Stability and function of JC viras large T antigen and T′ proteins are altered by mutation of their phosphorylated threonine 125 residues

Shiva K. Tyagarajan, Richard John Frisque

Research output: Contribution to journalArticle

16 Citations (Scopus)

Abstract

JC virus (JCV), a human polyomavirus, exhibits oncogenic activity in rodents and primates. The large tumor antigens (TAgs) of the polyomaviruses play key roles in viral replication and oncogenic transformation. Analyses of JCV TAg phosphorylation mutants indicated that the amino-terminal phosphorylation site at threonine 125 (T125) is critical to TAg replication function. TMs site is also conserved in the TAg splice variants T′135, T′136, and T′165. By constructing stable cell lines expressing JCV T125A and T125D mutants, we show that mutation of this phosphorylation site to alanine generates an unstable TAg; however, the stability of the three T′ proteins is unaffected. JCV T125A mutant proteins bind the retinoblastoma protein (RB) family members p107 and p130 with slightly reduced efficiencies and fail to induce the release of transcriptionally active E2F from RB-E2F complexes. On the other hand, cell lines expressing JCV T125D mutant proteins produce stable TAg and T′ proteins which bind p107 and p130 more efficiently than do the wild-type proteins. In addition, T125D mutant proteins efficiently induce the release of E2F from RB-E2F complexes. T125D mutant cell lines, unlike the T125A mutant lines, continue to grow under conditions of low serum concentration and anchorage independence. Finally, both T125A and T125D mutant viruses are replication defective. Phosphorylation of the T125 site is likely mediated by a cyclin-cyclin-dependent kinase, suggesting that JCV TAg and T′ protein functions that mediate viral replication and oncogenic transformation events are regulated in a cell cycle-dependent manner.

Original languageEnglish (US)
Pages (from-to)2083-2091
Number of pages9
JournalJournal of virology
Volume80
Issue number5
DOIs
StatePublished - Mar 1 2006

Fingerprint

JC Virus
Viral Tumor Antigens
Threonine
threonine
JC polyomavirus
antigens
mutation
Retinoblastoma Protein
Mutation
Mutant Proteins
mutants
Phosphorylation
E2F Transcription Factors
Proteins
proteins
phosphorylation
Cell Line
Polyomavirus Transforming Antigens
cell lines
Polyomavirus

All Science Journal Classification (ASJC) codes

  • Immunology
  • Virology

Cite this

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title = "Stability and function of JC viras large T antigen and T′ proteins are altered by mutation of their phosphorylated threonine 125 residues",
abstract = "JC virus (JCV), a human polyomavirus, exhibits oncogenic activity in rodents and primates. The large tumor antigens (TAgs) of the polyomaviruses play key roles in viral replication and oncogenic transformation. Analyses of JCV TAg phosphorylation mutants indicated that the amino-terminal phosphorylation site at threonine 125 (T125) is critical to TAg replication function. TMs site is also conserved in the TAg splice variants T′135, T′136, and T′165. By constructing stable cell lines expressing JCV T125A and T125D mutants, we show that mutation of this phosphorylation site to alanine generates an unstable TAg; however, the stability of the three T′ proteins is unaffected. JCV T125A mutant proteins bind the retinoblastoma protein (RB) family members p107 and p130 with slightly reduced efficiencies and fail to induce the release of transcriptionally active E2F from RB-E2F complexes. On the other hand, cell lines expressing JCV T125D mutant proteins produce stable TAg and T′ proteins which bind p107 and p130 more efficiently than do the wild-type proteins. In addition, T125D mutant proteins efficiently induce the release of E2F from RB-E2F complexes. T125D mutant cell lines, unlike the T125A mutant lines, continue to grow under conditions of low serum concentration and anchorage independence. Finally, both T125A and T125D mutant viruses are replication defective. Phosphorylation of the T125 site is likely mediated by a cyclin-cyclin-dependent kinase, suggesting that JCV TAg and T′ protein functions that mediate viral replication and oncogenic transformation events are regulated in a cell cycle-dependent manner.",
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Stability and function of JC viras large T antigen and T′ proteins are altered by mutation of their phosphorylated threonine 125 residues. / Tyagarajan, Shiva K.; Frisque, Richard John.

In: Journal of virology, Vol. 80, No. 5, 01.03.2006, p. 2083-2091.

Research output: Contribution to journalArticle

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AU - Frisque, Richard John

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N2 - JC virus (JCV), a human polyomavirus, exhibits oncogenic activity in rodents and primates. The large tumor antigens (TAgs) of the polyomaviruses play key roles in viral replication and oncogenic transformation. Analyses of JCV TAg phosphorylation mutants indicated that the amino-terminal phosphorylation site at threonine 125 (T125) is critical to TAg replication function. TMs site is also conserved in the TAg splice variants T′135, T′136, and T′165. By constructing stable cell lines expressing JCV T125A and T125D mutants, we show that mutation of this phosphorylation site to alanine generates an unstable TAg; however, the stability of the three T′ proteins is unaffected. JCV T125A mutant proteins bind the retinoblastoma protein (RB) family members p107 and p130 with slightly reduced efficiencies and fail to induce the release of transcriptionally active E2F from RB-E2F complexes. On the other hand, cell lines expressing JCV T125D mutant proteins produce stable TAg and T′ proteins which bind p107 and p130 more efficiently than do the wild-type proteins. In addition, T125D mutant proteins efficiently induce the release of E2F from RB-E2F complexes. T125D mutant cell lines, unlike the T125A mutant lines, continue to grow under conditions of low serum concentration and anchorage independence. Finally, both T125A and T125D mutant viruses are replication defective. Phosphorylation of the T125 site is likely mediated by a cyclin-cyclin-dependent kinase, suggesting that JCV TAg and T′ protein functions that mediate viral replication and oncogenic transformation events are regulated in a cell cycle-dependent manner.

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