Loss of heterozygosity of the BRCA1 and other loci on chromosome 17q in human prostate cancer

A putative tumor suppressor gene, the BRCA1 gene, on chromosome 17q21 has recently been identified and shown to be mutated in breast and ovarian cancers. We have undertaken the present study to explore the possible involvement of the BRCA1 and/or other potential genes on chromosome 17q in prostate cancer. Twenty-three patients were screened by PCR for loss of heterozygosity at five microsatellite loci spanning the region of 17q12-21. One of the loci (i.e., D17S855) studied is intragenic to the BRCA1. Forty-four and 40% of the informative cases showed loss of heterozygosity at the BRCA1 (D17S855) and D17S856 loci, respectively, whereas 10%, 10%, and 11% of the informative cases were positive for loss of heterozygosity at the D17S250, D17S579, and D17S588 loci, respectively. Overall, 52% (11/21) of the informative cases have allelic loss of at least one locus on chromosome 17q. Our data suggest that the BRCA1 and/or other genes within the interval between BRCA1 and D17S856 on 17q21 may be important in the pathogenesis of prostate cancer.

Solid tumor cells express functional "tethered ligand" thrombin receptor

Previous work demonstrated that alpha-thrombin promoted tumor cell adhesion to endothelium and extracellular matrix as well as enhanced the metastatic capacity of tumor cells. This study was initiated to investigate whether the thrombin effect on tumor cells is mediated through the "tethered ligand" thrombin receptor. RT-PCR analysis using primers based on the human thrombin receptors detected mRNA in human colon adenocarcinoma cells (clone A), whose authenticity was confirmed by Southern hybridization. The presence of thrombin receptor mRNA in rat (W256 carcinosarcoma) and mouse (melanoma) tumor cells was demonstrated by RT-PCR/Southern blotting using species-specific PCR primers. Sequencing of the PCR fragment of clone A cells revealed complete homology with the reported human cDNA sequence. Subsequently, tumor cells derived from three species, i.e., human, rat, and mouse, were found to express the thrombin receptor protein as revealed by immunoblotting using ligand peptide-derived mAb ATAP138, whose reactivity towards the M(r) approximately 66,000, potential thrombin receptor was blocked by preincubating the antibody with the immunogen peptide SFLLRNPNDKYEPF (TRP 14). Finally, peptides TRP 14 and TRP 7 (SFLLRNP), but not TRP 5 (FLLRN), were found to mimic alpha-thrombin in stimulating tumor cell adhesion to fibronectin, suggesting that the thrombin receptors expressed on solid tumor cells are biologically functional.

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.

12-Lipoxygenase in Lewis lung carcinoma cells: molecular identity, intracellular distribution of activity and protein, and Ca(2+)-dependent translocation from cytosol to membranes

Recently we demonstrated that Lewis lung (3LL) tumor cells express 12-lipoxygenase (12-LOX) mRNA and protein, respectively. In this study we partially sequenced the 12-LOX cDNA after reverse-transcription polymerase chain reaction amplification of 12-LOX mRNA from cultured 3LL cells. Comparison with platelet and leukocyte 12-LOX indicates that 3LL 12-LOX is identical with the platelet-type enzyme at least within the sequenced region. Further, we investigated the intracellular distribution of both 12-LOX enzyme protein and its activity which are prerequisites for understanding 12-LOX regulation. 12-LOX activity was monitored via the production of 12-hyroxyeicosatetraenoic acid from 3LL cells and their subcellular fractions using reverse-phase high performance liquid chromatography. 12-LOX protein was measured by direct slot blot and by Western Blotting. In 3LL cells, both 12-LOX activity and 12-LOX protein were predominantly localized in the cytosol. This 12-LOX activity was optimal at 37 degrees C. However at 24 degrees C and 10 degrees C, it showed 87% and 61% of this activity, respectively, thus differing distinctly from 12-LOX in platelets or rat basophilic leukemia cells. Incubation of 3LL cell homogenates with 0-100 microM free Ca2+ and subsequent separate analyses of cytosol and membrane fractions indicated that, as in platelets, an increase in intracellular free Ca2+ caused a loss of cytosolic 12-LOX activity. However, no significant Ca(2+)-induced increase in membrane-associated 12-LOX activity was observed under these conditions in 3LL cells. In contrast, at the 12-LOX protein level we observed a Ca(2+)-dependent loss in the cytosol and a concomitant increase in the membrane fraction. Thus, we suggest that 12-LOX in 3LL cells undergoes rapid translocation from cytosol to membrane in a Ca(2+)-dependent manner, but is no longer active or becomes inactivated at the membrane site.

12-lipoxygenases and 12(S)-HETE: role in cancer metastasis

Arachidonic acid metabolites have been implicated in multiple steps of carcinogenesis. Their role in tumor cell metastasis, the ultimate challenge for the treatment of cancer patients, are however not well-documented. Arachidonic acid is primarily metabolized through three pathways, i.e., cyclooxygenase, lipoxygenase, and P450-dependent monooxygenase. In this review we focus our attention on one specific lipoxygenase, i.e., 12-lipoxygenase, and its potential role in modulating the metastatic process. In mammalian cells there exist three types of 12-lipoxygenases which differ in tissue distribution, preferential substrates, and profile of their metabolites. Most of these 12-lipoxygenases have been cloned and sequenced, and the molecular and biochemical determinants responsible for catalysis of specific substrates characterized. Solid tumor cells express 12-lipoxygenase mRNA, possess 12-lipoxygenase protein, and biosynthesize 12(S)-HETE [12(S)-hydroxyeicosatetraenoic acid], as revealed by numerous experimental approaches. The ability of tumor cells to generate 12(S)-HETE is positively correlated to their metastatic potential. A large collection of experimental data suggest that 12(S)-HETE is a crucial intracellular signaling molecule that activates protein kinase C and mediates the biological functions of many growth factors and cytokines such as bFGF, PDGF, EGF, and AMF. 12(S)-HETE plays a pivotal role in multiple steps of the metastatic 'cascade' encompassing tumor cell-vasculature interactions, tumor cell motility, proteolysis, invasion, and angiogenesis. The fact that 12-lipoxygenase is expressed in a wide diversity of tumor cell lines and 12(S)-HETE is a key modulatory molecule in metastasis provides the rationale for targeting these molecules in anti-cancer and anti-metastasis therapeutic protocols.

Inhibition of radiation-enhanced expression of integrin and metastatic potential in B16 melanoma cells by a lipoxygenase inhibitor

Low-dose gamma radiation stimulates expression of phenotypic characteristics in B16 melanoma cells which regulate metastatic potential. A transient increase in the expression of an integrin receptor (alpha IIb beta 3) was observed after exposure of B16 melanoma cells to 0.25 to 2.0 Gy of gamma radiation. This increased receptor expression resulted in enhanced adhesion of tumor cells to fibronectin in vitro and increased experimentally induced metastasis in vivo. In this report, we determined a role for the 12-lipoxygenase metabolite, 12-HETE, in radiation-enhanced metastasis. A significant increase in biosynthesis of 12-HETE in B16 melanoma cells was detected < 5 min after exposure to 0.5 Gy gamma radiation. We then determined that radiation-enhanced expression of alpha IIb beta 3 integrin and adhesion of B16 melanoma cells to fibronectin in vitro and metastasis in vivo were reduced by treatment of the cells with the lipoxygenase inhibitor NDGA prior to irradiation. These findings suggest that low-dose radiation, at levels comparable to those used in fractionated or hyper-fractionated radiotherapy, increases the metastatic potential of surviving tumor cells via a rapid and transient alteration in lipoxygenase metabolism of arachidonic acid and surface expression of an integrin receptor.

Prostacyclin and its analogues: antimetastatic effects and mechanisms of action

More than a decade ago, prostacyclin, a dienoic bicyclic eicosanoid derived from the metabolism of arachidnoic acid, was found to possess potent inhibitory effects on tumor cell metastasis. Thereafter, several laboratories demonstrated the metastasis-suppressive activity of prostacyclin in a wide spectrum of tumor types. Due to the short half-life of prostacyclin, researchers have focused on looking for stable prostacyclin analogues which have extended half lives and increased bioavailabilities. Cicaprost, among other prostacyclin analogues tested, has been demonstrated, like prostacyclin, to effectively inhibit metastasis in several different animal models (i.e., both experimental and spontaneous metastasis models). Prostacyclin as well as cicaprost prevent not only hematogenous, but also lymphatic metastasis. Furthermore, these compounds also inhibit the growth of established micrometastases after removal of the primary tumors. Mechanistic studies revealed that the antimetastatic effects of prostacyclin and its analogues are more related to their interference with tumor cell-host interactions (such as tumor cell induced platelet aggregation, tumor cell adhesion to endothelial cells and subendothelial matrix, tumor cell induced endothelial cell retraction, etc.) than their direct inhibition of the growth of primary tumors. The potent and widespread metastasis-retarding effects of prostacyclin and its stable analogues in animal tumor models warrant their clinical trial in treating human cancer patients and preventing metastasis.

Autocrine motility factor induces differential 12-lipoxygenase expression and activity in high- and low-metastatic K1735 melanoma cell variants

A M(r) 55,000 tumor cell-secreted cytokine has been described which influenced the migration of the producing cells and was called autocrine motility factor (AMF). Activation of the cell surface receptor for AMF (gp78) was shown to stimulate production of a 12-lipoxygenase metabolite of arachidonic acid, 12-(S)-hydroxyeicosatetraenoic acid [12-(S)-HETE], in highly metastatic murine melanoma cells. AMF stimulated the motility of the high-metastatic (K1735-M1) but not the low-metastatic variant (K1735-Cl.11) of the K1735 murine melanoma and increased expression of the 12-lipoxygenase enzyme predominantly in the high-metastatic counterpart. The K1735-M1 cells responded to motile stimulation with increased endogenous 12-(S)-HETE production, and, reciprocally, exogenous 12-(S)-HETE up-regulated surface gp78 and caused gp78 translocation from an intracellular perinuclear pool to tubulovesicles which extended to the cell periphery in the K1735-M1 cells exclusively. These results suggest that differences in AMF responses may be due to alterations in the capacity of low-metastatic cells to transduce signals through 12-lipoxygenase or to involve downstream effector(s) of 12-(S)-HETE after gp78 activation.

A lipoxygenase metabolite, 12-(S)-HETE, stimulates protein kinase C-mediated release of cathepsin B from malignant cells

The process of tumor cell invasion of the basement membrane is proposed to consist of three steps: attachment, local proteolysis and migration. 12-(S)-HETE, a 12-lipoxygenase metabolite of arachidonic acid, upregulates surface expression of integrin cytoadhesins and an autocrine motility factor receptor, suggesting that this metabolite may play an important regulatory function in tumor cell invasion. In the present study, we determined whether 12-(S)-HETE affects surface expression and/or release of cathepsin B, a cysteine protease that has been implicated in focal degradation of basement membrane. Secretion and distribution of cathepsin B was evaluated in two model systems for various stages of neoplastic progression: (i) murine B16 melanoma lines of low (B16-F1) and high (B16a) lung colonization potential, and (ii) immortalized and ras-transfected MCF-10 human breast epithelial cells that differ in their invasive capacities in vitro. In the B16a cells, 12-(S)-HETE induced release of native and latent cathepsin B activity and concomitantly reduced cell-associated cathepsin B immunoreactivity. In contrast, 12-(S)-HETE did not induce the release of cathepsin B from B16-F1 cells, suggesting that there may be an enhanced response to 12-(S)-HETE in more malignant cells. This was confirmed in the MCF-10 system, in which 12-(S)-HETE was able to induce the release of cathepsin B from the ras-transfected cells, but not from the immortal cells. A simultaneous reduction in staining for cathepsin B was observed in the ras-transfected cells, but not in their immortal counterparts. The release of cathepsin B may be mediated by PKC as pretreatment of B16a cells with the selective PKC inhibitor calphostin C, but not with the PKA inhibitor H8, prevented the stimulated release of cathepsin B. In B16a cells, the release of cathepsin B was accompanied by a translocation toward the cell periphery of vesicles staining for cathepsin B, resulting in focal areas of accumulation of cathepsin B. After 12-(S)-HETE stimulation of the ras-transfected MCF-10 cells, cathepsin B was distributed homogeneously on the apical surface. Thus, 12-(S)-HETE can upregulate the surface expression on tumor cells of proteins able to mediate each of the three steps of tumor cell invasion: adhesion, degradation, and migration.

12(S)-HETE enhancement of prostate tumor cell invasion: selective role of PKC alpha

BACKGROUND

Prostate carcinoma has become the second most fatal cancer in American men. In Dunning R3327 rat prostate adenocarcinoma cells, elevated invasiveness positively correlates with metastatic potential. However, the mechanism(s) responsible for regulation of tumor cell motility and invasion is poorly understood. We have reported that a lipoxygenase metabolite of arachidonic acid, 12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], augments tumor cell metastatic potential through activation of protein kinase C (PKC).

PURPOSE

We proposed to determine the effect of 12(S)-HETE on the motility and invasion of low-metastatic rat prostate AT2.1 tumor cells and the effect of 12(S)-HETE activation of specific PKC isoform(s) in these processes.

METHODS

The motility of AT2.1 cells was determined by the colloidal gold phagokinetic track assay and the invasiveness measured as their ability to invade through basement membrane Matrigel-coated filters. Expression of PKC isoforms was determined by Western blotting of the whole cell lysate with isoform-specific anti-PKC antibodies. Cytosol and membrane fractions were prepared and the subcellular distribution of PKC was analyzed by Western blotting and activity assay. The effect of 12(S)-HETE on cell proliferation was examined. Data were analyzed for significance of difference with the two-sampled, two-sided Student's t test.

RESULTS

12(S)-HETE increased the motility and invasion of AT2.1 cells, and this 12(S)-HETE-increased motility and invasion were inhibited by a selective PKC inhibitor, calphostin C, as well as a Ca2 chelator, bis-(o-aminophenoxy)ethane-N,N,N',N'-tetraacetic acid/tetra(acetoxy-methyl)ester. AT2.1 cells expressed the PKC isoforms alpha and delta, and 12(S)-HETE increased the membrane association of PKC alpha but not delta. Further, the motility and invasion of AT2.1 cells were increased by thymelea toxin, a selective activator of PKC alpha over PKC delta.

CONCLUSION

12(S)-HETE augments the invasiveness of AT2.1 cells via selective activation of PKC alpha.

IMPLICATIONS

12(S)-HETE modulation of PKC alpha invasiveness may be an important mechanism of action for the regulation of the invasive potential of rat prostate carcinoma cells, and the 12-lipoxygenase enzyme and/or PKC alpha may serve as key targets for the development of anti-invasive agents useful for combating the spread of prostate cancer.

Endogenous 12(S)-HETE production by tumor cells and its role in metastasis

12(S)-Hydroxyeicosatetraenoic acid [12(S)-HETE] is the 12-lipoxygenase metabolite of arachidonic acid. Previously, we have demonstrated that exogenous 12(S)-HETE can activate protein kinase C, increase cell surface expression of integrins, enhance adhesion, induce endothelial cell retraction, and increase experimental metastasis of tumor cells. Because of these prominent effects of exogenous 12(S)-HETE on tumor cell metastatic potential, it is important to determine whether there is endogenous 12(S)-HETE production by tumor cells. In the present study, mRNAs from human, rat, and mouse platelets as well as human colon carcinoma (Clone A), rat Walker carcinoma (W256), and mouse melanoma (B16a) and lung carcinoma (3LL) were reverse transcribed and amplified by polymerase chain reaction with platelet 12-lipoxygenase specific primers. Identity of the polymerase chain reaction fragments was confirmed by sequencing. 12-Lipoxygenase protein was detected by Western blotting. Tumor cell-derived 12-HETE was determined by reverse phase-high performance liquid chromatography analysis. In addition, the effect of endogenous 12(S)-HETE on tumor cells was studied by using a platelet-type 12-lipoxygenase selective inhibitor (N-benzyl-N-hydroxy-5-phenylpentanamide). Our results suggest that some tumor cells express platelet-type 12-lipoxygenase mRNA, protein and metabolize arachidonic acid to 12(S)-HETE and that endogenous 12(S)-HETE, like the exogenous 12(S)-HETE, may play an important role in tumor cell adhesion to matrix in vitro and lung colonization in vivo.

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.

Regulation of melanoma-cell motility by the lipoxygenase metabolite 12-(S)-HETE

Cellular motility, a prerequisite for metastasis of tumor cells, is affected by a 55-kDa tumor-cell-secreted cytokine which influences the migration of the producing cells and is called autocrine motility factor (AMF). Previous studies indicated that AMF stimulates motility by binding to its receptor, a cell-surface glycoprotein of 78 kDa (gp78), inducing its phosphorylation, activating a pertussis toxin (PT)-sensitive G-protein, and stimulating inositol metabolism. However, the intracellular signaling mechanisms which transduce and regulate the AMF motility response remain largely unknown. 12-(S)-HETE, a lipoxygenase metabolite of arachidonic acid which affects the cytoskeletal architecture of murine melanoma cells, also stimulates cell motility independently of PT-sensitive G-proteins and up-regulates gp78 surface expression. 12-(S)-HETE induces the phosphorylation of gp78 in a manner analogous to AMF and the motility response of these murine melanoma cells to both AMF and 12-(S)-HETE is inhibited by protein kinase C inhibitors. Furthermore, perturbation of the AMF receptor stimulated endogenous biosynthesis of 12(S)HETE. These results suggest the existence of an "autocrine motility cycle" which influences melanoma cell motility by gp78 activation, and production of second messengers which affect the cytoskeletal architecture and expression of the AMF receptor itself.

Activity and protein distribution of 12-lipoxygenase in HEL cells: induction of membrane-association by phorbol ester TPA, modulation of activity by glutathione and 13-HPODE, and Ca(2+)-dependent translocation to membranes

The understanding of the intracellular regulation of 12-lipoxygenase requires a knowledge of the distribution of both enzyme protein and its activity. In human erythroleukemia cells, the membrane fraction contains about 90% of the total cellular 12-lipoxygenase activity, whereas only approximately 10% of 12-lipoxygenase activity resides in the cytosol. However, the majority of the cellular 12-lipoxygenase protein is found in the cytosol. Pretreatment of cells for 0-3 days with 160 nM TPA caused a marked, time-dependent increase in membrane-bound 12-lipoxygenase activity and protein, respectively. In contrast, the cytosolic amount of 12-lipoxygenase protein and activity, respectively, were minimally altered by this TPA treatment. Recombining the active membrane fraction with cytosol resulted in no significant inhibition of its 12-lipoxygenase activity, but the addition of GSH to the membrane fraction inhibited 12-lipoxygenase activity in a dose-dependent manner. On the other hand, the cytosolic enzyme can be rendered active in the presence of 1 microM 13-hydroperoxyoctadecadienoic acid. In HEL cell homogenates, a partial translocation of the cytosolic enzyme to the membrane takes place in a Ca(2+)-dependent manner, resulting in an increase in membrane-associated 12-lipoxygenase activity and a concomitant decrease in cytosolic 12-lipoxygenase activity above 0.1 microM Ca2+.

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.

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.

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.

Frequent loss of expression and loss of heterozygosity of the putative tumor suppressor gene DCC in prostatic carcinomas

The putative tumor suppressor gene DCC has been shown to be frequently lost or expressed at low levels in colorectal, gastric, pancreatic, and esophageal carcinomas. In the present study, the DCC gene and its mRNA expression in human and rat prostatic carcinoma cells as well as in prostatic carcinoma tissues were examined by reverse transcriptase-polymerase chain reaction and polymerase chain reaction-loss of heterozygosity. The DCC gene was present and expressed in normal prostatic cells. However, its expression was decreased or undetectable in all prostatic carcinoma cells from either humans (4 cell lines) or rats (5 cell lines). In patients, 12 of 14 cases (86%) showed reduced DCC expression and 5 of 11 informative cases (45%) showed loss of heterozygosity at the DCC locus. These results demonstrate that loss of DCC expression and loss of heterozygosity at the DCC locus are a frequent feature of prostatic carcinoma cells.

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.