Phorbol esters modulate the phosphorylation of human T-cell leukemia virus type I Tax.
The Tax protein from human T-cell leukemia virus type I (HTLV-I) 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-I 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 4 beta-phorbol-12 beta-myristate-13 alpha-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.
Fontes
J D
JD
Department of Pathology, University of Nebraska Medical Center, Omaha 68198-6495.
Strawhecker
J M
JM
Bills
N D
ND
Lewis
R E
RE
Hinrichs
S H
SH
D000595:Amino Acid Sequence; D000818:Animals; D004305:Dose-Response Relationship, Drug; D016356:Gene Products, tax / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008969:Molecular Sequence Data; D010449:Peptide Mapping; D010750:Phosphoproteins / Q000378:metabolism; D010766:Phosphorylation; D010768:Phosphoserine / Q000378:metabolism; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology*; D013997:Time Factors
D016356:Gene Products, tax; D010750:Phosphoproteins; D010768:Phosphoserine; D013755:Tetradecanoylphorbol Acetate