Article (Scientific journals)
Phosphorylation of bovine leukemia virus Tax protein is required for in vitro transformation but not for transactivation.
Willems, Luc; Grimonpont, Cathy; Kerkhofs, Pierre et al.
1998In Oncogene, 16 (17), p. 2165-76
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Keywords :
Animals; CDC2 Protein Kinase/metabolism; Calcium-Calmodulin-Dependent Protein Kinases/metabolism; Cattle; Cell Line; Cell Transformation, Viral/genetics; Fibroblasts; Gene Products, tax/antagonists & inhibitors/genetics/metabolism; Leukemia Virus, Bovine/genetics/physiology; Mice; Mice, Nude; Mutagenesis, Site-Directed; Phosphorylation; Rats; Rats, Inbred F344; Serine/genetics/metabolism; Spodoptera; Transcriptional Activation/physiology; Virus Replication/genetics
Abstract :
[en] The Tax proteins of the oncovirinae viruses are phosphorylated transcriptional activators that exhibit oncogenic potential. The role of phosphorylation in their functional activities remains unknown. As a model for the Human T-cell leukemia virus type I (HTLV-I), Bovine Leukemia Virus (BLV) permits the characterization of viral replication and leukemogenesis in vivo. Here, we show that the BLV Tax protein is phosphorylated on serine residues 106 and 293 both in insect and in mammalian cells. These sites can also be efficiently phosphorylated by the cdc2 and MAP kinases in vitro. Mutation of these residues does not affect the capacity of the Tax protein to function as a transactivator. Indeed, the Tax proteins mutated at one or both serines increase LTR-directed viral transcription at levels similar to those obtained with wild-type Tax in cell culture. Moreover, inhibition of Tax phosphorylation by W7, a calmodulin antagonist, does not alter its transactivation activity. Thus, phosphorylation on serines 106 and 293 is not required for transactivation by Tax. However, simultaneous substitution of both serines into alanine residues destroys the capacity of Tax to cooperate with the Ha-ras oncogene to transform primary rat embryo fibroblasts and induce tumors in nude mice. When the serines were replaced with aspartic acid residues, the oncogenic potential of Tax was maintained indicating that the negative charge rather than the phosphate group itself was required for Tax oncogenicity. Finally, to assess the role of the serine residues in vivo, recombinant viruses which express the Tax mutants were constructed and injected into sheep. It appeared that the mutated proviruses replicate at levels similar to the wild-type virus in vivo. We conclude that Tax phosphorylation is dispensable for transactivation and viral replication in vivo but is required for its oncogenic potential in vitro.
Disciplines :
Biochemistry, biophysics & molecular biology
Author, co-author :
Willems, Luc  ;  Université de Liège - ULiège > GIGA-Research - Gembloux Agro-Bio Tech
Grimonpont, Cathy
Kerkhofs, Pierre
Capiau, Carine
Gheysen, Dirk
Conrath, Karel
Roussef, Roussi
Mamoun, Robert
Portetelle, Daniel ;  Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
Burny, Arsène ;  Université de Liège - ULiège > Agro Biotech Gembloux
Adam, Emmanuelle
Lefebvre, Laurent
Twizere, Jean-Claude  ;  Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
Heremans, Hubertine
Kettmann, Richard ;  Université de Liège - ULiège > Gembloux Agro-Bio Tech > Gembloux Agro-Bio Tech
More authors (5 more) Less
Language :
English
Title :
Phosphorylation of bovine leukemia virus Tax protein is required for in vitro transformation but not for transactivation.
Publication date :
1998
Journal title :
Oncogene
ISSN :
0950-9232
eISSN :
1476-5594
Publisher :
Nature Publishing Group, Basingstoke, United Kingdom
Volume :
16
Issue :
17
Pages :
2165-76
Peer reviewed :
Peer Reviewed verified by ORBi
Available on ORBi :
since 11 January 2010

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