A new quantitative cytometric technique, termed the ArrayScan™, is described and used to measure NF-B nuclear translocation induced by interleukin (IL)-1 and tumor necrosis factor-␣ (TNF␣). The amount of p65 staining is measured in both the nuclei defined by Hoechst 33342 labeling and in the surrounding cytoplasmic area within a preselected number of cells/well in 96-well plates. Using this technique in synchronously activated human chondrocytes or HeLa cells, NF-B was found to move to the nucleus with a half-time of 7-8 min for HeLa and 12-13 min for chondrocytes, a rate in each case about 4 -5 min slower than that of IB␣ degradation. IL-1 receptor antagonist and anti-TypeI IL-1 receptor antiserum on the one hand and anti-TNF␣ and monoclonal anti-TNF receptor 1 antibodies on the other hand could be shown to respectively inhibit IL-1 and TNF␣ stimulation in both cell types. In contrast, a polyclonal anti-TNF receptor 1 antiserum exhibited both a 50% agonism and a 50% antagonism to a TNF␣ stimulation in a dose-dependent fashion, indicating that subtle functional responses to complex agonist and antagonist stimuli could be measured. The effects of different proteasome inhibitors to prevent IB␣ degradation and subsequent NF-B translocation could also be discriminated; LeuLeu-Leu aldehyde was only a partial inhibitor with an IC 50 of 2 M, while clastolactacystin ␤-lactone was a complete inhibitor with an IC 50 of 10 M. The nonselective kinase inhibitor K252a completely inhibited both IL-1 and TNF␣ stimulation in both cell types with an IC 50 of 0.4 M. This concentration, determined after a 20-min stimulation, was shown to be comparable with that obtained for inhibition of IL-6 production induced by a 100-fold lower IL-1 and TNF␣ concentration measured after 17 h of stimulation. These results suggest that the ArrayScan™ technology provides a rapid, sensitive, quantitative technique for measuring early events in the signal transduction of NF-B. IL-11 and TNF␣ are two master cytokines that induce an almost identical proinflammatory response, including the production of chemotactic cytokines, adhesion molecules, and enzymes such as cyclooxygenase, nitric-oxide synthetase, and matrix metalloproteinases (1, 2). Many of these effects are a result of the activation by both IL-1 and TNF␣ of the NF-B transcription factor pathway, which is associated with the activation of many cellular defense genes (3, 4). Composed of p65 (RelA) and p50 proteins, NF-B is normally present in the cytoplasm in an inactive state in a complex with members of the IB inhibitor protein family, chiefly the 37-kDa IB␣ form. In this complexed form, a nuclear localization sequence found on NF-B is masked by the IB␣, preventing nuclear translocation of NF-B, DNA binding, and subsequent transcriptional activation (5-12). IL-1 or TNF␣ receptor activation induces within several minutes the specific phosphorylation of Ser 32 and Ser 36 on IB␣, the destruction of the phosphorylated IB␣ protein by proteasomes, and the translocation of NF-B to the nucleus (13-1...

Many G-protein coupled receptors (GPCRs) undergo ligand-dependent homologous desensitization and internalization. Desensitization, defined as a decrease in the responsiveness to ligand, is accompanied by receptor aggregation on the cell surface and internalization via clathrin-coated pits to an intracellular endosomal compartment. In this study, we have taken advantage of the trafficking properties of GPCRs to develop a useful screening method for the identification of receptor mimetics. A series of studies were undertaken to evaluate the expression, functionality, and ligand-dependent trafficking of GPCR-green fluorescent protein (GFP) fusion conjugates stably transfected into HEK 293 cells. These GPCR-GFP expressing cells were then utilized in the validation of the ArrayScan™ (Cellomics™, Pittsburgh, PA), a microtiter plate imaging system that permits cellular and subcellular quantitation of fluorescence in whole cells. These studies demonstrated our ability to measure the internalization of a parathy-roid hormone (PTH) receptor-GFP conjugate after ligand treatment by spatially resolving internalized receptors. Internalization was time- and dose-dependent and appeared to be selective for PTH. Similar results were obtained for a β2-adrenergic receptor (β2AR)-GFP conjugate stably expressed in HEK 293 cells. The internalized GFP-labeled receptors were visualized as numerous punctate "spots" within the cell interior. An algorithm has been developed that identifies and collects information about these spots, allowing quantification of the internalization process. Variables such as the receptor-GFP expression level, plating density, cell number per field, number of fields scanned per well, spot size, and spot intensity were evaluated during the development of this assay. The method represents a valuable tool to screen for receptor mimetics and antagonists of receptor internalization in whole cells rapidly.

Epidermal growth factor (EGF) stimulates membrane protein phosphorylation in a human cell line, A-431. The known hepatic mitogenic action ofEGF and the reduction in EGF receptor number that occurs during liver regeneration led us to study whether EGF-dependent protein kinase activity was present in rat liver and whether its activity was altered after partial hepatectomy. Liver membranes, preincubated with or without EGF, were phosphorylated (0C, 15 sec) and subjected to NaDodSOd polyacrylamide gel electrophoresis and autoradiography. In microsomal fractions, EGF at 5-2000 ng/ml produced a dose-related stimulation of 32p incorporation into a single 170,000-dalton protein (p170). In plasma membranes, a similar EGF-dependent phosphorylation was present and was substantially enriched relative to the microsomal fraction. Acid hydrolysis of labeled microsomal fraction followed by ehosphoamino acid determination revealed that EGF stimulated 2p incorporation into phosphotyrosine residues. The EGF-dependent phosphorylation ofp170 was compared in microsomal fractions isolated from rats 36 hr after partial hepatectomy or sham operation. In the absence of EGF, in vitro labeling of p170 was similar. EGF stimulated the labeling of p170 in both groups, but the response was clearly diminished after partial hepatectomy. In the presence of EGF, the labeling of p170 in microsomal fraction from regenerating livers was only 47 ± 6% of that observed in membranes from sham-operated rats (P < 0.005). Reduction ofEGF-dependent phosphorylation during liver regeneration paralleled the loss of binding of '2I-labeled EGF. An increase in the EGF-independent phosphorylation of a 130,000-dalton protein was also observed after partial hepatectomy. The increase in the amount of this phosphoprotein was roughly equal to the loss ofEGF-stimulated p170 phosphorylation. Several additional proteins showed increased phosphorylation in membranes from partially hepatectomized rats. These findings indicate that alterations in membrane tyrosine residue phosphorylation occur during regulated growth in viva Epidermal growth factor (EGF) is mitogenic in many cultured cell lines (1) and stimulates DNA synthesis in hepatocytes, both in vitro (2) and in vivo (3). The plasma membrane receptor for EGF, a 150,000-to 180,000-dalton glycoprotein, binds EGF with high affinity and is subsequently internalized (1, 4). EGF rapidly alters ion and nutrient flux, but more prolonged exposure is needed to stimulate DNA synthesis (5). The mechanism by which EGF exerts these actions has not been established, but Carpenter et al (6) have shown that EGF stimulates the phosphorylation ofa number ofproteins in membranes from a human epidermoid carcinoma cell line, A-431. Cohen et at (7) have shown that the major protein phosphorylated in the EGF-dependent manner copurifies with the EGF receptor itself. The EGF-stimulated phosphorylation ofthe EGF receptor occurs in part on tyrosine residues both in cell membranes (8) and in cultured cells (9).Protein phosphorylation on tyr...

Epidermal growth factor, a potent mitogen, stimulates phosphorylation of its 170,000-dalton plasma membrane receptor. Dimethyl sulfoxide selectively increased phosphorylation of the epidermal growth factor receptor in rat liver microsomal fraction. Maximal stimulation occurred at 15 to 25 percent dimethyl sulfoxide and resembled the effect of epidermal growth factor in magnitude and rapidity. Like epidermal growth factor, dimethyl sulfoxide selectively stimulated tyrosine residue phosphorylation of this protein.