Are surgical trials with negative results being interpreted correctly?

BACKGROUND: Many published accounts of clinical trials report no differences between the treatment arms, while being underpowered to find differences. This study determined how the authors of these reports interpreted their findings. STUDY DESIGN: We examined 54 reports of surgical trials chosen randomly from a database of 110 influential trials conducted in 2008. Seven that reported having adequate statistical power (ß ≥ 0.9) were excluded from further analysis, as were the 32 that reported significant differences between the treatment arms. We examined the remaining 15 to see whether the authors interpreted their negative findings appropriately. Appropriate interpretations discussed the lack of power and/or called for larger studies. RESULTS: Three of the 7 trials that did not report an a priori power calculation offered inappropriate interpretations, as did 3 of the 8 trials that reported an a priori power < 0.90. However, we examined only a modest number of trial reports from 1 year. CONCLUSIONS: Negative findings in underpowered trials were often interpreted as showing the equivalence of the treatment arms with no discussion of the issue of being underpowered. This may lead clinicians to accept new treatments that have not been validated.

The multifaceted roles of chemokines in malignancy.

Tumor development and progression are multifactorial processes, regulated by a large variety of intrinsic and microenvironmental factors. A key role in cancer is played by members of the chemokine superfamily. Chemokines and their receptors are expressed by tumor cells and by host cells, in primary tumors and in specific metastatic loci. The effects of chemokines on tumorigenesis are diverse: While some members of the superfamily significantly support this process, others inhibit fundamental events required for tumor establishment and metastasis. The current review describes the multifaceted roles of chemokines in malignancy, addressing four major aspects of their activities: (1) inducing leukocyte infiltration to tumors and regulating immune functions, with emphasis on tumor-associated macrophages (and the chemokines CCL2, CCL5), T cells (and the chemokines CXCL9, CXCL10) and dendritic cells (and the chemokines CCL19, CCL20, CCL21); (2) directing the homing of tumor cells to specific metastatic sites (the CXCL12-CXCR4 axis); (3) regulating angiogenic processes (mainly the ELR(+)-CXC and non-ELR-CXC chemokines); (4) acting directly on the tumor cells to control their malignancy-related functions. Together, these different chemokine functions establish a net of interactions between the tumor cells and their microenvironment, and partly dictate the fate of the malignancy cascade.

Inflammation-associated immune suppression in cancer: the roles played by cytokines, chemokines and additional mediators.

Chronic inflammation and presence of inflammatory cells, primarily macrophages, at tumor sites are highly associated with specific malignancies. In these cases, the inflammatory milieu is overloaded with mediators that suppress immune activities at many levels: recognition of tumor-associated antigens, activation, the actual cytolysis of tumor cells and more. Local suppression of leukocyte functions at the inflammatory tumor site further contributes to profound immunosuppression of potential anti-tumor immune functions. The present review discusses the inflammatory setup in tumors and the factors inducing the presence of detrimental inflammatory macrophages at tumor sites. Moreover, the different mediators that contribute to inflammation-associated immune suppression, including primarily cytokines and chemokines but also prostaglandins and oxidants, are described. Bearing in mind the notion that under specific conditions the inflammatory mediators clearly contribute to malignancy, while in others they may exert surveillance missions against tumor cells, the potential therapeutic value of the inflammatory components is discussed.

Host microenvironment in breast cancer development: inflammatory cells, cytokines and chemokines in breast cancer progression: reciprocal tumor-microenvironment interactions.

A comprehensive overview of breast cancer development and progression suggests that the process is influenced by intrinsic properties of the tumor cells, as well as by microenvironmental factors. Indeed, in breast carcinoma, an intensive interplay exists between the tumor cells on one hand, and inflammatory cells/cytokines/chemokines on the other. The purpose of the present review is to outline the reciprocal interactions that exist between these different elements, and to shed light on their potential involvement in breast cancer development and progression.

A controlled trial of arthroscopic surgery for osteoarthritis of the knee.

BACKGROUND: Many patients report symptomatic relief after undergoing arthroscopy of the knee for osteoarthritis, but it is unclear how the procedure achieves this result. We conducted a randomized, placebo-controlled trial to evaluate the efficacy of arthroscopy for osteoarthritis of the knee. METHODS: A total of 180 patients with osteoarthritis of the knee were randomly assigned to receive arthroscopic débridement, arthroscopic lavage, or placebo surgery. Patients in the placebo group received skin incisions and underwent a simulated débridement without insertion of the arthroscope. Patients and assessors of outcome were blinded to the treatment-group assignment. Outcomes were assessed at multiple points over a 24-month period with the use of five self-reported scores--three on scales for pain and two on scales for function--and one objective test of walking and stair climbing. A total of 165 patients completed the trial. RESULTS: At no point did either of the intervention groups report less pain or better function than the placebo group. For example, mean (+/-SD) scores on the Knee-Specific Pain Scale (range, 0 to 100, with higher scores indicating more severe pain) were similar in the placebo, lavage, and débridement groups: 48.9+/-21.9, 54.8+/-19.8, and 51.7+/-22.4, respectively, at one year (P=0.14 for the comparison between placebo and lavage; P=0.51 for the comparison between placebo and débridement) and 51.6+/-23.7, 53.7+/-23.7, and 51.4+/-23.2, respectively, at two years (P=0.64 and P=0.96, respectively). Furthermore, the 95 percent confidence intervals for the differences between the placebo group and the intervention groups exclude any clinically meaningful difference. CONCLUSIONS: In this controlled trial involving patients with osteoarthritis of the knee, the outcomes after arthroscopic lavage or arthroscopic débridement were no better than those after a placebo procedure.

Possible co-regulation of genes associated with enhanced progression of mammary adenocarcinomas.

Tumor progression is a multistep process in which alterations in the expression of numerous gene products may give rise to highly malignant cellular variants. In the present study, we analyzed the differential expression of several genes in cellular variants of mammary adenocarcinomas with high or low malignancy potential, which originated in a common ancestor. To assess the generality of our findings, high and low malignancy variants were derived from two different mammary adenocarcinoma cell lines, namely DA3 and CSML cells. Of major importance is the fact that the differences between high- and low-malignancy variants observed in one system of mammary adenocarcinoma cells (DA3 cells) were identically reproduced in the other system of mammary adenocarcinoma cells (CSML cells). The high malignancy variants of tumors both DA3-high and CSML-high (previously called CSML-100), expressed higher levels of factors that induce monocyte migration than the low malignancy DA3-low and CSML-low (previously called CSML-0) variants. In addition, it was found that DA3-high and CSML-high cell variants expressed higher levels of monocyte chemoattractant protein-1 (MCP-1), interleukin-6 (IL-6) and matrix metalloproteinases (MMPs) than the low malignancy variants (DA3-low and CSML-low). These results suggest that MCP-1, IL-6 and MMPs potentially contribute to mammary adenocarcinoma progression and that their expression is regulated by a common pathway. The expression of MCP-1, IL-6 and MMPs in both DA3-high and CSML-high cells was up-regulated by tumor necrosis factor alpha (TNFalpha). The fact that TNFalpha exerted similar effects on the expression of these three factors in both cell systems raises the possibility of a coordinated co-regulation of tumor-promoting factors.

A possible role for CXCR4 and its ligand, the CXC chemokine stromal cell-derived factor-1, in the development of bone marrow metastases in neuroblastoma.

The homing of hemopoietic stem cells to the bone marrow is mediated by specific interactions occurring between CXCR4, which is expressed on hemopoietic stem cells, and its ligand, stromal cell-derived factor-1 (SDF-1), a CXC chemokine secreted by bone marrow stromal cells. In the present study we evaluated the possibility that neuroblastoma cells use a mechanism similar to that used by hemopoietic stem cells to home to the bone marrow and adhere to bone marrow stromal cells. Our study suggests that CXCR4 expression may be a general characteristic of neuroblastoma cells. SH-SY5Y neuroblastoma cells express not only CXCR4, but also its ligand, SDF-1. CXCR4 expression on SH-SY5Y neuroblastoma cells is tightly regulated by tumor cell-derived SDF-1, as demonstrated by the ability of neutralizing Abs against human SDF-1alpha to up-regulate CXCR4 expression on the tumor cells. The reduction in CXCR4 expression following short term exposure to recombinant human SDF-1alpha can be recovered as a result of de novo receptor synthesis. Recombinant human SDF-1alpha induces the migration of CXCR4-expressing SH-SY5Y neuroblastoma cells in CXCR4- and heterotrimeric G protein-dependent manners. Furthermore, SH-SY5Y cells interact at multiple levels with bone marrow components, as evidenced by the fact that bone marrow-derived constituents promote SH-SY5Y cell migration, adhesion to bone marrow stromal cells, and proliferation. These results suggest that SH-SY5Y neuroblastoma cells are equipped with adequate machinery to support their homing to the bone marrow. Therefore, the ability of neuroblastoma tumors to preferentially form metastases in the bone marrow may be influenced by a set of complex CXCR4-SDF-1 interactions.

Defining a link between gap junction communication, proteolysis, and cataract formation.

Disruption of the connexin alpha 3 (Cx46) gene (alpha 3 (-/-)) in mice results in severe cataracts within the nuclear portion of the lens. These cataracts are associated with proteolytic processing of the abundant lens protein gamma-crystallin, leading to its aggregation and subsequent opacification of the lens. The general cysteine protease inhibitor, E-64, blocked cataract formation and gamma-crystallin cleavage in alpha 3 (-/-) lenses. Using a new class of activity-based cysteine protease affinity probes, we identified the calcium-dependent proteases, m-calpain and Lp82, as the primary targets of E-64 in the lens. Profiling changes in protease activities throughout cataractogenesis indicated that Lp82 activity was dramatically increased in alpha 3 (-/-) lenses and correlated both spatially and temporally with cataract formation. Increased Lp82 activity was due to calcium accumulation as a result of increased influx and decreased outflux of calcium ions in alpha 3 (-/-) lenses. These data establish a role for alpha 3 gap junctions in maintaining calcium homeostasis that in turn is required to control activity of the calcium-dependent cysteine protease Lp82, shown here to be a key initiator of the process of cataractogenesis.

GCP-2-induced internalization of IL-8 receptors: hierarchical relationships between GCP-2 and other ELR(+)-CXC chemokines and mechanisms regulating CXCR2 internalization and recycling.

The chemotactic potencies of ELR(+)-CXC chemokines during acute inflammation are regulated by their binding affinities and by their ability to activate, desensitize, and internalize their specific receptors, CXCR1 and CXCR2. To gain insight into the fine mechanisms that control acute inflammatory processes, we have focused in this study on the highly potent ELR(+)-CXC chemokine Granulocyte Chemotactic Protein 2 (GCP-2), and on its ability to control the cell surface expression of CXCR1 and CXCR2. Although GCP-2 has been considered an effective ligand for both CXCR1 and CXCR2, our findings demonstrated that it was a potent inducer of CXCR2 internalization only. A functional hierarchy was shown to exist between GCP-2 and 2 other ELR(+)-CXC chemokines, IL-8 and NAP-2, in their abilities to induce CXCR1 and CXCR2 internalization, according to the following: IL-8 > GCP-2 > NAP-2. By the use of pertussis toxin (PTx), it was demonstrated that the actual events of G(alphai)-coupling to CXCR2 do not have a major role in the regulation of its internalization. Rather, CXCR2 internalization was shown to be negatively controlled by induction of signaling events, as indicated by the promotion of CXCR2 internalization following exposure to wortmannin, a potent inhibitor of phosphatidylinositol (PI) 3 kinases and PI4 kinases. Furthermore, our results suggest that rab11(+)-endosomes participate in the trafficking of CXCR2 through the endocytic pathway, to eventually allow its recycling back to the plasma membrane. To conclude, our findings shed light on the interrelationships between GCP-2 and other ELR(+)-CXC chemokines, and determine the mechanisms involved in the regulation of GCP-2-induced internalization and recycling of CXCR2. (Blood. 2000;95:1551-1559)

Elevated expression of the CC chemokine regulated on activation, normal T cell expressed and secreted (RANTES) in advanced breast carcinoma.

Breast carcinoma is the most common malignant disease among women and the second most lethal one. In search for a better understanding of the role of cellular mediators in the progression of this disease, we investigated the potential involvement of the CC chemokine Regulated on Activation, Normal T Cell Expressed and Secreted (RANTES) in breast carcinoma progression. To this end, RANTES expression was determined in breast tumor cell lines and in sections of breast carcinomas, followed by analysis of the incidence and intensity of its expression in different stages of the disease. Our study reveals that high and physiologically relevant levels of RANTES are constitutively produced by T47D and MCF-7 breast tumor cell lines. Analysis of RANTES expression in sections of breast carcinomas demonstrates a high incidence of RANTES expression in epithelial tumor cells; the chemokine was expressed in 74% of the sections. RANTES expression was rarely detected in normal duct epithelial cells or in epithelial cells that constitute benign breast lumps, which were located in proximity to tumor cells. High incidence and intensity of RANTES expression were detected in sections of most of the patients with stage II and stage III of the disease (expression was detected in 83 and 83.3%, respectively), whereas RANTES was expressed at a lower incidence and intensity in sections of patients with stage I of breast carcinoma (55% of the cases). Most importantly, the expression of RANTES was minimally detected in sections of patients diagnosed with benign breast disorders and of women that underwent reduction mammoplasty (15.4% of the cases). These results indicate that the expression of RANTES is directly correlated with a more advanced stage of disease, suggesting that RANTES may be involved in breast cancer progression. Moreover, it is possible that in patients diagnosed with benign breast disorders, RANTES expression may be indicative of an ongoing, but as yet undetectable, malignant process.

MUC1 isoform specific monoclonal antibody 6E6/2 detects preferential expression of the novel MUC1/Y protein in breast and ovarian cancer.

The products of the MUC1 gene are known to be highly expressed in human breast cancer cells. The best characterized MUC1 protein is a polymorphic, type 1 transmembrane molecule containing a large extracellular domain composed primarily of a variable number of 20 amino acid tandem repeats. We have recently identified a novel protein product of the MUC1 gene, the MUC1/Y protein, that is also a transmembrane protein but is devoid of the tandem repeat array and its immediate flanking sequences. To analyze its expression in tumor cells we generated monoclonal antibodies directed against the MUC1/Y extracellular domain (anti-MUC1/Yex MAbs). Epitope mapping identified the MAb, 6E6, which recognized the MUC1/Y isoform with exquisite specificity- the repeat-array-containing MUC1 isoform could not compete out this immunoreactivity. A 30mer peptide which is unique for MUC1/Y and corresponds to the "join" region generated by the MUC1/Y specific splice, abrogated all 6E6 MAb immunoreactivity towards MUC1/Y. Immunoprecipitation of the MUC1/Y protein with 6E6 MAbs revealed that, in contrast with the proteolytic cleavage of the tandem-repeat-array-containing MUC1 isoform, MUC1/Y is not cleaved. Flow cytometry analyses using the 6E6 MAbs demonstrated that the MUC1/Y isoform is expressed on the cell surface of both MCF-7 breast cancer cells and malignant epithelial cells present in effusions obtained from breast and ovarian cancer patients. Our results unequivocally establish that the MUC1/Y protein is expressed on the surface of breast cancer cells and cells of other epithelial malignancies. The anti-MUC1/Y MAbs described here can target MUC1/Y expressing tumor cells in vivo and are likely to be important reagents both for epithelial tumor diagnosis and immunotherapy.

MCP-1 expression as a potential contributor to the high malignancy phenotype of murine mammary adenocarcinoma cells.

The search for mechanisms that regulate tumor progression has motivated the authors' laboratory to establish a unique murine model system, consisting of two lines of DA3 mammary adenocarcinoma cells that were derived originally from a common ancestor but differed in their malignant potential. Studies indicated that the highly malignant phenotype manifested by one of the cell lines (termed Ly-6hi DA3 cells) was associated with high expression of the Ly-6E.1 antigen. To characterize the mechanisms controlling the high malignancy phenotype expressed by Ly-6hi DA3 cells, the study was focussed on the potential contribution of tumor-derived factors to the high malignancy phenotype expressed by these cells. To this end, the expression of CC chemokines, major chemoattractants of monocytes and T cells, by the highly malignant Ly-6hi DA3 cells as compared to the low malignancy Ly-6lo DA3 cells was evaluated. The results indicate that the highly malignant cells express higher levels of factors that induce monocyte migration than the low malignancy cells. Two CC chemokines were shown to be highly produced by Ly-6hi DA3 cells, MIP-1alpha and MCP-1, of which only the latter was shown to contribute to the high migratory activity expressed by the high malignancy Ly-6hi DA3 cells. Since MCP-1 may attract monocytes to tumor sites, these findings suggest that monocyte-derived mediators, such as growth factors or angiogenic cytokines, have pro-malignancy effects that contribute to the high malignancy phenotype expressed by Ly-6hi DA3 cells.

The breast cancer-associated MUC1 gene generates both a receptor and its cognate binding protein.

MUC1 proteins, some of which contain a mucin-like domain and others lacking this region, can be generated from the human breast cancer-associated MUC1 gene by alternative splicing. The MUC1/Y isoform is devoid of the mucin domain and is a cell membrane protein that undergoes transphosphorylation on both serine and tyrosine residues. We have identified cognate binding proteins that specifically interact with the extracellular domain of MUC1/Y. Coimmunoprecipitation analyses clearly revealed the presence of complexes composed of MUC1/Y and its cognate binding proteins in primary breast tumor tissue. MUC1/Y-expressing mammary tumor cells can be specifically targeted, in vivo, with the labeled cognate binding protein. The k(D) of MUC1/Y for its binding proteins was estimated as 1.2 nM. The MUC1/Y binding proteins are also derived from the MUC1 gene and represent the secreted mucin-like polymorphic MUC1 proteins MUC1/SEC and MUC1/REP, which contain a tandem repeat array. Whereas nonposttranslationally modified MUC1/Y bound efficiently to MUC1/SEC, the latter mucin-like protein had to be posttranslationally modified in a cell-type specific manner to bind MUC1/Y. The interaction of MUC1/Y with MUC1/SEC has important biological functional correlates: (a) it induces MUC1/Y phosphorylation; and (b) it has a pronounced effect on cell morphology. These findings suggest that MUC1/Y and MUC1/SEC form an active receptor/ cognate binding protein complex that can elicit cellular responses. The proteins comprising this complex are, thus, generated by alternative splicing from one and the same gene, namely the MUC1 gene.

Differential usage of the CXC chemokine receptors 1 and 2 by interleukin-8, granulocyte chemotactic protein-2 and epithelial-cell-derived neutrophil attractant-78.

The inflammatory response is mediated by a family of chemotactic cytokines, designated chemokines. The receptor usage of the CXC chemokine granulocyte chemotactic protein-2 (GCP-2) was compared with that of interleukin-8 (IL-8) and epithelial-cell-derived neutrophil attractant-78 (ENA-78). Chemokine activities were evaluated by measurement of intracellular calcium increase and by chemotaxis and binding assays, using CXC chemokine receptor (CXCR)-transfected cell lines. GCP-2 was equally potent at inducing a rise in [Ca2+]i in both CXCR1-transfected and CXCR2-transfected cells (minimal effective concentration 3 nM). IL-8 augmented the [Ca2+]i more efficiently in CXCR1-transfectants than in CXCR2-transfectants, whereas for ENA-78, threefold higher concentrations were necessary to obtain a calcium response in CXCR1-transfected cells than in CXCR2-transfectants. GCP-2 desensitized the calcium increase induced by IL-8 in both CXCR1-transfected and CXCR2-transfected cells, but ENA-78 only affected the IL-8-induced calcium response in CXCR2-transfectants. The half-maximal effective concentrations for migration of CXCR2-transfectants in response to GCP-2 and ENA-78 were similar (0.1 nM), whereas GCP-2 was tenfold more potent than ENA-78 on CXCR1-transfectants. Half-maximal migration of CXCR1-transfected and CXCR2-transfected cells was obtained with IL-8 at concentrations of no more than 0.01 nM. Radiolabeled IL-8 could efficiently be displaced from CXCR2 by IL-8, GCP-2 and ENA-78. In contrast, only IL-8 and GCP-2 but not ENA-78, competed for 125I-IL-8 binding to CXCR1. From these data, it can be concluded that, in addition to IL-8, GCP-2, but not ENA-78, efficiently binds to both CXCR1 and CXCR2. The differential receptor usage of the structurally related ELR+ CXC chemokines GCP-2 and ENA-78 is indicative of a different role in inflammatory reactions.

The differential ability of IL-8 and neutrophil-activating peptide-2 to induce attenuation of chemotaxis is mediated by their divergent capabilities to phosphorylate CXCR2 (IL-8 receptor B).

IL-8 and neutrophil-activating peptide-2 (NAP-2) are two closely related C-X-C chemokines that differ in their abilities to induce chemotaxis of human polymorphonuclear leukocytes (PMN). Although two IL-8R types are expressed by PMN, only CXCR2 binds NAP-2 and IL-8 with equally high affinity. By using enriched CXCR2-transfected 293 cells, we show that high doses of IL-8 induce attenuation of chemotaxis, while equivalent doses of NAP-2 do not. Phosphorylation analysis shows that IL-8 induces higher levels of phosphorylation of the carboxyl terminus of CXCR2 than does NAP-2, suggesting that the level of phosphorylation contributes to the ability of the chemokines to attenuate the chemotactic response. To directly evaluate this difference, we analyzed the ability of receptors mutated to delete regions that highly express potential phosphorylation sites to be phosphorylated and to mediate chemotactic attenuation. We found that a carboxyl terminus-truncated mutant of CXCR2 was not phosphorylated by high doses of IL-8, as determined by in vivo phosphorylation assays and by analysis of the electrophoretic mobility of the receptors on SDS-PAGE gels. This mutated receptor had a significantly lower ability to attenuate IL-8-induced chemotaxis, indicating that the attenuation of chemotaxis is mediated by chemokine-induced receptor phosphorylation. In conclusion, the data show that the greater ability of IL-8 to induce receptor phosphorylation contributes to its more potent attenuation of chemotaxis as compared with NAP-2. This differential phosphorylation by IL-8 and NAP-2 of CXCR2 provides a basis for the divergent outcome of PMN-induced inflammation in response to these two closely related C-X-C chemokines.

Preferential expression of novel MUC1 tumor antigen isoforms in human epithelial tumors and their tumor-potentiating function.

The human MUC1 gene expresses at least 2 type 1 membrane proteins: MUC1/REP, a polymorphic high m.w. MUC1 glycoprotein often highly expressed in breast cancer tissues and containing a variable number of tandem 20 amino acid repeat units, and the MUC1/Y protein, which lacks this repeat array and, therefore, is not polymorphic. Despite their documented importance in signal transduction processes, the relative expression of the 2 isoforms in epithelial tumors is unknown. Using antibody reagents which recognize different MUC1 domains, the expression of these isoforms in malignant epithelial cells has been evaluated. A comparison of the amounts of the 2 isoforms revealed preferential expression of the novel MUC1/Y protein in breast cancer tissue samples. Furthermore, although the MUC1/REP protein is almost undetectable in HeLa cervical adenocarcinoma epithelial cells, the MUC1/Y isoform is extensively expressed in these cells. The presence of the MUC1/Y sequence as well as that of an additional tandem-repeat-array-lacking isoform, designated MUC1/X, were demonstrated by reverse transcriptase PCR amplification of RNA extracted from HeLa and ovarian carcinoma cells. It has been shown previously that the MUC1 cytoplasmic domain interacts with the SH2 domain containing GRB2 protein, which transduces signals to ras, a protein which in its activated form can lead to cell transformation. We present here data demonstrating that MUC1/Y isoform expression increases the tumorigenic potential of DA3 mouse mammary epithelial cells; in contrast, potentiation of tumorigenicity is not observed with MUC1/REP expression. Our studies thus demonstrate that expression of the MUC1 gene in epithelial tumors can give rise to substantial levels of MUC1 proteins devoid of the tandem repeat array, which are generated by alternative splicing mechanisms.

Characterization of synthetic human granulocyte chemotactic protein 2: usage of chemokine receptors CXCR1 and CXCR2 and in vivo inflammatory properties.

Human granulocyte chemotactic protein 2 (GCP-2) has originally been isolated from cytokine-stimulated osteosarcoma cells as a chemokine coproduced in minute amounts together with interleukin 8. Human GCP-2 (75 residues) was synthesized on a 0.25-mmol scale using Fmoc chemistry. After disulfide bridge formation and purification, monomeric GCP-2 was recovered as a 6-kDa protein; the pure synthetic protein showed a molecular mass of 8076 Da as determined by matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). The exact amino acid sequence of synthetic GCP-2 was confirmed by Edman degradation. Synthetic GCP-2 was an equally active (minimal effective concentration of 1-3 nM) chemoattractant for neutrophilic granulocytes as was natural 75-residue GCP-2. At concentrations up to 30 nM, synthetic GCP-2 did not stimulate eosinophil, monocyte, or lymphocyte chemotaxis. GCP-2 induced a dose-dependent increase in [Ca2+]i in neutrophils, 1 nM being the minimal effective concentration. The GCP-2-induced [Ca2+]i increase was completely prevented by pertussis toxin. Prestimulation of neutrophils with equimolar concentrations of purified natural IL-8, GROalpha, GROgamma and ENA-78 abolished the [Ca2+]i increase in response to 1 nM GCP-2. Alternatively, the [Ca2+]i rise induced by these CXC chemokines was inhibited by pretreatment of neutrophils with GCP-2. GCP-2 stimulated [Ca2+]i increases in CXCR1- and CXCR2-transfected cells, demonstrating that GCP-2 binds to both IL-8 receptors. Intradermal injection of synthetic GCP-2 resulted in a dose-dependent neutrophil accumulation and plasma extravasation in rabbit skin. To provoke this skin reaction, GCP-2 (10 pmol/site) was nearly as effective as IL-8, indicating that it is an important complementary mediator of the inflammatory response.

IL-8 and NAP-2 differ in their capacities to bind and chemoattract 293 cells transfected with either IL-8 receptor type A or type B.

Two receptors for interleukin 8 (IL-8), IL-8rA and IL-8rB, have been cloned. Previous studies of neutrophils indicated that the two C-X-C chemokines, IL-8 and NAP-2, bind to IL-8rB with high affinity but that only IL-8 binds to IL-8rA with high affinity. In this study, human kidney embryonal 293 cells were transfected to express solely IL-8rA or IL-8rB (the cells are designated IL-8rA/293 and IL-8rB/293, respectively). The authors show that NAP-2 bound both IL-8rA and IL-9rB specifically. While NAP-2 and IL-8 bound IL-8rB with comparable high affinity (2.9 +/- 0.5 and 2.8 +/- 0.8 nM, respectively), NAP-2 showed a lower binding affinity to IL-8rA (9 +/- 2 nM) compared with IL-8 (1.3 +/- 0.5 nM). A lower number of binding sites was detected for NAP-2 than for IL-8 on IL-8rA/293 cells as well on IL-8rB/293 cells. On both cell types (IL-8rA/293 and IL-8rb/293), NAP-2 and IL-8 could completely inhibit [125I]NAP-2 binding, while unlabelled NAP-2 could only partially compete for [125I]IL-8 binding. Functional assays revealed that although NAP-2 is chemotactic for both IL-8rA/293 and IL-8rB/293 cells, it is less potent than IL-8. While NAP-2 induced chemotaxis of IL-8rB/293 cells at the same optimal concentrations as IL-8 (10-100 ng/ml), the induction of optimal migratory response of IL-8rA/293 cells required much higher concentrations of NAP-2 than IL-8 (1000-3000 ng/ml and 10-100 ng/ml, respectively). The dose-response curve of the IL-8rB/293 cells to IL-8 was bell shaped, while the response to NAP-2 was sustained at a plateau level even at concentrations as high as 3000 ng/ml. It is likely that tertiary structural differences between NAP-2 and IL-8 account for their divergent abilities to bind and chemoattract 293 cells transfected with either IL-8 receptor type A or type B.