The epidermal growth factor receptor family as a central element for cellular signal transduction and diversification

Homeostasis of multicellular organisms is critically dependent on the correct interpretation of the plethora of signals which cells are exposed to during their lifespan. Various soluble factors regulate the activation state of cellular receptors which are coupled to a complex signal transduction network that ultimately generates signals defining the required biological response. The epidermal growth factor receptor (EGFR) family of receptor tyrosine kinases represents both key regulators of normal cellular development as well as critical players in a variety of pathophysiological phenomena. The aim of this review is to give a broad overview of signal transduction networks that are controlled by the EGFR superfamily of receptors in health and disease and its application for target-selective therapeutic intervention. Since the EGFR and HER2 were recently identified as critical players in the transduction of signals by a variety of cell surface receptors, such as G-protein-coupled receptors and integrins, our special focus is the mechanisms and significance of the interconnectivity between heterologous signalling systems.

Can a decline in the population means of cardiovascular risk factors reduce the number of people at risk?

OBJECTIVE

To prove the possibility of shifting distribution of cardiovascular risk factors for a whole population over time and thereby to influence the prevalence of the corresponding disease states, according to the theory stated by Geoffrey Rose in 1985.

DESIGN

Examination of standardised data from the German Cardiovascular Prevention Study (GCP), a seven year long, population-based, multicentre intervention trial, concerned with decreasing risk factors for cardiovascular disease.

SETTING AND SUBJECTS

three cross sectional surveys of a population 25 to 69 years old in six study regions, and three nationwide cross sectional surveys in the former West Germany in 1984, 1988 and 1991.

MAIN OUTCOME MEASURES

The relation between the population mean for systolic and diastolic blood pressure, total serum cholesterol, body mass index, and alcohol intake, and the prevalence of the corresponding disease states, as are systolic (> or =140 and > or =160 mm Hg) and diastolic hypertension (> or =90 and > or =95 mm Hg), hypercholesterolaemia (> or =250 and > or =300 mg/dl), overweight (body mass index > or =30 kg/m2), and heavy drinking (weekly alcohol intake > or =300 g/week). Results are expressed as linear regression equations and Pearson correlation coefficients.

RESULTS

The correlation between the mean population values and prevalence of disease was close for blood pressures and body mass index. The Pearson coefficients, corrected for the influence of values increased above borderlines, were 0.86 and 0.81 respectively for systolic blood pressure, 0.88 and 0.91 for diastolic blood pressure, 0.28 and 0.52 for cholesterol, and 0.86 for the body mass index. The coefficient for alcohol intake was 0.55.

CONCLUSIONS

It seems possible to shift the risk distribution of a population for some physiological parameters over time with the effect of changing the disease prevalence. This strategy can be used successfully for specific preventive measures, as was strongly advocated by Geoffrey Rose.

Molecular characterization of a cDNA encoding functional human CLK4 kinase and localization to chromosome 5q35 [correction of 4q35]

Phosphorylated serine- and arginine-rich (SR) proteins play an important role in the formation of spliceosomes, possibly controlling the regulation of alternative splicing. Enzymes that phosphorylate the SR proteins belong to the family of CDC2/CDC28-like kinases (CLK). Employing nucleotide sequence comparison of human expressed sequence tag sequences to the murine counterpart, we identified, cloned, and recombinantly expressed the human orthologue to the murine CLK4 cDNA. When fused to glutathione S-transferase, the catalytically active human CLK4 is able to autophosphorylate and to phosphorylate myelin basic protein, but not histone H2B as a substrate. Inspection of mRNA accumulation demonstrated gene expression in all human tissues, with the most prominent abundance in liver, kidney, brain, and heart. Using fluorescence in situ hybridization, the human CLK4 cDNA was localized to band q35 on chromosome 5 [corrected].

A novel role for protein tyrosine phosphatase shp1 in controlling glial activation in the normal and injured nervous system

Tyrosine phosphorylation regulated by protein tyrosine kinases and phosphatases plays an important role in the activation of glial cells. Here we examined the expression of intracellular protein tyrosine phosphatase SHP1 in the normal and injured adult rat and mouse CNS. Our study showed that in the intact CNS, SHP1 was expressed in astrocytes as well as in pyramidal cells in hippocampus and cortex. Axotomy of peripheral nerves and direct cortical lesion led to a massive upregulation of SHP1 in activated microglia and astrocytes, whereas the neuronal expression of SHP1 was not affected. In vitro experiments revealed that in astrocytes, SHP1 associates with epidermal growth factor (EGF)-receptor, whereas in microglia, SHP1 associates with colony-stimulating factor (CSF)-1-receptor. In postnatal and adult moth-eaten viable (me(v)/me(v)) mice, which are characterized by reduced SHP1 activity, a strong increase in reactive astrocytes, defined by GFAP immunoreactivity, was observed throughout the intact CNS, whereas neither the morphology nor the number of microglial cells appeared modified. Absence of (3)[H]-thymidine-labeled nuclei indicated that astrocytic proliferation does not occur. In response to injury, cell number as well as proliferation of microglia were reduced in me(v)/me(v) mice, whereas the posttraumatic astrocytic reaction did not differ from wild-type littermates. The majority of activated microglia in mutant mice showed rounded and ameboid morphology. However, the regeneration rate after facial nerve injury in me(v)/me(v) mice was similar to that in wild-type littermates. These results emphasize that SHP1 as a part of different signaling pathways plays an important role in the global regulation of astrocytic and microglial activation in the normal and injured CNS.

Distracting painful injuries associated with cervical spinal injuries in blunt trauma

Distracting painful injuries (DPIs) may mask symptoms of spinal injury in blunt trauma victims and form an important element in a decision instrument used to identify individuals who require cervical spine radiography.

OBJECTIVE

To identify the types and frequencies of injuries that actually act as DPIs among blunt trauma patients undergoing cervical spinal radiography.

METHODS

This was a prospective observational study of consecutive blunt trauma victims presenting to an urban Level 1 regional trauma center between April 1, 1998, and September 30, 1998. Prior to cervical spinal radiography, treating physicians evaluated each patient to determine whether a DPI was present or absent and, if present, what type of injury was sustained. Injuries were categorized as fractures, soft-tissue injuries and lacerations, burns, visceral injuries, crush injuries, or other injuries.

RESULTS

Data were collected for 778 patients, between 1 month and 98 years old, of whom 264 (34%) were considered to have DPIs. Physicians were unable to determine the DPI status in 47 (6%) additional cases. Fractures accounted for a majority of DPIs (154, or 58%), 42 (16%) were soft-tissue injuries or lacerations, and 86 (34%) were due to a variety of other entities, including visceral, crush, burn, or other miscellaneous injuries. Among the 37 (5%) patients with an acute cervical spinal injury, 20 (54%) had a DPI, including three (8%) who had DPI as the only indication for cervical radiography.

CONCLUSIONS

A significant number of blunt trauma patients are believed by clinicians to have DPIs that can possibly mask the presence of cervical spinal injury. Fractures and trauma to soft tissues are the most common types of DPI.

Cloning and characterization of secretory tyrosine phosphatases of Mycobacterium tuberculosis

Two genes with sequence homology to those encoding protein tyrosine phosphatases were cloned from genomic DNA of Mycobacterium tuberculosis H(37)Rv. The calculated molecular masses of these two putative tyrosine phosphatases, designated MPtpA and MPtpB, were 17. 5 and 30 kDa, respectively. MPtpA and MPtpB were expressed as glutathione S-transferase fusion proteins in Escherichia coli. The affinity-purified proteins dephosphorylated the phosphotyrosine residue of myelin basic protein (MBP), but they failed to dephosphorylate serine/threonine residues of MBP. The activity of these phosphatases was inhibited by sodium orthovanadate, a specific inhibitor of tyrosine phosphatases, but not by okadaic acid, an inhibitor of serine/threonine phosphatases. Mutations at the catalytic site motif, cysteine 11 of MPtpA and cysteine 160 of MPtpB, abolished enzyme activity. Southern blot analysis revealed that, while mptpA is present in slow-growing mycobacterial species as well as fast-growing saprophytes, mptpB was restricted to members of the M. tuberculosis complex. These phosphatases were present in both whole-cell lysates and culture filtrates of M. tuberculosis, suggesting that these proteins are secreted into the extracellular medium. Since tyrosine phosphatases are essential for the virulence of several pathogenic bacteria, the restricted distribution of mptpB makes it a good candidate for a virulence gene of M. tuberculosis.

Negative regulation of growth hormone receptor/JAK2 signaling by signal regulatory protein alpha

Signal regulatory proteins (SIRPs) are receptor-like transmembrane proteins, the majority of which contain a cytoplasmic proline-rich region and four cytoplasmic tyrosines that, when phosphorylated, bind SH2 domain-containing protein tyrosine phosphatases (SHP). We demonstrated previously that growth hormone (GH) induces tyrosyl phosphorylation of SIRPalpha and association of SIRPalpha with SHP-2. The GH-activated tyrosine kinase JAK2 associates with and tyrosyl-phosphorylates SIRPalpha1. Here we show that JAK2-SIRPalpha1 association does not require phosphotyrosines in SIRPalpha1 or JAK2 or the proline-rich region of SIRPalpha1. However, when the C-terminal 30 amino acids of SIRPalpha1 containing the proline-rich region and tyrosine 495 are deleted, tyrosyl phosphorylation of SIRPalpha1 by JAK2 and association of SHP-2 with SIRPalpha1 are reduced. GH-dependent tyrosyl phosphorylation of JAK2 is reduced when wild-type SIRPalpha1 compared with SIRPalpha1 lacking the four cytoplasmic tyrosines (SIRP 4YF) is expressed in cells, suggesting that SIRPalpha1 negatively regulates GHR/JAK2 signaling. Consistent with reduced JAK2 activity, overexpression of wild-type SIRPalpha1 but not SIRP 4YF reduces GH-induced phosphorylation of ERKs 1 and 2, STAT3, and STAT5B. These results suggest that SIRPalpha1 is a negative regulator of GH signaling and that the ability of SIRPalpha1 mutants to negatively regulate GHR-JAK2 signaling correlates with their ability to bind SHP-2.

Inhibition of EGFR-mediated phosphoinositide-3-OH kinase (PI3-K) signaling and glioblastoma phenotype by signal-regulatory proteins (SIRPs)

Several growth factors and cytokines, including EGF, are known to induce tyrosine phosphorylation of Signal Regulatory Proteins (SIRPs). Consistent with the idea that increased phosphorylation activates SIRP function, we overexpressed human SIRPalpha1 in U87MG glioblastoma cells in order to examine how SIRPalpha1 modulates EGFR signaling pathways. Endogenous EGFR proteins are overexpressed in U87MG cells and these cells exhibit survival and motility phenotypes that are influenced by EGFR kinase activity. Overexpression of the SIRPalpha1 cDNA diminished EGF-induced phosphoinositide-3-OH kinase (PI3-K) activation in U87MG cells. Reduced EGF-stimulated activation of PI3-K was mediated by interactions between carboxyl terminus of SIRPalpha1 and the Src homology-2 (SH2)-containing phosphotyrosine phosphatase, SHP2. SIRPalpha1 overexpression also reduced the EGF-induced association between SHP2 and the p85 regulatory subunit of PI3-K. Inhibition of transformation and enhanced apoptosis following gamma-irradiation were observed in SIRPalpha1-overexpressing U87MG cells, and enhanced apoptosis was associated with reduced levels of bcl-xL protein. Furthermore, SIRPalpha1-overexpressing U87MG cells displayed reduced cell migration and cell spreading that was mediated by association between SIRPalpha1 and SHP2. However, SIRPalpha1-overexpressing U87MG clonal derivatives exhibited no differences in cell growth or levels of mitogen-activated protein kinase (MAPK) activation. These data reveal a pathway that negatively regulates EGFR-induced PI3-K activation in glioblastoma cells and involves interactions between SHP2 and tyrosine phosphorylated SIRPalpha1. These results also suggest that negative regulation of PI3-K pathway activation by the SIRP family of transmembrane receptors may diminish EGFR-mediated motility and survival phenotypes that contribute to transformation of glioblastoma cells. Oncogene (2000) 19, 3999 - 4010.

Targeting angiogenesis inhibits tumor infiltration and expression of the pro-invasive protein SPARC

The solid growth of high-grade glioma appears to be critically dependent on tumor angiogenesis. It remains unknown, however, whether the diffuse infiltration of glioma cells into healthy adjacent tissue is also dependent on the formation of new tumor vessels. Here, we analyze the relationship between tumor angiogenesis and tumor cell infiltration in an experimental glioma model. C6 cells were implanted into the dorsal skinfold chamber of nude mice, and tumor angiogenesis was monitored by intravital fluorescence videomicroscopy. Glioma infiltration was assessed by the extent of tumor cell invasion into the adjacent chamber tissue and by expression of SPARC, a cellular marker of glioma invasiveness. To test the hypothesis that glioma angiogenesis and glioma infiltration are codependent, we assessed tumor infiltration in both the presence and the absence of the angiogenesis inhibitor SU5416. SU5416 is a selective inhibitor of the VEGF/Flk-1 signal-transduction pathway, a critical pathway implicated in angiogenesis. Control tumors demonstrated both high angiogenic activity and tumor cell invasion accompanied by strong expression of SPARC in invading tumor cells at the tumor-host tissue border. SU5416-treated tumors demonstrated reduced vascular density and vascular surface in the tumor periphery accompanied by marked inhibition of glioma invasion and decreased SPARC expression. A direct effect of SU5416 on glioma cell motility and invasiveness was excluded by in vitro migration and invasion assays. These results suggest a crucial role for glioma-induced angiogenesis as a prerequisite for diffuse tumor invasion and a possible therapeutic role for anti-angiogenic compounds as inhibitors of both solid and diffuse infiltrative tumor growth.

Association of signal-regulatory proteins beta with KARAP/DAP-12

The signal-regulatory proteins (SIRP) are Ig-like cell surface receptors detected in hematopoietic and non-hematopoietic cells. SIRP are classified as SIRPalpha molecules, containing a 110- to 113-amino acid long, or SIRPbeta molecules, with a 5-amino acid long intracytoplasmic domain. SIRPalpha molecules belong to inhibitory immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing molecules. The majority of ITIM-bearing receptors are paired with activating isoforms, which share highly related extracytoplasmic domains but harbor a shorter cytoplasmic domain devoid of ITIM and contain a charged amino acid residue in their transmembrane domain. Activating receptors are associated with immunoreceptor tyrosine-based activation motif (ITAM)-bearing proteins, such as KARAP/DAP-12 and FcRgamma. In this report, we show that human SIRPbeta1 is included in an oligomeric complex with KARAP/DAP-12 in hematopoietic and non-hematopoietic transfectant cells as well as in human monocytes. The physical association between SIRPbeta1 and KARAP/DAP-12 results in the functional coupling of SIRPbeta1 engagement to the recruitment of the protein tyrosine kinase Syk and to serotonin release in RBL cell transfectants. Therefore our results show that SIRPbeta1 acts as an activating isoform of SIRPalpha molecules, confirming the co-existence of inhibitory ITIM-bearing molecules, recruiting SHP-1 and SHP-2 protein tyrosine phosphatases, and activating counterparts, whose engagement couples to protein tyrosine kinases via ITAM-bearing molecules.

SU6668 is a potent antiangiogenic and antitumor agent that induces regression of established tumors

Vascular endothelial growth factor, fibroblast growth factor (FGF), and platelet-derived growth factor (PDGF) and their cognate receptor tyrosine kinases are strongly implicated in angiogenesis associated with solid tumors. Using rational drug design coupled with traditional screening technologies, we have discovered SU6668, a novel inhibitor of these receptors. Biochemical kinetic studies using isolated Flk-1, FGF receptor 1, and PDGF receptor beta kinases revealed that SU6668 has competitive inhibitory properties with respect to ATP. Cocrystallographic studies of SU6668 in the catalytic domain of FGF receptor 1 substantiated the adenine mimetic properties of its oxindole core. Molecular modeling of SU6668 in the ATP binding pockets of the FIk-1/KDR and PDGF receptor kinases provided insight to explain the relative potency and selectivity of SU6668 for these receptors. In cellular systems, SU6668 inhibited receptor tyrosine phosphorylation and mitogenesis after stimulation of cells by appropriate ligands. Oral or i.p. administration of SU6668 in athymic mice resulted in significant growth inhibition of a diverse panel of human tumor xenografts of glioma, melanoma, lung, colon, ovarian, and epidermoid origin. Furthermore, intravital multifluorescence videomicroscopy of C6 glioma xenografts in the dorsal skinfold chamber model revealed that SU6668 treatment suppressed tumor angiogenesis. Finally, SU6668 treatment induced striking regression of large established human tumor xenografts. Investigations of SU6668 activity in cancer patients are ongoing in Phase I clinical trials.

Targeting angiogenesis inhibits tumor infiltration and expression of the pro-invasive protein SPARC

The solid growth of high-grade glioma appears to be critically dependent on tumor angiogenesis. It remains unknown, however, whether the diffuse infiltration of glioma cells into healthy adjacent tissue is also dependent on the formation of new tumor vessels. Here, we analyze the relationship between tumor angiogenesis and tumor cell infiltration in an experimental glioma model. C6 cells were implanted into the dorsal skinfold chamber of nude mice, and tumor angiogenesis was monitored by intravital fluorescence videomicroscopy. Glioma infiltration was assessed by the extent of tumor cell invasion into the adjacent chamber tissue and by expression of SPARC, a cellular marker of glioma invasiveness. To test the hypothesis that glioma angiogenesis and glioma infiltration are codependent, we assessed tumor infiltration in both the presence and the absence of the angiogenesis inhibitor SU5416. SU5416 is a selective inhibitor of the VEGF/Flk-1 signal-transduction pathway, a critical pathway implicated in angiogenesis. Control tumors demonstrated both high angiogenic activity and tumor cell invasion accompanied by strong expression of SPARC in invading tumor cells at the tumor-host tissue border. SU5416-treated tumors demonstrated reduced vascular density and vascular surface in the tumor periphery accompanied by marked inhibition of glioma invasion and decreased SPARC expression. A direct effect of SU5416 on glioma cell motility and invasiveness was excluded by in vitro migration and invasion assays. These results suggest a crucial role for glioma-induced angiogenesis as a prerequisite for diffuse tumor invasion and a possible therapeutic role for anti-angiogenic compounds as inhibitors of both solid and diffuse infiltrative tumor growth.

Measuring VEGF-Flk-1 activity and consequences of VEGF-Flk-1 targeting in vivo using intravital microscopy: clinical applications

Vascular endothelial growth factor (VEGF)-Flk-1/KDR tyrosine kinase signaling pathway plays a pivotal role in tumor angiogenesis. Targeting this angiogenic signaling pathway presents a promising alternative for the treatment of neoplasms. However, recent experimental and clinical studies have suggested that VEGF-Flk-1/KDR activity is unevenly distributed throughout the tumor microvasculature. To further evaluate this phenomenon, the regional differences in VEGF-Flk-1/KDR signaling activities in vivo were studied using intravital fluorescence videomicroscopy in an experimental murine brain tumor model. Regional VEGF-Flk-1/KDR was assessed using the small molecule inhibitor SU5416, which selectively inhibits the tyrosine kinase receptor Flk-1. C(6) glioblastoma cells were implanted into the dorsal skinfold chamber preparation of nude mice. The process of tumor vascularization was repeatedly assessed over 22 days. SU5416 treatment resulted in a significant reduction in tumor vascular density (p<0.05). Regional microvascular evaluation indicated that the magnitude of this antiangiogenic effect was pronounced in the more angiogenic and better vascularized peritumoral areas than in the intratumoral areas of the tumor microvasculature. These results demonstrate regional differences in Flk-1 activity in vivo that may have significant impact on the susceptibility of tumors to compounds that target VEGF-Flk-1/KDR. This finding should be considered in upcoming clinical trials targeting individual signal transduction systems in cancer patients.

Serine residues 1177/78/82 of the insulin receptor are required for substrate phosphorylation but not autophosphorylation

Serine residues of the human insulin receptor (HIR) may be phosphorylated and negatively regulate the insulin signal. We studied the impact of 16 serine residues in HIR by mutation to alanine and co-overexpression in human embryonic kidney (HEK) 293 cells together with the docking proteins insulin receptor substrate (IRS)-1, IRS-2, or (SHC) Src homologous and collagen-like. As a control, IRS-1 was also cotransfected with an HIR with a juxtamembrane deletion (HIR delta JM) and therefore not containing the domain required for interaction with IRS-1. Coexpression of HIR with IRS-1, IRS-2, and SHC strongly enhanced tyrosine phosphorylation of these proteins. A similar increase in tyrosine phosphorylation was observed in cells overexpressing IRS-1, IRS-2, or SHC together with all HIR mutants except HIR delta JM and a mutant carrying exchanges of serines 1177, 1178, and 1182 to alanine (HIR1177/78/82), although this mutant showed normal autophosphorylation. Analysis of total cell lysates with anti-phosphotyrosine antibodies showed that in addition to the overexpressed substrates, other cellular proteins displayed reduced levels of tyrosine phosphorylation in these cells. To study consequences for phosphatidylinositol 3-kinase (PI 3-kinase) activation, we established stable NIH3T3 fibroblast cell lines overexpressing wild-type HIR, HIR1177/78/82, and other HIR mutants as the control. Again, HIR1177/78/82 showed normal autophosphorylation but showed a clear decrease in tyrosine phosphorylation of endogenous IRS-1 and activation of PI 3-kinase. This decrease in kinase activity also occurred in an in vitro kinase assay towards recombinant IRS-1. Finally, we performed a separation of the phosphopeptides by high-performance liquid chromatography and could not detect any differences in the profiles of HIR and HIR1177/78/82. In conclusion, we have defined a region in HIR that is important for substrate phosphorylation but not autophosphorylation. Therefore, this mutant may provide new insights into the mechanism of kinase activation and substrate phosphorylation.

Class II phosphoinositide 3-kinases are downstream targets of activated polypeptide growth factor receptors

The class II phosphoinositide 3-kinases (PI3K) PI3K-C2alpha and PI3K-C2beta are two recently identified members of the large PI3K family. Both enzymes are characterized by the presence of a C2 domain at the carboxy terminus and, in vitro, preferentially utilize phosphatidylinositol and phosphatidylinositol 4-monophosphate as lipid substrates. Little is understood about how the catalytic activity of either enzyme is regulated in vivo. In this study, we demonstrate that PI3K-C2alpha and PI3K-C2beta represent two downstream targets of the activated epidermal growth factor (EGF) receptor in human carcinoma-derived A431 cells. Stimulation of quiescent cultures with EGF resulted in the rapid recruitment of both enzymes to a phosphotyrosine signaling complex that contained the EGF receptor and Erb-B2. Ligand addition also induced the appearance of a second, more slowly migrating band of PI3K-C2alpha and PI3K-C2beta immunoreactivity on sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Since both PI3K enzymes can utilize Ca(2+) as an essential divalent cation in lipid kinase assays and since the catalytic activity of PI3K-C2alpha is refractory to the inhibitor wortmannin, these properties were used to confirm the recruitment of each PI3K isozyme to the activated EGF receptor complex. To examine this interaction in greater detail, PI3K-C2beta was chosen for further investigation. EGF and platelet-derived growth factor also stimulated the association of PI3K-C2beta with their respective receptors in other cells, including epithelial cells and fibroblasts. The use of EGF receptor mutants and phosphopeptides derived from the EGF receptor and Erb-B2 demonstrated that the interaction with recombinant PI3K-C2beta occurs through E(p)YL/I phosphotyrosine motifs. The N-terminal region of PI3K-C2beta was found to selectively interact with the EGF receptor in vitro, suggesting that it mediates the association of this PI3K with the receptor. However, the mechanism of this interaction remains unclear. We conclude that class II PI3K enzymes may contribute to the generation of 3' phosphoinositides following the activation of polypeptide growth factor receptors in vivo and thus mediate certain aspects of their biological activity.

Epidermal growth factor receptor signal transactivation

Cross-communication between heterologous signaling systems and the epidermal growth factor receptor (EGFR) has been shown to be critical for a variety of biological responses: EGFR transactivation when G-protein-coupled receptors (GPCRs) are stimulated represents the paradigm of an interreceptor network that is dependent on G-proteins, kinases, metalloproteases, and growth factor precursors. Investigating the mechanism of this process will help expand our knowledge of physiological regulatory mechanisms and diverse pathophysiological disorders.

Color as an indicator of the organization and compactibility of binary powder mixes

The aim of this study was to relate the color of several binary mixes to their organization as observed by scanning electronic microscopy, and to their compactibility. Binary mixes of niflumic acid (yellow) with ethyl cellulose, hydroxypropylmethylcellulose, low-substituted hydroxypropylcellulose (L-HPC), and ibuprofen (all white) were prepared using different particle size ranges. Colors of the mixes were determined by diffuse reflectance spectroscopy using a chromameter. Linear correlation was observed between the yellowness index/whiteness index ratio (Y/W ratio) defined by the American Society for Testing and Materials (ASTM) standards and the mean particle size difference of the materials which governs the organization of the blend. Except for the least interacting mix, the niflumic acid/L-HPC series, the color of the blend was also related to the tensile strength of the tablets made from the binary mixes. Color could be an interesting indicator of the organization of a powder mix. Diffuse reflectance spectroscopy could be used as a quality control tool because any modification of the color of the mix may be an indicator of a modification of its compactibility.

The carboxyl-terminal tyrosine residue of protein-tyrosine phosphatase alpha mediates association with focal adhesion plaques

The receptor protein-tyrosine phosphatase alpha (PTPalpha) is involved in the activation of c-Src kinase as well as in down-regulation of the insulin signal. To investigate the role of PTPalpha in activation of the Src kinase in more detail we tried to overexpress this phosphatase in NIH3T3 fibroblasts. Although PTPalpha has been overexpressed in rat embryonic fibroblasts and in embryonic carcinoma cells and should increase mitogenic responses we were not able to achieve a detectable overexpression. In contrast, expression of partially (C442S) or completely inactive (C442S,C732S) PTPalpha or of phosphatase active PTPalpha containing mutation Y781F or Y798F was possible. The level of expression, however, was reduced to background after several passages of lines expressing PTPalphaC442S,C732S and PTPalphaY781F. When employed in a focus formation assay, only infection with virus encoding PTPalphaY798F induced Src-dependent formation of foci. In immunofluorescence studies, PTPalphaC442S and PTPalphaY781F but not PTPalphaY798F colocalized with proteins found in focal adhesion plaques. Treatment of PTPalphaC442S-overexpressing cells with vanadate abolished this colocalization and led to proteolytic processing of the phosphatase. We conclude that tyrosine 798 in PTPalpha is important for localization at focal adhesion plaques. Inhibition of phosphatases by vanadate treatment releases PTPalpha from focal adhesions.

Intravital fluorescence videomicroscopy to study tumor angiogenesis and microcirculation

Angiogenesis and microcirculation play a central role in growth and metastasis of human neoplasms, and, thus, represent a major target for novel treatment strategies. Mechanistic analysis of processes involved in tumor vascularization, however, requires sophisticated in vivo experimental models and techniques. Intravital microscopy allows direct assessment of tumor angiogenesis, microcirculation and overall perfusion. Its application to the study of tumor-induced neovascularization further provides information on molecular transport and delivery, intra- and extravascular cell-to-cell and cell-to-matrix interaction, as well as tumor oxygenation and metabolism. With the recent advances in the field of bioluminescence and fluorescent reporter genes, appropriate for in vivo imaging, the intravital fluorescent microscopic approach has to be considered a powerful tool to study microvascular, cellular and molecular mechanisms of tumor growth.

EGF receptor transactivation by G-protein-coupled receptors requires metalloproteinase cleavage of proHB-EGF

Cross-communication between different signalling systems allows the integration of the great diversity of stimuli that a cell receives under varying physiological situations. The transactivation of epidermal growth factor receptor (EGFR)-dependent signalling pathways upon stimulation of G-protein-coupled receptors (GPCRs), which are critical for the mitogenic activity of ligands such as lysophosphatidic acid, endothelin, thrombin, bombesin and carbachol, provides evidence for such an interconnected communication network. Here we show that EGFR transactivation upon GPCR stimulation involves proHB-EGF and a metalloproteinase activity that is rapidly induced upon GPCR-ligand interaction. We show that inhibition of proHB-EGF processing blocks GPCR-induced EGFR transactivation and downstream signals. The pathophysiological significance of this mechanism is demonstrated by inhibition of constitutive EGFR activity upon treatment of PC3 prostate carcinoma cells with the metalloproteinase inhibitor batimastat. Together, our results establish a new mechanistic concept for cross-communication among different signalling systems.

Cell type-specific activation of mitogen-activated protein kinases by CpG-DNA controls interleukin-12 release from antigen-presenting cells

Activation of antigen-presenting cells (APCs) by invariant constituents of pathogens such as lipopolysaccharide (LPS) or bacterial DNA (CpG-DNA) initiates immune responses. We have analyzed the mitogen-activated protein kinase (MAPK) pathways triggered by CpG-DNA and their significance for cytokine production in two subsets of APCs, i.e. macrophages and dendritic cells (DCs). We found that CpG-DNA induced extracellular signal-regulated kinase (ERK) activity in macrophages in a classic MEK-dependent way. This pathway up-regulated tumor necrosis factor production but down-regulated interleukin (IL)-12 production. However, in DCs, which produce large amounts of IL-12, CpG-DNA and LPS failed to induce ERK activity. Consistent with a specific negative regulatory role for ERK in macrophages, chemical activation of this pathway in DCs suppressed CpG-DNA-induced IL-12 production. Overall, these results imply that differential activation of MAP kinase pathways is a basic mechanism by which distinct subsets of innate immune cells regulate their effector functions.

Distribution of the receptor EphA7 and its ligands in development of the mouse nervous system

EphA7 is a receptor tyrosine kinase of the Eph family. We have mapped EphA7 immunoreactivity and ligand binding in mouse embryo heads and developing brain. Immunoreactivity for the full-length receptor is found in all the cell populations that express EphA7 mRNA. In particular, it is located on growing axons from EphA7-expressing neurons, both in the trigeminal nerve and in developing brain. In many cases it persists in terminal fields in adult brain. Ligand is detected in a largely complementary distribution in embryos, but is surprisingly weak or undetectable in the target regions of many EphA7-positive axons postnatally.

Segregation of the receptor EphA7 from its tyrosine kinase-negative isoform on neurons in adult mouse brain

The EphA7 gene encodes not only a typical receptor tyrosine kinase (TK+) but also an isoform lacking the tyrosine kinase domain (TK-). We have made antibodies to localise EphA7 TK+ and TK- isoforms in mouse brain. The TK- isoform was not detectable prenatally, despite reported expression of the TK- mRNA in the embryo. However, both TK+ and TK- isoforms showed striking distributions in adult brain. TK+ receptor immunoreactivity was strong in neuropil throughout most of the telencephalon, probably on fine arborisations from neurons which expressed EphA7 during development (in cerebral cortex, hippocampus, and striatum). In contrast, TK- receptor immunoreactivity was conspicuous on cell bodies and proximal dendrites of a limited number of neuronal types, some of which carried EphA7 TK+ receptor on their axons. This suggests that the TK- receptor, acting as a dominant negative antagonist, may ensure that the TK+ receptor only responds to signals encountered by the growing extremities of axons or dendrites.

Human signal-regulatory protein is expressed on normal, but not on subsets of leukemic myeloid cells and mediates cellular adhesion involving its counterreceptor CD47

Signal-regulatory proteins (SIRPs) comprise a novel transmembrane glycoprotein family involved in the negative regulation of receptor tyrosine kinase-coupled signaling pathways. To analyze the expression and function of SIRPs, we prepared soluble recombinant fusion proteins of the extracellular regions of SIRPalpha1 and SIRPalpha2, as well as a variety of monoclonal antibodies (MoAbs) against these domains. The antibodies reacted predominantly with monocytes, granulocytes, dendritic cells, and their precursors, as well as with bone marrow CD34(+), AC133(+), CD90(+) hematopoietic stem/progenitor cells. In contrast, SIRP expression was absent or significantly reduced on the majority of myeloid blasts from patients with acute myeloid leukemia (AML) or chronic myeloid leukemia (CML). Functional studies showed that the extracellular domains of SIRPalpha1 and SIRPalpha2 support adhesion of a number of primary hematopoietic cells and cell lines. This interaction could be blocked by 4 of 7 SIRPalpha1-reactive MoAbs. In addition, SIRPalpha1 and SIRPalpha2 competed for the same cell binding site, suggesting a common widely expressed SIRP ligand. In an approach to identify this molecule, MoAbs were generated against the SIRP-binding cell line CCRF-CEM, and MoAb CC2C6 was selected because of its capacity to inhibit cell binding to SIRPalpha1. Further analysis showed that this antibody recognized CD47, a ubiquitously expressed plasma membrane protein previously implicated in integrin function, host defense action, and neutrophil migration. In this study, we identify CD47 as the extracellular ligand for human SIRP and show that these two counterreceptors are involved in cellular adhesion.