THE EXPRESSION OF THE INTERLEUKIN-6 GENE IS INDUCED BY THE HUMAN-IMMUNODEFICIENCY-VIRUS-1 TAT PROTEIN

Human immunodeficiency virus 1 (HIV1) infection is associated with sev ere psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated pr oduction of interleukin 6 (IL-6) has been implicated in the pathogenes is of these diseases. The molecular mechanisms underlying the abnormal IL-6 secretion of HIV1-infected cells may include transactivation of the IL-6 gene by HIV1. To test this hypothesis, we used the pIL6Pr-chl oramphenicol acetyltransferase (CAT) plasmid, an IL-6 promoter-CAT con struct, as a target of the transactivating function of the HIV1 TAT pr otein. By cotransfecting the pIL6Pr-CAT and the tat-expressing pSVT8 p lasmid in MC3 B-lymphoblastoid or in HeLa epithelial cells, we observe d that TAT transactivates the human IL-6 promoter. These results were confirmed when pIL6Pr-CAT was transfected in MC3 or HeLa cells that co nstitutively expressed the tar gene in a sense (pSVT8 cells) or antise nse (pSVT10 cells) orientation. 5' deletion plasmids of pIL6Pr-CAT, in which regions at -658, -287, and -172 were inserted 5' to the cat gen e, were transiently transfected in pSVT10 and pSVT8 cells and showed t hat TAT-induced activation of the IL-6 promoter required a minimal reg ion located between -287 and -54 bp. Moreover, experiments with plasmi ds carrying the -658, -287, and -172 bp regions of the IL-6 promoter i nserted downstream to a TAR-deleted HIV1-LTR identified the sequence o f -172 to -54 as the minimal region of the IL-6 promoter required for TAT to transactivate the TAR-deleted HIV1-LTR. By DNA-protein binding experiments, tat-transfected cells expressed a consistent increase in kappa B and nuclear factor (NF)-IL-6 binding activity. Accordingly, th e pDRCAT and IL-1REK9CAT, carrying tandem repeats of NF-kappa B or NF- IL6 binding motifs, respectively, were activated in TAT-expressing cel ls. The biological relevance of the TAT-induced IL-6 secretion was add ressed by generating 7TD1 cells, an IL-6-dependent mouse cell line, st ably expressing the tat gene. These tat-positive cells expressed the e ndogenous IL-6 gene, secreted high amounts of murine IL-6, and grew ef ficiently in the absence of exogenous IL-6. Moreover, the tat-positive 7TD1 cells sustained the growth of parental 7TD1 cells and showed a d ramatic increase in their tumorigenic potency. These results suggest t hat TAT protein may play a role in the pathogenesis of some HIV1-assoc iated diseases by modulating the expression of host cellular genes.