Sp1 Cooperates with the ets Transcription Factor, GABP, to Activate the CD18 (β2 Leukocyte Integrin) Promoter

Abstract

CD18, the ␤ chain of the leukocyte integrins, plays a crucial role in immune and inflammatory responses. CD18 is expressed exclusively by leukocytes, and it is transcriptionally regulated during the differentiation of myeloid cells. The ets factors, PU.1 and GABP, bind to three ets sites in the CD18 promoter, which are essential for high level myeloid expression of CD18. We now identify two binding sites for the transcription factor, Sp1, that flank these ets sites. Sp1 is the only factor from myeloid cells that binds to these sites in a sequencespecific manner. Mutagenesis of these sites abrogates Sp1 binding and significantly reduces the activity of the transfected CD18 promoter in myeloid cells. Transfection of Sp1 into Drosophila Schneider cells, which otherwise lack Sp1, activates the CD18 promoter dramatically. GABP also activates the CD18 promoter in Schneider cells. Co-transfection of Sp1 and GABP activates CD18 more than the sum of their individual effects, indicating that these factors cooperate to transcriptionally activate myeloid expression of CD18. These studies support a model of high level, lineagerestricted gene expression mediated by cooperative interactions between widely expressed transcription factors.Monocytes and granulocytes, which are collectively known as myeloid cells, play crucial roles in immune and inflammatory responses. As myeloid cells differentiate from immature bone marrow precursor cells, they express characteristic genes that are required in their roles as immune effector cells. Most genes that are expressed during myeloid differentiation are regulated at the level of transcription (1). Characterization of the DNA sequences and transcription factors that control myeloid gene expression has provided important insights into the molecular basis of normal myeloid differentiation.CD18 (␤ 2 leukocyte integrin) is a cell surface adhesion molecule that forms heterodimers with CD11a, CD11b, or CD11c to generate the antigens LFA-1, Mo-1 (Mac-1), and p150/95, respectively. These leukocyte-specific receptors mediate cell-cell and cell-matrix interactions and play important roles in immune and inflammatory responses (2). The clinical significance of CD18 is illustrated by leukocyte adhesion deficiency, in which insufficient CD18 causes recurrent bacterial and fungal infections and can lead to premature death (3).Expression of CD18 is restricted to myeloid cells and lymphocytes. CD18 expression increases significantly during myeloid differentiation due to increased transcription (4 -7). We (4) and others (8, 9) have cloned the gene that encodes CD18 and characterized its promoter. The transfected CD18 promoter exhibits the leukocyte-specific and myeloid-inducible activity of the endogenous CD18 gene (10). We have previously shown that two ets-related transcription factors, PU.1 and GABP, bind to the CD18 promoter and cooperate to activate leukocyte-specific expression of CD18 (10, 11).Sp1 is a DNA-binding nuclear protein that functions as a transcriptional activator (12)(13)(14). We now de...

AML-1, PU.1, and Sp3 regulate expression of human bactericidal/permeability-increasing protein

“…Sp1 and Sp3 are ubiquitously expressed transcription factors (reviewed in [42]). Sp1 is involved in the regulation of both azurophil granule proteins, e.g., elastase [43] and specific granule proteins e.g., lactoferrin, CD18 [44,45]. Sp3 can act either as a transcriptional activator or as a repressor, depending on the promoter and cellular context [46] and is essential for erythroid and myeloid haematopoesis [47].…”

The Zinc Finger Transcription Factor Transforming Growth Factor β-Inducible Early Gene-1 Confers Myeloid-specific Activation of the Leukocyte Integrin CD11d Promoter

“…To understand the molecular mechanisms responsible for expression of CD11d, we previously isolated a genomic clone containing the 5Ј-untranslated portion of CD11d and showed that cell-specific expression of this gene is mediated through both Sp1 and Sp3 (15). Regulation by members of the Sp transcription factor family appears to be a common theme for expression of the leukocyte integrin genes as functional Sp1 sites are also found in the CD11a-c (16 -18) and CD18 (19) genes. Because a number of transcription factors, including PU.1, GABP␣, GABP␤, c-Jun, c-Fos, Ets, and c/EBP, were shown to functionally interact at sites adjacent to the Sp1 binding sites on the CD11a-c and CD18 genes (7), we reasoned that the CD11d promoter may also be regulated by transcription factors binding near the Sp1/Sp3 site.…”

GA-Binding Protein and p300 Are Essential Components of a Retinoic Acid-Induced Enhanceosome in Myeloid Cells

“…The proximal promoter, which includes the first 96 nucleotides upstream of the transcriptional start site, consists of two Sp1 sites and three ets-binding sites. Functional cooperation between Sp1 and the ets factors, GA-binding protein (GABP) and PU.1, increases expression of CD18 in myeloid cells (23,24,26). The distal enhancer, which lies nearly 1 kb upstream of the transcriptional start site, contains an RARE (6).…”