Generation of GPI-linked CCL5 based chemokine receptor antagonists for the suppression of acute vascular damage during allograft transplantation

Limiting the acute vascular damage associated with leukocyte infiltration is a central issue in solid organ transplantation. The family of chemotactic cytokines (chemokines) helps to regulate leukocyte recruitment. Systemic treatment with the chemokine ligand-5 (CCL5) based antagonist Met-RANTES has previously shown to suppress acute damage to transplanted kidneys by blocking effector cell recruitment. To address problems associated with systemic long-term administration of chemokine receptor antagonists, a chemokine based reagent was designed to be integrated into endothelial surfaces of the organ just before transplantation. Proteins anchored by glycosylphosphatidylinositol (GPI), when purified and added to cells, are efficiently incorporated into their cell surface membranes. A series of modifications were introduced into the CCL5 protein to generate a functional antagonist. These included the addition of an N-terminal methionine group, a mutation to render the protein a dimer and a GPI signal sequence for surface expression. The resultant protein was stably expressed in CHO cells, GPI anchorage was confirmed and the protein purified by FPLC. Exogenously administered Met-CCL5(dimer)-GPI was efficiently inserted into the membrane of microvascular endothelial cells. The reagent is being tested in murine models of renal transplantation. The effect on subsequent immune induced damage will be assessed.

Exogenously added GPI-anchored tissue inhibitor of matrix metalloproteinase-1 (TIMP-1) displays enhanced and novel biological activities

The family of tissue inhibitors of metalloproteinases (TIMPs) exhibits diverse physiological/biological functions including the inhibition of active matrix metalloproteinases, regulation of proMMP activation, cell growth, and the modulation of angiogenesis. TIMP-1 is a secreted protein that can be detected on the cell surface through its interaction with surface proteins. The diverse biological functions of TIMP-1 are thought to lie, in part, in the kinetics of TIMP-1/MMP/surface protein interactions. Proteins anchored by glycoinositol phospholipids (GPIs), when purified and added to cells in vitro, are incorporated into their surface membranes. A GPI anchor was fused to TIMP-1 to generate a reagent that could be added directly to cell membranes and thus focus defined concentrations of TIMP-1 protein on any cell surface independent of protein-protein interaction. Unlike native TIMP-1, exogenously added GPI-anchored TIMP-1 protein effectively blocked release of MMP-2 and MMP-9 from osteosarcoma cells. TIMP-1-GPI was a more effective modulator of migration and proliferation than TIMP-1. While control hTIMP-1 protein did not significantly affect migration of primary microvascular endothelial cells at the concentrations tested, the GPI-anchored TIMP-1 protein showed a pronounced suppression of endothelial cell migration in response to bFGF. In addition, TIMP-1-GPI was more effective at inducing microvascular endothelial proliferation. In contrast, fibroblast proliferation was suppressed by the agent. Reagents based on this method should assist in the dissection of the protease cascades and activities involved in TIMP biology. Membrane-fixed TIMP-1 may represent a more effective version of the protein for use in therapeutic expression.

Identification of a signal transduction pathway that regulates MMP-9 mRNA expression in glomerular injury

Podocytes contribute to the filtration barrier within the kidney. The integrin-linked kinase (ILK) plays an important role in podocyte adhesion to the glomerular basement membrane, signal transduction and phenotype regulation. We demonstrate that ILK activity is also associated with upregulation of matrix metalloproteinase-9 (MMP-9) mRNA levels during podocyte stress. A synthetic ILK inhibitor blocked MMP-9 mRNA upregulation but showed no effect on TIMP-1 or MMP-2 mRNA expression. Interestingly, a corresponding increase in MMP-9 secretion was not observed, suggesting that MMP-9 mRNA production in podocytes is regulated via ILK, whereas additional signaling pathways may mediate the post-transcriptional regulation of MMP-9.

Molecular and in silico characterization of a promoter module and C/EBP element that mediate LPS-induced RANTES/CCL5 expression in monocytic cells

The chemokine RANTES/CCL5 is a proinflammatory agent produced by a variety of tissues in response to specific stimuli. In human monocytes, RANTES/CCL5 transcription is up-regulated rapidly and transiently in response to LPS. We describe here two regions that help control LPS-driven transcription from the human RANTES/CCL5 promoter in monocytic cells. These sites were analyzed by using DNase I footprinting, transient transfection assays, site-directed mutagenesis, and EMSA. RANTES site E (R(E), -125/-99) constitutively binds C/EBP proteins in monocytic Mono Mac 6 cells. Mutation of region R(E) led to a significant (40%-50%) reduction in LPS-induced promoter reporter activity. Region R(AB) is composed of tandem kB-like elements R(A) and R(B) (-73/-34). These sites working in concert act as an LPS-responsive promoter module. R(A) constitutively binds Sp1, and Rel p50/p65 following LPS stimulation. Either factor can mediate transcriptional effects at R(A). Induced Rel p50/p50 binding to site R(B) is required for LPS regulation of RANTES/CCL5 transcription. A series of computer models based on the RANTES/CCL5 promoter were generated to represent the organization of these functional elements. The models could identify LPS-regulated promoters in human, other vertebrate, and viral sequences in various databases.

ATF and Jun transcription factors, acting through an Ets/CRE promoter module, mediate lipopolysaccharide inducibility of the chemokine RANTES in monocytic Mono Mac 6 cells

The chemokine RANTES is produced by a variety of tissues, including cells of the monocyte/macrophage lineage. RANTES expression is rapidly and transiently up-regulated in primary monocytes and the monocytic cell line Mono Mac 6 in response to stimulation by the bacterial product lipopolysaccharide (LPS). Transient transfection of Mono Mac 6 cells with RANTES reporter-promoter deletion constructs, in conjunction with DNase I footprinting and heterologous reporter gene assays, allowed identification of an LPS-responsive region within the RANTES promoter. Electrophoretic mobility shift assays (EMSA), methylation interference and EMSA supershift experiments were used to characterize sequences and transcription factors responsible for this LPS inducibility. The region, termed RANTES site G [R(G)], contains consensus sites for Ets and CRE/AP-1-like elements. Site-directed mutagenesis of the Ets site resulted in a loss of only 15 % of promoter activity, while mutation of the CRE/AP-1 site led to a loss of 40 % of LPS-induced promoter activity. The Ets site constitutively binds the Ets family member PU.1. LPS stimulation leads to an induction of ATF-3 and JunD factor binding to the CRE/AP-1 site. Thus, LPS induction of RANTES transcription is mediated, in part, through the activation and selective binding of ATF and Jun nuclear factors to the R(G) promoter module.