title: T-cell receptor/CD28 engagement when combined with prostaglandin E2 treatment leads to potent activation of human T-cell leukemia virus type 1.
abstract: Infection with human T-cell leukemia virus type 1 (HTLV-1) is characterized by long latency periods, indicating that viral gene expression is under tight control. There is presently little information available regarding the nature of extracellular stimuli that can transactivate the regulatory elements of HTLV-1 (i.e., long terminal repeat [LTR]). To gain insight into the biological importance of externally induced activation pathways in virus gene expression, primary and established T cells were transfected with HTLV-1-based reporter gene vectors and then were treated with agents that cross-linked the T-cell receptor (TCR) or the costimulatory CD28 molecule with prostaglandin E(2) (PGE(2)). We demonstrated that a potent induction of HTLV-1 LTR-driven reporter gene activity was seen only when the three agents were used in combination. Interestingly, similar observations were made when using C91/PL, a cell line that carries integrated HTLV-1 proviral DNA. This TCR-CD28-PGE(2)-mediated increase in virus transcription was dependent on protein kinase A activation and induction of the cAMP response element binding protein. Experiments with a mutated reporter construct further revealed the importance of the Tax-responsive elements in the HTLV-1 LTR in the observed up regulation of virus gene expression when TCR/CD28 engagement was combined with PGE(2) treatment. The protein tyrosine kinases p56(lck) and the transmembrane tyrosine phosphatase CD45 were all found to be involved in TCR-CD28-PGE(2)-directed increase in HTLV-1 LTR activity. This study presents new information on the possible mechanisms underlying reactivation of this retrovirus.
mesh_terms: D018106:CD28 Antigens / Q000502:physiology*; D002460:Cell Line; D017362:Cyclic AMP Response Element-Binding Protein / Q000502:physiology; D017868:Cyclic AMP-Dependent Protein Kinases / Q000502:physiology; D015232:Dinoprostone / Q000494:pharmacology*; D015368:Human T-lymphotropic virus 1 / Q000235:genetics* / Q000502:physiology*; D006801:Humans; D017493:Leukocyte Common Antigens / Q000502:physiology; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck) / Q000502:physiology; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D011948:Receptors, Antigen, T-Cell / Q000502:physiology*; D020218:Response Elements; D020079:Terminal Repeat Sequences; D014158:Transcription, Genetic; D014775:Virus Activation; D014779:Virus Replication
chemical_list: D018106:CD28 Antigens; D017362:Cyclic AMP Response Element-Binding Protein; D011948:Receptors, Antigen, T-Cell; D019860:Lymphocyte Specific Protein Tyrosine Kinase p56(lck); D017868:Cyclic AMP-Dependent Protein Kinases; D017493:Leukocyte Common Antigens; D054562:Protein Tyrosine Phosphatase, Non-Receptor Type 1; D015232:Dinoprostone