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RIIIA Can Function as a NK/T Cell-Specific Restriction Element, Which Involves Binding of Sp1 Transcription Factor1
Department of Clinical Immunology, Hannover Medical School, Hannover, Germany
The low-affinity receptor for IgG (human Fc
RIIIA) is selectively
expressed by a subset of T lymphocytes, NK cells, and macrophages. To
understand the mechanisms underlying this pattern of cell type-specific
expression, we initially identified alternative promoters, Pmed1/2 and
Pprox, in the 5' end of the Fc
RIIIA gene. In this study, we
focused on the Pmed1 promoter and demonstrated this 93-bp region to be
highly specific in governing restriction to NK/T cell lines. This
property of Pmed1 is context independent and can extend to a disparate
promoter. Deletion analysis defined a contribution of two separate
elements located to the 5' 21-bp (-942/-922) and 3' 72-bp
(-921/-850) regions of Pmed1 in conferring NK/T cell specificity. The
5' part of Pmed1 contains binding sites for Sp1 and NK
element-recognizing factors and substitution mapping studies revealed a
critical requirement of the Sp1-I site. The importance of Sp1
protein to regulate maximal Pmed1 promoter activity was further
established by EMSAs and cotransfection experiments in Sp1-null
Drosophila SL2 cells. Our data suggest that Sp1 can
contribute, in part, to NK/T cell restriction and further indicate that
the Fc
RIIIA Pmed1 sequence might be useful to direct the NK/T
cell-specific expression of heterologous genes.
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