Regulation of a cell type-specific silencer in the human interleukin-3 gene promoter by the transcription factor YY1 and an AP2 sequence-recognizing factor.

Negative regulation of cytokine gene transcription is an important mechanism in maintaining homeostasis of immune function. In this study, we characterized a silencer element in the human interleukin-3 gene promoter that is responsible for the cell-specific expression of interleukin-3. This silencer activity was proposed to be mediated by an unidentified nuclear inhibitory protein (NIP). In this study, we have identified two nuclear factors that are responsible for the silencer activity in T cells. The NIP element forms four specific DNA-protein complexes (designated as complexes A-D) with the Jurkat nuclear proteins. Complex A contains a nuclear protein that shares DNA-binding specificity with the transcription factor AP2 (designated as an AP2 sequence-recognizing factor (ASRF)). Formation of this ASRF complex is required for the NIP silencer function, as mutation of the ASRF-binding site abrogated the silencer activity. Complex B contains the nuclear factor YY1 (Yin-Yang 1), whose function is to down-regulate ASRF activity in the silencer. YY1 activity is supported by data from mutation and cotransfection analyses. Complexes C and D are formed by nonspecific binding proteins and do not express any regulatory activity in the NIP element. These data indicate that a cell type-specific silencer activity might be determined by a unique profile of ubiquitous transcription factors.