Synergistic effects of Candida and Escherichia coli on gut barrier function

BACKGROUND

Disruption of the indigenous gut microflora with overgrowth of gram-negative bacteria and Candida species is common in the critically ill patient. These organisms readily translocate in vitro, which may cause septic complications and organ failure. A synergistic effect between Escherichia coli and C. albicans in polymicrobial infections has been demonstrated. An interaction between these organisms at the mucosal barrier is unknown.

METHODS

Ca(CO2) monolayers were grown to confluence in a two compartment culture system. E. coli and C. albicans or E. coli alone were added to the apical chambers. Secretory immunoglobulin A was added to half of the apical chambers as well. Cell cultures were incubated for a total of 240 minutes. Basal media were sampled at timed intervals for quantitative culture. Monolayer integrity was confirmed by serial measurement of transepithelial electrical resistance.

RESULTS

Secretory immunoglobulin A decreased bacterial translocation across Ca(CO2) monolayers challenged with E. coli alone. Transepithelial passage of E. coli was significantly increased by coculture of bacteria with C. albicans. Augmentation of bacterial translocation by Candida occurred even in the presence of secretory immunoglobulin A.

CONCLUSIONS

Candida colonization of the GI tract may impair mucosal barrier defense against gram-negative bacteria. The clinical role of gut antifungal prophylaxis in protecting against gut derived gram-negative sepsis is speculative.

Mitogen-activated protein kinase (MAPK) regulates the expression of progelatinase B (MMP-9) in breast epithelial cells

Mitogen-activated protein kinases (MAPKs) play a major role in the mitogenic signal transduction pathway and are essential components of both growth and differentiation. Constitutive activation of the MAPK cascade is associated with the carcinogenesis and metastasis of human breast and renal cell carcinomas. The gelatinases B (MMP-9) and A (MMP-2) are 2 members of the matrix metalloproteinase (MMPs) family which are expressed in human cancers and thought to play a critical role in tumor cell invasion and metastasis. In a previous study, we have shown that EGF and amphiregulin upregulate MMP-9 in metastatic SKBR-3 cells but have no effect on MMP-2 secretion. We now investigated specific step(s) in EGF-induced signalling associated with regulation of cell proliferation and MMP-9 induction. EGF-induced signalling in SKBR-3 cells was blocked by relatively specific inhibitors either on ras (FPT inhibitor-1) or P13 kinase (Wortmannin) or by reduction in EGF-induced tyrosine kinase activity (RG 13022). Blocking these signalling pathways significantly inhibited of EGF-induced cell proliferation but only partially reduced in EGF-induced MMP-9 secretion. In contrast, when SKBR-3 cells were exposed to MEK inhibitor (PD 98059) or MAPK inhibitors (Apigenin or MAPK antisense phosphorothioate oligodeoxynucleotides), EGF-induced cell proliferation, MMP-9 induction and invasion through reconstituted basement membrane were significantly reduced. Our results suggest that interfering with MAPK activity may provide a novel means of controlling growth and invasiveness of tumors in which the signalling cascade is activated.

Mitogen-activated protein kinase (MAPK) regulates the expression of progelatinase B (MMP-9) in breast epithelial cells

Mitogen-activated protein kinases (MAPKs) play a major role in the mitogenic signal transduction pathway and are essential components of both growth and differentiation. Constitutive activation of the MAPK cascade is associated with the carcinogenesis and metastasis of human breast and renal cell carcinomas. The gelatinases B (MMP-9) and A (MMP-2) are 2 members of the matrix metalloproteinase (MMPs) family which are expressed in human cancers and thought to play a critical role in tumor cell invasion and metastasis. In a previous study, we have shown that EGF and amphiregulin upregulate MMP-9 in metastatic SKBR-3 cells but have no effect on MMP-2 secretion. We now investigated specific step(s) in EGF-induced signalling associated with regulation of cell proliferation and MMP-9 induction. EGF-induced signalling in SKBR-3 cells was blocked by relatively specific inhibitors either on ras (FPT inhibitor-1) or P13 kinase (Wortmannin) or by reduction in EGF-induced tyrosine kinase activity (RG 13022). Blocking these signalling pathways significantly inhibited of EGF-induced cell proliferation but only partially reduced in EGF-induced MMP-9 secretion. In contrast, when SKBR-3 cells were exposed to MEK inhibitor (PD 98059) or MAPK inhibitors (Apigenin or MAPK antisense phosphorothioate oligodeoxynucleotides), EGF-induced cell proliferation, MMP-9 induction and invasion through reconstituted basement membrane were significantly reduced. Our results suggest that interfering with MAPK activity may provide a novel means of controlling growth and invasiveness of tumors in which the signalling cascade is activated.

Radiation induced endothelial cell retraction in vitro: correlation with acute pulmonary edema

We determined the effects of low dose radiation (<200 cGy) on the cell-cell integrity of confluent monolayers of pulmonary microvascular endothelial cells (PMEC). We observed dose- and time-dependent reversible radiation induced injuries to PMEC monolayers characterized by retraction (loss of cell-cell contact) mediated by cytoskeletal F-actin reorganization. Radiation induced reorganization of F-actin microfilament stress fibers was observed > or =30 minutes post irradiation and correlated positively with loss of cell-cell integrity. Cells of irradiated monolayers recovered to form contact inhibited monolayers > or =24 hours post irradiation; concomitantly, the depolymerized microfilaments organized to their pre-irradiated state as microfilament stress fibers arrayed parallel to the boundaries of adjacent contact-inhibited cells. Previous studies by other investigators have measured slight but significant increases in mouse lung wet weight >1 day post thoracic or whole body radiation (> or =500 cGy). Little or no data is available concerning time intervals <1 day post irradiation, possibly because of the presumption that edema is mediated, at least in part, by endothelial cell death or irreversible loss of barrier permeability functions which may only arise 1 day post irradiation. However, our in vitro data suggest that loss of endothelial barrier function may occur rapidly and at low dose levels (< or =200 cGy). Therefore, we determined radiation effects on lung wet weight and observed significant increases in wet weight (standardized per dry weight or per mouse weight) in < or =5 hours post thoracic exposure to 50 200 cGy x-radiation. We suggest that a single fraction of radiation even at low dose levels used in radiotherapy, may induce pulmonary edema by a reversible loss of endothelial cell-cell integrity and permeability barrier function.

Synergistic effect of hyperoxia and immunoglobulin A on mucosal barrier defense

BACKGROUND

Hyperoxia has been reported to be protective against gut-derived sepsis. Although secretory immunoglobulin A (IgA) is primarily responsible for humoral defense of mucosal surfaces, a potential synergistic effect with hyperoxia is unknown. An asanguineous cell monolayer system was used to study these aspects in vitro.

METHODS

MDCK cells were grown as polarized monolayers in a two-chamber culture system. Apical chambers were inoculated with 10(8) Escherichia coli M14 with or without polyclonal IgA and incubated in a 21 or 95% O2 environment. Basal medium was sampled at 90 and 180 minutes for bacterial translocation. In a second experiment, MDCK cells were lysed at 90 minutes and intracellular bacteria were quantitated.

RESULTS

Bacterial translocation was decreased versus normoxia by the treatment groups IgA without hyperoxia or IgA with hyperoxia at 90 minutes. Bacterial internalization at 90 minutes was reduced to the greatest extent by the combined effects of hyperoxia and IgA. Translocation data at 180 minutes confirmed the additional protective effect of hyperoxia with IgA.

CONCLUSION

Hyperoxia exerts a significant protective effect on barrier function independent of enhanced leukocyte function. Hyperoxia has an added effect to the mucosal defense provided by IgA.

Bradykinin blocks angiotensin II-induced hypertrophy in the presence of endothelial cells

Angiotensin-converting enzyme inhibitors block left ventricular hypertrophy in vivo. A component of this effect has been attributed to tissue accumulation of bradykinin. Little is known regarding the effect of bradykinin on cardiomyocytes. The objectives of the present study were to define the effects of bradykinin on isolated ventricular cardiomyocytes (from adult and neonatal rat hearts) and to determine the extent to which bradykinin blocks hypertrophy in vitro. Bradykinin was found to be a hypertrophic agonist, as defined by increased protein synthesis and atrial natriuretic peptide secretion and expression. Bradykinin (10 micromol/L) increased [3H]phenylalanine incorporation by 23+/-3% in adult and by 36+/-10% in neonatal cardiomyocytes. Constitutive atrial natriuretic peptide secretion by neonatal myocytes was increased 357+/-103%. All effects of bradykinin were abolished by the B2-kinin receptor antagonist Hoe 140. These increases were similar in magnitude to those observed with phenylephrine (20 micromol/L) and angiotensin II (1 micromol/L). However, in cardiomyocytes cocultured with endothelial cells, bradykinin did not increase protein synthesis. Angiotensin II increased [3H]phenylalanine incorporation by 24+/-3% in adult cardiomyocytes in monoculture and by 22+/-2% in adult rat cardiomyocytes cocultured with endothelial cells. Bradykinin abolished this angiotensin II-induced hypertrophy in myocytes cultured with endothelial cells but not in myocytes studied in the absence of endothelial cells. In conclusion, bradykinin has a direct hypertrophic effect on ventricular myocytes. The presence of endothelial cells is required for the antihypertrophic effects of bradykinin. The results suggest that the increase in local concentration of bradykinin associated with angiotensin-converting enzyme inhibition is an important mechanism by which hypertrophy can be blocked. Manifestation of this mechanism appears to require bradykinin-stimulated release of paracrine factor(s) from endothelial cells, which are also able to block the hypertrophic effects of Ang II.

Secretory immunoglobulin A blocks hypoxia-augmented bacterial passage across Madin-Darby canine kidney cell monolayers

OBJECTIVE

To study the relative impact of previous hypoxic exposure and the addition of secretory immunoglobulin A (IgA) on bacterial translocation.

DESIGN

In vitro randomized experimental study.

MATERIALS AND METHODS

Transfected Madin-Darby canine kidney epithelial cells were grown as monolayers in a two-chamber tissue culture system. Stationary growth phase Escherichia coli M14 were inoculated in the apical chamber with medium or medium containing polymeric secretory IgA. Tissue culture dishes were then placed in a 21 or 5% O2 incubator environment for 90 minutes followed by a 21% O2 environment. Medium from the basal compartment was then obtained at timed intervals for bacterial culture.

MEASUREMENT AND MAIN RESULTS

Bacterial translocation increased with time in co-culture. Previous hypoxic exposure augmented translocation across the monolayers. The addition of IgA blocked translocation under both normoxic and hypoxic conditions.

CONCLUSION

Secretory IgA is important in mucosal defense under both normal and shock conditions.

An in vitro model to assess mucosal immune function and bacterial translocation

The importance of secretory immunoglobulin A (IgA) on intestinal barrier function has gained increasing acceptance. However, due to the complexity of the intestinal microenvironment, the relative role of secretory IgA (sIgA) in mucosal defense has been difficult to study in vivo. Polarized Madin-Darby canine kidney (MDCK) epithelial cells expressing the complementary DNA (cDNA) for the polymeric Ig receptor were grown as monolayers in an in vitro two-chamber cell culture system to study the impact of sIgA on bacterial translocation (BT). Polymeric sIgA or media alone was added to the apical chambers of cell monolayers followed by apical inoculation with bacteria. The basal compartment was sampled at timed intervals thereafter to determine BT. Bacterial passage across the MDCK epithelial cell monolayers occurred in a time and bacterial inoculum concentration gradient. Addition of sIgA led to significant reductions in BT across the epithelial cell monolayers. This is a useful model for further investigation on the role of sIgA in intestinal barrier function.

Tumor progression and angiogenesis: cathepsin B & Co

Experimental and clinical evidence reveals that the growth of solid tumors is dependent on angiogenesis. Proteolytic enzymes such as plasminogen activators and matrix metalloproteinases have been implicated in this neovascularization. The role of lysosomal proteases in this process has yet to be explored. Increased expression of the lysosomal cysteine protease cathepsin B has been observed in many etiologically different tumors, including human brain, prostate, breast, and gastrointestinal cancers. Immunohistochemical and in situ histochemical studies have demonstrated expression of cathepsin B in neovessels induced during malignant progression of human glioblastoma and prostate carcinomas. In these two tumor types, neovessels stain strongly for cathepsin B compared with the normal microvasculature. As an initial point to elucidate whether cathepsin B is an important component of the angiogenic response in tumours, we analyzed expression of cathepsin B in endothelial cells during neovessel formation. We present evidence for strong immunostaining of cathepsin B in rat brain microvascular endothelial cells as they form capillary tubes in vitro. This finding is discussed within the general framework of the role of proteolytic enzymes in tumor invasion and angiogenesis.

Transcriptional activation of endothelial cell integrin alpha v by protein kinase C activator 12(S)-HETE

Previous work demonstrated that 12(S)-HETE [12(S)-hydroxyeicosatetraenic acid], a lipoxygenase metabolite of arachidonic acid, stimulates the surface expression of integrin alpha v beta 3 on mouse lung vascular endothelial cells (CD clone 3) in a post-transcriptional and protein kinase C (PKC)-dependent fashion. In this study we examined the effect of 12(S)-HETE on the expression of integrin receptors alpha v beta 3 and alpha 5 beta 1 in a different clone of a mouse endothelial cell population derived from lung microvasculature (designated CD clone 4). The results indicated that 12(S)-HETE transcriptionally activates the gene expression of integrin alpha v as assessed by quantitative reverse transcription/polymerase chain reaction/Southern hybridization, RNase protection assay, solution hybridization, and northern blotting. The induction of alpha v mRNA occurred within 1 hour, peaked at approximately 4 hours (2- to 4-fold increase), persisted for up to 16 hours, and thereafter gradually declined. The PKC activator phorbol 12-myristate 13-acetate (PMA) induced the alpha v mRNA, in a similar way. 12(S)-HETE treatment did not, in contrast, alter the mRNA levels of integrin subunit alpha 5 or beta 1. The induction of alpha v mRNA appeared to be protein synthesis-independent, since cycloheximide did not alter the 12(S)-HETE effect. 12(S)-HETE also did not appear to alter the mRNA half-life of alpha v. On the other hand, 12(S)-HETE-induced increase in alpha v mRNA levels was PKC-dependent, since pretreatment of CD clone 4 cells with calphostin C significantly inhibited 12(S)-HETE-increased alpha v mRNA. Nuclear runoff experiments revealed that the increase in alpha v mRNA results from an enhanced gene transcription. Facilitated alpha v gene transcription resulted in an increased surface expression of alpha v beta 3 protein, which resulted in an increased cell adhesion to vitronectin. The above observations, in conjunction with our previous experimental data, suggest that 12(S)-HETE may employ diverse mechanisms to stimulate the integrin alpha v beta 3 expression in vascular endothelial cells, which could play important roles in tumor cell adhesion, angiogenesis, hemostasis, and many other vascular events.

Endothelial cell interactions with synthetic peptides from the carboxyl-terminal heparin-binding domains of fibronectin

Fibronectin (FN) plays an important role in endothelial cell adhesion, spreading, and motility. Within FN, a number of functional domains have been identified, including the 33/66-kD carboxyl-terminal heparin-binding fragments, which support the adhesion of vascular endothelial cells. A number of synthetic peptides representing amino acid sequences within the 33/66-kD fragments have been shown to promote the adhesion, spreading, and migration of a variety of cell types. Our working hypothesis is that one or more of these sequences may also mediate vascular endothelial cell adhesion, spreading, and migration to the 33/66-kD fragments. In support of this hypothesis, we have demonstrated that endothelial cells from various sources adhered in a concentration-dependent manner to surfaces coated with FN, the 33/66-kD fragments, and synthetic peptides derived from the 33/66-kD fragments of FN. FN and the 33/66-kD fragments also promoted endothelial cell spreading and migration. Although each of the six synthetic peptides tested supported endothelial cell adhesion, only one of these peptides within the carboxyl-terminal heparin-binding domain (FN-C/H-V) promoted endothelial cell spreading and migration. Cell spreading on FN-C/H-V, as well as on FN and the 33/66-kD fragments, was associated with the formation of a well-developed actin cytoskeleton and the formation of focal contacts. FN-C/H-V (but not scrambled FN-C/H-V) inhibited cell spreading on FN and the 33/66-kD fragments in a concentration-dependent manner. FN-C/H-V had a modest effect on the adhesion of a clonal population of rat heart endothelial cells (RHE-1A) to the 33/66-kD fragments of FN and no effect on RHE-1A cell adhesion to FN. These findings suggest that peptide FN-C/H-V is unique among this group of peptides derived from the 33/66-kD heparin-binding fragments of FN in its ability to promote the adhesion, spreading, and migration of vascular endothelial cells and further suggest that the sequence defined by this peptide plays an important role in vascular endothelial cell interactions with the 33/66-kD fragments of FN.

12(S)-HETE is a mitogenic factor for microvascular endothelial cells: its potential role in angiogenesis

12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid] is a lipoxygenase metabolite of arachidonic acid. Treatment of murine-lung-derived microvascular endothelial cells (CD clone 4) with exogenous 12(S)-HETE promoted wound healing of injured endothelial cell monolayers. 12(S)-HETE, in a time- and dose-dependent manner, enhanced the growth of CD clone 4 cells. Thymidine incorporation assays demonstrated that 12(S)-HETE increased the DNA synthesis by > 4 fold. In addition, normal endothelial cell growth stimulated by serum could be dose-dependently inhibited by a select 12-lipoxygenase inhibitor (BHPP), suggesting that 12(S)-HETE is a physiological mitogenic factor for microvascular endothelial cells.

Angiopeptin (BIM23014C) inhibits vascular smooth muscle cell migration in vitro through a G-protein-mediated pathway and is associated with inhibition of adenylyl cyclase and cyclic AMP accumulation

Angiopeptin (AP: BIM23014C), a cyclic analogue of the peptide hormone somatostatin, inhibits intimal hyperplasia after balloon angioplasty. This inhibition has been attributed to a direct inhibitory effect on smooth muscle cell (SMC) proliferation. However, the SMC that proliferate in the intima and contribute to intimal hyperplasia arrive there by migrating from the injured media, suggesting that SMC migration may also play an important role in this process. Indeed, in the experiments we describe, AP inhibited the migration of rat aortic SMC cells (RA-SMC) in response to type I collagen, the predominant form of collagen in the vessel media, and did so dose dependently. RA-SMC migration was inhibited 70% in the presence of AP 100 nM. RA-SMC adhesion to type I collagen in these conditions was not inhibited, suggesting that AP does not interfere with RA-SMC recognition of type I collagen; instead, it blocks subsequent signaling events that are necessary for RA-SMC migration in response to type I collagen. AP inhibited the forskolin-stimulated accumulation of cyclic AMP by RA-SMC (35% at 30 nM). In addition, pertussis toxin (PT), which blocks Gi-mediated inhibition of adenylyl cyclase, blocked the inhibitory effect of AP on cyclic AMP (cAMP) accumulation and also blocked the inhibitory effect of AP on RA-SMC migration. These findings suggest that the inhibitory effect of AP on intimal hyperplasia is due at least in part to its effects on SMC migration and that these effects are mediated by a Gi-dependent pathway and may involve inhibition of adenylyl cyclase and cAMP accumulation.

Inhibition of TPA and 12(S)-HETE-stimulated tumor cell adhesion by prostacyclin and its stable analogs: rationale for their antimetastatic effects

We have investigated the regulatory role of PGI2 and its stable analogs, i.e., iloprost and cicaprost, on 12(S)-HETE- and TPA-enhanced tumor cell integrin expression and adhesion. Walker 256 carcinosarcoma cells express alpha IIb beta 3 integrin receptors, which mediate their adhesion to endothelium, subendothelial matrix and fibronectin. Adhesion is enhanced by treatment with exogenous 12(S)-HETE but not 12(R)-HETE or other lipoxygenase-derived hydroxy fatty acids, as well as by TPA. Both 12(S)-HETE and TPA enhanced alpha IIb beta 3 expression on W256 cells. PGI2 iloprost and cicaprost inhibited both 12(S)-HETE- and TPA-enhanced adhesion to endothelium and subendothelial matrix as well as alpha IIb beta 3 expression on W256 cells. The mechanism responsible for the effect of PGI2 was explored. Prostacyclin treatment of W256 cells resulted in an enhanced production of cAMP in a time- and dose-dependent manner. Pre-treatment of tumor cells with increasing concentrations of adenosine resulted in a dose-dependent decrease in the PGI2 effect on TPA or 12(S)-HETE-enhanced adhesion, suggesting that the PGI2 effect is mediated through PKA. Dibutyryl cAMP also blocked the 12(S)-HETE- or TPA-enhanced adhesion, and adenosine pre-treatment did not result in an inhibition of the dibutyryl cAMP effect. Collectively, our results suggest that the cyclooxygenase metabolite PGI2 can antagonize the lipoxygenase metabolite 12(S)-HETE- and TPA-enhanced alpha IIb beta 3 expression and tumor cell adhesion via activation of adenylate cyclase and elevation of intracellular levels of cAMP.

Angiotensin II induces TGF-beta 1 production in rat heart endothelial cells

Angiotensin II (AII) was found to stimulate TGF-beta 1 gene expression in rat heart endothelial cells in a dose- and time-dependent manner. The maximal induction of TGF-beta 1 mRNA was achieved by 6 h after the addition of AII. This induction was blocked by losartan, an AT1 receptor antagonist and by calphostin C, a protein kinase C inhibitor. Addition of actinomycin D and cycloheximide abolished the induction. TGF-beta 1 promoter activities were stimulated 5-fold by AII. TGF-beta 1 secreted by the rat heart endothelial cells in response to AII was in a latent form and could be activated by mild heat treatment. These results suggest that AII stimulates TGF-beta 1 production by a protein kinase C-dependent pathway which is dependent upon de novo RNA synthesis and protein synthesis. Since endothelial cells line the blood vessels and sense the rise in AII associated with hypertension, the release of TGF-beta 1 by these cells may provide the initial trigger leading to cardiac fibrosis in angiotensin-renin-dependent hypertension.

Biosynthesis of 12(S)-hydroxyeicosatetraenoic acid by B16 amelanotic melanoma cells is a determinant of their metastatic potential

BACKGROUND

We have previously demonstrated that the metastatic potential of tumor cells can be increased by treatment with exogenous 12(S)hydroxyeicosatetraenoic acid [12(S)-HETE], a lipoxygenase metabolite of arachidonic acid. However, the biosynthesis of the authentic lipid mediator by tumor cells, and especially the correlation of its biosynthesis to tumor cell metastatic capacity have not been characterized. In addition, a role for other mono HETEs in influencing tumor cell metastatic behavior has been suggested, but conclusive evidence is lacking. In this study, we analyzed the biosynthesis of mono HETEs from arachidonic acid in tumor cells of different metastatic ability and correlated biosynthesis to metastatic potential.

EXPERIMENTAL DESIGN

The biosynthesis of mono HETEs by low and high metastatic subpopulations of B16 amelanotic melanoma (B16a) cells was analyzed by high performance liquid chromatography (HPLC). The identity of biosynthetic 12-HETE was confirmed by gas chromatography/mass spectrometry (GC/MS) and its stereochemical structure assigned by chiral phase HPLC. The effect of a lipoxygenase inhibitor on the biosynthesis of mono HETEs and its effect on metastatic behavior was examined.

RESULTS

HPLC analysis revealed that low (LM180) and high (HM340) metastatic B16a cells exhibited different profiles and efficiencies for conversion of arachidonic acid to mono HETEs. LM180 cells produced equal quantities of 12-HETE and 5-HETE. In contrast, HM340 cells synthesized predominantly 12-HETE and small amounts of 15-, 11- and 5-HETEs. At equal concentrations of substrate, four times more 12-HETE was synthesized by HM340 cells than by LM180 cells. The identity of biosynthetic 12-HETE was confirmed by gas chromatography/mass spectrometry and chiral phase HPLC demonstrated that it was the S enantiomer. The biosynthesis of 12(S)-HETE, but not other HETEs, was significantly inhibited by a lipoxygenase inhibitor, N-benzyl-N-hydroxy-5-phenylpentanamide. N-benzyl-N-hydroxy-5-phenylpentanamide, in a dose-dependent manner, decreased the adhesion of HM340 cells to murine pulmonary microvessel endothelium in vitro and lung colony formation in vivo. Furthermore, re-introduction of 12(S)-HETE, but not other mono HETEs, to HM340 cells pretreated with N-benzyl-N-hydroxy-5-phenylpentanamide, increased their adhesion to endothelium.

CONCLUSIONS

Biosynthesis of 12(S)-HETE by tumor cells is a determinant of their metastatic potential and inhibition of 12(S)-HETE biosynthesis in tumor cells may be a crucial target for intervening in metastasis.

Activation of microvascular endothelium by eicosanoid 12(S)-hydroxyeicosatetraenoic acid leads to enhanced tumor cell adhesion via up-regulation of surface expression of alpha v beta 3 integrin: a posttranscriptional, protein kinase C- and cytoskeleton-dependent process

Tumor cell interaction with endothelial cells is a crucial step leading to organ-selective metastasis. Adhesion of murine B16 amelanotic melanoma cells (B16a) to murine microvascular endothelial cells (CD3) was enhanced, in a dose- and time-dependent manner, by pretreating CD3 cells with 12(S)-hydroperoxyeicosatetraenoic acid [i.e., 12(S)-HETE], a 12-lipoxygenase metabolite of arachidonic acid. The metabolic precursor of 12(S)-HETE, 12-HPETE (12-hydroperoxyeicosatetraenoic acid) also enhanced B16a cell adhesion to CD3 monolayers, whereas other lipoxygenase products, i.e., 5(S), 11(S), and 15(S)-HETEs were ineffective. 12(S)-HETE-enhanced tumor cell adhesion was blocked by treating endothelial cells with antibodies against the alpha v beta 3 complex or against individual subunits but not with antibodies against alpha 5 beta 1. In contrast, neither of these two integrins appeared to be involved in tumor cell adhesion to unstimulated endothelium. Flow cytometric analysis, immunofluorescent labeling, and image analysis indicated that 12(S)-HETE induced a time- and dose-dependent increase in the surface expression of alpha v beta 3 but not alpha 5 beta 1 on CD3 cells. The increased surface expression of alpha v beta 3 on endothelial cells did not result from an increased transcription or translation of alpha v beta 3 message as confirmed by quantitative reverse transcription-polymerase chain reaction, Northern blotting, and quantitative Western blotting. Instead, subcellular fractionation studies revealed an increased translocation of alpha v beta 3 integrins from the cytosolic pool to the membrane fractions. Pretreatment of endothelial cells with several cytoskeleton-disrupting agents (i.e., cycloheximide or acrylamide to disrupt intermediate filament vimentin, cytochalasin D to disrupt microfilaments, colchicine or Nocodazole to disrupt microtubules) abolished the 12(S)-HETE-enhanced alpha v beta 3 surface expression as well as tumor cell adhesion to endothelial cells. Also, pretreatment of CD3 cells with protein kinase C inhibitor calphostin C, but not with protein kinase A inhibitor H8, blocked 12(S)-HETE-enhanced alpha v beta 3 surface expression and tumor cell adhesion. Collectively, these results suggest that eicosanoid 12(S)-HETE modulates tumor cell interaction with endothelium via protein kinase C- and cytoskeleton-dependent up-regulation of the surface expression of alpha v beta 3 integrin.

Tumor cell-derived 12(S)-hydroxyeicosatetraenoic acid induces microvascular endothelial cell retraction

Our previous work demonstrated that the 12-lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE] induced a nondestructive and reversible retraction of cultured endothelial cells. In the current study we tested the hypothesis that tumor cells produce 12(S)-HETE during their interactions with endothelial cells which in turn induces endothelial cell retraction. Coincubation of Lewis lung carcinoma cells or elutriated B16 amelanotic melanoma (B16a) cells but not 3T3 fibroblasts with microvascular endothelial cells (CD3) resulted in a time- and concentration-dependent retraction of the CD3 monolayers as revealed by quantitative binding assays and phase contrast microscopy. Lewis lung carcinoma cell-induced endothelial cell retraction was blocked by specific lipoxygenase inhibitors but not by cyclooxygenase inhibitors, suggesting the involvement of a lipoxygenase metabolite(s). Radioimmunoassay and high-performance liquid chromatography analysis of tumor cell extracts identified 12(S)-HETE as the major lipoxygenase metabolite of arachidonic acid and tumor cell generation of 12(S)-HETE was specifically blocked by a select 12-lipoxygenase inhibitor N-benzyl-N-hydroxy-5-phenyl-pentamide. The identity and stereochemistry of tumor cell-derived 12-HETE was substantiated by gas chromatography-mass spectrometry analysis and chiral phase high-performance liquid chromatography, respectively. Lewis lung carcinoma cell adhesion to CD3 monolayers was accompanied by an enhanced 12(S)-HETE biosynthesis by tumor cells, which paralleled the tumor cell-induced endothelial cell retraction in a cell number-dependent manner. Pretreatment of tumor cells with N-benzyl-N-hydroxy-5-phenylpentamide inhibited both increased 12(S)-HETE biosynthesis and tumor cell-induced endothelial cell retraction. Highly metastatic variants of elutriated B16a cells which had been shown to produce large quantities of 12(S)-HETE induced significant CD3 cell retraction, while low metastatic subpopulations of B16a cells which synthesized no or little 12(S)-HETE did not induce endothelial cell retraction. These results suggest that 12(S)-HETE synthesis during tumor cell-endothelial cell interactions may represent a key contributory factor in cancer metastasis.

Enhanced endothelial cell retraction mediated by 12(S)-HETE: a proposed mechanism for the role of platelets in tumor cell metastasis

Platelets have been hypothesized to contribute to tumor cell metastasis, but the underlying mechanism(s) remain unknown. We demonstrate here that one mechanism whereby platelets may facilitate metastasis is by potentiating tumor cell-induced endothelial cell retraction, a prerequisite for the extravasation of most tumor cell types. The integrity of cultured microvascular endothelial cell (CD3 cells) monolayers was perturbed by 12[S]-hydroxyeicosatetraenoic acid (12(S)-HETE), a lipoxygenase metabolite of arachidonic acid, as well as by tumor cells (i.e., Lewis lung carcinoma cells or 3LL). 3LL cells induced a concentration- and time-dependent retraction of the CD3 monolayers, as assessed by quantitative binding assays as well as by phase-contrast microscopy. In contrast, normal murine fibroblasts (3T3) did not induce endothelial cell retraction. 3LL cell-induced endothelial cell retraction was potentiated, in a dose- and time-dependent manner, by homologous murine platelets while platelets alone did not induce endothelial cell retraction. Platelet-enhanced, tumor cell-induced endothelial cell retraction was inhibited by treating either tumor cells or platelets with the lipoxygenase inhibitors nordihydroguaiaretic acid or N-benzyl-N-hydroxy-5-phenylpentanamide (BHPP) as well as by PGI2 or its analogs iloprost and ZK96.480 (cicaprost), but not by the cyclooxygenase inhibitor aspirin (ASA). Tumor cells, upon adhesion to endothelium, initiated 12(S)-HETE biosynthesis, which was inhibited by pretreating tumor cells with BHPP but not with ASA. Additionally, 12(S)-HETE biosynthesis during tumor cell-endothelial cell adhesion was significantly enhanced by the addition of homologous platelets. Collectively, these results suggest that tumor cell-platelet-endothelial cell interactions lead to enhanced biosynthesis of 12(S)-HETE by tumor cells and/or platelets, which in turn induces endothelial cell retraction, thus facilitating tumor cell extravasation and metastasis.

Isolation and characterization of cerebral resistance vessel endothelium in culture

Organ-derived endothelia have been shown to exhibit distinct patterns of morphology and growth responsiveness in vitro. This report describes the development, cloning and establishment of long-term serial cultures of rat vascular endothelial cells derived from cerebrocortical resistance vessels (small arteries and arterioles). Modification of our previous published technique for establishing resistance vessel-derived smooth muscle cells (RV-SMC) resulted in enhanced levels of endothelial outgrowth from collagenase-treated microvessel fragments. Although primary culture growth consisted predominantly of SMC, subsequent subcultivation of these cultures revealed the presence of distinct endothelial cell clusters within the SMC monolayer. Serial cloning of these isolates resulted in a homogeneous population of cells with the characteristic endothelial cobblestone growth pattern and positive immunofluorescence for factor VIII-related antigen. Previously established RV-SMC frozen stocks provided an additional source for obtaining resistance vessel endothelial cells. This was made possible by the slow proliferation rate of early-passage RV-SMC and their inability to withstand freezing procedures. Endothelial cells from both preparations were identical and designated resistance vessel derived endothelial cells RV-EC. Upon long-term cultivation (> P15), confluent RV-EC cultures expressed spontaneous multicellular cord development that stained positive for factor VIII-related antigen. Cell growth studies demonstrated that RV-EC were capable of significant growth when maintained in serum-free conditions. Growth kinetics using serum-free conditioned medium demonstrated mitogenic activity indicating the presence of an autocrine growth factor. Increase growth responsiveness was also noted in RV-EC when treated with a variety of peptide growth factors. These results indicate that resistance vessel endothelium can be successfully isolated and maintained in long-term serial cultures. Furthermore, the availability of cultured EC and SMC from this unique microvascular site will enable examination of cerebrovascular endothelial-smooth muscle cell interactions in vitro and may help to elucidate the mechanisms of altered vascular function in disease states.

Identification of PECAM-1 in solid tumor cells and its potential involvement in tumor cell adhesion to endothelium

PECAM-1 (CD31/EndoCAM) is an adhesion molecule in the immunoglobulin supergene family that is expressed on endothelial cells, platelets, and some hematopoietic lineage cells. In this paper, using several polyclonal and monoclonal antibodies against PECAM-1, we identified PECAM-1 molecules on human, rat, and murine solid tumor cell lines. Immunocytochemical labeling and flow cytometric analysis using either polyclonal, monoclonal, or Fab portion of the antibodies against PECAM-1 detected a distinct distribution on tumor cell surface. Immunoblotting revealed proteins ranging from 120 to 130 kDa in tumor cells derived from different species. Immunoprecipitation and subcellular fractionation studies indicated that PECAM-1 is constitutively expressed on the surface of human tumor cells (i.e. colon adenocarcinoma). The specificity of a major polyclonal anti-PECAM-1 used in the current study (i.e. SEW-3) was confirmed by the preabsorption studies. PECAM-1 molecules on tumor cells appear to bear terminal carbohydrate moieties (i.e. sialic acid residues) different from those on platelets, since neuraminidase treatment of tumor cells, unlike platelets, did not result in a mobility shift. Polymerase chain reaction (PCR) analysis of genomic DNA derived from tumor cell lines of different species revealed the presence of PECAM-1 gene in the genome. The mRNAs of PECAM-1 in tumor cells were detected by reverse transcription-PCR followed by Southern hybridization. Screening of more than 20 human, rat, and murine solid tumor cell lines indicated that PECAM-1 is widely expressed, although the level of expression varies considerably among different cell lines. The expression of PECAM-1 message in tumor cells was confirmed by Northern blotting. DNA sequencing of the PCR fragment revealed that human tumor cell PECAM-1 matches 100% to the human endothelial cell counterpart. Finally, it was demonstrated that tumor cell PECAM-1 is involved in mediating tumor cell adhesion to endothelium, as evidenced by the ability of anti-PECAM-1 antibodies to decrease the adhesion of unstimulated tumor cells to microvascular endothelial cells.

Low dose radiation-induced endothelial cell retraction

We characterized in vitro the effects of gamma-radiation (12.5-100 cGy) on pulmonary microvascular endothelial cell (PMEC) morphology and F-actin organization. Cellular retraction was documented by phase-contrast microscopy and the organization of actin microfilaments was determined by immunofluorescence. Characterization included radiation dose effects, their temporal duration and reversibility of the effects. A dose-dependent relationship between the level of exposure (12.5-100 cGy) and the rate and extent of endothelial retraction was observed. Moreover, analysis of radiation-induced depolymerization of F-actin microfilament stress fibres correlated positively with the changes in PMEC morphology. The depolymerization of the stress fibre bundles was dependent on radiation dose and time. Cells recovered from exposure to reform contact inhibited monolayers > or = 24 h post-irradiation. Concomitantly, the depolymerized microfilaments reorganized to their preirradiated state as microfilament stress fibres arrayed parallel to the boundaries of adjacent contact-inhibited cells. The data presented here are representative of a series of studies designed to characterize low-dose radiation effects on pulmonary microvascular endothelium. Our data suggest that post-irradiation lung injuries (e.g. oedema) may be induced with only a single fraction of therapeutic radiation, and thus microscopic oedema may initiate prior to the lethal effects of radiation on the microvascular endothelium, and much earlier than would be suggested by the time course for clinically-detectable oedema.

Regulation of endothelin-1 mRNA by angiotensin II in rat heart endothelial cells

In a series of experiments carried out in cultured endothelial cells derived from rat hearts (RHE), angiotensin II (AII) is shown to stimulate preproendothelin-1 mRNA in a dose- and time-dependent manner. The induction of preproendothelin-1 mRNA is rapid, reaching a maximal level 1 h after the addition of AII (1 x 10(-8) M). The mRNA levels decline rapidly to basal levels in 4 h. The addition of Losartan (Dup 753; 1 x 10(-6) M), an AII receptor (type I) antagonist, blocks the AII effect. Calphostin C, a potent protein kinase C inhibitor, is able to abolish this effect of AII suggesting that the induction of preproendothelin-1 mRNA is mediated by a protein kinase C-dependent pathway. Since endothelial cells line the inner surface of the myocardium and blood vessels and sense the rise of AII associated with renovascular hypertension at the endothelial surface, these data suggest that endothelin which is produced by RHE cells in response to AII could be an important mediator which may play a role in modulating gene expression in AII-mediated cardiac hypertrophy.

The lipoxygenase metabolite, 12(S)-HETE, induces a protein kinase C-dependent cytoskeletal rearrangement and retraction of microvascular endothelial cells

We previously reported that a lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], induced large vessel endothelial cell (EC) retraction and increased tumor cell adhesion to exposed extracellular matrix (Honn et al., FASEB J. 3, 2285-2293, 1989). Here, we present evidence that 12(S)-HETE induces the retraction of microvascular ECs in a time- and concentration-dependent manner. The EC retraction was observed 15 min after 12(S)-HETE treatment and reached a peak level between 1 and 2 h. The monolayer reformed by 24 h. Silver staining and "gap-FRAP" experiments suggest that 12(S)-HETE altered the normally apposed cell junctions and impaired gap junction-mediated cell-cell communication. It appears that the 12(S)-HETE effect was mediated by cytoskeletal alteration. The first observed alteration in EC cytoskeleton following 12(S)-HETE stimulation is vimentin bundling, followed by the rearrangement and disruption of vinculin-containing adhesion plaques and/or simultaneous redistribution of alpha-actinin and disruption of spectrin. These changes are accompanied by progressive microfilament dissolution. During the same time interval, alpha-actinin is mobilized to the cell periphery at cell "ruffles." However, 12(S)-HETE showed little or no effects on actin-binding proteins filamin and tropomyosin or on microtubules. 12(S)-HETE effects on these cytoskeletal elements were fully reversible by 24 h and appeared to be mediated through enhancing protein phosphorylation. Following 12(S)-HETE (0.1 microM) treatment increased phosphorylation of proteins that comigrated with myosin light chain (20 kDa), actin (42 kDa), and vimentin (57 kDa) were observed. The enhanced phosphorylation of these cytoskeletal proteins was confirmed by 2D gel analysis. The phosphorylation-promoting effect of 12(S)-HETE on cytoskeletal proteins could be totally abolished by calphostin C, partially inhibited by staurosporine, but was not influenced by N-[2-(methylamine)ethyl]-5-isoquinolinesilfonamide dihydrochloride (HS), suggesting that the 12(S)-HETE effect was mediated via protein kinase C. This was further substantiated by quantitative experiments demonstrating that calphostin C, but not H8, inhibited 12(S)-HETE-induced EC retraction.

5-Hydroxytryptamine1-like receptors linked to increases in intracellular calcium concentration and inhibition of cyclic AMP accumulation in cultured vascular smooth muscle cells derived from bovine basilar artery

Vascular smooth muscle cells derived from bovine basilar artery by the explant method were grown in culture. In the presence of 1 microM forskolin and the phosphodiesterase inhibitor rolipram, 5-hydroxytryptamine (5-HT) agonists inhibited by 90 to 100% the accumulation of intracellular cyclic AMP (cAMP) with a rank order of potency 5-carboxamidotryptamine (5-CT) > or = 5-HT > 5-benzyloxytryptamine = sumatriptan > RU24969 [5-methoxy-3(1,2,3,6-tetrahydro-4-pyridinyl)-1H indole succinate] > (+/-)-8-hydroxydipropylaminotetralin. In suspensions of cells loaded with the calcium-sensitive probe fura-2, 5-CT and 5-HT caused a biphasic increase in the concentration of intracellular free calcium ([Ca++]i) that consisted of both transient and sustained phases. The transient phase was reduced and the sustained phase abolished in the absence of extracellular calcium. The EC50 for 5-CT-induced increase in [Ca++]i (6 nM) was similar to that for inhibition of cAMP accumulation (1.3 nM). Both the inhibition of cAMP accumulation and increase in [Ca++]i were inhibited by the antagonist methiothepin (pA2 = 8.9), but not by the antagonists ketanserin, spiperone and pindolol. Both the inhibition of cAMP accumulation and increase in [Ca++]i were attenuated by greater than 85% in cells that were pretreated with pertussis toxin. PI turnover was not stimulated by 5-CT. The rank order of agonist potency, as well as the antagonist sensitivity, indicates responses mediated by one or more 5-HT1-like-type receptors.(ABSTRACT TRUNCATED AT 250 WORDS)

Thrombin increases the metastatic potential of tumor cells

Initial arrest of tumor cells in the microvasculature and their attachment to the endothelium and subendothelial matrix (SEM) are essential prerequisites for metastasis to occur. Factors mediating these interactions are viewed as important determinants of the tumor-cell metastatic phenotype. In this work we have studied the effects of thrombin, its analogs and its precursors on the adhesive properties and metastatic potential of tumor cells. We show that alpha-thrombin, the native form of the key coagulation enzyme, is capable of enhancing tumor-cell adhesion to both the endothelium and SEM components represented by fibronectin. Subclotting, physiological concentrations of alpha-thrombin produced a 2- to 5-fold increase in tumor-cell adhesion. A bell-shaped dose-response curve was observed, with maximal effect at 0.1 U/ml. Maximum effect occurred when cells were exposed to the agonist for 15 min and exposure for up to 4 hr resulted in enhanced tumor-cell adhesion. Prolonged incubation with thrombin resulted in a decline in the thrombin-enhanced adhesion which reached unstimulated control levels by 24 hr. Thrombin precursors and active-site-inhibited thrombin analogs only had minimal adhesion-enhancing activity; nitro- and exosite-alpha-thrombin, which retain a functional active site, mimicked, although to a lesser degree, the action of alpha-thrombin. Tumor-cell incubation with thrombin resulted in an upregulated cell-surface expression of the alpha11b beta 3 integrin, a receptor mediating interactions between tumor cells and endothelial cells, and between tumor cells and SEM. Antibodies against alpha 11b beta 3 integrin effectively inhibited thrombin-enhanced tumor-cell adhesion. Thrombin effects on tumor cells involved the PKC signal transduction pathway as thrombin-enhanced adhesion was inhibited by pre-incubation with PKC inhibitors and a transient PKC translocation from cytosol to membrane was observed following thrombin challenge. In vivo, thrombin-treated tumor cells demonstrated a 2-fold increase in their lung-colonizing ability. In contrast to the adhesion results, the metastasis-enhancing effects of alpha-thrombin were mimicked by a thrombin precursor (prothrombin) and thrombin analogs.

Phenotypic properties of cultured tumor cells: integrin alpha IIb beta 3 expression, tumor-cell-induced platelet aggregation, and tumor-cell adhesion to endothelium as important parameters of experimental metastasis

The present study was undertaken to investigate the factors involved in determining the metastatic potential of cultured cells derived from solid tumors. We first investigated the effects of cell source and culture conditions on lung colony formation by i.v. injected B16a (B16 amelanotic melanoma) cells and inhibition of tumor colony formation by the thromboxane A2 synthase inhibitor, CGS14854. Prolonged culture resulted in a 10-fold decrease in the incidence of B16a lung colonies, whereas passage in vivo for 150 days did not affect lung colony formation by tumor cells isolated from enzymatic dispersates by centrifugal elutriation. Cultured B16a cells maintained at low density (LD) and harvested at low passage (LP) formed significantly more lung colonies than B16a cells harvested at high densities (HD) or high passage (HP). Over-confluent tumor cells produced even lower number of lung colonies. Lung colony formation by elutriated B16a cells (i.e., cells freshly isolated from tumor tissue) was consistently inhibited by CGS14854, whereas inhibition of lung colony formation by cultured B16a cells was dependent upon culture conditions. CGS14854 was ineffective or less effective against HD/HP B16a cells. The differences in lung colony formation between LD, HD and elutriated B16a cells were not due to differential cell-cycle distribution. Mechanistic studies indicated that LD/LP tumor cells induced aggregation of homologous platelets, whereas HD/HP B16a cells failed to induce significant platelet aggregation. Aggregation of homologous platelets correlated positively with lung-colonizing ability. Additionally, LD/LP cells demonstrated higher adhesion to endothelium than HD/HP B16a cells. Finally, LD/LP B16a cells expressed higher levels of alpha IIb beta 3 integrins than HD/HP tumor cells, as determined by flow cytometry and immunofluorescence.

Protein kinase C-dependent effects of 12(S)-HETE on endothelial cell vitronectin receptor and fibronectin receptor

12(S)-HETE, a lipoxygenase metabolite of arachidonic acid induced a nondestructive and reversible endothelial cell (EC) retraction. 12(S)-HETE induced EC retraction was inhibited by protein kinase C inhibitors calphostin C and staurosporine but not by the protein kinase A inhibitor H8. The role of EC integrins alpha v beta 3 and alpha 5 beta 1 in 12(S)-HETE induced EC retraction was investigated. In confluent EC cultures, alpha v beta 3 is localized to focal adhesions at both the cell body and cell-cell borders and is colocalized with vinculin-containing focal adhesions. In contrast, alpha 5 beta 1 is primarily enriched at the cell-cell borders, demonstrating codistribution with cell cortical microfilaments and extracellular fibronectin. Both receptors were functional in mediating cell-cell or cell-matrix interactions based on the observations that specific antibodies inhibited EC adhesion to intact subendothelial matrix and disrupted the monolayer integrity. 12(S)-HETE induced a multistep, temporally defined redistribution of the alpha v beta 3-containing focal adhesions, leading to an eventual decrease in alpha v beta 3 plaques in the retracted ECs. This effect of 12(S)-HETE was inhibited by calphostin C but not by H8. The alterations of alpha v beta 3-containing focal adhesions preceded the development of EC retraction. 12(S)-HETE also enhanced EC alpha v beta 3 surface expression as revealed by immunofluorescence, flow cytometry, and digitized image analysis. 12(S)-HETE-induced alpha v beta 3 rearrangement (i.e., decreased focal adhesion localization and enhanced surface expression) did not result from altered mRNA transcription (as revealed by semi-quantitative RT-PCR analysis) or protein translation (as revealed by Western blotting). In contrast to its effect on alpha v beta 3, 12(S)-HETE did not demonstrate a temporally related, well-defined effect on the distribution pattern and the surface expression of alpha 5 beta 1, although the cell-cell border staining pattern of alpha 5 beta 1 was disrupted due to EC retraction. It is concluded that 12(S)-HETE-induced decrease of alpha v beta 3 localization to focal adhesions may contribute to the development of EC retraction and that 12(S)-HETE induced increase in alpha v beta 3 surface expression may promote adhesion of inflammatory leukocytes as well as tumor cells to endothelium.

12(S)-HETE promotes tumor-cell adhesion by increasing surface expression of alpha V beta 3 integrins on endothelial cells

The present work was undertaken to investigate the regulatory role of 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, in the surface expression of alpha v beta 3 integrin receptors in endothelial cells (rat aortic endothelial cells, or RAEC). Several monoclonal and polyclonal antibodies localized alpha v beta 3 in focal adhesions in both subconfluent and post-confluent RAEC. RAEC alpha v beta 3 integrins were further characterized by immunoblotting and immunoprecipitation. 12(S)-HETE, but not 12(R)-HETE or other lipoxygenase-derived hydroxy fatty acids, induced a dose-dependent increase in alpha v beta 3 surface expression in RAEC, which was antagonized by prostacyclin or its analog iloprost as well as by 13-HODE, a 15-lipoxygenase product of linoleic acid. 12(S)-HETE promoted RAEC adhesion to vitronectin, an effect inhibited by antibodies against alpha v beta 3. 12(S)-HETE also promoted tumor-cell (W256 carcinosarcoma) adhesion to vitronectin, which was inhibited by various antibodies against alpha IIb beta 3 but not by an antibody against alpha v. W256 adhesion to 12(S)-HETE-treated RAEC demonstrated a significant increase, which was inhibited by anti-alpha v, -beta 3, or -alpha v beta 3 antibodies and by 13-HODE. Western blotting, immunoprecipitation and reverse transcription-polymerase chain reaction indicated that W256 carcinosarcoma cells expressed alpha IIb beta 3 integrins but not alpha v beta 3. The results suggest that the lipoxygenase metabolites [i.e., 12(S)-HETE and 13-HODE] play a significant role in modulating tumor-cell interactions with endothelium by enhancing endothelial cell integrin (e.g., alpha v beta 3) expression.

12(S)-HETE-induced microvascular endothelial cell retraction results from PKC-dependent rearrangement of cytoskeletal elements and alpha V beta 3 integrins

12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, has been demonstrated to induce a reversible retraction of vascular endothelial cells (EC). 12(S)-HETE-induced microvascular EC retraction was blocked by a selective protein kinase C inhibitor, calphostin C, but not by the protein kinase A inhibitor, H8. EC exposed to 12(S)-HETE demonstrated a gradual dissolution of actin microfilaments and a decrease of vinculin-containing focal adhesions. The intermediate filaments, vimentin, also underwent extensive reorganization (i.e., filament bundling and enrichment to the cell filapodia) following 12(S)-HETE treatment. In vivo phosphorylation studies revealed that 12(S)-HETE induced a hyperphosphorylation of several major cytoskeletal proteins including myosin light chain, actin, and vimentin. The increased phosphorylation of these cytoskeletal proteins following 12(S)-HETE stimulation was abolished by calphostin C but not by H8. Confluent EC express alpha v beta 3 in focal adhesions at both the cell body and the cell-cell borders. 12(S)-HETE induced a sequential rearrangement of the alpha v beta 3-containing focal adhesions, resulting in a general decrease in alpha v beta 3 integrin receptors, especially in those retracted EC. 12(S)-HETE-induced rearrangement of alpha v beta 3 was inhibited by calphostin C but not by H8. In contrast to alpha v beta 3, confluent EC enrich alpha 5 beta 1 integrin receptors primarily at the cell-cell borders, colocalizing with extracellular fibronectin and cell cortical microfilaments. 12(S)-HETE treatment also disrupted the cell-border distribution pattern of alpha 5 beta 1 as EC retracted, but no distinct alterations (such as time-related redistribution and quantitative differences) in alpha 5 beta 1 were observed.

Thrombin enhances tumor cell adhesive and metastatic properties via increased alpha IIb beta 3 expression on the cell surface

The association between blood coagulation and cancer growth and metastatic dissemination is not yet completely understood. In this study we demonstrate that thrombin is capable of enhancing tumor cell adhesive properties and thereby increases tumor cell metastatic potential. Following exposure to alpha-thrombin, Walker 256 carcinosarcoma cells and B16 amelanotic melanoma cells became more adherent to both endothelial cell monolayers and the subendothelial matrix component, fibronectin. Preincubation of W256 and B16a cells with doses of alpha-thrombin from 0.01 to 10.0 U/ml produced a bell shape dose-response curve with the maximal effect (a 2-5-fold increase in adhesion) observed at 0.1 U/ml (corresponding to 0.8 nM). Complexes of alpha-thrombin with its inhibitors, hirudin and antithrombin III-heparin, diminished its effect on tumor cell adhesion. The effect of thrombin on tumor cell adhesion may be mediated by the alpha IIb beta 3 integrin as thrombin increased cell surface expression of the alpha IIb beta 3 complex. The significance of the in vitro observations was further substantiated by results of in vivo studies. Pretreatment of B16a cells with alpha-thrombin resulted in a 2-fold increase in the number of metastatic lung colonies in an experimental metastasis model. The data indicate a new role for thrombin in the metastatic spread of cancer.

Fatty acid modulation of tumor cell adhesion to microvessel endothelium and experimental metastasis

Tumor cell interaction with the endothelium of the vessel wall is a rate limiting step in metastasis. The fatty acid modulation of this interaction was investigated in low (LM) and high (HM) metastatic B16 amelanotic melanoma (B16a) cells. 12(S)-HETE increased the adhesion of LM cells to endothelium derived from pulmonary microvessels. All other monohydroxy and dihydroxy fatty acids were ineffective. LTB4 induced a modest stimulation but LTC4, LTD4, LTE4 as well as LXA4 and LXB4 were ineffective. The 12(S)-HETE enhanced adhesion of B16a cells was inhibited by pretreatment with 13(S)-HODE but not by 13(R)-, 9(S)-HODE or 13-OXO-ODE. 13(S)-HODE decreased adhesion of HM B16a cells to endothelium. 12(S)-HETE enhanced surface expression of integrin alpha IIb beta 3 and monoclonal antibodies against this integrin but not against alpha 5 beta 1, blocked enhanced but not basal adhesion to endothelium. Intravenous injection of 12(S)-HETE treated LM cells resulted in increased lung colonization (experimental metastasis). This effect was specific for 12(S)-HETE and was inhibited by 13(S)-HODE but not by other HODE's. 12(S)-HETE also enhanced lung colonization by HM cells and 13(S)-HODE decreased lung colonization by HM cells. Our results suggest a highly specific bidirectional modulation of metastatic phenotype and lung colonization by 12(S)-HETE and 13(S)-HODE.

Protein-kinase-C inhibitor calphostin C reduces B16 amelanotic melanoma cell adhesion to endothelium and lung colonization

We recently reported that the Ca(2+)- and phospholipid-dependent protein kinase, protein kinase C (PKC), was involved in rat Walker carcinosarcoma cell adhesion to large-vessel endothelium. We extended our studies to explore the role of this kinase in the adhesion to small-vessel endothelium and lung colonization of murine B16 amelanotic melanoma (B16a). Subpopulations of B16a cells, which differ in lung-colonization potentials, were isolated by centrifugal elutriation from solid tumors. In this study, we demonstrate that cells from a high metastatic sub-population (HM340), when compared with cells from a low metastatic sub-population (LM180), exhibit elevated levels of total cellular as well as membrane-bound PKC. The increase in PKC in cells from the HM340 correlates positively to their increased ability to adhere to murine pulmonary-microvessel endothelial-cell monolayer, and to form pulmonary colonies in syngeneic mice. Calphostin C, a potent and selective PKC inhibitor, decreases in a dose-dependent manner the adhesion to endothelium and the lung colonization of cells from both the low and the high metastatic sub-populations with IC50 at sub-micromolar concentrations. In conclusion, our results suggest that PKC may be a key element in regulating tumor-cell metastasis and that PKC inhibitors may be anti-metastatic agents.

Alpha IIb beta 3 integrin expression and function in subpopulations of murine tumors

Subpopulations of B16 amelanotic melanoma (B16a) cells, isolated by centrifugal elutriation from enzymatically dispersed solid tumors, demonstrated different abilities to form lung colonies when injected intravenously. In contrast, no differences in experimental metastasis were observed among subpopulations obtained from Lewis lung (3LL) tumors. Lung colonization by B16a and 3LL subpopulations correlated positively with observed differences (B16a) or lack of differences (3LL) in tumor cell ability to induce aggregation of homologous platelets, to adhere to subendothelial matrix or fibronectin, and with the percentage of cells in the G2/M phase of the cell cycle. Both B16a and 3LL cells express alpha IIb beta 3 integrin receptors; however, differences in the receptor expression level were found only among B16a subpopulations. Comparison of the amount of alpha IIb beta 3 receptor expressed on cell surface with tumor cell ability to induce platelet aggregation (TCIPA) and to adhere to fibronectin or subendothelial matrix revealed a positive correlation. Pretreatment of tumor cells with alpha IIb beta 3-specific antibodies inhibited tumor cell matrix adhesion, TCIPA, and lung colony formation. We propose that alpha IIb beta 3 integrin receptor expression, tumor cell matrix adhesion, and tumor cell-induced platelet aggregation can be important parameters to indicate the metastatic potential of some tumor cells and that the alpha IIb beta 3 is a multifunctional receptor involved in both tumor cell-matrix and tumor cell-platelet interactions. Further, the correlation among cell cycle phase, metastatic ability, and receptor expression suggests that metastatic propensity may be transiently expressed and/or increased in some tumor cell subpopulations.

Increased expression of alpha IIb beta 3 integrin in subpopulations of murine melanoma cells with high lung-colonizing ability

Four subpopulations of B16 amelanotic melanoma cells, possessing different abilities to induce platelet aggregation (TCIPA) and to form lung colonies, were isolated by centrifugal elutriation. The expression of alpha IIb beta 3, alpha v beta 3 and alpha 5 beta 1 integrins was examined in the 4 subpopulations in order to determine the relationship between integrin receptor expression and tumor-cell metastatic potential. The mRNA of alpha IIb, alpha 5, beta 1 and beta 3 was detectable in the 4 subpopulations by Northern blotting. A gradual increase in mRNAs and cell-surface immunoreactivity of the alpha IIb beta 3 receptor, but not in their gene copies, was observed from the low to the high metastatic subpopulations. The ability of tumor cells to adhere to fibronectin and subendothelial matrix (SEM) increased in parallel. In the high metastatic cells, the alpha IIb beta 3 receptors, but not the alpha 5 beta 1 receptors, were localized to focal adhesion plaques. Incubation of the high metastatic cells with alpha IIb beta 3-specific antibodies reduced their matrix adhesion, TCIPA and lung-colonizing abilities. In contrast, in the low met- astatic cells, SEM adhesion and lung-colony formation were not affected by anti-alpha IIb beta 3 antibody treatment. Incubation of either the low or the high metastatic subpopulation with an alpha 5 beta 1-specific antibody had no effect in vitro and showed a slight inhibition of lung colonization in vivo. Our results suggest that several phenotypic characteristics of the enhanced metastatic potential of B16a subpopulations may be mediated by increased expression of alpha IIb beta 3 receptors and that expression of these receptors may be regulated at the transcriptional level.

Endothelin stimulates protein synthesis in smooth muscle cells

The present work was carried out to assess the effect of endothelin on the relative synthesis of protein, RNA, and DNA in confluent rat aortic smooth muscle cells (SMC) derived from Wistar-Kyoto (WKY) rats maintained under serum-free medium in the presence or absence of insulin, transferrin, and selenium. Insulin stimulated protein synthesis by 42%. Endothelin (1 x 10(-7) M) rapidly induced protein synthesis by 22% (-insulin) and 30% (+insulin). Prior treatment of SMC for 4 h with endothelin resulted in 50% (-insulin) and 38% (+insulin) increase in protein synthesis. The stimulatory effect of endothelin on protein synthesis could be partially blocked by 1-(5-isoquinolinylsulfonyl)-2-methylpiperazine, a protein kinase C inhibitor. Atrial natriuretic factor had no effect on either the basal protein synthesis or protein synthesis stimulated by endothelin. Furthermore, endothelin stimulated RNA synthesis by twofold but had no effect on DNA synthesis in SMC derived from WKY rats. In contrast, SMC derived from spontaneously hypertensive rats showed increased DNA synthesis and cell growth after endothelin stimulation. These studies show that this hormone may play a pivotal role in the development of vascular hypertrophy in hypertension.

Lipoxygenase metabolites of arachidonic and linoleic acids modulate the adhesion of tumor cells to endothelium via regulation of protein kinase C

12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE) and 13(S)-hydroxyoctadecadienoic acid (13[S]-HODE), lipoxygenase metabolites of arachidonic acid and linoleic acid, respectively, previously have been suggested to regulate tumor cell adhesion to endothelium during metastasis. Adhesion of rat Walker carcinosarcoma (W256) cells to a rat endothelial cell monolayer was enhanced after treatment with 12(S)-HETE and this 12(S)-HETE enhanced adhesion was blocked by 13(S)-HODE. Protein kinase inhibitors, staurosporine, calphostin C, and 1-(5-isoquinoline-sulfonyl)-2-methylpiperazine, inhibited the 12(S)-HETE enhanced W256 cell adhesion. Depleting W256 cells of protein kinase C (PKC) with phorbol 12-myristate-13-acetate abolished their ability to respond to 12(S)-HETE. Treatment of W256 cells with 12(S)-HETE induced a 100% increase in membrane-associated PKC activity whereas 13(S)-HODE inhibited the effect of 12(S)-HETE on PKC translocation. High-performance liquid chromatographic analysis revealed that in W256 cells 12-HETE and 13-HODE were two of the major lipoxygenase metabilites of arachidonic acid and linoleic acid, respectively. Therefore, these two metabolites may provide an alternative signaling pathway for the regulation of PKC. Further, these findings suggest that the regulation of tumor cell adhesion to endothelium by 12(S)-HETE and 13(S)-HODE may be a PKC-dependent process.

Mesothelial cells produce a chemoattractant for lung fibroblasts: role of fibronectin

Pleural fibrosis may complicate several types of non-exudative pleural injury. Although the pathogenesis of such lesions is poorly understood, it is conceivable that mesothelial cells may recruit fibroblasts to sites of pleural damage. In order to test this possibility, conditioned medium from cultured rat mesothelial cells was tested for chemoattractant activity towards RL-87 rat lung fibroblasts. For this purpose, rat pleural or pericardial mesothelial cells were maintained in vitro for 6 to 96 h. Conditioned medium from each source was obtained at defined culture times and tested for chemotactic activity in a 48-well microchemotaxis assembly. A progressive, time-dependent increase in fibroblast chemoattractant activity was detected in both pleural and pericardial mesothelial cell conditioned medium samples. This effect was maximal in 96-h cultures. Checkerboard analysis revealed that the conditioned medium was truly chemotactic for lung fibroblasts. Characterization of the chemoattractant demonstrated that it was a nondialyzable (greater than 16 kD), thermolabile (100 degrees C for 15 min), acid-stable (pH 2.5), trypsin-sensitive, and pepsin-sensitive protein. The chemotaxin was shown to be fibronectin, since activity was abolished, in a dose-dependent manner, by treatment with anti-rat fibronectin antiserum as well as by passage through a gelatin agarose affinity column. This product consisted of two bands on sodium dodecyl sulfate polyacrylamide gel electrophoresis of apparent molecular masses 250 and 220 kD. The secretion of a mesothelial cell-derived fibroblast chemoattractant may play a role in the response of the pleura to injury and in the pathogenesis of pleural fibrosis.

Modulation of extracellular matrix proteins by endothelial cells undergoing angiogenesis in vitro

Angiogenesis results in part from the response of endothelial cells to the integrated action of morphogenic factors and extracellular matrix proteins. In this study we identified specific components of the extracellular matrix that were modulated in endothelial cells derived from bovine aorta and rat cerebral microvessels, both of which spontaneously form cords and tubes under standard culture conditions. SPARC (secreted protein, acidic and rich in cysteine) was upregulated 4.2-fold in aortic and 10-fold in microvascular cultures that had organized into cords and/or tubes. This Ca(2+)-binding glycoprotein was synthesized primarily by endothelial cells in the process of cord formation. Transcription of type I collagen was initiated in aortic endothelial cells undergoing angiogenesis in vitro and showed a 12-fold increase in similar cultures of microvascular cells. Type VIII collagen protein was upregulated to a lesser degree (4.3-fold in aortic and 1.8-fold in microvascular cells). Dense cytoplasmic staining for these two collagen types was seen in cells directly participating in the organization of cords. In contrast, the disparate levels of fibronectin observed in both types of endothelium indicated an indirect or secondary role for this glycoprotein in cord/tube formation in vitro. These results identify SPARC, type I collagen, and type VIII collagen as extracellular matrix components that are actively synthesized by endothelial cells undergoing angiogenesis in vitro. Moreover, expression of these proteins during the formation of tubes and cords appears to follow a biosynthetic program that is common to endothelial cells from both the macrovasculature and microvasculature.

Production of a transforming growth factor-beta-like growth factor by RSV-transformed rat cerebral microvascular endothelial cells

This study describes the preliminary characterization of a Rous sarcoma virus (RSV)-transformed rat cerebral microvascular endothelial cell (RCE-T1)-derived growth factor with biological properties similar to transforming growth factor-beta (TGF-beta). A significant portion of this RCE-T1-derived TGF-beta-like growth factor was secreted in an active form and its secretion was elevated 2- to 3-fold in late passage cultures comprised of rapidly growing, less differentiated cells exhibiting reduced sensitivity to the growth-inhibitory effects of exogenous TGF-beta 1. These data suggest that the RCE-T1 cell line may be a useful system in which to study the role of autocrine TGF-beta production in normal and aberrant endothelial cell growth.

An in vivo study of the role of the tumor cell cytoskeleton in tumor cell-platelet-endothelial cell interactions

We recently reported that disruption of tumor cell microfilaments or intermediate filaments resulted in an inhibition of the ability of tumor cells to induce the aggregation of homologous platelets in vitro (H. Chopra et al., Cancer Res., 48: 3787-3800, 1988). Previous investigators demonstrated that disruption of the tumor cell cytoskeleton decreases the ability of these cells to form lung colonies. We proposed that this latter effect is due, in part, to decreased interaction of tumor cells with platelets, following their arrest in the microvasculature. To test this hypothesis, B16 amelanotic melanoma cell microtubules, microfilaments, or vimentin intermediate filaments were disrupted with colchicine (50 microns), cytochalasin D (50 microns), or cycloheximide (50 microns), respectively, and then cells were tail vein injected into syngeneic mice. Both cytochalasin D- and cycloheximide-treated cells formed fewer lung colonies than did control cells. Colchicine, however, failed to inhibit lung colony formation. Neither colchicine nor cycloheximide treatment altered initial pulmonary arrest; however, fewer cycloheximide-treated cells remained in the lungs 8 h postinjection. Greater than 90% of control or colchicine-treated cells were found to be associated with activated platelets, and they also demonstrated typical cell membrane process formation 10 min and 8 h post-tumor cell injection. In contrast, less than 10% of cycloheximide-treated cells were in contact with activated platelets 10 min postinjection. However, by 8 h approximately 90% of cycloheximide-treated cells were in contact with activated platelets. This recovery coincided with the reformation of the B16 amelanotic melanoma vimentin intermediate filament network and the reacquisition of the ability to induce platelet aggregation in vitro. Neither colchicine nor cycloheximide treatment altered initial B16 amelanotic melanoma cell adhesion to murine microvessel-derived endothelial cells. This study provides in vivo evidence in support of our previous findings that disruption of certain cytoskeletal elements (i.e., vimentin intermediate filaments) inhibits the tumor cell ability to activate platelets. This study also suggests that platelet activation may stabilize the initial tumor cell arrest in the microvasculature.

Effects of epidermal growth factor and transforming growth factor-beta 1 on rat heart endothelial cell anchorage-dependent and -independent growth

This report describes the effects of epidermal growth factor (EGF) and transforming growth factor-beta 1 (TGF-beta 1) on the anchorage-dependent and -independent growth of rat heart endothelial cells (RHE-1A). When RHE-1A cells were grown in monolayer culture with medium containing 10% fetal bovine serum (FBS) supplemented with epidermal growth factor (0.1-100 ng/ml), growth was stimulated fivefold when compared to that of cells grown in medium containing 10% FBS alone. The stimulatory effect of EGF on RHE-1A cell monolayer growth was dose-dependent and half-maximal at 5 ng/ml. The addition of TGF-beta 1 in the range 0.1-10 ng/ml had no effect on RHE-1A cell monolayer growth when added to medium containing 10% FBS alone or 10% FBS supplemented with EGF (50 ng/ml). RHE-1A cells failed to grow under anchorage-independent conditions in 0.3% agar medium containing 10% FBS. In the presence of EGF, however, colony formation increased dramatically. The stimulatory effect of EGF was dose-dependent in the range 0.1-100 ng/ml and was half-maximal at 5 ng/ml. In contrast to its effects under anchorage-dependent conditions, TGF-beta 1 (0.1-10 ng/ml) antagonized the stimulatory effects of EGF on RHE-1A cell anchorage-independent growth. The inhibitory effect of TGF-beta 1 was dose-dependent and half-maximal at 0.1 ng/ml. EGF-induced RHE-1A soft agar colonies were isolated and reinitiated in monolayer culture. They retained the cobblestone morphology and contact-inhibition characteristic of normal vascular endothelial cells. Each of the clones continued to express Factor VIII antigen. These findings suggest that TGF-beta may influence not only endothelial cell proliferation but also anchorage dependence. These effects may in turn be of relevance to endothelial cell growth and angiogenesis in vivo.

Enhanced tumor cell adhesion to the subendothelial matrix resulting from 12(S)-HETE-induced endothelial cell retraction

A 12-lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid (12[S]-HETE), which is produced by platelets and tumor cells, was tested for its ability to induce retraction of endothelial cell monolayers. The induction of endothelial cell retraction is a critical step in tumor cell metastasis. Endothelial cells demonstrated reversible retraction in response to 12(S)-HETE, but did not respond to the stereoisomer 12(R)-HETE or to unrelated 5-lipoxygenase (i.e., 5[S]-HETE) or 15-lipoxygenase (i.e., 15[S]-HETE) metabolites. Endothelial cells did not demonstrate loss of viability in response to 12(S)-HETE. The induction of retraction was both dose and time dependent. Scanning electron microscopy confirmed that 12(S)-HETE induced endothelial cell retraction and revealed collapsed filopodia on their surface, the appearance of spaces between endothelial cells and the underlying subendothelial matrix, in addition to large gaps between adjacent endothelial cells. Tumor cell adhesion to endothelial cell monolayers was enhanced 1 h after pretreatment of monolayers with 12(S)-HETE but not after pretreatment with other lipoxygenase metabolites. Tumor cell adhesion to endothelial cell monolayers 36 h after pretreatment with 12(S)-HETE was not different from adhesion to untreated monolayers. Therefore we suggest that 12(S)-HETE generated during tumor cell-platelet-endothelial cell interactions may induce reversible endothelial cell retraction, allowing tumor cell access to the subendothelial matrix, which is a critical step in their eventual extravasation from the microvasculature during hematogenous metastasis.

Angiogenesis in rat aorta ring explant cultures

This report describes the utilization of rat aorta "rings" as explants to study angiogenesis. Under short-term culture conditions, ring explants transferred at 3- to 4-day intervals showed growth (differential migration) of endothelial and/or smooth muscle cell populations. On the other hand, explants maintained for long-term (up to 3 weeks) without transfer, developed extensive out-growths of new vascular channels radiating on and through the established cell sheet. Examination of adventitia stripped ring segments, before culture revealed the presence of areas containing small vessel remnants embedded in the outer aorta wall. In addition, cultures of adventitial tissue alone yielded a variety of cell types including the occasional presence of vascular cells with developing channel formation. Immunofluorescent and ultrastructural examination of long-term aorta explant cultures revealed that these channels consisted of endothelial cells that exhibited positive reactivity for factor VIII antibody. In order to determine the influence of aorta-derived cells on vascular channel development, various vessel treatments and manipulations were performed before explant culture, to eliminate the influence of either the endothelium and/or adventitia-associated microvasculature remnants. Thus results clearly showed that the presence of both constituents is required to initiate the angiogenic response in this in vitro culture model. In addition, short-term aortic ring explant culture is an efficient and reliable technique for the isolation and culture of endothelium and smooth muscle cells from large vessels of the rat. More importantly, long-term maintenance of aorta explant cultures provides a novel self-contained system to study new vessel growth and development, and represents an attractive alternative model for defining the cellular processes regulating angiogenesis.

Bidirectional control of membrane expression and/or activation of the tumor cell IRGpIIb/IIIa receptor and tumor cell adhesion by lipoxygenase products of arachidonic acid and linoleic acid

Lewis lung carcinoma cells express a plasma membrane receptor (i.e., IRGpIIb/IIIa) which is immunologically and functionally related to the platelet aggregation receptor complex (i.e., GpIIb/IIIa). Both fluorescence microscopy and flow cytometric analysis reveal that surface expression and/or activation of this tumor cell receptor is enhanced by a phorbol ester [i.e., 12-O-tetradecanoylphorbol-13-acetate (TPA)] and a lipoxygenase metabolite of arachidonic acid; 12-hydroxyeicosatetraenoic acid (i.e., 12-HETE). TPA-enhanced expression appears to be mediated by a lipoxygenase metabolite, as this effect can be reversed by lipoxygenase inhibitors but not by cyclooxygenase inhibitors. In parallel with these results both TPA and 12(S)-HETE [but not 12(R)-HETE] enhance tumor cell adhesion to endothelial cells, subendothelial matrix and fibronectin, but not to type IV collagen. TPA-enhanced adhesion can be reduced by lipoxygenase inhibitors but not by cyclooxygenase inhibitors and in addition, stimulated adhesion can be blocked by pretreatment of tumor cells with specific polyclonal or monoclonal antibodies which react against IRGpIIb/IIIa. 12(S)-HETE-enhanced adhesion can also be inhibited by these same antibodies. In contrast, a lipoxygenase product of linoleic acid, 13(S)-hydroxyoctadecadienoic acid, inhibited TPA and 12(S)-HETE-enhanced tumor cell adhesion to endothelial cells, subendothelial matrix, and fibronectin. These results suggest that (a) IRGpIIb/IIIa is a multifunctional receptor which mediates tumor cell adhesion to a variety of biological substrata, (b) TPA enhances surface expression and/or activation of this receptor possibly via a lipoxygenase metabolite of arachidonic acid, and (c) these effects are opposed by a lipoxygenase metabolite of linoleic acid.

Anti-idiotypic antibody as a probe for ANF receptor

Generation of anti-idiotypic antibodies (anti-Id) is a rapid and new approach to produce anti-receptor antibodies without isolation of the receptor. This report describes the production of polyclonal anti-ANF anti-Id antibodies. These antibodies could inhibit the binding of [125I]-ANF to its receptor on aortic smooth muscle cells. Immunoblot analysis of detergent Chaps-solubilized adrenal gland membranes indicated that these anti-Id antibodies could recognize an Mr 130,000 band under nonreducing condition and an Mr 70,000 band under reducing condition. In addition, these antibodies could slightly increase the production of cyclic GMP in aortic smooth muscle cells.

Lipoxygenase products regulate IRGpIIb/IIIa receptor mediated adhesion of tumor cells to endothelial cells, subendothelial matrix and fibronectin

Tumor cell adhesion to endothelial cells, subendothelial matrix, and fibronectin is stimulated by the lipoxygenase metabolite of arachidonic acid, 12(S)-HETE, but not by 12(R)-HETE, 5-HETE or 15-HETE. Adhesion is also stimulated by the phorbol ester TPA, an effect inhibited by lipoxygenase but not cyclooxygenase inhibitors. TPA and 12(S)-HETE mediated adhesion is due, in part, to an integrin receptor (i.e., IRGpIIb/IIIa) related to the platelet glycoprotein IIb/IIIa complex and is inhibited by specific monoclonal and polyclonal antibodies against platelet IIb/IIIa. TPA and 12(S)-HETE stimulated adhesion is also inhibited by a lipoxygenase product of linoleic acid; i.e., 13-HODE. These results suggest bidirectional control of tumor cell adhesion by lipoxygenase products of arachidonic acid (increase) and linoleic acid (decrease).

Role of tumor cytoskeleton and membrane glycoprotein IRGpIIb/IIIa in platelet adhesion to tumor cell membrane and tumor cell-induced platelet aggregation

Components of the tumor cell cytoskeleton (i.e., microtubules, microfilaments, and intermediate filaments) have been reported to affect metastatic ability, since disruption of these components leads to a decrease in metastasis. One mechanism of metastasis which has not been previously considered is the decreased interaction of tumor cells with platelets. We present evidence that disruption of the tumor cell cytoskeleton decreases the ability of tumor cells to aggregate homologous platelets. This effect is dependent upon the disruption of microfilaments/intermediate filaments but not disruption of microtubules. In addition, tumor cell platelet interactions require the lateral mobility of specific receptors (i.e., clustering) on the tumor cell plasma membrane. A membrane glycoprotein immunologically related to the platelet glycoprotein IIb/IIIa complex was identified on Walker 256 carcinosarcoma cells using specific polyclonal and monoclonal antibodies and Northern blot analysis using complementary DNA probes for IIb and IIIa. Mobility of this receptor is dependent upon tumor cell microfilaments/intermediate filaments, but not microtubules. Furthermore, treatment of tumor cells with specific antibodies to the platelet glycoprotein IIb/IIIa complex inhibits tumor cell-platelet interaction at the macroscopic level (i.e., aggregation) and at the ultrastructural level (i.e., platelet adhesion to the tumor cell surface). These results suggest that this immunologically related glycoprotein IIb/IIIa is a receptor for platelet binding to the tumor cell surface, an event which precedes overt platelet aggregation and is dependent upon an intact tumor cell microfilament and intermediate filament network. Therefore, the decreased metastasis observed by others following disruption of the tumor cell cytoskeleton may be due, in part, to a decreased tumor cell-platelet interaction.

Rat heart-derived endothelial and smooth muscle cell cultures: isolation, cloning and characterization

This report describes the initiation, cloning and establishment of long-term serial cultures of rat heart-derived vascular endothelial (EC) and smooth muscle cells (SMC). Populations of these cells derived from both the macro-and microcirculation were obtained utilizing isolated heart perfusion technique. Elimination of potential mesothelial cell contamination was achieved by ethanol fixation of the pericardial surface prior to perfusion. Initial outgrowths from perfusate yielded both endothelial (rapid adhering) and smooth muscle (slow adhering) appearing cell populations. Subsequent pooling of individual EC colonies resulted in maintaining, with gradual subcultivation, a stable homogeneous population which was designated RHE-parent. Upon continual subculture late passage (greater than P10) RHE-parent cell cultures expressed a marked heterogeneity in endothelial phenotypes. Cloning experiments resulted in establishing two distinct EC populations designated RHE-clone 1A and RHE-clone 2A. All RHE cell cultures exhibited the typical cobblestone growth pattern and positive immunofluorescent staining for factor VIII related antigen. In contrast, rat heart-derived smooth muscle cell (RH-SMC) cultures displayed the typical multilayered 'hill and valley' pattern and positive fluorescence for SMC-specific actin and myosin antibodies. Additional EC preparations, obtained without prior fixation of the pericardial surface, revealed cell clusters which stained positive for cytokeratin. On the other hand, RHE parent and cloned populations stained exclusively for vimentin, further confirming the absence of mesothelial cell contamination in these cultures. Cell growth studies on early (less than P10) and late (greater than P10) passage RHE-parent population revealed markedly different cell growth responses and cell morphology. Both EC cloned populations and more notably RHE-parent (less than P10) cultures were capable of significant growth when maintained in limiting serum concentration. Growth studies using serum-free RHE-parent conditioned medium demonstrated mitogenic activity when tested on RHE-parent cultures indicating the presence of an endothelial cell-derived growth factor. These studies indicate that long-term RHE and RH-SMC derived cell cultures can serve as a useful model to study the biology of vascular cells derived from different sites. In addition the demonstration of mitogenic activity in these cultures will enable us to explore further the nature of this response and compare this phenomenon with growth factors identified in large vessel cell systems.