The expression of the interleukin 6 gene is induced by the human immunodeficiency virus 1 TAT protein.

Abstract

SummaryHuman immunodeficiency virus 1 (HIV1) infection is associated with severe psoriasis, B cell lymphoma, and Kaposi's sarcoma. A deregulated production of interleukin 6 (IL-6) has been implicated in the pathogenesis of these diseases. The molecular mechanisms underlying the abnormal IL-6 secretion of HIVl-infected cells may include transactivation of the IL-6 gene by HIV1.To test this hypothesis, we used the plL6Pr-chloramphenicol acetyltransferase (CAT) plasmid, an IL-6 promoter-CAT construct, as a target of the transactivating function of the HIV1 TAT protein. By cotransfecting the pIL6Pr-CAT and the tat-expressing pSVT8 plasmid in MC3 B-lymphoblastoid or in HeLa epithelial cells, we observed that TAT transactivates the human IL-6 promoter. These results were confirmed when plL6Pr-CAT was transfected in MC3 or HeLa cells that constitutively expressed the tat gene in a sense (pSVT8 cells) or antisense (pSVT10 cells) orientation. 5' deletion plasmids of plL6Pr-CAT, in which regions at -658, -287, and -172 were inserted 5' to the cat gene, were transiently transfected in pSVT10 and pSVT8 cells and showed that TAT-induced activation of the IL-6 promoter required a minimal region located between -287 and -54 bp. Moreover, experiments with plasmids carrying the -658, -287, and -172 bp regions of the IL-6 promoter inserted downstream to a TAR-deleted HIV1-LTR identified the sequence of -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 KB and nuclear factor (NF)-IL-6 binding activity. Accordingly, the pDRCAT and IL-lkEK9CAT, carrying tandem repeats of NF-KB or NF-IL6 binding motifs, respectively, were activated in TAT-expressing cells. The biological relevance of the TAT-induced IL-6 secretion was addressed by generating 7TD1 cells, an IL-6-dependent mouse cell line, stably expressing the tat gene. These tat-positive cells expressed the endogenous IL-6 gene, secreted high amounts of murine IL-6, and grew efficiently in the absence of exogenous IL-6. Moreover, the tat-positive 7TD1 cells sustained the growth of parental 7TD1 cells and showed a dramatic increase in their tumorigenic potency. These results suggest that TAT protein may play a role in the pathogenesis of some HIVl-associated diseases by modulating the expression of host cellular genes.

Morphological, Histochemical, Immunohistochemical, and Ultrastructural Characterization of Tumors and Dysplastic and Non-Neoplastic Lesions Arising in BK Virus/tat Transgenic Mice

“…Indeed, it was shown that Tat induces the expression of several cytokines, such as tumor necrosis factor, 42 interleukin-2, 43 interleukin-6, 33,44 and transforming growth factor-␤. 45 The nature of the cooperation between BKV TAg and Tat protein in the pathogenesis of the lesions appearing in BKV/tat transgenic mice seems to be mainly related to the transcriptional activation of tat promoter by BKV TAg, which is a potent transactivator of the HIV-1 LTR.…”

“…23,30 Experimental evidence also indicates that Tat regulates the expression of cellular genes, modulating cell functions. [31][32][33] Tat is highly angiogenic in vivo, 30,34 and transgenic mice expressing the tat gene develop skin lesions closely resembling the early phases of KS. 35,36 In a previous study, transgenic mice were generated by means of a recombinant DNA (pRPU3R-Tat) containing BKV early region and the HIV-1 tat gene, directed by the HIV-1 long terminal repeat (LTR).…”

An inflammation-inducible adenoviral expression system for local treatment of the arthritic joint

“…43,44 It is known that the TAT protein can transactivate inflammatory host genes, 45 including the IL-6 gene. 46 It is plausible that the transactivation of IL-6 gene causes activation of the C3 promoter, which can explain the higher background levels found with the C3-Tat/HIV two-component system as compared to our IL-1/IL-6 construct (Figures 7 and 9). It must be emphasized that the basal transgene levels and the fold induction using the C3-Tat/HIV two-component system were far better in adenoviral-transfected HepG2 cells and in primary rat synovial fibroblasts.…”

Functions of Tat: the versatile protein of human immunodeficiency virus type 1

“…In vivo studies have shown that Tat deregulates the expression levels of several cytokines (Scala et al, 1994;Westendorp et al, 1994;Bannasser & Bahraoui, 2002). By using a vector expressing IL-6 under the control of the IL-6 promoter, it has been demonstrated that Tat transactivates the human IL-6 promoter (Scala et al, 1994).…”