Transcriptional regulation of mouse L-selectin

L-selectin mediates the initial tethering and rolling of lymphocytes in high endothelial venules. To study the transcriptional regulation of mouse L-selectin, we cloned 4.5 kb 5'-flanking sequences of the mouse sell. Luciferase analysis of serial 5'-deletion mutants showed that the first 285 bp was sufficient to drive high promoter activity in EL4 cells, but not in Sell-negative HeLa cells, suggesting that this fragment harbors the minimal mouse sell promoter and contains cis-elements for lymphocyte-specific expression. Site-directed mutagenesis and chromatin immunoprecipitation showed that Mzf1, Klf2, Sp1, Ets1, and Irf1 bind to and activate the mouse sell promoter. Over expression of these transcription factors in EL4 cells increased expression of sell mRNA. Silencing the expression of Sp1 by siRNA significantly decreased sell promoter activity in EL4 cells. We conclude that sell transcription is regulated by Mzf1, Klf2, Sp1, Ets1, and Irf1.

Transcriptional regulation of L-selectin (35.19)

L-selectin mediates tethering and rolling of lymphocytes in high endothelial venules. To study the transcriptional regulation of L-selectin, we cloned 5′-flanking sequences of the murine L-selectin gene 1084 bp upstream of the translational start site. Analysis of the 5′-flanking sequence shows no TATA box, but an Initiator-like element present around position −104. Multiple transcription initiation sites were mapped between −119 and −15 by 5′RACE. Transfection of serially truncated 5′-flanking regions linked to a reporter gene in Jurkat and EL-4 cells identified that nucleotides −2 to −284 contained the elements to drive high level gene expression. Transfection of the constructs into COS 7 cells, which lacks L-seletin, showed negligible luciferase activity. Within this region we identified several cis-elements, including IRF-2, Sp1, Ets-1, MZF-1. Site-directed mutagenesis of the putative binding sites showed that both Sp1 and Ets binding sites were positive regulatory elements. EMSA and CHIP confirmed the specific binding of Sp1, MZF-1, and Ets1. These results provide a molecular basis for further investigation of the involvement of L-selectin in regulating lymphocyte tethering and rolling.

Induction of LFA-1-dependent neutrophil rolling on ICAM-1 by engagement of E-selectin

OBJECTIVE

To study rolling of mouse neutrophils on E-selectin and ICAM-1 in an ex vivo flow chamber system.

METHODS

The authors developed a small autoperfused flow chamber (20 x 200-microm cross section) that allows direct visualization of cells with and without fluorescent labeling and does not require recirculation of blood.

RESULTS

Neutrophils rolled on E-selectin alone, but were unable to interact with immobilized ICAM-1. When ICAM-1 was co-immobilized with E-selectin, the number of cells that rolled was doubled, but no significant firm adhesion was observed. This phenomenon was specific for E-selectin, and no enhancement of rolling was observed when P-selectin was immobilized with ICAM-1. The increased neutrophil rolling seen on E-selectin and ICAM-1 substrates required beta2 integrins. Treating mice with antibodies to the beta2 integrins LFA-1 and Mac-1 showed that LFA-1 was primarily responsible for mediating rolling on ICAM-1 in this model. Increased rolling on E-selectin and ICAM-1 was significantly reduced following administration of a specific p38 mitogen-activated protein kinase (MAPK) inhibitor.

CONCLUSION

The data show that neutrophil rolling on E-selectin leads to partial activation of LFA-1, enabling LFA-1-dependent rolling on ICAM-1. This mechanism is likely to amplify and accelerate neutrophil recruitment in inflammation.

A novel class of small functional peptides that bind and inhibit human alpha-thrombin isolated by mRNA display

Here we report the in vitro selection of novel small peptide motifs that bind to human alpha-thrombin. We have applied mRNA display to select for thrombin binding peptides from an unbiased library of 1.2 x 10(11) different 35-mer peptides, each containing a random sequence of 15 amino acids. Two clones showed binding affinities ranging from 166 to 520 nM. A conserved motif of four amino acids, DPGR, was identified. Clot formation of human plasma is inhibited by the selected clones, and they downregulate the thrombin-mediated activation of protein C. The identified peptide motifs do not share primary sequence similarities to any of the known natural thrombin binding motifs. As new inhibitors for human thrombin open interesting possibilities in thrombosis research, our newly identified peptides may provide further insights into this field of investigation and may be possible candidates for the development of new anti-thrombotic agents.