INDUCTION OF SP1 PHOSPHORYLATION AND NF-KAPPA-B-LNDEPENDENT HIV PROMOTER DOMAIN ACTIVITY IN T-LYMPHOCYTES STIMULATED BY OKADAIC ACID

In contrast to the purely enhancer-dependent effect of cytokines such as TNF on the activity of the HIV regulatory region (LTR), we observed that okadaic acid (OKA) activates HIV transcription through both the enhancer, responding to the factor NF-kappa B, and the promoter domain of the LTR. The inducibility of HIV LTR-driven luciferase expression constructs in lymphoblastoid cells stimulated by OKA depended on both functional Sp1 binding elements and the ability of the TATA box to bin d the protein TBP. in both transformed and normal lymphocytes, OKA sti mulation induced intense phosphorylation of the constitutively express ed Sp1 protein in the nucleus, a property of OKA not shared by TNF, ph orbol ester, or PHA and interleukin 2. Responsiveness of LTR construct s deleted of kappa B elements to HIV Tat expression was increased upon OKA but not TNF stimulation. Our results suggest that SP1 phosphoryla tion induced by OKA, a selective inhibitor of the serine-threonine pho sphatase PP2A, facilitates the formation of a transcription complex in volving general transcription factors, HIV Tar, and Sp1 proteins. The formation of this complex would increase, independently of an in syner gy with NF-kappa B, the low basal activity of the HIV LTR observed in normal T lymphocytes. (C) 1995 Academic Press, Inc.