Induction of HIAP-1 synthesis by HTLV-1 Tax. The impact of Tax on endogenous HIAP-1 expression was investigated in Jurkat T cells and in Tax-immortalized primary human T cells (Tesi). (A) Jurkat cells (10⁷) were transfected with the indicated amounts of the Tax expression plasmid pcTax. Empty vector plasmid was added to obtain equal amounts of transfected DNA. After 48 hours RNA was extracted, cDNA prepared, and the amounts of HIAP-1 and β-actin transcripts (internal standard) were analyzed by real-time RT-PCR. The relative mRNA copy numbers of HIAP-1 and Tax mRNA were determined as multiples of the β-actin mRNA copy number. The correlation between Tax and HIAP-1 mRNA relative copy numbers is highly significant at the .01 level (2-tailed). (B) Human T cells transformed by a repressible TAX gene (Tesi) were kept under condition of induced (Tesi) and repressed Tax (Tesi + Tet [tetracycline]) expression. RNA was analyzed by RT-PCR and quantified by real-time RT-PCR. The relative mRNA copy numbers of HIAP-1 and Tax mRNA were determined as multiples of the β-actin mRNA copy number. The columns represent the mean of 3 experiments; the error bars indicate standard deviation.