Abstract
CD11d encodes the latest alpha-subunit of the leukocyte integrin family to be discovered, and it is expressed predominantly in myelomonocytic cells. We have isolated a genomic clone that contains CD11d and showed this gene to be 11,461 bp downstream and oriented in the same direction as the related CD11c gene. CD11d transcription begins 69-79 nucleotides upstream of the ATG codon. Transfection analysis of CD11d-luc reporter constructs revealed that the -173 to +74 region is sufficient to confer leukocyte-specific expression of luciferase in myelomonocytic cells (THP1 and HL60), B-cells (IM9), and T-cells (Jurkat). Transfection analysis showed that down-regulation of CD11d expression by phorbol ester was myelomonocyte-specific and is mediated by one or more cis-elements within the -173 to +74 region. In vitro DNase I footprint analysis and electrophoretic mobility shift analysis showed that Sp1 and Sp3 bind at -63 to -40. Deletion of the Sp-binding site significantly reduced CD11d promoter activity. Overexpression of either Sp1 or Sp3 in THP1 cells led to activation of the CD11d promoter even in the presence of phorbol ester, whereas down-regulation of either factor by antisense oligonucleotides decreased CD11d promoter activity. In contrast, overexpression of Sp3 in IM9 and Jurkat cells down-regulated CD11d promoter expression. In vivo genomic footprinting revealed that the -63 to -40 region is bound by a Sp protein in unstimulated HL60 cells but not in phorbol ester-stimulated HL60 cells. In contrast, this site is bound in both unstimulated and phorbol ester-stimulated IM9 and Jurkat cells. Together, these results show that myelomonocyte-specific phorbol ester down-regulation of CD11d is mediated through both Sp1 and Sp3.
Highlights
The integrins are a large family of membrane glycoproteins composed of noncovalently associated ␣- and -subunits that mediate cell-cell and cell-matrix interactions [1, 2]
We show that the Ϫ173 to ϩ74 region of the CD11d gene is sufficient to confer leukocyte-specific expression in transfected cells that is dependent on both Sp1 and Sp3
Structural Analysis of the 5Ј-Flanking Region of the Human CD11d Gene—The identification of CD11d, a novel leukocyte integrin ␣-subunit on myelomonocytic cells, prompted us to begin an analysis of the transcriptional regulation of the CD11d gene
Summary
The integrins are a large family of membrane glycoproteins composed of noncovalently associated ␣- and -subunits that mediate cell-cell and cell-matrix interactions [1, 2]. Transfection analysis of CD11d-luc reporter constructs revealed that the ؊173 to ؉74 region is sufficient to confer leukocyte-specific expression of luciferase in myelomonocytic cells (THP1 and HL60), B-cells (IM9), and T-cells (Jurkat). The Ϫ173 to ϩ74 region is sufficient to confer leukocyte-specific activation of the CD11d promoter, since luciferase activity from CD11d(Ϫ173/ϩ74)-luc transfected into IM9 and Jurkat cells was increased 24- and 30-fold, respectively (Fig. 5, B and C).
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