Phorbol esters modulate the phosphorylation of human T-cell leukemia virus type I Tax

J. D. Fontes, J. M. Strawhecker, N. D. Bills, R. E. Lewis, S. H. Hinrichs

Research output: Contribution to journalComment/debatepeer-review

22 Scopus citations


The Tax protein from human T-cell leukemia virus type I (HTLV-1) is a 40- kDa phosphoprotein capable of activating transcription from its own long terminal repeat (LTR), as well as increasing the transcription of cellular genes. Transcriptional activation of the HTLV-1 LTR has been demonstrated via a cyclic-AMP-responsive element within the 21-bp Tax-responsive elements of the LTR. Phorbol esters also upregulate expression via the LTR. Since phosphorylation of Tax may play a role in these processes, we investigated the relative effects of kinase-stimulating agents on 32P incorporation into Tax. Our studies demonstrated that the phorbol ester 4β-phorbol-12β- myristate-13α-acetate greatly stimulated Tax phosphorylation in a time- and dose-dependent manner. In contrast, 8-bromoadenosine 3'-5'-cyclic monophosphate induced little stimulation of Tax phosphorylation. Tax phosphorylation occurred only on serine residues and was mapped to a single tryptic fragment in both Tax-producing human lymphocytes and mouse fibroblast cells.

Original languageEnglish (US)
Pages (from-to)4436-4441
Number of pages6
JournalJournal of virology
Issue number7
StatePublished - 1993

ASJC Scopus subject areas

  • Microbiology
  • Immunology
  • Insect Science
  • Virology


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