Interleukin-8 secreted by endothelial cells induces chemotaxis of melanoma cells through the chemokine receptor CXCR1

c-Src is the primary signaling mediator of polychlorinated biphenyl-induced interleukin-8 expression in a human microvascular endothelial cell line

Interleukin-8/CXCL8 (IL-8) is a prominent factor that modulates endothelial cell proliferation, migration, and angiogenesis. Therefore, the present study focused on the regulatory mechanisms of IL-8 expression induced by environmental pollutants such as polychlorinated biphenyls (PCBs). Treatment of human microvascular endothelial cells (HMECs) with specific PCB congener, 2,2',4,6,6'-pentachlorobiphenyl (PCB 104), dose dependently increased levels of IL-8 mRNA and secreted protein. IL-8-neutralizing antibody inhibited migration of endothelial cells stimulated by conditioned media derived from PCB 104-treated HMECs. Site-directed mutagenesis of the IL-8 promoter- and DNA-binding assays revealed that activator protein 1 (AP-1) and nuclear factor kappaB (NF-kappaB) sites are required for PCB 104-induced IL-8 transcription. Most importantly, pharmacological inhibition of Src kinase activity or overexpression of dominant-negative c-src in HMECs resulted in a significant decrease in IL-8 expression and promoter activity. In contrast, ectopic expression of activated c-Src markedly increased promoter activity of IL-8. These stimulatory effects of dominant-positive c-src were abrogated by mutagenesis of AP-1- and NF-kappaB-binding sites in the IL-8 promoter.

Malignant effusions are sources of fibronectin and other promigratory and proinvasive components

Metastatic dissemination is the primary cause of death in ovarian cancer (OvCa) patients, and dissemination to pleural and peritoneal effusions is a common clinical event. Effusion samples were collected from 15 OvCa patients. Twenty-six samples were collected prospectively, two were archival, and eight were taken from patients with other malignancies. Twenty-nine samples were from malignant ascites, and seven specimens were pleural fluids. In addition, six ascites and two pleural fluids from noncancer patients were studied as effusion controls. Effusion supernatants were tested for migration-stimulation activity, using A2058 human melanoma cells as the index responder cell. Malignant samples induced a 400-1200% increase in migration. Sixty percent of the migration was inhibited by incubation of the malignant fluid with antifibronectin (FN) antibody, in contrast to 75% inhibition of control fluid-stimulated migration (P = 0.017). Gelatin zymography and Western blot analyses showed that latent and activated MMP-2 and MMP-9 collagenases, and tissue inhibitor of metalloproteinase-2 (TIMP-2) were present in all malignant fluids. Serial samples were taken from several patients, and a trend for correlation between MMPs and clinical behavior of the tumors was shown. Free TIMP-2 correlated with CA-125 levels in two patients for whom serial samples were available. The demonstration of promigratory and proinvasive activity in malignant effusions is consistent with their association with other metastatic disease in OvCa patients and their function as a haven for metastatic cells.

Autocrine role of interleukin-8 in induction of endothelial cell proliferation, survival, migration and MMP-2 production and angiogenesis

Interleukin-8 (IL-8/CXCL8), a paracrine angiogenic factor, modulates multiple biologic functions in CXCR1 and CXCR2 expressing endothelial cells. Several reports suggest that inflammation, infection, cellular stress and tumor presence regulate IL-8 production in endothelial cells. In the present study, we test the hypothesis that IL-8 regulates multiple biological effects in endothelial cells in an autocrine manner. We examined the autocrine role of IL-8 in regulating angiogenesis by using a neutralizing antibody to IL-8, CXCR1 or CXCR2 in human vein umbilical endothelial cell (HUVEC) and human dermal microvascular endothelial cell (HMEC). Neutralizing antibody to IL-8, CXCR1 or CXCR2 inhibited endothelial cell proliferation, and MMP-2 production as compared to cells cultured with medium alone or control antibody. In addition, we observed that the number of apoptotic cells was significantly higher in anti-IL-8, anti-CXCR1 and anti-CXCR2 treated endothelial cells, which coincided with decreased survival-associated gene expression. We observed reduced migration of endothelial cells treated with anti-IL-8 and anti-CXCR2 antibody, but not anti-CXCR1 antibody as compared to controls. Further, we observed an inhibition of capillary tube formation and neovascularization following treatment with anti-IL-8, anti-CXCR1 and anti-CXCR2 antibodies. Together these data suggest that IL-8 functions as an important autocrine growth and angiogenic factor in regulating multiple biological activities in endothelial cells.

Involvement of Src family kinases in N-cadherin phosphorylation and beta-catenin dissociation during transendothelial migration of melanoma cells

N-cadherin is recruited to the heterotypic contact during transendothelial migration of melanoma cells in a coculture system with tumor cells seeded on top of a monolayer of endothelial cells. However, beta-catenin dissociates from N-cadherin and redistributes to the nucleus of transmigrating melanoma cells to activate gene transcription. In this report, we demonstrate that Src becomes activated at the heterotypic contact between the transmigrating melanoma cell and neighboring endothelial cells. Src activation shows close temporal correlation with tyrosine phosphorylation of N-cadherin. Expression of a dominant-negative Src in melanoma cells blocks N-cadherin phosphorylation, beta-catenin dissociation, and nuclear translocation in transmigrating cells, consistent with the involvement of Src family kinases. In in vitro binding assays, Src-mediated phosphorylation of the N-cadherin cytoplasmic domain results in a significant reduction in beta-catenin binding. Although five phospho-tyrosine residues can be identified on the N-cadherin cytoplasmic domain by mass spectrometry, site-specific mutagenesis indicates that Tyr-860 is the critical amino acid involved in beta-catenin binding. Overexpression of N-cadherin carrying the Y860F mutation inhibits the transmigration of transfected cells across the endothelium. Together, the data suggest a novel role for tyrosine phosphorylation of N-cadherin by Src family kinases in the regulation of beta-catenin association during transendothelial migration of melanoma cells.

Mitogenic effects of interleukin-8/CXCL8 on cancer cells

Interleukin (IL)-8 contributes to cancer progression through its multiple functions. Its angiogenic effects are well known, but more recently it has been found to be mitogenic for some cancer cells. Many cancer cells constitutively produce IL-8 and also express the IL-8 receptors, CXCR1 and 2 on the cell membrane. It has been established that IL-8 is an autocrine growth factor for a variety of human cancer cells. The mitogenic effects of IL-8 directly stimulate growth of cancer mass, and it may play a critical role for cancer cells to regrow in metastatic sites.

A Preliminary Study of Imiquimod Treatment in Variants of Basal Cell Carcinoma

Imiquimod is a topical immune response modifier that has proved efficacious in the treatment of the superficial variant of basal cell carcinoma. The nodular variant of basal cell carcinoma has shown moderate response to imiquimod; other variants have not been tested. The mechanism of action is largely unknown; however, studies indicate the mechanism involves alteration of local cytokine production. The objective of this study is to evaluate the cytokine response of imiquimod in all variants of basal cell carcinoma. Ten patients were selected who had clinically and histologically proven basal cell carcinoma. All lesions were treated with imiquimod once a day, 5 days a week, for 3 weeks. After a 3-week rest period, the lesions were rebiopsied. All biopsy specimens were analyzed via polymerase chain reaction (PCR) for various cytokines. Nine of 10 lesions resolved clinically, which included nodular, superficial, infiltrative, adenoid, and micro-nodular variants. The cytokine with the greatest change pre- and post-treatment was IL-8, which decreased an average of 44 per cent ( P = 0.06). We concluded that topical 5 per cent imiquimod is an effective treatment of various subtypes of basal cell carcinoma. IL-8, which plays an important role in the development and metastasis of melanoma, may be involved in the mechanism of action of imiquimod on cutaneous malignancies. Larger studies are needed to prove the efficacy of imiquimod on nonsuperficial variants of basal cell carcinoma and cutaneous melanoma metastasis.

Transendothelial migration of melanoma cells involves N-cadherin-mediated adhesion and activation of the beta-catenin signaling pathway

Cancer metastasis is a multistep process involving many types of cell-cell interactions, but little is known about the adhesive interactions and signaling events during extravasation of cancer cells. Transendothelial migration of cancer cells was investigated using an in vitro assay, in which melanoma cells were seeded on top of a monolayer of endothelial cells. Attachment of melanoma cells on the endothelium induced a twofold increase in N-cadherin expression in melanoma cells and the redistribution of N-cadherin to the heterotypic contacts. Transendothelial migration was inhibited when N-cadherin expression was repressed by antisense RNA, indicating a key role played by N-cadherin. Whereas N-cadherin and beta-catenin colocalized in the contact regions between melanoma cells and endothelial cells during the initial stages of attachment, beta-catenin disappeared from the heterotypic contacts during transmigration of melanoma cells. Immunolocalization and immunoprecipitation studies indicate that N-cadherin became tyrosine-phosphorylated, resulting in the dissociation of beta-catenin from these contact regions. Concomitantly, an increase in the nuclear level of beta-catenin occurred in melanoma cells, together with a sixfold increase in beta-catenin-dependent transcription. Transendothelial migration was compromised in cells expressing a dominant-negative form of beta-catenin, thus supporting a regulatory role of beta-catenin signaling in this process.

Interleukin-8/CXCL8 is a growth factor for human lung cancer cells

Interleukin-8/CXCL8 (IL-8) is a chemokine and angiogenic factor. Recently, IL-8 was identified as an autocrine growth factor in several human cancers. Here, we investigated the expression and function of IL-8 in lung cancer cells. The expressions of IL-8 and its receptors, CXCR1 and CXCR2, were examined in a panel of non-small cell lung cancer (NSCLC) and small cell lung cancer (SCLC) cell lines. Using reverse transcription–polymerase chain reaction (RT–PCR) and enzyme-linked immunosorbent assay, we found that all NSCLC cell lines tested produced modest or high levels of IL-8 (up to 51 ng ml⁻¹ 10⁶ cells⁻¹). Expression of CXCR1 and CXCR2 was found by RT–PCR and flow cytometry in two out of three cell lines. In contrast, SCLC cell lines produced very low or undetectable levels of IL-8, but expressed CXCR1 and CXCR2. We next investigated whether IL-8 could act as an autocrine growth factor in two NSCLC cell lines (H460 and MOR/P) expressing both IL-8 and its receptors. We found that cell proliferation was attenuated by anti-IL-8 neutralising antibody to 71 and 76% in H460 and MOR/P, respectively (P<0.05). Exogenous IL-8 significantly stimulated cell proliferation in four SCLC cell lines tested in a dose-dependent fashion. Cell proliferation was increased by between 18% (P<0.05) and 37% (P<0.05). Stimulation of cell proliferation by IL-8 was also demonstrated by analysis of proliferating cell nuclear antigen expression and cell cycle in H69 cells. Furthermore, we investigated which receptor(s) mediated the mitogenic function of IL-8 in lung cancer cells. We found that cell proliferation was significantly reduced by anti-CXCR1 antibody but not by anti-CXCR2 antibody. In conclusion, IL-8 can act as an autocrine and/or paracrine growth factor for lung cancer cells, and the mitogenic function of IL-8 in lung cancer is mediated mainly by CXCR1 receptor.

Oxidative stress and thioredoxin-interacting protein promote intravasation of melanoma cells

Although intravasation may be a critical rate-limiting step in the metastatic cascade, the role of oxidative stress in intravasation is unknown. We tested the hypothesis that reactive oxygen species (ROS), regulated by thioredoxin interacting protein (Txnip) through the action of thioredoxin (Trx), influence human SK-MEL-28 melanoma cell reverse (basolateral-to-apical) transendothelial migration (TEM) in vitro as a model for intravasation. Reverse transendothelial migration was dose-dependently induced by hydrogen peroxide 2.4-fold for 0.1 microM (P < 0.01) and 3.9-fold for 1 microM (P < 0.001) vs. control, and this effect was blocked by the antioxidant N-acetylcysteine. Overexpression of Txnip by infecting melanoma cells with adenovirus increased TEM 3-fold vs. control (P < 0.001), and this increase was blocked by N-acetylcysteine, indicating a redox-sensitive mechanism. Conversely, thioredoxin overexpression blocked hydrogen peroxide-induced TEM. Exposure to ultraviolet-A radiation increased ROS 1.8-fold (P < 0.01), and this was accompanied by a 45% reduction (P < 0.05) in thioredoxin activity and an 11.4-fold (P < 0.001) increase in Txnip gene expression. These data suggest that TEM of melanoma cells during intravasation is in part mediated by ROS-sensitive cellular signaling cascades, may be controlled by Txnip and its interaction with thioredoxin that in turn modulates cellular levels of oxidative stress, and may be initiated by ultraviolet-A induction of this cascade.

Rabbit neutrophil chemotactic protein (NCP) activates both CXCR1 and CXCR2 and is the functional homologue for human CXCL6

Neutrophil chemotactic protein (NCP) is a rabbit CXC chemokine with activating and chemotactic properties on neutrophilic granulocytes. Although its selective activity on neutrophils is demonstrated, its interactions with specific chemokine receptors are not defined. For further functional characterization, NCP was chemically synthesized and was found to be equipotent as natural NCP in neutrophil chemotaxis. To identify its human homologue, we separately expressed two potential rabbit NCP receptors (CXCR1 and CXCR2) in Jurkat cells. Pure synthetic NCP was equally efficient to promote chemotaxis through either rabbit CXCR1 or CXCR2. Moreover, chemotaxis assays on rabbit CXCR1 and CXCR2 transfectants showed that NCP uses the same receptors as interleukin-8 (IL-8), a major rabbit CXC chemokine, but not rabbit GROalpha, which only recognized CXCR2. In addition, specific inhibitors for CXCR1 or CXCR2 reduced rabbit neutrophil chemotaxis induced by NCP and rabbit IL-8. Furthermore, NCP and the structurally related human CXCR1/CXCR2 agonist CXCL6/GCP-2 (granulocyte chemotactic protein-2) cross-desensitized each other in intracellular calcium release assays on human neutrophils, further indicating that both chemokines share the same receptors. The inflammatory role of NCP was also evidenced by its potent granulocytosis inducing capacity in rabbits upon systemic administration. This study provides in vitro and in vivo evidences that NCP is the functional rabbit homologue for human CXCL6/GCP-2 rather than the most related CXCR2 agonist CXCL5/ENA-78 (epithelial cell-derived neutrophil activating peptide-78). It is concluded that the rabbit is a better model to study human neutrophil activation compared to mice, which lack CXCL8/IL-8.

The epithelial-mesenchymal transition of colon carcinoma involves expression of IL-8 and CXCR-1-mediated chemotaxis

The epithelial-mesenchymal transition (EMT) is an essential component of embryonic development, tissue remodeling, and wound repair. In addition, many epithelial tumors, including colorectal carcinomas, appear to undergo this transition that may facilitate their invasion. Using a novel model of EMT in colon carcinoma in which the inflammatory cytokine TNF-alpha accelerates this TGF-beta directed process, we report that TNF-alpha stimulation upregulates expression of the chemokine IL-8, and that this upregulation is dependent on the transcription factor NF-kappaB. Significantly, this effect is not merely an inflammatory response by these colon carcinoma cells because IL-8 expression is induced in cells undergoing a TGF-beta-driven EMT in the absence of exogenous TNF-alpha. During the EMT, a concomitant increase in the chemokine receptor CXCR-1, but not CXCR-2, also occurs. Moreover, both IL-8 and CXCR-1 function in the chemokinetic and chemotactic migration of colon carcinoma cells as assessed by antibody inhibition studies. These studies establish that the regulated expression of a specific chemokine and its receptor are linked to the EMT and they provide a biochemical framework for understanding the mechanisms by which the EMT promotes migration.

Inhibition of metastasis of tumor cells overexpressing thymidine phosphorylase by 2-deoxy-L-ribose

Thymidine phosphorylase (TP) catalyzes the reversible conversion of thymidine to thymine, thereby generating 2-deoxy-D-ribose-1-phosphate, which upon dephosphorylation forms 2-deoxy-D-ribose (D-dRib), a degradation product of thymidine. We have previously shown that D-dRib promotes angiogenesis and chemotaxis of endothelial cells and also confers resistance to hypoxia-induced apoptosis in some cancer cell lines. 2-Deoxy-L-ribose (L-dRib), a stereoisomer of D-dRib, can inhibit D-dRib anti-apoptotic effects and suppressed the growth of KB cells overexpressing TP (KB/TP cells) transplanted into nude mice. In this study, we examined the ability of L-dRib to suppress metastasis of KB/TP cells using two different models of metastasis. The antimetastatic effect of L-dRib was first investigated in a liver-metastasis model in nude mice inoculated with KB/TP cells. Oral administration of L-dRib for 28 days at a dose of 20 mg/kg/day significantly reduced the number of metastatic nodules in the liver and suppressed angiogenesis and enhanced apoptosis in KB/TP metastatic nodules. Next, we compared the ability of L-dRib and tegafur alone or in combination to decrease the number of metastatic nodules in organs in the abdominal cavity in nude mice receiving s.c. of KB/TP cells into their backs. L-dRib (20 mg/kg/day) was significantly (P < 0.05) more efficient than tegafur (100 mg/kg/day) in decreasing the number of metastatic nodules in organs in the abdominal cavity. By in vitro invasion assay, L-dRib also reduced the number of invading KB/TP cells. L-dRib anti-invasive activity may be mediated by its ability to suppress the enhancing effect of TP and D-dRib on both mRNA and protein expression of vascular endothelial growth factor and interleukin-8 in cultured KB cells. These findings suggest that L-dRib may be useful in a clinical setting for the suppression of metastasis of tumor cells expressing TP.