ZFX transactivation of the HIV-1 LTR is cell specific and depends on core enhancer and TATA box sequences

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Abstract
The ZFX gene is ubiquitously transcribed and highly conserved among vertebrates. The integrity of Zfx, its murine homologue, has been shown to be important for growth during embryogenesis and sustained gamete production. Alternative splicing was shown to result in production of mRNAs coding for either ZFX804 or a shorter isoform initiated downstream, ZFX575. ZFX575 was previously shown to be a potent transactivator of the HLA-A11 promoter. Here, the HIV-1 LTR is also shown to be potently transactivated by ZFX575 in several cell types, while ZFX804 activity is found to be similar to that of ZFX575, null or intermediary according to the cell type. In all cell types, the HIV-1 TATA box sequence is a key element of transactivation, while the Sp1 or NFκB sites are variably required, according to the cell type. Overall, the results suggest that ZFX575 and ZFX804 could play a role in HIV-1 LTR induction as co-activators enhancing productive interactions between upstream transactivators and the basal transcription complexes recruited by the TATA box.