Chemokines and their role in tumor growth and metastasis

MCP-1 expression in CNS-1 astrocytoma cells: implications for macrophage infiltration into tumors in vivo

Gliomas are among the most resistant tumors to conventional anti-tumor therapy, and are typified by their highly infiltrative nature and ill-defined borders. Macrophages constitute a major proportion of the tumor cell mass in both primary human gliomas and as shown here, a CNS-1 glioma model. The objective of this study was to identify tumor-cell-derived chemotactic factor(s) which participate in macrophage recruitment into tumors in vivo. This study demonstrates the constitutive expression of monocyte chemoattractant protein-1 (MCP-1), a potent monocyte chemoattractant, by the rat astrocytoma cell line CNS-1. Characterization of cytokine expression by CNS-1 cells in vitro revealed the constitutive expression of TGF-beta but not other proinflammatory cytokines. However, numerous cytokines were detected in CNS-I tumors in vivo including Ltbeta, IL-1alpha, IL-1beta, TNF-alpha, TNF-beta, IL-10, and IFN-gamma. Attenuation of MCP- I release from CNS-1 cells using an anti-sense approach revealed no significant alterations in macrophage infiltration into tumors in vivo, suggesting redundancy in the signal(s) involved in macrophage recruitment. Depletion of peripheral macrophages using liposome-encapsulated clodronate revealed no significant differences in tumor growth or in the degree of macrophage infiltration into CNS-1 tumors in vivo. These results indicate that CNS-1 cells produce chemotactic factors which likely participate in macrophage recruitment into tumors in vivo. Whether or not macrophage recruitment confers a growth advantage for the tumor remains to be determined.

Platelet activating factor inhibits the expression of matrix metalloproteinases and affects invasiveness and differentiation in a system of human neuroblastoma clones

Platelet Activating Factor (PAF), an inflammatory bioactive lipid, has been shown to be involved in the regulation of the activity of matrix metalloproteinases (MMPs). In view of the role played by MMPs in tumor cell invasiveness, we investigated whether PAF influences MMP activity in a system of neuroblastoma clones, the AA5 and AE12 cells, isolated from the human LaN1 neuroblastoma cell line. These clones were characterized by an inverse relationship between invasiveness and differentiative capacity and by the expression of specific cell surface PAF receptors. We found that the levels of mRNAs specific for MMP-2 and for MT1-MMP, the MMP-2 activator, were reduced in both clones treated with 300 nM PAF. These changes are consistent with the reduced secretion and activation of MMP-2 found in the neuroblastoma clones exposed to PAF. These effects were accompanied by an inhibition of invasiveness through Matrigel and by a promotion of differentiation, as revealed by an increased percentage of cells with neurites. The finding that both neuroblastoma clones exposed to the metalloproteinase inhibitors, BB3103 and 1,10-phenanthroline, increased their differentiative capacity and reduced their invasiveness through Matrigel, represents a further indication that PAF modulates differentiation and invasiveness by affecting the activity of MMPs.

Regulation of nitric oxide production by murine peritoneal macrophages treated in vitro with chemokine monocyte chemoattractant protein 1

Monocyte chemoattractant protein 1 (MCP-1) is an important mediator of monocyte/macrophage recruitment and activation at the sites of chronic inflammation and neoplasia. In the current study, the role of nitrogen monoxide (NO) in the activation of murine peritoneal macrophages to the tumoricidal state in response to in vitro MCP-1 treatment and the regulatory mechanisms involved therein were investigated. Murine peritoneal macrophages upon activation with MCP-1 showed a dose- and time-dependent production of NO together with increased tumoricidal activity against P815 mastocytoma cells. N-monomethyl-l-arginine (L-NMMA), a specific inhibitor of the l-arginine pathway, inhibited the MCP-1-induced NO secretion and generation of macrophage-mediated tumoricidal activity against P815 (NO-sensitive, TNF-resistant) cells but not the L929 (TNF-sensitive, NO-resistant) cells. These results indicated l-arginine-dependent production of NO to be one of the effector mechanisms contributing to the tumoricidal activity of MCP-1-treated macrophages. Supporting this fact, expression of iNOS mRNA was also detected in the murine peritoneal macrophages upon treatment with MCP-1. Investigating the signal transduction pathway responsible for the NO production by the MCP-1-activated murine peritoneal macrophages, it was observed that the pharmacological inhibitors wortmannin, H-7 (1-(5-isoquinoline sulfonyl)-2-methyl piperazine dihydrochloride), and PD98059 blocked the MCP-1-induced NO production, suggesting the probable involvement of phosphoinositol-3-kinase, protein kinase C, and p42/44 MAPkinases in the above process. Various modulators of calcium and calmodulin (CaM) such as EGTA, nifedipine, TMB-8 (3,4,5-trimethoxybenzoic acid-8-(diethylamino)octyl ester), A23187, and W-7 (N-(6-aminohexyl)-5-chloro-1-napthalenesulfonamide) were also found to modulate the in vitro macrophage NO release in response to MCP-1. This observation indicated the regulatory role of calcium/CaM in the process of MCP-1-induced macrophage NO production. Similarly, the role of serine/threonine and protein tyrosine phosphatases in the above pathway was suggested using the specific inhibitors of these phosphatases, okadaic acid and sodium orthovanadate.

Expression of proangiogenic chemokine Gro 1 in low and high metastatic variants of Pam murine squamous cell carcinoma is differentially regulated by IL-1alpha, EGF and TGF-beta1 through NF-kappaB dependent and independent mechanisms

We previously reported that chemokine Growth Regulated Oncogene 1 (Gro 1) is over-expressed in murine squamous cell carcinoma (SCC) with metastatic tumor progression. The enhanced expression of Gro-1 gene by SCC is regulated by activation of nuclear factor-kappaB (NF-kappaB), leading to accelerated tumor growth, angiogenesis and metastasis in vivo. In our study, we investigated the effect of the regulatory cytokines, IL-1alpha, EGF and TGF-beta1 on activation of NF-kappaB and Gro1 in primary and metastatic sublines of the murine SCC Pam 212. We found that Gro 1 expression could be induced by IL-1alpha or EGF in the low cytokine producing Pam 212 cells, but no significant induction was observed in high cytokine producing and metastatic LY-2 cells. Conditioned medium from LY-2 containing functional IL-1alpha induced Gro 1 expression in Pam 212 cells, which can be blocked by IL-1 receptor antagonist (IL-1RA). IL-1RA, however, had a minimal effect on constitutive Gro 1 production by LY-2 cells. TGF-beta1 suppressed constitutive as well as IL-1alpha and EGF-inducible Gro 1 production in both Pam 212 and LY-2 cells. IL-1alpha and EGF, but not TGF-beta1, were found to activate NF-kappaB in Pam 212, whereas none of the stimulants showed a significant effect on constitutive activation of NF-kappaB in LY-2 cells. Overexpression of a super repressor IkappaBalphaM in Pam 212 inhibited NF-kappaB binding activity, which led to impaired Gro 1 induction by IL-1alpha and EGF. These results demonstrate that IL-1alpha, EGF, and TGF-beta1 are important modulators of Gro 1 expression in SCC. Different responses to these modulators observed along with SCC metastatic progression may suggest a transition mechanism(s) for Gro 1 expression from host factor dependent to an independent stage involving NF-kappaB activation. Published 2001 Wiley-Liss, Inc.

The treatment, management and prevention of oesophageal cancer

The combination of a rising incidence and a poor survival rate makes oesophageal cancer a major health issue. Adenocarcinoma of the oesophagus is associated with one of the commonest pre-malignant lesions recognised, Barrett's metaplasia. This provides a focus for early detection and intervention. The subjects of acid suppression, bile reflux, COX-2 inhibition and ablation therapy will be discussed herewith. Established carcinoma is now rarely treated by surgery alone and this review discusses the benefits of multimodality therapy combined with more accurate staging techniques. Finally an emerging understanding of the molecular events that characterise the transition to carcinoma may provide novel targets in cancer therapy such as epidermal growth factor receptor (EGFR) and TNF-alpha. This review will focus on some of the future developments in the treatment of oesophageal cancer.

Novel immunotherapy for peritoneal dissemination of murine colon cancer with macrophage inflammatory protein-1beta mediated by a tumor-specific vector, HVJ cationic liposomes

A critical issue for cancer treatment is control of metastatic or disseminated tumors. Although immune gene therapy has been considered as a possible strategy for treatment of such tumors, successful results have not yet been obtained. To evoke antitumor immunity more efficiently, macrophage inflammatory protein-1beta (MIP-1beta) was used for gene therapy of colon cancer in mice. Injection of hemagglutinating virus of Japan (HVJ) cationic liposomes-MIP-1beta into subcutaneous tumor masses resulted in local expression of MIP-1beta and local accumulation of CD4(+) T lymphocytes. Few studies of cancer gene therapies have targeted peritoneal dissemination. In a mouse model of peritoneal dissemination of colon tumor, we used a luciferase-based assay to demonstrate that HVJ cationic liposomes had high tumor specificity and were effective vectors for transfer of genes in peritoneal dissemination. When mice were treated by intraperitoneal injection of HVJ cationic liposomes containing the MIP-1beta gene, the survival periods of the MIP-1beta-treated mice were significantly longer than those of control mice. Therefore, this HVJ cationic liposome strategy may serve as a powerful tool against peritoneal disseminated cancer.

Bioinformatic identification of potential autocrine signaling loops in cancers from gene expression profiles

Many biological signaling pathways involve autocrine ligand-receptor loops; misregulation of these signaling loops can contribute to cancer phenotypes. Here we present an algorithm for detecting such loops from gene expression profiles. Our method is based on the hypothesis that for some autocrine pathways, the ligand and receptor are regulated by coupled mechanisms at the level of transcription, and thus ligand-receptor pairs comprising such a loop should have correlated mRNA expression. Using our database of experimentally known ligand-receptor signaling partners, we found examples of ligand-receptor pairs with significantly correlated expression in five cancer-based gene expression datasets. The correlated ligand-receptor pairs we identified are consistent with known autocrine signaling events in cancer cells. In addition, our algorithm predicts new autocrine signaling loops that can be verified experimentally. Chemokines were commonly members of these potential autocrine pathways. Our analysis also revealed ligand-receptor pairs with expression patterns that may indicate cellular mechanisms for preventing autocrine signaling.

Urokinase plasminogen activator and plasmin efficiently convert hemofiltrate CC chemokine 1 into its active

We have previously isolated from human hemofiltrate an N-terminally truncated form of the hemofiltrate CC chemokine 1 (HCC-1), and characterized HCC-1[9-74] as a strong agonist of CCR1, CCR5, and to a lower extent CCR3. In this study, we show that conditioned media from human tumor cell lines PC-3 and 143B contain proteolytic activities that convert HCC-1 into the [9-74] form. This activity was fully inhibited by inhibitors of urokinase-type plasminogen activator (uPA), including PA inhibitor-1, an anti-uPA mAb, and amiloride. Pure preparations of uPA processed HCC-1 with high efficiency, without further degrading HCC-1[9-74]. Plasmin could also generate HCC-1[9-74], but degraded the active product as well. The kinetics of HCC-1 cleavage by uPA and plasmin (Michaelis constant, K(m), of 0.76 +/- 0.4 microM for uPA, and 0.096 +/- 0.05 microM for plasmin; catalytic rate constant, k(cat): 3.36 +/- 0.96 s(-1) for uPA and 6 +/- 3.6 s(-1) for plasmin) are fully compatible with a role in vivo. The activation of an abundant inactive precursor into a broad-spectrum chemokine by uPA and plasmin directly links the production of uPA by numerous tumors and their ability to recruit mononuclear leukocytes, without the need for the transcriptional activation of chemokine genes.

Ligation of the Fas antigen stimulates chemokine secretion in pancreatic cancer cell line PANC-1

BACKGROUND AND AIM

The role of chemokines in the process of immune cell infiltration into pancreatic cancer tissue has been reported. In this study, we investigated the induction of chemokines (interleukin (IL)-8 and monocyte chemoattractant protein (MCP)-1) by Fas antigen (Ag)-stimulation in a human pancreatic cancer cell line, PANC-1.

METHODS

The chemokine secretion was evaluated by using an ELISA and a northern blot, and the activation of nuclear factor-kappa B (NF-kappa B) was assessed by using an electrophoretic gel mobility shift assay (EMSA).

RESULTS

The Fas antigen (Ag) stimulation clearly induced an increase in IL-8 and MCP-1 secretion in PANC-1 cells. This effect was also observed at the mRNA level. The induction of chemokine secretion by Fas Ag stimulation required de novo gene expression and protein synthesis. The pretreatment with interferon (IFN)-gamma markedly enhanced the effects of Fas Ag stimulation; IFN-gamma pretreatment and Fas Ag stimulation synergistically induced not only apoptosis but also IL-8 and MCP-1 secretion. Flow cytometric analysis demonstrated that IFN-gamma significantly enhanced Fas Ag expression. In addition, Fas Ag stimulation actually evoked NF-kappa B activation in this cell line.

CONCLUSION

Our results indicate that Fas Ag stimulation can induce chemokine secretion in PANC-1 cells, suggesting the contribution of Fas stimulation to the accumulation of immune cells in pancreatic cancer tissue.

Analysis of CC chemokine and chemokine receptor expression in solid ovarian tumours

To understand the chemokine network in a tissue, both chemokine and chemokine receptor expression should be studied. Human epithelial ovarian tumours express a range of chemokines but little is known about the expression and localisation of chemokine receptors. With the aim of understanding chemokine action in this cancer, we investigated receptors for CC-chemokines and their ligands in 25 biopsies of human ovarian cancer. CC-chemokine receptor mRNA was generally absent from solid tumours, the exception being CCR1 which was detected in samples from 75% of patients. CCR1 mRNA localised to macrophages and lymphocytes and there was a correlation between numbers of CD8(+) and CCR1 expressing cells (P = 0.031). mRNA for 6 CC-chemokines was expressed in a majority of tumour samples. In a monocytic cell line in vitro, we found that CCR1 mRNA expression was increased 5-fold by hypoxia. We suggest that the CC-chemokine network in ovarian cancer is controlled at the level of CC-chemokine receptors and this may account for the phenotypes of infiltrating cells found in these tumours. The leukocyte infiltrate may contribute to tumour growth and spread by providing growth survival factors and matrix metalloproteases. Thus, CCR1 may be a novel therapeutic target in ovarian cancer.

Chemokine signaling and functional responses: the role of receptor dimerization and TK pathway activation

A broad array of biological responses, including cell polarization, movement, immune and inflammatory responses, and prevention of HIV-1 infection, are triggered by the chemokines, a family of structurally related chemoattractant proteins that bind to specific seven-transmembrane receptors linked to G proteins. Here we discuss one of the early signaling pathways activated by chemokines, the JAK/STAT pathway. Through this pathway, and possibly in conjunction with other signaling pathways, the chemokines promote changes in cellular morphology, collectively known as polarization, required for chemotactic responses. The polarized cell expresses the chemokine receptors at the leading cell edge, to which they are conveyed by rafts, a cholesterol-enriched membrane fraction fundamental to the lateral organization of the plasma membrane. Finally, the mechanisms through which the chemokines promote their effect are discussed in the context of the prevention of HIV-1 infection.

Multi-faceted analyses of a highly metastatic human lung cancer cell line NCI-H460-LNM35 suggest mimicry of inflammatory cells in metastasis

This study established and characterized low-metastatic revertant and parental clones of a highly metastatic human lung cancer cell line, NCI-H460-LNM35 (hereafter referred to as LNM35). Expression-profiling analysis revealed that up-regulation of various proinflammatory cytokines and angiogenic chemotactic chemokines was present in LNM35. Further, while COX-2 itself is known to be inducible in inflammation, COX-2 expression levels correlated well with the capabilities of these clones for not only in vitro motility and invasion but also in vivo metastasis, and COX-2 inhibitors were shown for the first time to reduce lung cancer metastasis in vivo. These findings suggest that lung cancer cells may mimic inflammatory cells in the process of metastasis.

Therapeutic relevance of altered cytokine expression

Cytokines and their receptors have numerous physiological functions. Altered concentrations of these mediators are associated with various afflictions. For example, over-expression of cytokines has been associated with altered drug concentrations and activity. Greater concentrations of cardiovascular drugs have been observed in humans and laboratory animals with various types of inflammatory disorders compared to healthy controls. Interestingly, the observed higher concentrations of drugs such as propranolol and verapamil have not been associated with increased effects. Indeed, reduced response to these cardiovascular drugs is observed, suggestive of cytokine-mediated downregulation of receptors. Increased cytokine concentrations have also been associated with decreased response to drugs used in treatment of other disorders such as AIDS, asthma and psychiatric diseases. This reduced response to drug in the presence of altered cytokine concentrations is especially relevant to the elderly population which has a greater incidence of multiple diseases and elevated concentrations of various cytokines compared to younger individuals. Furthermore, inflammatory conditions and their accompanied increased over-expression of cytokines are suggested to be the main determinants of therapeutic failure in myocardial infarction and angina. Therefore, altered cytokine concentrations may influence therapeutic outcomes of pharmacotherapy and result in treatment failure.

Osteopontin deficiency reduces experimental tumor cell metastasis to bone and soft tissues

Osteopontin has been implicated in the metastasis of tumors, and human tumors with high metastatic activity often express osteopontin at high levels. Osteopontin contains an arginine-glycine-aspartate (RGD) motif that is recognized by integrin family members to promote various cell activities including attachment to substrate and it is abundant in bone, to which certain tumors preferentially metastasize. Therefore, we investigated the role of osteopontin in the experimental metastasis of tumor cells using recently established osteopontin-deficient mice. B16 melanoma cells, which produce little osteopontin, were injected into the left ventricle of osteopontin-deficient mice or wild-type mice. Animals were killed 2 weeks after injection. The number of tumors was reduced in the bones of osteopontin-deficient mice compared with the bones in wild-type mice. The number of tumors in the adrenal gland also was reduced. To investigate the osteopontin effect on metastases via a different route, we injected B16 melanoma cells into the femoral vein. Through this route, the number of lung tumors formed was higher than in the intracardiac route and was again less in osteopontin-deficient mice compared with wild-type mice. In conclusion, in an experimental metastasis assay, the number of tumors found in bone (after intracardiac injection) and lung (after left femoral vein injection) was significantly reduced in osteopontin-deficient mice compared with wild-type mice. Tumor numbers in other organs examined were small and not significantly different in the two situations.

Involvement of chemokine receptors in breast cancer metastasis

Breast cancer is characterized by a distinct metastatic pattern involving the regional lymph nodes, bone marrow, lung and liver. Tumour cell migration and metastasis share many similarities with leukocyte trafficking, which is critically regulated by chemokines and their receptors. Here we report that the chemokine receptors CXCR4 and CCR7 are highly expressed in human breast cancer cells, malignant breast tumours and metastases. Their respective ligands CXCL12/SDF-1alpha and CCL21/6Ckine exhibit peak levels of expression in organs representing the first destinations of breast cancer metastasis. In breast cancer cells, signalling through CXCR4 or CCR7 mediates actin polymerization and pseudopodia formation, and subsequently induces chemotactic and invasive responses. In vivo, neutralizing the interactions of CXCL12/CXCR4 significantly impairs metastasis of breast cancer cells to regional lymph nodes and lung. Malignant melanoma, which has a similar metastatic pattern as breast cancer but also a high incidence of skin metastases, shows high expression levels of CCR10 in addition to CXCR4 and CCR7. Our findings indicate that chemokines and their receptors have a critical role in determining the metastatic destination of tumour cells.

The transient expression of C-C chemokine receptor 8 in thymus identifies a thymocyte subset committed to become CD4+ single-positive T cells

Developing T cells journey through the different thymic microenvironments while receiving signals that eventually will allow some of them to become mature naive T cells exported to the periphery. This maturation can be visualized by the phenotype of the developing cells. CCR8 is a ss-chemokine receptor preferentially expressed in the thymus. We have developed 8F4, an anti-mouse CCR8 mAb that is able to neutralize the ligand-induced activation of CCR8, and used it to characterize the CCR8 protein expression in the different thymocyte subsets. Taking into account the intrathymic lineage relationships, our data showed that CCR8 expression in thymus followed two transient waves along T cell maturation. The first one took place in CD4(-) CD8(-) double-negative thymocytes, which showed a low CCR8 expression, and the second wave occurred after TCR activation by the Ag-dependent positive selection in CD4(+) CD8(+) double-positive cells. From that maturation stage, CCR8 expression gradually increased as the CD4(+) cell differentiation proceeded, reaching a maximum at the CD4(+) CD8(-) single-positive stage. These CD4(+) cells expressing CCR8 were also CD69(high) CD62L(low) thymocytes, suggesting that they still needed to undergo some differentiation step before becoming functionally competent naive T cells ready to be exported from the thymus. Interestingly, no significant amounts of CCR8 protein were detectable in CD4(-) CD8(+) thymocytes. Our data showing a clear regulation of the CCR8 protein in thymus suggest a relevant role for CCR8 in this lymphoid organ, and identify CCR8 as a possible marker of thymocyte subsets recently committed to the CD4(+) lineage.

Natural proteolytic processing of hemofiltrate CC chemokine 1 generates a potent CC chemokine receptor (CCR)1 and CCR5 agonist with anti-HIV properties

Hemofiltrate CC chemokine (HCC)-1 is a recently described human chemokine that is constitutively expressed in numerous tissues and is present at high concentrations in normal plasma. Using a cell line expressing CC chemokine receptor (CCR)5 as a bioassay, we isolated from human hemofiltrate an HCC-1 variant lacking the first eight amino acids. HCC-1[9-74] was a potent agonist of CCR1, CCR3, and CCR5 and promoted calcium flux and chemotaxis of T lymphoblasts, monocytes, and eosinophils. It also blocked entry of HIV-1 strains using CCR5 as coreceptor. Limited tryptic digestion of HCC-1 generated the active variant. Conditioned media from several tumor cell lines activated HCC-1 with a high efficiency, and this activity could be inhibited by serine protease inhibitors. Our results indicate that HCC-1 represents a nonfunctional precursor that can be rapidly converted to the active chemokine by proteolytic processing. This process represents an additional mechanism by which tumor cells might generate chemoattractant molecules and recruit inflammatory cells. It might also affect HIV-1 replication in infected individuals and play an important role in AIDS pathogenesis.

Isolation and characterization of a new chemokine receptor gene, the putative chicken CXCR1

This study delineates the isolation and characterization of a novel chemokine receptor gene, the putative chicken CXC receptor 1 (cCXCR1). Using a human CXCR1 probe, we isolated several positive clones from a chicken genomic library. One of the clones contained a fragment of approximately 5000bp that hybridized strongly with the hCXCR1 probe. This fragment was sequenced and subjected to a variety of computer analyses. The open reading frame for this gene predicts a seven transmembrane domain protein with all the characteristics of a chemokine receptor and with 67% sequence homology to hCXCR1, 65% to hCXCR2 and also with considerable sequence homology to other human chemokine receptors such as hCXCR4 (50%), hCCR2 (49%) and hCCR1 (49%). However, the homology to a previously isolated potential G-protein-coupled receptor for chickens (AvCRL1) is only 47%. Using 5' RACE, two transcription initiation sites were identified suggesting the potential for the expression of two protein isoforms (I and II) in vivo. The promoter for the putative cCXCR1 contains a variety of consensus transcription factor binding elements that can potentially be involved in the expression of this chicken receptor upon stimulation by stress-inducing agents. RT-PCR analysis was used to determine the pattern of expression of the larger isoform (I) of this receptor in a variety of tissues. This form of the receptor is expressed primarily in the organs of the gastrointestinal tract, tissues that are frequently exposed to stress-inducing agents, but not in the central nervous system, tissues that are protected from insult by the blood barrier. Using the same RT-PCR approach we show that stress-inducing agents, such as 'first-hand' and 'second-hand' cigarette smoke components, tumor promoters and thrombin, differentially stimulate the expression of the isoform I in primary fibroblasts. Thrombin is an enzyme that plays many important roles in thrombosis, angiogenesis and wound healing and exposure to both cigarette smokes and/or to tumor promoters can lead to tumorigenesis. Therefore, upregulation of chemokines and their receptors by stress-inducing agents can confer highly regulated modulation of cellular responses to traumatic and pathological situations.

Flavonoid baicalin inhibits HIV-1 infection at the level of viral entry

Baicalin (BA) is a flavonoid compound purified from medicinal plant Scutellaria baicalensis Georgi and has been shown to possess anti-inflammatory and anti-HIV-1 activities. In an effort to elucidate the mechanism of the anti-inflammatory effect of BA, we recently found that this flavonoid compound was able to form complexes with selected chemokines and attenuated their capacity to bind and activate receptors on the cell surface. These observations prompted us to investigate whether BA could inhibit HIV-1 infection by interfering with viral entry, a process known to involve interaction between HIV-1 envelope proteins and the cellular CD4 and chemokine receptors. We found that BA at the noncytotoxic concentrations, inhibited both T cell tropic (X4) and monocyte tropic (R5) HIV-1 Env protein mediated fusion with cells expressing CD4/CXCR4 or CD4/CCR5. Furthermore, presence of BA at the initial stage of HIV-1 viral adsorption blocked the replication of HIV-1 early strong stop DNA in cells. Since BA did not inhibit binding of HIV-1 gp120 to CD4, we propose that BA may interfere with the interaction of HIV-1 Env with chemokine coreceptors and block HIV-1 entry of target cells. Therefore, BA can be used as a basis for developing novel anti-HIV-1 agents.

The flavonoid baicalin exhibits anti-inflammatory activity by binding to chemokines

Baicalin (BA) is a flavonoid compound purified from the medicinal plant Scutellaria baicalensis Georgi and has been reported to possess anti-inflammatory and anti-viral activities. In order to elucidate the mechanism(s) of action of BA, we tested whether BA could interfere with chemokines or chemokine receptors, which are critical mediators of inflammation and infection. We observed that BA inhibited the binding of a number of chemokines to human leukocytes or cells transfected to express specific chemokine receptors. This was associated with a reduced capacity of the chemokines to induce cell migration. Co-injection of BA with CXC chemokine interleukin-8 (IL-8) into rat skin significantly inhibited IL-8 elicited neutrophil infiltration. BA did not directly compete with chemokines for binding to receptors, but rather acted through its selective binding to chemokine ligands. This conclusion was supported by the fact that BA cross-linked to oxime resin bound chemokines of the CXC (stromal cell-derived factor (SDF)-1alpha, IL-8), CC (macrophage inflammatory protein (MIP)-1beta, monocyte chemotactic protein (MCP)-2), and C (lymphotactin (Ltn)) subfamilies. BA did not interact with CX3C chemokine fractalkine/neurotactin or other cytokines, such as TNF-alpha and IFN-gamma, indicating that its action is selective. These results suggest that one possible anti-inflammatory mechanism of BA is to bind a variety of chemokines and limit their biological function.

Antitumor effects of the mouse chemokine 6Ckine/SLC through angiostatic and immunological mechanisms

Mouse 6Ckine/SLC (secondary lymphoid tissue chemokine) is a chemotactic factor for dendritic cells, T cells, and NK cells in vitro. In addition, mouse 6Ckine/SLC interacts with the chemokine receptor CXCR3, as do several chemokines with antiangiogenic properties. These dual properties of mouse 6Ckine/SLC were tested for the induction of an antitumor response by transducing the C26 colon carcinoma tumor cell line with a cDNA encoding mouse 6Ckine/SLC. The C26-6CK-transduced cells showed reduced tumorigenicity in immunocompetent or in nude mice. Part of this effect was likely due to angiostatic mechanisms as shown by immunohistochemistry and Matrigel assay. C26-6CK tumors were also heavily infiltrated with leukocytes, including granulocytes, dendritic cells, and CD8+ T cells. In vivo, anti-CD8 treatment increased the tumorigenicity of the C26-6CK tumor cells, and tumor-infiltrating CD8+ T cells had the phenotype of memory effector cells, suggesting the induction of cytotoxic tumor-specific T lymphocytes. On the other hand, anti-asialo-GM1 depletion also increased the tumorigenicity of C26-6CK cells, supporting the participation of NK cells. Finally, tumor-infiltrating dendritic cells had the phenotype and functional features of immature dendritic cells. Overall, these results suggest that mouse 6Ckine/SLC has strong antitumor effects by inducing both angiostatic, CD8+ T cell-mediated, and possibly NK-mediated tumor resistance mechanisms.

The biology of chemokines and their receptors

During the last five years, the development of bioinformatics and EST databases has been primarily responsible for the identification of many new chemokines and chemokine receptors. The chemokine field has also received considerable attention since chemokine receptors were found to act as co-receptors for HIV infection (1). In addition, chemokines, along with adhesion molecules, are crucial during inflammatory responses for a timely recruitment of specific leukocyte subpopulations to sites of tissue damage. However, chemokines and their receptors are also important in dendritic cell maturation (2), B (3), and T (4) cell development, Th1 and Th2 responses, infections, angiogenesis, and tumor growth as well as metastasis (5). Furthermore, an increase in the number of chemokine/receptor transgenic and knock-out mice has helped to define the functions of chemokines in vivo. In this review we discuss some of the chemokines' biological effects in vivo and in vitro, described in the last few years, and the implications of these findings when considering chemokine receptors as therapeutic targets.

The expression of chemokine genes correlates with nuclear factor-kappaB activation in human pancreatic cancer cell lines

Chemokines may regulate the process of immune cell infiltration that is often found in pancreatic cancer. In this study, we investigated the secretion of the chemokines [interleukin (IL)-8, monocyte chemoattractant protein (MCP)-1, and RANTES (regulated on activation, normal T cell expressed and secreted)] in human pancreatic cancer cell lines. The chemokine secretion in three pancreatic cancer cell lines (PANC-1, MIA PaCa-2, and BxPC-3) was evaluated by enzyme-linked immunosorbent assay (ELISA) and Northern blot, and the activation of nuclear factor-kappaB (NF-kappaB) and NF-IL6 was assessed by an electrophoretic gel mobility shift assay (EMSA). Without any stimulation, IL-8 secretion was detected in all cell lines, and MCP-1 secretion was detected in PANC-1 and MIA PaCa-2 cells. However, RANTES secretion was not detected in all cells. The addition of IL-1beta and tumor necrosis factor (TNF)-alpha strongly enhanced IL-8, MCP-1, and RANTES secretion; these responses were observed at the mRNA level as well as at the protein level. IL-1beta and TNF-alpha induced a rapid activation of nuclear factor (NF)-kappaB in PANC-1 cells, and the increase in chemokine mRNA expression correlated with NF-kappaB activation. The activation of NF-IL6 was modest. A blockade of NF-kappaB activation by TPCK markedly reduced the IL-1beta- and TNF-alpha-induced chemokine gene expression. Our findings indicate that chemokines are produced by pancreatic cancer cells, and suggest that these factors may contribute to the accumulation of tumor-associated immune cells. In addition, the transcriptional activation of chemokine genes in pancreatic cancer cells may be closely associated with NF-kappaB activation.

Co-evolution of proteins with their interaction partners

The divergent evolution of proteins in cellular signaling pathways requires ligands and their receptors to co-evolve, creating new pathways when a new receptor is activated by a new ligand. However, information about the evolution of binding specificity in ligand-receptor systems is difficult to glean from sequences alone. We have used phosphoglycerate kinase (PGK), an enzyme that forms its active site between its two domains, to develop a standard for measuring the co-evolution of interacting proteins. The N-terminal and C-terminal domains of PGK form the active site at their interface and are covalently linked. Therefore, they must have co-evolved to preserve enzyme function. By building two phylogenetic trees from multiple sequence alignments of each of the two domains of PGK, we have calculated a correlation coefficient for the two trees that quantifies the co-evolution of the two domains. The correlation coefficient for the trees of the two domains of PGK is 0. 79, which establishes an upper bound for the co-evolution of a protein domain with its binding partner. The analysis is extended to ligands and their receptors, using the chemokines as a model. We show that the correlation between the chemokine ligand and receptor trees' distances is 0.57. The chemokine family of protein ligands and their G-protein coupled receptors have co-evolved so that each subgroup of chemokine ligands has a matching subgroup of chemokine receptors. The matching subfamilies of ligands and their receptors create a framework within which the ligands of orphan chemokine receptors can be more easily determined. This approach can be applied to a variety of ligand and receptor systems.

In vivo expression of the novel CXC chemokine BRAK in normal and cancerous human tissue

Using differential display, we cloned a gene with reduced expression in short-term explants of head and neck squamous cell carcinoma (HNSCC) tumors compared to cultured normal oral epithelial cells. The differentially expressed gene was identical to the recently cloned CXC chemokine BRAK, which is ubiquitously expressed in normal tissue extracts but is absent from many tumor cell lines in vitro. To define the cell populations expressing BRAK in vivo, in situ mRNA hybridization was performed on normal and cancerous tissues from six different histological sites. The predominant normal cell type constitutively expressing BRAK in vivo was squamous epithelium. Expression in tumors was heterogeneous, with the majority of HNSCCs and some cervical squamous cell carcinomas (SCCs) showing loss of BRAK mRNA. Although absent in unstimulated peripheral blood mononuclear cells, high levels of BRAK were consistently found in infiltrating inflammatory cells (with lymphocyte morphology) in nearly all cancers examined. Furthermore, BRAK expression was demonstrated in B cells and monocytes, after stimulation of peripheral blood mononuclear cells with lipopolysaccharide. This study demonstrates for the first time up-regulation of BRAK mRNA by inflammatory cells in the tumor microenvironment and lost expression from certain cancers in vivo. The data suggest that BRAK may have a role in host-tumor interactions.

Inhibition of Tyrosine Kinase Activation Blocks the Down-Regulation of CXC Chemokine Receptor 4 by HIV-1 gp120 in CD4+ T Cells

Because the binding of HIV-1 envelope to CD4 initiates a configurational change in glycoprotein 120 (gp120), enabling it to interact with fusion coreceptors, we investigated how this process interferes with the expression and function of CXC chemokine receptor 4 (CXCR4) in CD4+ T lymphocytes. A recombinant gp120 (MN), after preincubation with CD4+ T lymphocytes, significantly inhibited the binding and chemotaxis of the cells in response to the CXCR4 ligand stromal cell-derived factor-1α (SDF-1α), accompanied by a markedly reduced surface expression of CXCR4. gp120, but not SDF-1α, induced rapid tyrosine phosphorylation of src-like kinase p56lck in CD4+ T cells, whereas both gp120 and SDF-1α caused phosphorylation of the CXCR4. The tyrosine kinase inhibitor herbimycin A abolished the phosphorylation of p56lck and CXCR4 induced by gp120 in association with maintenance of normal expression of cell surface CXCR4 and a migratory response to SDF-1α. Thus, a CD4-associated signaling molecule(s) including p56lck is activated by gp120 and is required for the down-regulation of CXCR4.