Human p150,95 alpha-subunit: genomic organization and analysis of the 5'-flanking region

Integrin αEβ7: molecular features and functional significance in the immune system

Alpha E beta 7 (αEβ7) is an α-I domain-containing integrin that is highly expressed by a variety of leukocyte populations at mucosal sites including intraepithelial T cells, dendritic cells, mast cells, and T regulatory cells (Treg). Expression depends largely or solely on transforming growth factor beta (TGF-β) isoforms. The best characterized ligand for αEβ7 is E-cadherin on epithelial cells, though there is evidence of a second ligand in the human system. An exposed acidic residue on the distal aspect of E-cadherin domain 1 interacts with the MIDAS site in the αE α-I domain. By binding to E-cadherin, αEβ7 contributes to mucosal specific retention of leukocytes within epithelia. Studies on αE knockout mice have identified an additional important function for this integrin in allograft rejection and have also indicated that it may have a role in immunoregulation. Recent studies point to a multifaceted role for αEβ7 in regulating both innate and acquired immune responses to foreign antigen.

Epigenetically mediated loss of UDP-GlcNAc 2-epimerase/ManNAc kinase expression in hyposialylated cell lines

The bifunctional enzyme UDP-GlcNAc 2-epimerase/ManNAc kinase is the key enzyme in sialic acid biosynthesis. Loss of UDP-GlcNAc 2-epimerase activity results in a hyposialylated phenotype as shown for two human hematopoietic cell lines that lack the specific mRNA. We found that treatment with the DNA methylation inhibitor 5'-aza-2'-deoxycytidine (5-aza-dC) restored the UDP-GlcNAc 2-epimerase/ManNAc kinase mRNA, as well as enzyme activity and cell surface sialylation. Increase of UDP-GlcNAc 2-epimerase activity by 5-aza-dC treatment was also found for a rat Morris hepatoma cell line. These results indicate a regulation of UDP-GlcNAc 2-epimerase/ManNAc kinase expression on the transcriptional level by DNA methylation.

The Haspin gene: location in an intron of the integrin alphaE gene, associated transcription of an integrin alphaE-derived RNA and expression in diploid as well as haploid cells

Haspin is a serine/threonine kinase, recently identified in mice, that is thought to regulate cell cycle and differentiation of haploid germ cells. Here, the haspin gene is identified within an intron of the integrin alphaE gene. Transcription occurs from a bi-directional CpG island-associated promoter that also generates an alternatively spliced integrin alphaE derived RNA. Remarkably, the human and murine haspin genes lack introns, and have features of retroposons. The human haspin cDNA reveals that the human and murine proteins are 83% identical in the C-terminal kinase domain, but only 53% identical in the N-terminal region. The haspin kinase domain has structural features that distinguish it from previously characterized proteins and suggest that haspin is a member of a new family of protein kinases. Although formerly thought to be expressed selectively in the testes, haspin is also transcribed at lower levels in thymus, bone marrow, fetal liver and other fetal tissues, and in all proliferating cell lines tested. Thus haspin is likely to be important in regulation of diploid as well as haploid cell differentiation in a variety of tissues.

Structural and functional characterization of the leukocyte integrin gene CD11d. Essential role of Sp1 and Sp3

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.

Sp3 mediates transcriptional activation of the leukocyte integrin genes CD11C and CD11B and cooperates with c-Jun to activate CD11C

The leukocyte integrin genes CD11c and CD11b are expressed predominately in myelomonocytic cells. In previous experiments, the -70 to -65 and -121 to -103 regions of the CD11c promoter and the -66 to -59 region of the CD11b promoter were shown to be essential for Sp1-mediated activation of these genes. In vivo genomic footprinting had also revealed cell-specific binding of protein, presumably Sp1, to these regions. In this study, electrophoretic mobility shift analysis showed that the Sp1-related factor, Sp3, also binds at or near these same regions. Cotransfection of Sp3 along with CD11c promoter-luciferase constructs into Sp-deficient Drosophila Schneider 2 cells showed that Sp3 could activate the CD11c promoter. Deletion of both the -70 to -65 and -121 to -103 regions of the CD11c promoter resulted in the loss of activation by Sp3. Both sites showed activation by Sp3; however, the -70 to -65 region was more responsive to Sp3 than to Sp1. Similar transfection analysis of the -66 to -59 region of the CD11b promoter showed Sp3-dependent expression. Further, cotransfection analysis in Drosophila cells showed that Sp3, as was previously shown for Sp1, also synergizes with c-Jun to activate CD11c. Antisense experiments that knocked out endogenous Sp3 expression in the myelomocytic cell line, HL60, revealed that Sp3 participates in activation of the CD11c and CD11b promoters in vivo.

Sp1 binds two sites in the CD11c promoter in vivo specifically in myeloid cells and cooperates with AP1 to activate transcription

The leukocyte integrin gene, CD11c, is transcriptionally regulated and is expressed predominantly on differentiated cells of the myelomonocytic lineage. In this study we have demonstrated that the regions -72 to -63 and -132 to -104 of the CD11c promoter contain elements responsible for phorbol ester-induced differentiation of the myeloid cell line HL60. DNase I footprinting analysis revealed that these regions can bind purified Sp1, and supershift analysis with Sp1 antibody confirmed that Sp1 in HL60 nuclear extracts could bind these regions. Transfection analysis of CD11c promoter-chloramphenicol acetyltransferase constructs containing deletions of these Sp1-binding sites revealed that these sites are essential for expression of the CD11c gene in HL60 cells but not in the T-cell line Molt4 or the cervical carcinoma cell line HeLa. Moreover, cotransfection of pPacSp1 along with these CD11c promoter-chloramphenicol acetyltransferase constructs into Sp1-deficient Drosophila Schneider 2 cells verified that these sites are essential for Sp1-dependent expression of the CD11c promoter. In vivo genomic footprinting revealed that Sp1 contacts the CD11c promoter within the regions -69 to -63 and -116 to -105 in phorbol 12-myristate 13-acetate-differentiated HL60 cells but not in undifferentiated HL60 cells or in Molt4 or HeLa cells. Cotransfection assays in HL60 cells revealed that Sp1 acts synergistically with Ap1 to activate CD11c. Further, both Sp1 sites are capable of cooperating with AP1. In vitro DNase I footprinting analysis with purified Sp1 and c-jun proteins showed that Sp1 binding could facilitate binding of c-jun. We propose that myeloid-specific expression of the CD11c promoter and is facilitated by cooperative interaction between the Sp1- and Ap1-binding sites.

Regulation of the leukocyte integrin gene CD11c is mediated by AP1 and Ets transcription factors

The leukocyte integrin gene, CD11c, encodes the chi subunit of the p150,95 (CD11c.CD18) receptor. Expression of the CD11c gene is predominately seen in monocytes, but has also been detected in some B- and T-cell neoplasms and in some large-cell lymphomas of uncertain origin. To elucidate the molecular mechanisms that govern the expression of CD11c, we have cloned and characterized the promoter region of this gene. The DNase I footprint and mobility shift analyses revealed five sites within the -86 to +40 region that interact with nuclear proteins. The -62 to -44 region contains two consensus sequences for AP1 (referred to as AP1-1 and AP1-2) and were shown to bind purified c-jun protein. Co-transfection of c-fos and c-jun expression constructs with a CD11c promoter-CAT fusion into HL60 cells led to a 6.7-fold increase in CD11c promoter activity. We show that c-fos and c-jun mediate their effects through both AP1-1 and AP1-2 which function in an additive manner. Regions -42 to -34 and -13 to -5 contain consensus sequences for Ets factors (referred to as Ets C and Ets A, respectively). Deletion of Ets resulted in a significant reduction in phorbol ester-induced expression of CD11c, whereas deletion of Ets A led to only a modest loss in CD11c expression. We show that Ets C cooperates with the AP1 sites to regulate CD11c expression.

The leukocyte integrin gene CD11c is transcriptionally regulated during monocyte differentiation

The leukocyte integrins, LFA-1, Mac-1 and p150,95, are heterodimeric proteins that consist of a distinct alpha and a common beta subunit. The beta subunit gene (CD18) is constitutively expressed on all leukocytes, however, the alpha subunit genes for LFA-1, Mac-1 and p150,95 (CD11a, CD11b and CD11c, respectively) show cell- and developmental stage-specific expression. We investigated the regulation of the CD11c gene in the promyeloblastic leukemic cell line, HL60, following differentiation along the monocytic pathway with phorbol 12-myristate 13-acetate (PMA). The steady-state level of CD11c mRNA increased markedly over 48 hr from the undetectable level present before differentiation. The half-life of CD11c MRNA in differentiated HL60 cells was not unusually long and similar to that of CD18 mRNA found in both undifferentiated and differentiated cells which suggested that altered mRNA stability did not account for the appearance of CD11c mRNA. Nuclear run-on analysis revealed that transcriptional activation during differentiation resulted in the appearance of CD11c mRNA. Inhibition of protein synthesis by cycloheximide in undifferentiated HL60 cells did not result in transcriptional activation of the CD11c gene. However, there was a significant increase (approximately eight-fold) in the steady-state level of CD18 mRNA which was not the result of transcriptional activation. Inhibition of protein synthesis in differentiated HL60 cells did not lead to significant changes in the steady-state levels of either CD11c or CD18 mRNAs. These findings indicated that the CD11c gene is regulated by transcriptional mechanisms which require prior protein synthesis. Transcriptional activation of the CD18 gene as a result of differentiation with PMA also requires protein synthesis. Further, in the absence of protein synthesis in undifferentiated HL60 cells, post-transcriptional mechanisms stabilize CD18 mRNA.