Commercial ChIP-Seq Library Preparation Kits Performed Differently for Different Classes of Protein Targets

Background

Chromatin immunoprecipitation followed by high-throughput sequencing (ChIP-Seq) is a powerful method commonly used to study global protein-DNA interactions including both transcription factors and histone modifications. We have found that the choice of ChIP-Seq library preparation protocol plays an important role in overall ChIP-Seq data quality. However, very few studies have compared ChIP-Seq libraries prepared by different protocols using multiple targets and a broad range of input DNA levels.

Results

In this study, we evaluated the performance of 4 ChIP-Seq library preparation protocols (New England Biolabs [NEB] NEBNext Ultra II, Roche KAPA HyperPrep, Diagenode MicroPlex, and Bioo [now PerkinElmer] NEXTflex) on 3 target proteins, chosen to represent the 3 typical signal enrichment patterns in ChIP-Seq experiments: sharp peaks (H3K4me3), broad domains (H3K27me3), and punctate peaks with a protein binding motif (CTCF). We also tested a broad range of different input DNA levels from 0.10 to 10 ng for H3K4me3 and H3K27me3 experiments.

Conclusions

Our results suggest that the NEB protocol may be better for preparing H3K4me3 (and potentially other histone modifications with sharp peak enrichment) libraries; the Bioo protocol may be better for preparing H3K27me3 (and potentially other histone modifications with broad domain enrichment) libraries, and the Diagenode protocol may be better for preparing CTCF (and potentially other transcription factors with well-defined binding motifs) libraries.  For ChIP-Seq experiments using novel targets without a known signal enrichment pattern, the NEB protocol might be the best choice, as it performed well for each of the 3 targets we tested across a wide array of input DNA levels.

Integrative analysis of the characteristics of lipid metabolism-related genes as prognostic prediction markers for hepatocellular carcinoma

OBJECTIVE

Dysregulated lipid metabolism has been reported in the progression of hepatocellular carcinoma (HCC). In the present study, we investigated the molecular characteristics of lipid-metabolism-related genes (IMRGs) as prognostic markers for HCC.

MATERIALS AND METHODS

Multi-dimensional bioinformatics analyses were performed to comprehensively analyze IMRGs, and to construct prognostic prediction signatures.

RESULTS

Data of 770 HCC patients and their corresponding 776 IMRGs were downloaded from three databases. Patients were classified into 2 molecular clusters that were associated with overall survival, clinical characteristics, and immune cells. The biological functions of the IMRGs differentially expressed between the 2 clusters were associated with tumor-related metabolic pathways. A 6 IMRG signature (6-IS), consisting of FMO3, SLC11A1, RNF10, KCNH2, ME1, and ZIC2, was established as an independent prognostic factor for HCC. The performance of the signature of 6-IS prognostic was verified in a validation set and compared to an external data set. It was revealed that the 6-IS could effectively predict the prognosis of patients with HCC.

CONCLUSIONS

This study provides new insights into the role of IMRGs in the pathogenesis of HCC, and presents a novel signature (6-IS) to predict the prognosis of HCC.

NANOG promotes cancer stem cell characteristics and prostate cancer resistance to androgen deprivation

Cancer cell molecular mimicry of stem cells (SC) imbues neoplastic cells with enhanced proliferative and renewal capacities. In support, numerous mediators of SC self-renewal have been evinced to exhibit oncogenic potential. We have recently reported that shRNA-mediated knockdown of the embryonic stem cell (ESC) self-renewal gene NANOG significantly reduced the clonogenic and tumorigenic capabilities of various cancer cells. In this study, we sought to test the potential pro-tumorigenic functions of NANOG, particularly, in prostate cancer (PCa). Using quantitative RT-PCR, we first confirmed that PCa cells expressed NANOG mRNA primarily from the NANOGP8 locus on chromosome 15q14. We then constructed a lentiviral promoter reporter in which the -3.8 kb NANOGP8 genomic fragment was used to drive the expression of green fluorescence protein (GFP). We observed that NANOGP8-GFP⁺ PCa cells exhibited cancer stem cell (CSC) characteristics such as enhanced clonal growth and tumor regenerative capacity. To further investigate the functions and mechanisms of NANOG in tumorigenesis, we established tetracycline-inducible NANOG overexpressing cancer cell lines, including both prostate (Du145 and LNCaP) and breast (MCF-7) cancer cells. NANOG induction promoted drug-resistance in MCF-7 cells, tumor regeneration in Du145 cells, and, most importantly, castration-resistant tumor development in LNCaP cells. These pro-tumorigenic effects of NANOG were associated with key molecular changes, including an upregulation of molecules such as CXCR4, IGFBP5, CD133 and ALDH1. The present gain-of-function studies, coupled with our recent loss-of-function work, establish the integral role for NANOG in neoplastic processes and shed light on its mechanisms of action.

Highly purified CD44+ prostate cancer cells from xenograft human tumors are enriched in tumorigenic and metastatic progenitor cells

CD44 is a multifunctional protein involved in cell adhesion and signaling. The role of CD44 in prostate cancer (PCa) development and progression is controversial with studies showing both tumor-promoting and tumor-inhibiting effects. Most of these studies have used bulk-cultured PCa cells or PCa tissues to carry out correlative or overexpression experiments. The key experiment using prospectively purified cells has not been carried out. Here we use FACS to obtain homogeneous CD44(+) and CD44(-) tumor cell populations from multiple PCa cell cultures as well as four xenograft tumors to compare their in vitro and in vivo tumor-associated properties. Our results reveal that the CD44(+) PCa cells are more proliferative, clonogenic, tumorigenic, and metastatic than the isogenic CD44(-) PCa cells. Subsequent molecular studies demonstrate that the CD44(+) PCa cells possess certain intrinsic properties of progenitor cells. First, BrdU pulse-chase experiments reveal that CD44(+) cells colocalize with a population of intermediate label-retaining cells. Second, CD44(+) PCa cells express higher mRNA levels of several 'stemness' genes including Oct-3/4, Bmi, beta-catenin, and SMO. Third, CD44(+) PCa cells can generate CD44(-) cells in vitro and in vivo. Fourth, CD44(+) PCa cells, which are AR(-), can differentiate into AR(+) tumor cells. Finally, a very small percentage of CD44(+) PCa cells appear to undergo asymmetric cell division in clonal analyses. Altogether, our results suggest that the CD44(+) PCa cell population is enriched in tumorigenic and metastatic progenitor cells.

Novel protection strategy for pulmonary transplantation

BACKGROUND

Ischemia-reperfusion injury continues to represent a significant challenge to successful lung transplantation. Traditional pulmonary ischemic protection is performed using hypothermic hyperkalemic depolarizing solutions to reduce the metabolic demands of the ischemic organ. Measures to further reduce the effects of ischemic injury have focused on the reperfusion period. We tested the hypothesis that novel physiologic hyperpolarizing solutions-using ATP-dependent potassium channel (K(ATP)) openers-given at the induction of ischemia, will reduce cellular injury and provide superior graft function even after prolonged periods of ischemia.

METHODS

An isolated blood-perfused ventilated rabbit lung model was used to study lung injury. Airway, left atrial, and pulmonary artery pressures were measured continuously during the 2-h reperfusion period. Oxygenation, as a surrogate of graft function, was measured using intermittent blood gas analysis of paired left atrial and pulmonary artery blood samples. Graft function was measured by oxygen challenge technique (F(i)O(2) = 1.0). Wet-to-dry ratio was measured at the conclusion of the 2-h reperfusion period. Control (Group I) lungs were perfused with modified Euro-Collins solution (depolarizing) and reperfused immediately (no ischemia). Traditional protection lungs were perfused with modified Euro-Collins flush solution and stored for 4 h (Group II) or 18 h (Group III) at 4 degrees C before reperfusion. Novel protection (Group IV) lungs were protected with a hyperpolarizing solution containing 100 nM Aprikalim, a specific K(ATP) channel opener, added to the modified Euro-Collins flush solution and underwent 18 h of ischemic storage at 4 degrees C before reperfusion.

RESULTS

Profound graft failure was measured after 18 h of ischemic storage with traditional protection strategies (Group III). Graft function was preserved by protection with hyperpolarizing solutions even for prolonged ischemic periods (Group IV). Wet-to-dry weight ratio, airway, left atrial, and pulmonary artery pressures were not significantly different between the groups.

CONCLUSIONS

We have created a model of predictable lung injury. Membrane hyperpolarization with a K(ATP) channel opener (PCO) provides superior prolonged protection from ischemia-reperfusion injury in an in vitro model of pulmonary transplantation.

Lack of replicative senescence in cultured rat oligodendrocyte precursor cells

Most mammalian somatic cells are thought to have a limited proliferative capacity because they permanently stop dividing after a finite number of divisions in culture, a state termed replicative cell senescence. Here we show that most oligodendrocyte precursor cells purified from postnatal rat optic nerve can proliferate indefinitely in serum-free culture if prevented from differentiating; various cell cycle-inhibitory proteins increase, but the cells do not stop dividing. The cells maintain high telomerase activity and p53- and Rb-dependent cell cycle checkpoint responses, and serum or genotoxic drugs induce them to acquire a senescence-like phenotype. Our findings suggest that some normal rodent precursor cells have an unlimited proliferative capacity if cultured in conditions that avoid both differentiation and the activation of checkpoint responses that arrest the cell cycle.

Evidence that axon-derived neuregulin promotes oligodendrocyte survival in the developing rat optic nerve

It was previously shown that newly formed oligodendrocytes depend on axons for their survival, but the nature of the axon-derived survival signal(s) remained unknown. We show here that neuregulin (NRG) supports the survival of purified oligodendrocytes and aged oligodendrocyte precursor cells (OPCs) but not of young OPCs. We demonstrate that axons promote the survival of purified oligodendrocytes and that this effect is inhibited if NRG is neutralized. In the developing rat optic nerve, we provide evidence that delivery of NRG decreases both normal oligodendrocyte death and the extra oligodendrocyte death induced by nerve transection, whereas neutralization of endogenous NRG increases the normal death. These results suggest that NRG is an axon-associated survival signal for developing oligodendrocytes.

Long-term culture of purified postnatal oligodendrocyte precursor cells. Evidence for an intrinsic maturation program that plays out over months

Oligodendrocytes myelinate axons in the vertebrate central nervous system (CNS). They develop from precursor cells (OPCs), some of which persist in the adult CNS. Adult OPCs differ in many of their properties from OPCs in the developing CNS. In this study we have purified OPCs from postnatal rat optic nerve and cultured them in serum-free medium containing platelet-derived growth factor (PDGF), the main mitogen for OPCs, but in the absence of thyroid hormone in order to inhibit their differentiation into oligodendrocytes. We find that many of the cells continue to proliferate for more than a year and progressively acquire a number of the characteristics of OPCs isolated from adult optic nerve. These findings suggest that OPCs have an intrinsic maturation program that progressively changes the cell's phenotype over many months. When we culture the postnatal OPCs in the same conditions but with the addition of basic fibroblast growth factor (bFGF), the cells acquire these mature characteristics much more slowly, suggesting that the combination of bFGF and PDGF, previously shown to inhibit OPC differentiation, also inhibits OPC maturation. The challenge now is to determine the molecular basis of such a protracted maturation program and how the program is restrained by bFGF.

Apoptosis induction by a novel anti-prostate cancer compound, BMD188 (a fatty acid-containing hydroxamic acid), requires the mitochondrial respiratory chain

We recently developed a class of novel anti-prostate cancer compounds, cyclic hydroxamates that elicit a potent apoptotic response in many tumor cells cultured in vitro (D.G. Tang et al., Biochem. Biophys. Res. Commun., 242: 380-384, 1998). The lead compound, termed BMD188, induces programmed cell death in a variety of prostate cancer cells in vitro as well as in vivo (L. Li et al., Anticancer Res., 19: 51-70, 1999). BMD188 kills androgen-independent prostate cancer cells as well as prostate cancer cells with a multidrug-resistance phenotype. The apoptotic effect of BMD188 in prostate cancer cells does not depend on cell cycle, p53 status, or its purported target, arachidonate 12-lipoxygenase, but does require caspase activation and seems to involve mitochondria. To synthesize more specific and effective anti-prostate cancer hydroxamic acid compounds, it is important to understand their mechanism(s) of action. In the present study, we studied the role of mitochondrial respiratory chain (MRC) in BMD188-induced apoptosis in androgen-independent prostate cancer PC3 cells and compared its effect with that of staurosporine (STS), a widely used apoptosis inducer. Several lines of evidence indicate that BMD188-induced cell death depends on MRC: (a) the death could be significantly inhibited by several complex-specific respiration inhibitors; (b) respiration-deficient rho0 cells were more resistant than wild-type parent cells to apoptosis induction by BMD188; and (c) BMD188 induced a rapid increase in reactive oxygen species in mitochondria, an up-regulation of cytochrome c oxidase subunits, a biphasic alteration (i.e., an early hyperpolarization, followed by later hypopolarization) in the mitochondrial membrane potential (delta psi(m)), dramatic changes in mitochondrial morphology and distribution prior to caspase activation, and an abnormal proliferation of mitochondria at the ultrastructural level. By contrast, STS-induced PC3 apoptosis seemed not to depend on MRC. Taken together, the data suggest that the MRC represents a functional target for anti-prostate cancer hydroxamates.

Hospital volume can serve as a surrogate for surgeon volume for achieving excellent outcomes in colorectal resection

OBJECTIVE

To examine the association of surgeon and hospital case volumes with the short-term outcomes of in-hospital death, total hospital charges, and length of stay for resection of colorectal carcinoma.

METHODS

The study design was a cross-sectional analysis of all adult patients who underwent resection for colorectal cancer using Maryland state discharge data from 1992 to 1996. Cases were divided into three groups based on annual surgeon case volume--low (< or =5), medium (5 to 10), and high (>10)--and hospital volume--low (<40), medium (40 to 70), and high (> or =70). Poisson and multiple linear regression analyses were used to identify differences in outcomes among volume groups while adjusting for variations in type of resections performed, cancer stage, patient comorbidities, urgency of admission, and patient demographic variables.

RESULTS

During the 5-year period, 9739 resections were performed by 812 surgeons at 50 hospitals. The majority of surgeons (81%) and hospitals (58%) were in the low-volume group. The low-volume surgeons operated on 3461 of the 9739 total patients (36%) at an average rate of 1.8 cases per year. Higher surgeon volume was associated with significant improvement in all three outcomes (in-hospital death, length of stay, and cost). Medium-volume surgeons achieved results equivalent to high-volume surgeons when they operated in high- or medium-volume hospitals.

CONCLUSIONS

A skewed distribution of case volumes by surgeon was found in this study of patients who underwent resection for large bowel cancer in Maryland. The majority of these surgeons performed very few operations for colorectal cancer per year, whereas a minority performed >10 cases per year. Medium-volume surgeons achieved excellent outcomes similar to high-volume surgeons when operating in medium-volume or high-volume hospitals, but not in low-volume hospitals. The results of low-volume surgeons improved with increasing hospital volume but never equaled those of the high-volume surgeons.

Hormone-refractory prostate cancer cells express functional follicle-stimulating hormone receptor (FSHR)

PURPOSE

Understanding growth regulation in hormone-refractory prostate cancer may provide avenues for novel treatment interventions. This study was conducted to characterize the expression of the receptor (FSHR) for follicle-stimulating hormone (FSH) in androgen-independent prostate cancer cell lines and in human malignant prostate tissues.

MATERIALS AND METHODS

Western blotting, immunohistochemistry (IHC), and flow cytometric analysis were used to study the expression of FSHR. The effect of FSH on cell growth and clonogenicity was studied using proliferation and clonogenic assays.

RESULTS

Immunohistochemistry revealed expression of FSH in PC3 and Du145 cells. FSHR was identified in PC3 and Du145 cells, as well as in human adenocarcinoma of the prostate. The specificity of the FSHR detected on prostate cancer tissues or cells by IHC and Western blotting was confirmed by preabsorbing the antibodies with the immunizing antigens. Stimulation of these hormone-refractory cells with FSH triggered a proliferative response in vitro, suggesting that the receptor is biologically active.

CONCLUSION

Hormone-refractory prostate cancer cells express FSH and biologically active FSHR. Our results suggest that FSHR and its ligand may play a role in the regulation of the growth of hormone-refractory prostate cancers.

Prostate secretory protein (PSP94) suppresses the growth of androgen-independent prostate cancer cell line (PC3) and xenografts by inducing apoptosis

BACKGROUND

PSP94 (prostate secretory protein of 94 aa; also called PIP), one of the predominant proteins secreted into the seminal fluid, was proposed as an independent diagnostic/prognostic marker for prostate cancers. It was also shown to inhibit rat prostate cancer growth. In this study, we investigated the effect of purified PSP94 on the growth of androgen-independent human prostate cancer cells (PC3) and its potential mechanism of action.

METHODS AND RESULTS

PSP94, in a dose- and time-dependent manner, inhibited the growth of PC3 cells. The protein demonstrated a stronger inhibitory effect on the colony-forming ability of PC3 cells in soft agar. A daily injection of PSP94 at 5 microg/kg/body weight resulted in a 50-60% inhibition in the growth of PC3 xenografts in athymic mice. PC3 cell growth inhibition by PSP94 resulted from cell death characteristic of morphological apoptosis, which was confirmed by dual fluorescence microscopy, electron microscopy, and DNA fragmentation assays. Mechanistic studies indicated that PSP94 enhanced the expression of proapoptotic protein Bax without affecting Bcl-2 levels.

CONCLUSIONS

This study suggests that PSP94 may represent a novel, apoptosis-based, antitumor agent applicable to the treatment of hormone-refractory human prostate cancers.

A novel hydroxamic acid compound, BMD188, demonstrates anti-prostate cancer effects by inducing apoptosis. I: In vitro studies

BACKGROUND

Prostate cancer is the most frequently diagnosed malignancy in the Western countries. Apoptosis-targeted drug development could represent a specific and effective weapon against the disease (Tang and Porter, 32: 284-293, 1997). We previously demonstrated that the arachidonate 12-lipoxygenase and its metabolic products could function as survival factors for many solid tumors (Tang et al., Proc. Natl. Acad. Sci. USA 93: 5241-5246, 1996; Tang and Honn, J. Cell. Physiol. 172: 155-170, 1997).

MATERIALS AND METHODS

In this study, we synthesized a series of novel cyclic hydroxamic acid compounds that demonstrated varying degrees of inhibitory effects on the arachidonate 12-lipoxygenase. Subsequently we studied the effects of these novel compounds on human prostate cancer cells. First, all these compounds were screened on androgen-independent PC3 adenocarcinoma cells. Second, based on the results (i.e., the LD50 values) of the primary, secondary and tertiary screening, lead compounds were determined. Third, the lead compounds were utilized to study their cytotoxic effects on various prostate cancer cells as well as several types of normal cells. Finally, the molecular nature of the cell death was thoroughly characterized and the potential mechanisms of cell death were determined.

RESULTS

About 30% of the compounds screened induced a strong apoptotic death of androgen-independent prostate cancer cells, PC3, with an LD50 mostly at 10-20 microM. A lead compound, BMD188 [cis-1-hydroxy-4-(1-naphthyl)-6-octylpiperidine-2-one], was subsequently identified which inhibited the growth of PC3 cells with an LD50 at approximately 10 microM. Comparative studies indicated that BMD188 induced a more potent apoptotic response in PC3 cells than several conventional chemotherapeutic drugs. Furthermore, unlike the above drugs, BMD188 could induce 100% apoptosis in tumor cells. BMD188 also caused apoptosis of other types of prostate cancer cells including cells with multidrug resistance phenotype, independent of the androgen-dependence and p53 status. By contrast, BMD188 generally demonstrated 2-5 fold lower cytotoxicity towards several normal cell types including normal prostate epithelial cells. The growth inhibition by BMD188 was due to apoptosis induction as evidenced by DNA ladder formation, PARP [poly(ADP-ribose)polymerase] cleavage, and typical apoptotic morphology. BMD188-induced apoptosis does not depend on its inhibitory effects on lipoxygenase since target cells (i.e., PC3 and Du145) did not express the lipoxygenase mRNA and protein. In contrast, the apoptosis-inducing effect of BMD188 in PC3 cells could be significantly inhibited by serine protease inhibitors TPCK and TLCK as well as by caspase inhibitors DEVD and zVAD. The involvement of caspases in the apoptotic effects of BMD188 was further confirmed by the activation of caspase-3 (CPP32). In the accompanying paper, we show that BMD188 also inhibits the primary growth and local invasion of Du145 prostate cancer cells orthotopically implanted into the SCID or athymic nude mice.

CONCLUSION

The data presented here suggest that these novel cyclic hydroxamic acid compounds, via induction of apoptotic death, may find potential clinical applications in the treatment of human prostate cancers.

Extract of Solanum muricatum (Pepino/CSG) inhibits tumor growth by inducing apoptosis

BACKGROUND

Apoptosis, or programmed cell death, is characterized by certain distinct morphological and biochemical features. Most chemotherapeutic drugs exert their anti-tumor effects by inducing apoptosis. Therefore, an effective compound inducing apoptosis appears to be a relevant strategy to suppress various human tumors. In a search for tumor inhibitors from various kinds of plants, we found that extracts from Solanum muricatum (CSG) can inhibit tumor growth both in vivo and in vitro by inducing apoptosis.

MATERIALS AND METHODS

A lyophilized aqueous fraction extracted from Solanum muricatum (CSG4) was used in this study. The human cell lines tested include: prostate (PC3, DU145), stomach (MKN45), liver (QGY-7721, SK-HEP-1), breast (MDA-MB-435), ovarian (OVCAR), colon (HT29) and lung (NCI-H209) cancer cells; NHP (prostate), HUVEC (umbilical vein endothelial cell), and WI-38 (lung diploid fibroblasts) normal cells. The cell survival was determined by either Cell Titer MTS cell proliferation kit or trypan blue dye exclusion assay. The apoptosis was analyzed by (a) apoptotic morphology by light microscopy; (b) DNA ladder formation; (c) PARP cleavage assay.

RESULTS

a) CSG possesses selective cytotoxic activity against all the tumor cell lines being tested. The LD50 value is 561-825 micrograms/ml. b) CSG showed a much lower cytotoxicity to NHP, HUVEC and WI-38 normal cell lines with LD50 value being 2.8-3.2 mg/ml, which is 3-6 fold higher than on tumor cells. c) The in vivo study demonstrated that injection of CSG (100 micrograms) directly into tumor mass can reduce the tumor volume dramatically in nude mice inoculated with MKN45 gastric cancer cells. d) CSG-mediated tumor growth inhibition is through induction of apoptotic cell death, as manifested by (a) typical apoptotic morphology; (b) DNA ladder formation; and (c) PARP cleavage assay.

CONCLUSION

Taken together, the present study suggests, for the first time, that CSG may represent promising new chemical entity which preferentially targets various tumor cells by triggering apoptosis.

A novel hydroxamic acid compound, BMD188, demonstrates anti-prostate cancer effects by inducing apoptosis. II: In vivo efficacy and pharmacokinetic studies

BACKGROUND

In the preceding paper, we demonstrated that, BMD188 [cis-1-hydroxy-4-(1-naphthyl)-6-octylpiperidine-2-one], a newly synthesized cyclic hydroxamic acid compound, induces potent apoptotic death of prostate cancer cells in vitro. In this project, we studied the in vivo pharmacokinetic behavior and anti-tumor efficacy of this novel compound.

MATERIALS AND METHODS

A bioavailability/elimination study was first performed using radiolabeled BMD188 administered to rats through intraperitoneal (i.p.), intravenous (i.v). or oral (p.o.) routes. Based on these pharmacokinetic data as well as pilot experiments on in vivo toxicity, two sets of efficacy studies, with i.p. administered BMD188, were performed in SCID mice or athymic nude mice which had been orthotopically transplanted with Du145 human prostate cancer cells. Tumor growth rate was measured and the final tumor weights and sizes determined. Subsequently, histopathological data were obtained and tumor tissue sections were used for apoptosis (i.e., TUNEL) staining.

RESULTS

The pharmacokinetic studies revealed low (approximately 8%) absorption through the p.o. route and high (approximately 70%) absorption through the i.p. route. The average plasma half life (T1/2) of BMD188 was approximately 50 h. Post-absorption, plasma elimination of radioactivity was similar to that in animals given [3H]-188 intravenously. The in vivo efficacy results indicate that i.p. administered BMD188 significantly inhibited the primary growth and local invasion of Du145 prostate cancer cells orthotopically implanted into SCID or athymic nude mice. The tumor-inhibitory effect of BMD188 was due to apoptosis induction in vivo, as revealed by histological analysis as well as TUNEL staining of the tumor tissue sections.

CONCLUSION

Collectively, the preceding in vitro and the current in vivo studies suggest that BMD188 and its analogs may find clinical applications in the treatment of prostate cancer patients by inducing apoptotic death of prostate cancer cells.

Extended survivability of prostate cancer cells in the absence of trophic factors: increased proliferation, evasion of apoptosis, and the role of apoptosis proteins

This project was undertaken to study the survival properties of various prostate cells, including normal (NHP), BPH (benign prostate hyperplasia), primary carcinoma (PCA), and metastatic prostate cancer cells (LNCaP, PC3, and Du145), in the absence of trophic factors. Cell proliferation and cell death were quantitated by enumerating the number of live cells using MTS/PMS kit and of dead (apoptotic) cells using 4',6-diamidino-2-phenylindole dihydrochloride nuclear staining. These cells demonstrated an overall survivability in the order of BPH < NHP < LNCaP < PC3 < PCA < Du145. Upon growth factor deprivation, NHP/BPH cells rapidly underwent apoptosis, leading to a decreased number of live cells. PCA/PC3/Du145 cells, in contrast, demonstrated an initial phase of aggressive growth during which apoptosis rarely occurred, followed by a "plateau" phase in which cell loss by apoptosis was compensated by cell proliferation, followed by a later phase in which apoptosis exceeded the cell proliferation. LNCaP cells demonstrated survival characteristics between those of NHP/BPH and PCA/PC3/Du145 cells. We concluded that the increased survivability in prostate cancer cells results from enhanced cell proliferation as well as decreased apoptosis. The molecular mechanisms for evasion of apoptosis in prostate cancer cells were subsequently investigated. Quantitative Western blotting was used to examine the protein expression of P53 and P21WAF-1, Bcl-2 and Bcl-X(L) (anti-apoptotic proteins), and Bax, Bak, and Bad (proapoptotic proteins). The results revealed that, upon trophic factor withdrawal, NHP and BPH cells upregulated wild-type p53 and proapoptotic proteins Bax/Bad/Bak and down-regulated the expression of P21. Furthermore, NHP and BPH cells endogenously expressed little or no Bcl-2. In sharp contrast, prostate cancer cells expressed nonfunctional P53 and various amounts of Bcl-2 proteins. Upon deprivation, these cancer cells up-regulated P21 and Bcl-2 and/or BclX(L), lost response to withdrawal-induced up-regulation of Bax/Bad/Bak or decreased or even completely lost Bax expression and expressed some novel proteins such as P25 and P54/55 complex. These data together suggest that prostate cancer cells may use multiple molecular mechanisms to evade apoptosis, which, together with increased proliferation, contribute to extended survivability of prostate cancer cells in the absence trophic factors.

12(S)-hydroxyeicosatetraenoic acid increases the actin microfilament content in B16a melanoma cells: a protein kinase-dependent process

12(S)-hydroxyeicosatetraenoic acid [12(S)-HETE], a lipoxygenase metabolite of arachidonic acid, has been shown to be involved in a wide variety of cellular activities (i.e., adhesion, spreading, motility, invasion) which promote metastasis to occur in tumor cells. In this study, several techniques (Western blotting, flow cytometry and DNase I assay) were performed to examine the alterations in the distribution of G- and F-actin expressed in B16a melanoma cells. Each of these methods independently revealed that 12(S)-HETE treatment (0.1 mM, 15 min) resulted in an increase in the F-actin content in the cytoskeletal preparations. Since the integrity of cytoskeletal networks (i.e., actin filaments) can be dynamically regulated through protein phosphorylation, we investigated the potential role of several protein kinases in the 12(S)-HETE-induced actin polymerization. By flow cytometric analysis, 12(S)-HETE was found to increase the actin filament contents. This effect could be inhibited by protein kinase C (PKC) inhibitors (calphostin C and staurosporine) as well as by protein tyrosine kinase (PTK) inhibitor (genistein) but not by protein kinase A inhibitor (H8), suggesting that the 12(S)-HETE effect involves PKC and PTK. This conclusion is consistent with the observations that phorbol 12-myristate-13-acetate (PMA) mimics the biological effect of 12(S)-HETE in promoting the F-actin formation in B16a cells. As a final analysis, direct protein phosphorylation studies indicate that 12(S)-HETE treatment led to enhanced phosphorylation of myosin light chain, which may contribute to the increased stress fiber formation following 12(S)-HETE stimulation.

Role of protein kinase C and phosphatases in 12(S)-HETE-induced tumor cell cytoskeletal reorganization

Adherent B16 amelanotic melanoma (B16a) cells exposed to fatty acid 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, demonstrated a gradual dissolution of stress fibers and bundling-together of vimentin. The 12(S)-HETE effects on tumor cell cytoskeleton appeared 5 min after treatment, became prominent approximately 15 min following stimulation, and generally disappeared by 30 min. Simultaneous treatment of cells with 12(S)-HETE and okadaic acid (OA) prevented disappearance of the 12(S)-HETE effects by 30 min. Quantitative double immunoblotting of actin and vimentin indicated that actin, but not vimentin, underwent a time-related depolymerization. On the other hand, enhanced phosphorylation of vimentin but not of actin was observed after 12(S)-HETE treatment. 12(S)-HETE-enhanced vimentin phosphorylation was abolished by protein kinase C (PKC) inhibitor calphostin C, thus suggesting the involvement of PKC.

Apoptosis in the absence of cytochrome c accumulation in the cytosol

Cytochrome c release from mitochondria to and subsequent accumulation in the cytosol has been considered a prerequisite for apoptosis. In this study, we present evidence for apoptosis induction without accumulation of cytochrome c in the cytosol. U937 lymphoma cells treated with staurosprine released cytochrome c from mitochondria to cytosol prior to PARP cleavage and DNA fragmentation. However, U937 cells treated with BMD188 (a hydroxamic acid and a potent apoptosis inducer) did not demonstrate any cytochrome c accumulation in the cytosol during apoptosis induction. This different pattern of cytochrome c alterations was also observed with these two inducers on leukemic HL60 cells and epithelial PC3 cells. Furthermore, when PC3 cells were treated with a panel of apoptosis-inducing agents, it was found that camptothecin, bleomycin, VP16 and TNF-alpha induced varying amounts of cytosolic accumulation of cytochrome c either prior to or concurrent with PARP cleavage while vinblastine and BHPP did not. Taken together, the present results suggest that cytochrome c accumulation in the cytosol during apoptosis is a cell type- and inducer-dependent phenomenon.

BMD188, A novel hydroxamic acid compound, demonstrates potent anti-prostate cancer effects in vitro and in vivo by inducing apoptosis: requirements for mitochondria, reactive oxygen species, and proteases

A newly synthesized cyclic hydroxamic acid compound, BMD188 [cis-1-hydroxy-4-(1-naphthyl)-6-octylpiperidine-2-one], was found to induce the apoptotic death of cultured prostate cancer cells by activating caspase-3. Orally administered BMD188 significantly inhibited the primary growth of prostate cancer cells (Du145) orthotopically implanted into SCID mice. Mechanistic studies indicated that BMD188 did not alter the protein levels of several Bcl-2 family members. In contrast, the BMD188 effect required three essential factors: reactive oxygen species (ROS), the mitochondrial respiratory chain function, and proteases. First, the apoptosis-inducing effect of BMD188 could be blocked by ROS scavengers such as Desferal. Second, both BMD188-induced PARP cleavage as well as PC3 cell apoptosis could be dramatically inhibited by several complex-specific mitochondrial respiration blockers. The involvement of mitochondria was also supported by the observations that BMD188 dramatically altered the mitochondrial distribution and morphology without affecting the cellular ATP levels. Finally, the apoptosis-inducing effect of BMD188 in PC3 cells could be significantly inhibited by serine protease inhibitors (TPCK and TLCK) as well as by caspase inhibitors (zVAD-fmk and DEVD-CHO). Collectively, the present study suggests that BMD188 and its analogs may find clinical applications in the treatment of prostate cancer patients by inducing apoptotic death of prostate cancer cells.

Actin cleavage in various tumor cells is not a critical requirement for executing apoptosis

Actin is a major cytoskeletal protein which is involved in many physiological cellular functions such as motility, cell shape, and adhesion. Recently, actin has also been reported to be cleaved by apoptotic proteases (i.e., caspases) and this cleavage is thought to contribute to the apoptotic process. However, conflicting data also exists as to whether actin represents a true caspase substrate during apoptosis induction in vivo (i.e., inside the cells). In this study, we critically examined the actin cleavage patterns during apoptosis of several tumor cell lines derived from three different species (i.e., mouse, rat, and human). Our findings demonstrate that: 1) actin cleavage in vivo is not a common phenomenon since apoptosis caused by multiple inducers in most cell types examined occurs without evidence of actin degradation; and 2) in certain cell types (e.g., U937), spontaneous, actin cleavage is observed which is not prevented by various specific chemical/peptide inhibitors of proteases such as caspases or serine proteases although apoptosis per se is retarded by some of these inhibitors. Our results conclude that actin is not a critical substrate for apoptotic proteases in vivo during apoptosis.

Suppression of W256 carcinosarcoma cell apoptosis by arachidonic acid and other polyunsaturated fatty acids

Serum-cultured rat W256 carcinosarcoma cells of the monocytoid origin undergo rapid apoptosis in response to the lipoxygenase inhibitor NDGA (nordihydroguaiaretic acid). Exogenous arachidonic acid (AA), in a time- and dose-dependent fashion, suppressed NDGA-induced W256 cell apoptosis as well as DNA fragmentation, with the maximal effect observed at approximately 25 microM. Mobilization of endogenous AA by calcium ionophore A23187 provided an even stronger and longer-lasting protection against NDGA-caused cell death. The A23187 effect on AA release as well as W256 cell death can be blocked by bromophenacyl bromide, thus suggesting involvement of phospholipase A2 activation. Serum withdrawal similarly caused W256 cells to undergo typical apoptosis, which was not rescued by several growth factors commonly found in serum. However, exogenous AA suppressed serum starvation-induced W256 cell apoptosis and significantly extended cell survival in a dose-dependent manner. Lipoxygenase products, 12(S)- and 15(S)-, but not 5(S)-hydroxyeicosatetraenoic acid (HETE), in a dose-dependent fashion, also prevented both NDGA- and serum-starvation-induced W256 cell apoptosis. AA appears to suppress W256 cell apoptosis via distinct signaling pathway(s) since it does not prevent cell death triggered by several other inducers. Examination of a panel of polyunsaturated fatty acids revealed that alpha-linolenic and linoleic acid can also suppress NDGA-induced W256 cell apoptosis. Our data suggest that AA and other polyunsaturated fatty acids and/or their metabolites may enhance tumor growth not only by promoting cell proliferation but also by suppressing apoptosis.

Target to apoptosis: a hopeful weapon for prostate cancer

BACKGROUND

Prostate cancer is the most commonly diagnosed neoplasm and the second leading cause of male death in this country. Multiple genetic and epigenetic factors have been implicated in the oncogenesis and progression of prostate cancer. However, the molecular mechanisms underlying the disease remain largely unknown. The major difficulty in the clinical management of prostate cancer stems from the reality that reliable and accurate diagnostic/prognostic biomarkers are not available and that effective treatment regimens for hormone-resistant prostate cancers are yet to be developed.

METHODS

The present review, through extensive literature research, summarizes the most recently accumulated experimental and clinical data on the relationship between apoptosis and prostate cancer. We analyze the possibility of inducing prostate cancer cell apoptosis by: 1) androgen ablation by castration or biochemical antagonists: 2) chemotherapeutic drugs or natural/synthetic chemicals; 3) manipulation of apoptosis-related oncoproteins; and 4) modulation of intracellular signal transducers.

RESULTS

1) Prostate cancer, like most other solid tumors, represents a very heterogeneous entity. Most prostate cancers, at the time of clinical diagnosis, present themselves as mixtures of androgen-dependent and androgen-independent cells. 2) Most prostate cancers respond initially to androgen ablation since the population of androgen-dependent cells undergoes rapid apoptosis upon androgen withdrawal. However, androgen ablation rarely cures patients, most of whom will experience recurrence due to takeover of the tumor mass by androgen-independent tumor cells as well as the emergence of apoptosis-resistant clones as a result of further genetic alterations such as bcl-2 amplification. 3) On the other hand, although androgen-independent prostate cancer cells do not undergo apoptosis upon androgen blocking, they do maintain the appropriate molecular machinery of apoptosis. Therefore, certain conventional chemotherapy drugs can eliminate androgen-independent cancer cells by inducing apoptosis. 4) However, most drugs used in chemotherapy induce apoptosis or mediate cytotoxicity only in proliferating cancer cells. Human prostate cancer cells demonstrate very slow growth kinetics. Thus, novel chemical/natural products need be identified to eradicate those nonproliferating cancer cells. In this regard, the angiogenesis inhibitor, linomide, and a plant extract, beta-lapachone, demonstrate very promising apoptosis-inducing effects on prostate cancer cells in a proliferation-independent manner. 5) An alternative way to modulate the apoptotic response is by interfering with the expression levels of essential regulatory molecule of apoptosis. Bcl-2 and p53 represent two prime targets for such manipulations. 6) Finally, modulation of signal transduction pathways (e.g., intracellular Ca2+ levels, PKC activity) involved in apoptosis may also induce and/or enhance the apoptotic response of prostate cancer cells.

CONCLUSIONS

Modulation of apoptotic response represents a novel mechanism-based approach which may help identify novel drugs and/or develop new therapeutic regimens for the treatment of prostate cancers.

Apoptosis of W256 carcinosarcoma cells of the monocytoid origin induced by NDGA involves lipid peroxidation and depletion of GSH: role of 12-lipoxygenase in regulating tumor cell survival

Arachidonate lipoxygenases (LOX) and their products play an important role in mediating growth factor-supported tumor cell proliferation and growth. The LOX pathway may also be critical in regulating tumor cell survival and apoptosis. Blocking the 12-LOX gene expression with sequence-specific antisense oligos or its activity with general or isoform-specific LOX inhibitors induces a strong apoptotic response in rat W256 carcinosarcoma cells of the monocytoid origin (Tang et al., 1996, Proc. Natl. Acad. Sci. U.S.A., 93:5241-5246). In the present study, several molecular approaches confirmed the predominant expression of platelet-type 12-LOX in W256 cells, with no or little expression of 5- and 15-LOX. NDGA, a general LOX inhibitor and BHPP, a 12-LOX-selective inhibitor, induced rapid and dose-dependent apoptosis of serum-cultured W256 cells as well as several other tumor (in particular leukemia) cell lines, thus suggesting a potential role for LOX in mediating serum-supported tumor cell survival. The molecular mechanism of NDGA-induced W256 cell death was subsequently investigated. NDGA-induced apoptosis could be significantly postponed by overexpression of 12-LOX, thus suggesting that the NDGA effect is, at least partly, dependent on its inhibition of LOX (i.e., 12-LOX). W256 cell apoptosis induced by NDGA could also be effectively inhibited by GSH-elevating or thiol agents as well as by lipid peroxidation inhibitors and an inhibitor of mitochondria respiratory chain rotenone. Further experiments demonstrated that NDGA treatment triggered rapid lipid peroxidation leading to the depletion of cytosolic and mitochondrial GSH pools. Interestingly, the lipid peroxidation induced by NDGA could not be inhibited by conventional free radical scavengers nor by cyclooxygenase or cytochrome P-450 monooxygenase inhibitors. In summary, the present work suggests a role of 12-LOX in regulating serum (growth factor)-supported survival of certain tumor cells.

Arachidonate lipoxygenases as essential regulators of cell survival and apoptosis

Arachidonic acid (AA) metabolites derived from both cyclooxygenase (COX) and lipoxygenase (LOX) pathways transduce a variety of signals related to cell growth. Here, we report that the AA LOX pathway also functions as a critical regulator of cell survival and apoptosis. Rat Walker 256 (W256) carcinosarcoma cells express 12-LOX and synthesize 12(S)- and 15(S)-hydroxyeicosatetraenoic acids as their major LOX metabolites. W256 cells transfected with 12-LOX-specific antisense oligonucleotide or antisense oligonucleotides directed to conserved regions of LOXs underwent time- and dose-dependent apoptosis. Likewise, treatment of W256 cells with various LOX but not COX inhibitors induced apoptotic cell death, which could be partially inhibited by exogenous 12(S)- or 15(S)-hydroxyeicosatetraenoic acids. The W256 cell apoptosis induced by antisense oligos and LOX inhibitors was followed by a rapid downregulation of bcl-2 protein, a dramatic decrease in the bcl-2/bax ratio, and could be suppressed by bcl-2 overexpression. In contrast, p53, which is wild type in W256 cells, did not undergo alterations during apoptosis induction. The results suggest that the LOX pathway plays an important physiological role in regulating apoptosis.

Melanoma cell spreading on fibronectin induced by 12(S)-HETE involves both protein kinase C- and protein tyrosine kinase-dependent focal adhesion formation and tyrosine phosphorylation of focal adhesion kinase (pp125FAK)

Our previous work demonstrated that 12(S)-HETE, a lipoxygenase metabolite of arachidonic acid, promoted B16 amelanotic melanoma (B16a) cell spreading on fibronectin. In the current study, we investigated the biochemical mechanisms of the 12(S)-HETE induced response. 12(S)-HETE treatment resulted in a time-dependent increase in B16a cell spreading on fibronectin, which was blocked by either calphostin C or by genistein but not by H8. Two hours following cell plating, both spontaneous and 12(S)-HETE promoted cell spreading reached their maximum (nearly 100%). Spontaneous cell spreading was inhibited by the select 12-lipoxygenase inhibitor, BHPP, whose inhibitory effect could be overcome by increasing doses of exogenous 12(S)-HETE. 12(S)-HETE-treated B16a cells plated on either fibronectin or cultured on their own extracellular matrix demonstrated increased vinculin and tyrosine-phosphorylated proteins, which were colocalized at focal adhesions. The increase in vinculin localization to focal adhesions appeared to be a post-transcriptional process, since 12(S)-HETE treatment did not alter the overall protein level of vinculin in tumor cells, but resulted in a specific enrichment of vinculin to focal adhesions. Pretreatment of B16a cells with either calphostin C or genistein abolished 12(S)-HETE-increased formation of vinculin- and phosphotyrosine-containing focal adhesions. Immunoblotting using antiphosphotyrosine antibody 4G10 demonstrated, following 12(S)-HETE stimulation, an increased tyrosine phosphorylation of several proteins in focal adhesions; most prominently, a approximately 155 kd protein, a 120-130 kd protein cluster, a 76 kd protein, and a 42/44 kd complex. Immunoprecipitation with anti-phosphotyrosine antibody PY20 revealed increased tyrosine phosphorylation, post 12(S)-HETE stimulation, of proteins migrating at 120, 76, and 42/44 kd, of which the 120 kd protein co-migrated with pp125FAK. Immunoprecipitation with anti-FAK antibody BC-3 followed by immunoblotting with anti-phosphotyrosine antibody RC20H demonstrated a time-dependent hyperphosphorylation of pp125FAK. The present study suggests that 12(S)-HETE promoted melanoma cell spreading on fibronectin involves tyrosine phosphorylation of pp125FAK and protein kinase C- and tyrosine kinase-dependent focal adhesion formation.

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.

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.

Immunomorphological characterization and effects of 12-(S)-HETE on a dynamic intracellular pool of the alpha IIb beta 3-integrin in melanoma cells

In metastatic B16a murine melanoma cells, alpha IIb beta 3 integrin was shown to be one of the key adhesion molecules responsible for matrix adhesion and spreading. Upon stimulation, alpha IIb beta 3 can be upregulated at the cell surface due to translocation of the receptor to the plasma membrane from an intracellular pool. Here we have characterized this integrin pool as a tubulovesicular structure (TVS) corresponding to endosomes. TVS was found to be associated temporarily with microtubules and intermediate filaments especially after protein kinase C (PKC) stimulation with a lipoxygenase metabolite of arachidonic acid, 12-(S)-hydroxyeicosatetraenoic acid [12-(S)-HETE]. After PKC stimulation, the predominantly vesicular TVS became elongated and alpha IIb beta 3 appeared at the apical plasma membrane and microvilli. Disruption of either the microtubules or intermediate filaments prevented the 12-(S)-HETE effect both on vesicular to tubular transition of TVS as well as on surface expression of this integrin. The connection with the Golgi system of the integrin-containing TVS was proved by a Golgi-inhibitor (brefeldin A) pretreatment, which prevented the PKC-stimulation-induced TVS elongation and subsequent receptor-upregulation at the cell surface. After a soluble ligand binding (mAb to the alpha IIb beta 3 complex) the surface receptor endocytosed back to the TVS indicating the presence of a dynamic, cytoskeleton associated integrin pool in melanoma cells.

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-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.

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.

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.

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.

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.

Studies on the role of platelet eicosanoid metabolism and integrin alpha IIb beta 3 in tumor-cell-induced platelet aggregation

Platelet eicosanoid metabolism resulting from tumor-cell-induced platelet aggregation (TCIPA) was examined in a homologous in vitro system. Rat Walker 256 carcinosarcoma cells induced the aggregation of rat platelets via a thrombin-dependent mechanism with concomitant production of eicosanoid metabolites (e.g., 12-HETE, TXA2). TCIPA was dependent on the concentration of tumor cells inducing aggregation, as well as cyclooxygenase and lipoxygenase products. Cyclooxygenase inhibitors, but not lipoxygenase inhibitors, blocked platelet aggregation induced in vitro by a low concentration of agonist. At a high agonist concentration, neither cyclooxygenase nor lipoxygenase inhibitors alone affected platelet aggregation; however, the combined inhibition of both the cyclooxygenase and lipoxygenase pathways resulted in subsequent inhibition of platelet aggregation regardless of agonist concentration. The extent of platelet TXA2 and 12-HETE biosynthesis was likewise dependent on and correlated with agonist concentration. The inhibitors used in this study did not significantly inhibit protein kinase C activity at the doses tested. Platelet surface glycoprotein alpha IIb beta 3 play an important role in platelet aggregation. The effect of platelet cyclooxygenase and lipoxygenase inhibition in regulating alpha IIb beta 3 surface expression was examined by flow cytometric analysis. Thrombin stimulation of washed rat platelets resulted in significantly increased surface expression of platelet alpha IIb beta 3 integrin complex. The enhanced surface expression was not inhibited by a cyclooxygenase inhibitor (aspirin), a thromboxane synthase inhibitor (CGS-14854) or a thromboxane receptor antagonist (SQ 29,548), nor was it stimulated by a thromboxane A2 mimic (pinane-thromboxane A2). However, alpha IIb beta 3 expression was blocked by lipoxygenase inhibition and stereospecifically increased by the platelet lipoxygenase metabolite 12(S)-HETE. These results suggest that both the platelet lipoxygenase and cyclooxygenase pathways are important for TCIPA but that different mechanisms of action are involved.

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.