CCAAT/enhancer-binding proteins modulate human T cell leukemia virus type 1 long terminal repeat activation

CCAAT/enhancer-binding protein (C/EBP) basic region/leucine zipper (bZIP) transcription factors have been shown to form heterodimers with cAMP-responsive element binding protein 2 (CREB-2), a transcription factor involved in regulating basal and Tax-mediated transactivation of the human T cell leukemia virus type 1 (HTLV-1) long terminal repeat (LTR). In cells of the monocyte-macrophage lineage (proposed to play a role in HTLV-1 pathogenesis as an accessory target cell), several members of the C/EBP family are expressed at high levels and may have functional impact on both basal and Tax-mediated transactivation of the HTLV-1LTR. Basal activation of the HTLV-1LTR was enhanced by overexpression of C/EBPO, C/EBP6, or C/EBPE, whereas transactivation of the LTR by Tax was inhibited by overexpression of C/EBP alpha and C/EBP. Inhibition of Tax-mediated transactivation of the HTLV-1LTR was co-activator-independent, did not require C/EBP binding to the Tax-responsive elements, and may involve heterodimerization with CREB factors. (c) 2006 Elsevier Inc. All rights reserved.