Paul J. Zavodny

Purification of ADAM 10 from bovine spleen as a TNFα convertase

We have purified a protease with characteristics of TNFα convertase from bovine spleen membranes. Peptide sequencing of the purified protein identified it as ADAM 10 (Genbank accession no. Z21961). This metalloprotease cleaves a recombinant proTNFα substrate to mature TNFα, and can cleave a synthetic peptide substrate to yield the mature TNFα amino terminus in vitro. The enzyme is sensitive to a hydroxamate inhibitor of MMPs, but insensitive to phosphoramidon. In addition, cloned ADAM 10 mediates proTNFα processing in a processing‐incompetent cell line.

Blocking ion channel KCNN4 alleviates the symptoms of experimental autoimmune encephalomyelitis in mice

The KCNN4 potassium‐ion channel has been reported to play an important role in regulating antigen‐induced T cell effector functions in vitro. This study presents the first evidence that a selective KCNN4 blocker, TRAM‐34, confers protection against experimental autoimmune encephalomyelitis (EAE) in the mouse model. Treatment with the KCNN4 blocker did not prevent infiltration of T cells in the spinal cord, but resulted in the reduction of both the protein and the message levels of TNF‐α and IFN‐γ as well as the message levels of several other pro‐inflammatory molecules in the spinal cord. Plasma concentrations of TRAM‐34 within a 24‐h period were between the in vitro IC50 and IC90 values for the KCNN4 channel. The effect of TRAM‐34 was reversible, as indicated by the development of clinical EAE symptoms within 48 h after withdrawal of treatment. In summary, our data support the idea that KCNN4 channels play a critical role in the immune response during the development of MOG‐induced EAE in C57BL/6 mice.

Evaluation of Signal Transduction Pathways in Chemoattractant-Induced Human Monocyte Chemotaxis

The intracellular signaling pathways involved in human monocyte chemotaxis toward a variety of chemoattractant molecules were evaluated using selected pharmacological agents. Neither phosphatidylinositol-3-kinase (PI3K) or extracellular signal-regulated kinase (ERK) activity were required for monocyte migration toward monocyte chemoattractant protein-1 (MCP-1), RANTES (Regulated on Activation, Normal T cell Expressed and Secreted), macrophage inflammatory protein-1α (MIP-1α) or formyl-Met-Leu-Phe (fMLP), since pretreatment with wortmannin or LY294002, or with PD098059, had no effect on the chemotactic response. Addition of forskolin and IBMX significantly attenuated chemotaxis to each of these chemoattractants and was reversed by co-treatment with Rp-cAMP, a competitive inhibitor of cAMP-dependent protein kinase A. Incubation with the protein kinase C (PKC) inhibitor GF109203X-HCl (GF109) did not affect monocyte migration, but pretreatment of monocytes with PMA significantly impaired the response to each of these chemotactic agents. Inhibition by PMA was reversed by co-treatment with GF109, implying that heterologous PKC activation is capable of desensitizing chemokine and fMLP-induced monocyte chemotaxis. These results help to define the signalling pathways involved in human monocyte chemotaxis and suggest pharmacological approaches to evaluating the cross-desensitization of chemoattractant-induced leukocyte migration.

Pharmacological characterization of the chemokine receptor, hCCR1 in a stable transfectant and differentiated HL-60 cells: antagonism of hCCR1 activation by MIP-1β

C‐C chemokine receptor‐1 (CCR1) has been implicated in mediating a variety of inflammatory conditions including multiple sclerosis and organ rejection. Although originally referred to as the MIP‐1α/RANTES receptor, CCR1 is quite promiscuous and can be activated by numerous chemokines. We used radioligand binding and [35S]‐GTPγS exchange assays in membranes from a cell line transfected to express CCR1 (Ba/F3‐hCCR1) to characterize a panel of chemokines (HCC‐1, MIP‐1α, MIP‐1β, MIP‐1δ, MPIF‐1, MCP‐2, MCP‐3, and RANTES) as CCR1 ligands. In this recombinant model, these chemokines displaced 125I‐MIP‐1α with a wide range of potencies and, with the exception of MCP‐2, acted as full agonists in stimulating [35S]‐GTPγS exchange. We then assessed the utility of HL‐60 cells cultured with known differentiating agents (PMA, DMSO, dibutyryl‐cAMP or retinoic acid) for investigating CCR1 pharmacology. In [35S]‐GTPγS exchange assays, membranes from cells cultured with retinoic acid (4–6 days) were the most responsive to activation by MIP‐1α and MPIF‐1. FACS analysis and comparative pharmacology confirmed that these activities were mediated by CCR1. Using [35S]‐GTPγS exchange assays, intracellular calcium flux and/or whole cell chemotaxis assays in HL‐60(Rx) cells, we validated that MIP‐1α was the most potent CCR1 ligand (MIP‐1α>MPIF‐1>RANTESMIP‐1β) although the ligands differed in their efficacy as agonists. MPIF‐1 was the more efficacious (MPIF‐1>RANTES=MIP‐1α>>MIP‐1β). 125I‐MIP‐1β binding in Ba/F3‐hCCR1 and HL‐60(Rx) membranes was competitively displaced by MIP‐1α, MPIF‐1 and MIP‐1β. The binding Ki for these chemokines with 125I‐MIP‐1β were essentially identical in the two membrane systems. Lastly, MIP‐1β antagonized [35S]‐GTPγS exchange, Ca2+ flux and chemotaxis in HL‐60(Rx) cells in response to robust agonists such as MIP‐1α, RANTES and MPIF‐1. Based on our results, we propose that MIP‐1β could function as an endogenous inhibitor of CCR1 function.

Expression of human inducible nitric oxide synthase in Escherichia coli

We have expressed active full‐length human inducible nitric oxide synthase (iNOS) in E. coli. Expression required co‐expression with calmodulin, a particularly tight‐binding cofactor. The extracts also required tetrahydrobiopterin to display activity. Specific activity of the purified recombinant iNOS was similar to iNOS purified from murine macrophages. This result indicates that no special processing events unique to eucaryotic cells are necessary for iNOS activity.

Pharmacological characterization of human S1P4 using a novel radioligand, [4,5-3H]-dihydrosphingosine-1-phosphate

Sphingosine‐1‐phosphate (S1P) is a bioactive lipid that affects a variety of cellular processes through both its actions as a second messenger and via activation of a family of G protein‐coupled receptors (S1P1–5). The study of S1P receptor pharmacology, particularly S1P4, has been hindered by the lack of high‐affinity radioligands with good specific activity. The studies presented herein characterize [3H]DH‐S1P as a stable, high‐affinity radioligand for S1P4 pharmacology. Using a transfected Ba/F3 cell line selected for high hS1P4 surface expression, we compared the consequences of different cellular backgrounds and commercial sources of sphingophospholipids on S1P4 characterization. The development and subsequent use of the assay described has enabled us to extensively and definitively characterize the pharmacology of the human S1P4 receptor.

A highly sensitive and specific assay using a novel human growth hormone cDNA reporter gene regulated by the human interleukin-4 inducible germline ε transcript promoter

We have successfully developed a highly sensitive and specific assay system for human interleukin-4 (IL-4) regulated gene expression. It is based on a human Jijoye cell line with the germline epsilon transcript promoter joined to the human growth hormone (hGH) cDNA. The germline epsilon transcript promoter is responsive to IL-4 and involved in immunoglobulin heavy chain class switching. We cloned hGH complementary DNA (cDNA) as the reporter gene instead of using conventional hGH genomic DNA which failed to generate any IL-4 inducible clone in human Jijoye cells. The two IL-4 inducible cell lines with the hGH cDNA reporter show high signal/noise ratio for IL-4-mediated induction (60-90 fold). The response to IL-4 is dose-dependent with ED50 of 10 pM. As expected, there is no response to other human cytokines and growth factors, as well as mouse IL-4. The mutant hIL-4 antagonist hIL-4.Y124D inhibits the induction mediated by native hIL-4. These IL-4 inducible cell lines provide a sensitive, specific assay system to study IL-4-regulated gene expression, and in particular the regulation of the germline epsilon promoter.