Secretion of Extracellular Factor(s) Induced by X-Irradiation Activates the HIV Type 1 Long Terminal Repeat through Its κB Motif

Abstract

X-irradiation has been used in the treatment of several human diseases, including AIDS-related-malignancies. X-irradiation might induce the transcription and the replication of human immunodeficiency virus type 1 (HIV-1) and enhance nuclear factor kappa B (NF-kappaB). In the present article we show that the activation of the HIV-1 long terminal repeat (LTR) by direct X-irradiation can be mimicked by coculture of transfected cells with X-irradiated nontransfected (HIV-1-negative) cells. In the human colonic carcinoma cell line HT29, the activation seems to depend on an extracellular factor(s) released by a cell line treated with X-rays. The HIV-1 LTR cis-acting element conferring X-indirect responsiveness was identified as the kappaB tandem motif. The two main nuclear HIV-1 kappaB-binding complexes activated by X-direct and -indirect irradiation were the NF-kappaB p50/p65 and c-Rel/p65 heterodimers. Nuclear NF-kappaB activation was dependent on protein neosynthesis. It was partially inhibited by 100 microM pyrrolidine dithiocarbamate, a potent antioxidant drug, but was not correlated with a significant decrease in cellular IkappaBalpha. Furthermore, X-irradiation induces the expression of several cytokine genes generally associated with stress response and antibodies against interleukin 6 and TNF-alpha partially inhibited the X-indirect activation of the HIV-1 LTR. The use of protein kinase C (PKC)-specific inhibitor and of forskolin, an adenylate cyclase activator, suggests that a PKC-dependent pathway and the cAMP intracellular concentration could play a role in the X-indirect enhancement of HIV-1 LTR transcription in the HT29 cell line. In addition, supernatants of an X-irradiated HT29 cell culture activated the HIV-1 stimulation in infected peripheral blood monocytes.