Activation of a cryptic splice site in the tax gene of HTLV-I by a single nucleotide change

Increased production of viral proteins by a 3'-LTR-deleted infectious clone of human T-cell leukemia virus type 1

We previously reported that a full-length provirus of HTLV-1 was directly constructed from the HTLV-1-transformed cell line MT-2 using overlapping polymerase chain reaction (PCR) and cloned into a plasmid vector (pFL-MT2). 293T cells transfected with pFL-MT2 alone did not produce virus particles because there was no expression of the viral transactivator protein Tax, whereas cells transfected with pFL-MT2 plus a Tax expression vector produced virus-like particles. In the process of constructing the HTLV-1 provirus by overlapping PCR, we also constructed an incomplete molecular clone, in which the 3' long terminal repeat (LTR) was replaced with the endogenous human gene, which resulted in the expression of a tax gene shorter by 43 bp. This incomplete molecular clone alone expressed Tax and produced the viral protein in transfected cells. Various clones were then constructed with different lengths of the 3' LTR and lacking the reverse-direction TATA box. The clones contained over 113 bp of the 3' LTR, with no reverse-direction TATA box, which might express the full-length tax gene, and did not produce the viral antigen. These results suggest that Tax in which the C-terminal portion is deleted is more strongly expressed than the wild-type protein and has transcriptional activity.

Current topics in prevention of human T-cell leukemia virus type i infection: NF-kappa B inhibitors and APOBEC3

Human T-cell leukemia virus type I (HTLV-I) is the first human retrovirus and causes adult T-cell leukemia/lymphoma (ATL). Constitutive activation of nuclear factor-kappa B (NF-kappa B) in the leukemic cells is essential for their growth and survival. Thus, NF-kappa B inhibitors have been attracting attention as a potential strategy to treat ATL. Recently, the field of retrovirus research has been stimulated by the discovery of an innate host defense factor, APOBEC3, against the retroviruses. HTLV-I is relatively resistant to the antiviral effects of APOBEC3. To clarify the resistance of HTLV-I against APOBEC3 might contribute to the design of effective therapeutic approaches.