, C., Micoli, K., Bauerova, H., Pichova, I., Hunter, E. (2005). Amino Acid Residues in the Cytoplasmic Domain of the Mason-Pfizer Monkey Virus Glycoprotein Critical for Its Incorporation into Virions. J. Virol. 79: 11559-11568 [Abstract] [Full Text]  


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