Estrogen receptor mediated inhibition of cancer cell invasion and motility: an overview

Bowes melanoma cells secrete heregulin, which can promote aggregation and counteract invasion of human mammary cancer cells

Invasiveness, the ability of cancer cells to migrate beyond the normal tissue boundaries, often leads to metastasis and thereby usually turns cancer into a fatal disease. At the molecular level, the E-cadherin/catenin complex is an example of a powerful invasion suppressor in epithelial cells. Since the absence of melanocytes has been associated with disturbances in epithelial organization, we decided to investigate the influence of molecules secreted by melanocytes on the function of the E-cadherin/catenin complex. We used the Bowes melanoma cell line as a source of such molecules. The conditioned medium of Bowes melanoma stimulated aggregation of human MCF-7/6 mammary adenocarcinoma cells at short (30 min) and long (24-72 hr) notice. This effect could be inhibited by MB2, an antibody against human E-cadherin. Conditioned medium of Bowes melanoma also inhibited invasion of MCF-7/6 cells into precultured chick heart fragments. Candidate molecules such as insulin, insulin-like growth factor I, follistatin and interleukins were ruled out to be responsible for the effects, but heregulin mimicked some of the effects of the conditioned medium. Our data indicate that heregulin stimulates aggregation and inhibits invasion of MCF-7/6 cells via activation of the E-cadherin/catenin complex.

P-cadherin is up-regulated by the antiestrogen ICI 182,780 and promotes invasion of human breast cancer cells

P-cadherin expression in breast carcinomas has been associated with tumors of high histologic grade and lacking estrogen receptor-alpha, suggesting a link between these proteins. In the MCF-7/AZ breast cancer cell line, blocking estrogen receptor-alpha signaling with the antiestrogen ICI 182,780 induced an increase of P-cadherin, which coincided with induction of in vitro invasion. Retroviral transduction of MCF-7/AZ cells, as well as HEK 293T cells, showed the proinvasive activity of P-cadherin, which requires the juxtamembrane domain of its cytoplasmic tail. This study establishes a direct link between P-cadherin expression and the lack of estrogen receptor-alpha signaling in breast cancer cells and suggests a role for P-cadherin in invasion, through its interaction with proteins bound to the juxtamembrane domain.

Estrogens and their receptors in breast cancer progression: a dual role in cancer proliferation and invasion

Estrogens play an important role in regulating the growth and differentiation of normal, premalignant and malignant cell types, especially breast epithelial cells, through interaction with two nuclear estrogen receptors (ERalpha and ERbeta). In this review, we present a brief overview of the actions of estrogens in the different steps of breast carcinogenesis, including cancer progression to metastasis, and of their clinical consequences in the prevention, prognosis and treatment of the disease. The requirement of estrogen receptors, mainly of the alpha subtype, in normal mammary gland differentiation and growth has been evidenced by estrogen receptor deficiency in animals. The promotion of breast cancer carcinogenesis by prolonged exposure to estrogens is well-documented and this has logically led to the use of anti-estrogens as potentially chemopreventive agents. In breast cancer progression, however, the exact roles of estrogen receptors have been less well established but they may possibly be dual. Estrogens are mitogenic in ER-positive cells and anti-estrogens are an efficient adjuvant therapy for these tumors. On the other hand, the fact that estrogens and their receptors protect against cancer cell invasiveness through distinct mechanisms in experimental models may explain why the presence of ER is associated with well-differentiated and less invasive tumors.

The Expression of Fascin, an Actin-Bundling Motility Protein, Correlates with Hormone Receptor–Negative Breast Cancer and a More Aggressive Clinical Course

The invasion and metastasis of tumor cells is a major cause of mortality in cancer patients. In the current study, we investigated the expression of fascin, an actin-bundling motility-associated protein, in 210 invasive breast carcinomas with corresponding 5-year clinical follow-up. Fascin expression was compared with hormone receptor (ER/PR) status, HER2 status, cancer grade, cancer stage, metastasis pattern, disease-free survival, and overall survival. Fascin expression was seen in 16% (33/210) of the cases and correlated with ER negativity (22/33, P < 0.001), PR negativity (21/33, P < 0.001), Bloom-Richardson grade 3 (19/29, P < 0.001), and advanced stage (stage 3 or 4, P=0.04).There was no correlation between fascin expression and HER2 status or pattern of metastases. Patients whose tumors were positive for fascin showed both a decreased mean disease-free survival (74.44 versus 100.52 months, P = 0.002) and mean overall survival (77.58 versus 98.98 months, P = 0.002), independent of tumor stage and HER2 status, but not independent of ER/PR status or cancer grade. Given fascin's role in altering cell motility, overexpression may contribute to a more aggressive clinical course in ER/PR-negative breast cancers. If so, then fascin may represent a new molecular target for therapeutic intervention in patients with ER-negative breast cancer.

Fibronectin and type IV collagen activate ERα AF-1 by c-Src pathway: effect on breast cancer cell motility

The expression of estrogen receptor alpha (ERalpha) is generally associated with a less invasive and aggressive phenotype in breast carcinoma. In an attempt to understand the role of ERalpha in regulating breast cancer cells invasiveness, we have demonstrated that cell adhesion on fibronectin (Fn) and type IV Collagen (Col) induces ERalpha-mediated transcription and reduces cell migration in MCF-7 and in MDA-MB-231 cell lines expressing ERalpha. Analysis of deleted mutants of ERalpha indicates that the transcriptional activation function (AF)-1 is required for ERalpha-mediated transcription as well as for the inhibition of cell migration induced by cell adhesion on extracellular matrix (ECM) proteins. In addition, the nuclear localization signal region and some serine residues in the AF-1 of the ERalpha are both required for the regulation of cell invasiveness as we have observed in HeLa cells. It is worth noting that c-Src activation is coincident with adhesion of cells to ECM proteins and that the inhibition of c-Src activity by PP2 or the expression of a dominant-negative c-Src abolishes ERalpha-mediated transcription and partially reverts the inhibition of cell invasiveness in ERalpha-positive cancer cells. These findings address the integrated role of ECM proteins and ERalpha in influencing breast cancer cell motility through a mechanism that involves c-Src and seems not to be related to a specific cell type.

Estrogens and epithelial ovarian cancer

OBJECTIVE

Molecular mechanisms involved in ovarian carcinogenesis are still unclear, but there is growing evidence that estrogens promote tumor progression in an epithelial ovarian cancer (EOC) subgroup.

METHODS

We reviewed current knowledge on the effects of estrogens in ovarian carcinogenesis and new potential research focuses concerning hormonal therapy of EOC.

RESULTS

Experimentally, estrogen stimulates the growth of ovarian tumor cell lines expressing estrogen receptors (ER). We and other authors have demonstrated differential expression of ERalpha or beta during ovarian carcinogenesis, with overexpression of ERalpha as compared to ERbeta in cancer. This differential expression in ER suggests that estrogen-induced proteins may act as ovarian tumor-promoting agents. Among these proteins, c-myc, fibulin-1, cathepsin-D, or several kallikreins may play a role, since high expression levels have been found in EOC. Consistently, recent prospective epidemiological studies have indicated that estrogen replacement therapy in postmenopausal women may increase ovarian cancer incidence and mortality.

CONCLUSION

Questions on the estrogen-sensitivity and potential benefits of new hormone therapies in an EOC subgroup should be readdressed in the light of recent experimental and clinical data.

Grb2 regulation of the actin-based cytoskeleton is required for ligand-independent EGF receptor-mediated oncogenesis

Mutations within members of the EGF/ErbB receptor family frequently release the oncogenic potential of these receptors, resulting in the activation of downstream signaling events independent of ligand regulatory constraints. We previously have demonstrated that the signal transduction events originating from S3-v-ErbB, a ligand-independent, oncogenic EGF receptor mutant, are qualitatively distinct from the ligand-dependent mitogenic signaling pathways associated with the wild-type EGF receptor. Specifically, expression of S3-v-ErbB in primary fibroblasts results in anchorage-independent growth, increased invasive potential, and the formation of a transformation-specific phosphoprotein signaling complex, all in a Ras-independent manner. Here we demonstrate the transformation-specific interaction between two components of this complex: the adaptor protein Grb2 and the cytoskeletal regulatory protein caldesmon. This interaction is mediated via both the amino-terminal SH3 and central SH2 domains of Grb2, and the amino-terminal (myosin-binding) domain of caldesmon. Expression of a dominant-negative Grb2 deletion mutant, which lacks the carboxy-terminal SH3 domain, in fibroblasts expressing S3-v-ErbB results in a reduction in phosphoprotein complex formation, the loss of anchorage-independent growth, and a reduction in invasive potential. Together, these results demonstrate a Ras-independent role for Grb2 in modulating cytoskeletal function during ligand-independent EGF receptor-mediated transformation, and provide further support for the hypothesis that ligand-independent oncogenic signaling is qualitatively distinct from ligand-dependent mitogenic signaling by the EGF receptor.

Activation of matrix metalloproteinase-2 and -9 by 2- and 4-hydroxyestradiol

Breast cancer patients frequently develop metastases. This process requires the degradation of extracellular matrix proteins which act as a barrier to tumour cell passage. These proteins can be degraded by proteases, mainly the matrix metalloproteinases (MMPs). MMP-2 and -9 which are frequently detected in breast cancer tissues. ProMMPs are released from cancer cells, and their activation is considered to be a crucial step in metastases development. In breast cancer, estrogen metabolism is altered favouring the accumulation of 2- and 4-hydroxyestradiol (2- and 4-OHE(2)). These estradiol metabolites can generate free radicals. Since reactive species are known activators of proMMPs, this study was designed to determine if the free radicals generated by 2- and 4-OHE(2) can activate proMMP-2 and -9. Activation of MMPs by hydroxyestradiol was determined by monitoring the cleavage of a fluorogenic peptide and by zymography analysis. Both estradiol metabolites activated the MMP-2 and -9. 4-OHE(2) was a more potent activator than 2-OHE(2), which reflects its higher capacity to generate free radicals. ProMMPs activation was mainly mediated through O(2)*-, although the free radical HO* also activated the proMMPs but to a lesser extent. ProMMPs activation was not observed with estrogens that cannot generate free radicals, i.e. estradiol, estrone, 2- and 4-methoxyestradiol, and 16alpha-hydroxyestrone. These results demonstrate that 2- and 4-OHE(2) at a concentration as low as 10(-8)M can activate the proMMP-2 and -9 and might play an important role in the invasion of breast cancer cells.

Favorable prognostic value of tissue human kallikrein 11 (hK11) in patients with ovarian carcinoma

Human kallikrein 11 (hK11/trypsin-like serine protease/TLSP, encoded by the KLK11 gene) is a member of the kallikrein family of secreted serine proteases. Recently, we developed a highly sensitive and specific immunoassay for hK11 and found that this protease is expressed in the prostate, stomach and trachea as well as in amniotic fluid and milk of lactating women. Elevated serum hK11 levels were found in 60% of men with prostate cancer and 70% of women with ovarian cancer. Also, hK11 expression was found to be under the regulation of steroid hormones, particularly estrogens, at the level of KLK11 transcription. We hypothesized that hK11 may be implicated in endocrine-related malignancies and serve as a novel prostate and ovarian cancer serological marker. The aim of our study was to examine if hK11 expression in ovarian tumors bears any prognostic significance. The concentration of hK11 (ng per mg of total protein) in 104 ovarian tumor cytosolic extracts was quantified and correlated with clinicopathologic variables and outcome over a median follow-up period of 67 months. Outcome was defined as progression-free survival (PFS) and overall survival (OS). hK11 concentration in ovarian tumor cytosols ranged from 0-21 ng/mg of total protein, with a median of 0.54 ng/mg. An optimal cutoff value of 0.54 ng/mg was selected to categorize tumors as hK11-positive or -negative. hK11-positive tumors were more frequently associated with early stage (Stage I/II) disease, pre-/peri-menopausal status and patients who exhibited complete or partial response to chemotherapy (p < 0.05). Univariate analysis revealed that patients with hK11-positive tumors had a significantly decreased risk of relapse with a hazard ratio (HR) of 0.45 (p = 0.007) and death (HR of 0.34, p = 0.005). Cox multivariate analysis indicated that hK11 was an independent prognostic indicator of OS (HR of 0.41, p = 0.025). Kaplan-Meier survival curves further confirmed that women with hK11-positive tumors have longer PFS and OS (p = 0.005 and p = 0.003, respectively). Similarly, in the subgroup of patients with grade 1-2 tumors, hK11-positivity was associated with higher OS in both univariate and multivariate analysis (HR of 0.23 and 0.17, p < 0.05). Finally, in women with optimal debulking after surgery (<1 cm residual tumor), hK11 positivity was associated with a slower disease progression. These results indicate that hK11 is a novel, independent marker of favorable prognosis in patients with ovarian cancer.

Phenotypic differentiation of human breast cancer cells by 1,3 cyclic propanediol phosphate

Breast cancer cells in their virulent undifferentiated state are characterized by lack of functional estrogen receptors (ER) and/or progesterone receptors (PR) as well as relatively low levels of other normal differentiation markers such as milk proteins and lipid droplets. To date, no method for in situ elevation of the state of differentiation of breast cancer cells has yet been proven effective in patients. We have recently shown that 1,3 cyclic propanediol phosphate (1,3 cPP), an analog of 1,3 cyclic glycerophosphate (1,3 cGP), can promote morphological, neuronal-like differentiation in pheochromocytoma-12 cells in vitro. In view of this observation, we tested the potential of 1,3 cPP to elevate the state of cellular differentiation of the human breast cancer cell lines MCF-7 (ER(+)) and HCC1954 (ER(-)), as characterized by the expression of steroid receptors, casein kinase, lipid droplet histology and signal-transduction gene profiles. In the range of 5-100 microM 1,3 cPP the in vitro expression of ER-alpha, PR and casein kinase increased by approximately 2-fold while the mRNA transcription increased by 2-6-fold. Moreover, following 9-12 days of incubation with 1,3 cPP, HCC1954 cells exhibited a significant increase in the production of lipid droplets as observed by Oil Red O staining. The in vivo effect of 1,3 PP on MCF-7 xenografted into nude mice was also determined. After 4 biweekly i.p. injections of 0.5 mg 1,3 cPP per mouse, tumors in the 1,3 cPP treated virtually did not grow at all while the tumors in the control group grew rapidly. Based on these findings, we propose that this novel differentiating compound has the potential to transform the malignant tumor phenotype into a near-normal phenotype, as well as to sensitize the tumor cells to anti-estrogen therapy via upgrading the status of steroid hormone receptors.

The enzymatic inactivation of the fatty acid amide class of signaling lipids

The fatty acid amide (FAA) class of signaling lipids modulates a number of neurobehavioral processes in mammals, including pain, sleep, feeding, and locomotor activity. Representative FAAs include the endogenous cannabinoid anandamide and the sleep-inducing lipid oleamide. Despite activating several neuroreceptor systems in vitro, most FAAs produce only weak and transient behavioral effects in vivo, presumably due to their expeditious catabolism. This review focuses on one enzyme, fatty acid amide hydrolase (FAAH) that appears to play a major role in regulating the amplitude and duration of FAA signals in vivo. In particular, we will highlight a series of recent papers that have investigated the physiological functions of the mouse and human FAAH enzymes. Collectively, these studies promote FAAH as a central component of FAA signaling pathways, especially those mediated by the endocannabinoid anandamide, and suggest that this enzyme may represent an attractive pharmaceutical target for the treatment of pain and related neurophysiological disorders.

Flavonoid effects relevant to cancer

Flavonoids, such as daidzein and genistein, present in dietary plants like soybean, have unique chemical properties with biological activity relevant to cancer. Many flavonoids and polyphenols, including resveratrol in red wine and epigallocatechin gallate in green tea, are known antioxidants. Some of these compounds have estrogenic (and antiestrogenic) activity and are commonly referred to as phytoestrogens. A yeast-based estrogen receptor (ER) reporter assay has been used to measure the ability of flavonoids to bind to ER and activate estrogen responsive genes. Recently, estrogenic compounds were also shown to trigger rapid, nongenomic effects. The molecular mechanisms, however, have not been completely detailed and little information exists regarding their relevance to cancer progression. As a preliminary step toward elucidating rapid phytoestrogen action on breast cancer cells, we investigated the effect of 17-beta estradiol (E2), genistein, daidzein and resveratrol on the activation status of signaling proteins that regulate cell survival and invasion, the cell properties underlying breast cancer progression. The effect of these estrogenic compounds on the activation, via phosphorylation, of Akt/protein kinase B (Akt) and focal adhesion kinase (FAK) were analyzed in ER-positive and -negative human breast cancer cell lines. E2, genistein and daidzein increased whereas resveratrol decreased both Akt and FAK phosphorylation in nonmetastatic ER-positive T47D cells. In metastatic ER-negative MDA-MB-231 cells, all estrogenic compounds tested increased Akt and FAK phosphorylation. The inhibitory action of resveratrol on cell survival and proliferation is ER dependent. Therefore, all estrogenic compounds tested, including resveratrol, may exert supplementary ER-independent nongenomic effects on cell survival and migration in breast cancer cells.

Proteomic profiling of mechanistically distinct enzyme classes using a common chemotype

Proteomics research requires methods to characterize the expression and function of proteins in complex mixtures. Toward this end, chemical probes that incorporate known affinity labeling agents have facilitated the activity-based profiling of certain enzyme families. To accelerate the discovery of proteomics probes for enzyme classes lacking cognate affinity labels, we describe here a combinatorial strategy. Members of a probe library bearing a sulfonate ester chemotype were screened against complex proteomes for activity-dependent protein reactivity, resulting in the labeling of at least six mechanistically distinct enzyme classes. Surprisingly, none of these enzymes represented targets of previously described proteomics probes. The sulfonate library was used to identify an omega-class glutathione S-transferase whose activity was upregulated in invasive human breast cancer lines. These results indicate that activity-based probes compatible with whole-proteome analysis can be developed for numerous enzyme classes and applied to identify enzymes associated with discrete pathological states.

Evaluation of a gemcitabine-doxorubicin-paclitaxel combination schedule through flow cytometry assessment of apoptosis extent induced in human breast cancer cell lines

Combination chemotherapy with gemcitabine (Gem), doxorubicin (Dox), and paclitaxel (Pac) (GAT) has been considered attractive as first-line treatment in metastatic breast cancer. We compared the potential of various schedules of GAT to induce apoptosis on MDA-MB-231, MCF7, and T47D human breast cancer cell lines. The extent of apoptotic induction was analyzed by flow cytometry with 7-aminoactinomycin D (7AAD) staining. Differences between various schedules in terms of apoptotic induction were statistically significant (P < 0.05). The most effective apoptotic induction regimen was achieved by the sequence: Dox for 16 h followed by Pac + Gem. Schedules employing a 16-h interval between drug administrations induced higher levels of apoptosis in human breast cancer cell lines compared with schedules using a 4-h interval. The therapeutic efficacy of the experimental results shown in this paper has been clinically corroborated in a phase II trial in metastatic breast cancer patients.

Activation of antimetastatic Nm23-H1 gene expression by estrogen and its alpha-receptor

Metastasis of various malignant cells is inversely related to the abundance of the Nm23-H1 protein. The role of estrogens in tumor metastasis has now been investigated by examining the effect of E2 on the expression of the Nm23-H1 gene. Three human breast carcinoma cell lines, in which endogenous ERalpha is expressed at different levels, were used as a tool to assess the role of ERalpha in Nm23-H1 gene-mediated metastasis. E2 induced time-dependent increases in the abundance of Nm23-H1 mRNA and protein, with the extent of these effects correlating with the level of expression of ERalpha. E2 induced a marked decrease in the invasive activity of MCF-7 and BT-474 cells but had no effect on BCM-1 cells, which had virtually no ERalpha. Consistent with these results, the ER-mediated Nm23-H1 promoter activity was inhibited 3-fold by the E2 antagonist, ICI 182,780. Deletion analysis of the promoter region of the Nm23-H1 gene identified a positive estrogen-responsive element located in -108/-94. ER protein bound specifically to the -108/-79 fragment with high avidity. These results indicate that E2, acting through ERalpha, activated transcription of the Nm23-H1 gene via a positive estrogen-responsive element in the promoter region of the gene. These results suggest that E2 could suppress tumor metastasis by activating the expression of the Nm23-H1 gene.

8-Prenylnaringenin, the phytoestrogen in hops and beer, upregulates the function of the E-cadherin/catenin complex in human mammary carcinoma cells

The E-cadherin/catenin complex is a powerful invasion suppressor in epithelial cells. It is expressed in the human MCF-7 breast cancer cell line family, but functionally defective in the invasive MCF-7/6 variant. Previous experiments have shown that IGF-I, tamoxifen, retinoic acid and tangeretin are able to upregulate the function of this complex in MCF-7/6 cells. We investigated the effect of 8-prenylnaringenin (8-PN), the phytoestrogen present in hops and beer, on aggregation, growth and invasion in MCF-7/6 cells. 8-PN was found to stimulate E-cadherin-dependent aggregation and growth of MCF-7/6 cells in suspension. These effects could be inhibited by the pure anti-estrogen ICI 182,780. 8-PN did not affect invasion of MCF-7/6 cells in the chick heart assay in vitro. In all these aspects 8-PN mimics the effects of 17beta-estradiol on MCF-7/6 cells.

Concurrent hypermethylation of multiple genes is associated with grade of oligodendroglial tumors

Current evidence suggests that epigenetic changes play an important role in the evolution of human cancers. In this study, we evaluated whether hypermethylation of CpG islands at the gene promotor regions of several tumor-related genes is involved in the carcinogenesis of oligodendroglial tumors. We examined the methylation status of 11 genes in a series of 43 oligodendroglial tumors (19 oligodendrogliomas, 13 anaplastic oligodendrogliomas, 9 oligoastrocytomas, and 2 anaplastic oligoastrocytomas) by methylation-specific polymerase chain reaction. Our results showed that hypermethylation of CpG islands was detectable in 8 of 11 genes studied and 74% of tumors were hypermethylated in at least 1 gene. Promotor hypermethylations were detected in O6-methylguanine-DNA methyltransferase (MGMT), RB1, estrogen receptor, p73, p16INK4a, death-associated protein kinase, p15INK4b, and p14ARF at 60%, 34%, 30%, 16%, 12%, 10%, 7%, and 2%, respectively. No hypermethylation was detected in the promotors of glutathione-S-transferase P1, von Hippel-Lindau or the DNA mismatch repair (hMLH1) genes. Statistical analysis revealed that concordant hypermethylation of at least 2 genes, p16INK4a and p15INK4b were significantly associated with anaplastic oligodendroglial tumors, and hypermethylation of MGMT was significantly associated with loss of chromosome 19q and with combined loss of chromosomes 1p and 19q. More importantly, several candidate tumor suppressor genes such as p16INK4a, p15INK4b, and p73 that were previously reported as unmutated in oligodendroglial tumors were found to be hypermethylated in their CpG islands. Taken together, we conclude that hypermethylation of CpG islands is a common epigenetic event that is associated with the development of oligodendroglial tumors.

Dolichol-phosphate-mannose-3 (DPM3)/prostin-1 is a novel phospholipase C-gamma regulated gene negatively associated with prostate tumor invasion

The most ominous development in tumor progression is the transition to an invasive and metastatic phenotype. Little is known, however, about the molecular alterations that cause a tumor to become invasive. In view of this, we have used microarray expression analysis to evaluate the expression profiles of a unique panel of human DU145 prostate cancer sublines that vary in their invasive potential. The three DU145 sublines expressed epidermal growth factor (EGF) receptors that differed in their ability to activate phospholipase C-gamma (PLC gamma). Three-way analyses yielded 11 genes out of 4608 genes screened that associated directly or inversely with invasive potential. The gene whose expression correlated most strongly with lack of invasion was identified as a potential invasion suppressor and called prostin-1. Pharmacological inhibition of PLC gamma (U73122) confirmed that PLC gamma signaling suppressed prostin-1 in that U73122 treatment caused induction of prostin-1 in PLC gamma competent cells. The prostin-1 gene, conserved through phylogeny, is induced by androgen in LNCaP cells and encodes a 92 amino acid protein. The protein shares no extensive homologies with other known genes, yet was recently identified as a small stabilizer subunit of the dolichol-phosphate-mannose (DPM) synthase complex. That DPM3/prostin-1 might suppress tumor progression was supported by the finding that exogenous expression in COS cells leads to apoptosis. These findings support the use of model cell lines to identify putative tumor suppressors and promoters.

Tumor invasion as dysregulated cell motility

Investigations across a range of disciplines over the past decade have brought the study of cell motility and its role in invasion to an exciting threshold. The biophysical forces proximally involved in generating cell locomotion, as well as the underlying signaling and genomic regulatory processes, are gradually becoming elucidated. We now appreciate the intricacies of the many cellular and extracellular events that modulate cell migration. This has enabled the demonstration of a causal role of cell motility in tumor progression, with various points of 'dysregulation' of motility being responsible for promoting invasion. In this paper, we describe key fundamental principles governing cell motility and branch out to describe the essence of the data that describe these principles. It has become evident that many proposed models may indeed be converging into a tightly-woven tapestry of coordinated events which employ various growth factors and their receptors, adhesion receptors (integrins), downstream molecules, cytoskeletal components, and altered genomic regulation to accomplish cell motility. Tumor invasion occurs in response to dysregulation of many of these modulatory points; specific examples include increased signaling from the EGF receptor and through PLC gamma, altered localization and expression of integrins, changes in actin modifying proteins and increased transcription from specific promoter sites. This diversity of alterations all leading to tumor invasion point to the difficulty of correcting causal events leading to tumor invasion and rather suggest that the underlying common processes required for motility be targeted for therapeutic intervention.

Increased expression of fascin, motility associated protein, in cell cultures derived from ovarian cancer and in borderline and carcinomatous ovarian tumors

Fascin bundles actin microfilaments within dynamic cellular structures such as microspikes, stress fibers and membrane ruffles. Fascin overexpression induces membrane protrusions and increased cell motility, and is highly expressed in various transformed cells, and in specialized normal cells including neuronal, endothelial and dendritic cells. In breast cancer, fascin expression correlates with high-grade tumors. To investigate whether fascin might be a predictor factor for ovarian cancer progression, eighteen cell cultures derived from ovarian cancer, and thirty four archival paraffin-embedded material of normal versus borderline and carcinomatous ovaries were stained by immunocytochemistry and immunohistochemistry with fascin Mab 55K-2. Overall expression of the fascin protein was found in 50% (9/18) of cell cultures derived from original samples of ovarian tumors. Expression of fascin protein was found in 67% (6/9) of cell cultures derived from patients diagnosed with stage IV disease, and 33% (3/9) of cell cultures from patients diagnosed with stage II/III. There was no clear relationship between fascin expression and histologic types, tumor grade, or DNA ploidy. However, 75% of cell cultures, which developed into a xenograft after intraperitoneal inoculation, showed fascin expression, while 86% of non-tumorigenic cell cultures did not show fascin expression. Expression of fascin in these established ovarian tumor cell cultures was significantly associated with the ability for these cells to grow intraperitoneally (P < 0.05). Furthermore, fascin was never expressed in normal epithelial ovarian tissues, but was present in all pathologic ovaries. Both diffuse and focal patterns were observed in borderline ovarian tumors (67% and 33%), advanced primary ovarian cancer (67% and 33%) and metastatic ovarian cancer (89% and 11%). Therefore, our data suggest that fascin could serve as a prognostic factor for abnormal ovarian epithelial pathology and could be a novel target for the treatment of ovarian cancer.

Estrogen regulated proteases and antiproteases in ovarian and breast cancer cells

Cathepsin D (cath-D), an estrogen-regulated protease appears mostly to increase the number of tumor cells rather than their invasion or motility through the extracellular matrix. Estradiol is mitogenic but in vitro it also inhibits invasion and motility. In this review, we discuss the mechanism of this inhibition and the hormonal regulation of other proteases and protease inhibitors possibly involved in the control of tumor cell invasion by estrogens.

Effects of estrogens and hormone replacement therapy on breast cancer risk and on efficacy of breast cancer therapies

This review summarises preclinical and clinical data on effects of endogenous and exogenous estrogens on probability of breast cancer diagnosis, and on the course and efficacy of breast cancer therapies. The data indicate that higher endogenous estrogen exposure (e.g. pregnancy, early menarche and late menopause, estrogen levels in future breast cancer patients, obesity) or exogenous estrogens (oral contraceptives; hormone replacement therapies) may be associated with an increased probability of breast cancer diagnosis. However, there is little evidence that estrogens have deleterious effects on the course of breast cancer. Moreover, increased incidence of breast cancer diagnosis after prolonged hormone replacement therapy (HRT) use seems to be associated with clinically less advanced disease. In studies assessing both diagnosis and mortality, HRT is frequently associated with reduced mortality compared to never users. The interaction of progestagens and estrogens on the probability of breast cancer diagnosis is complex and dependent on type of progestagens and regimens employed. Efficacy of current treatment modalities for breast cancer (surgery, irradiation, adjuvant therapy or chemotherapy) is not negatively influenced by estrogens at concentrations considerably higher than those attained with current HRT preparations. Although it cannot be excluded that estrogens increase the probability of breast cancer diagnosis, available data fail to demonstrate that, once breast cancer has been diagnosed, estrogens worsen prognosis, accelerate the course of the disease, reduce survival or interfere with the management of breast cancer. It may therefore be concluded that the prevalent opinion that estrogens and estrogen treatment are deleterious for breast cancer, needs to be revisited. However, results of ongoing prospective, randomised clinical trials with different HRT regimens in healthy women or breast cancer survivors are needed to provide more definite conclusions about risks and benefits of HRT.

Unliganded and liganded estrogen receptors protect against cancer invasion via different mechanisms

While estrogens are mitogenic in breast cancer cells, the presence of estrogen receptor a (ERalpha) clinically indicates a favorable prognosis in breast carcinoma. To improve our understanding of ERalpha action in breast cancer, we used an original in vitro method, which combines transient transfection and Matrigel invasion assays to examine its effects on cell invasiveness. ERalpha expression in MDA-MB-231 breast cancer cells reduced their invasiveness by 3-fold in the absence of hormone and by 7-fold in its presence. Integrity of hormone and DNA-binding domains and activating function 2 were required for estradiol-induced inhibition, suggesting that transcriptional activation of estrogen target genes was involved. In contrast, these domains were dispensable for hormone-independent inhibition. Analysis of deletion mutants of ERalpha indicated that amino acids 179-215, containing the N-terminal zinc finger of the DNA-binding domain, were required for ligand-independent receptor action. Among different members of the nuclear receptor family, only unliganded ERalpha and ERbeta reduced invasion. Calreticulin, a Ca2+-binding protein that could interact with amino acids 206-211 of ERalpha, reversed hormone-independent ERalpha inhibition of invasion. However, since calreticulin alone also inhibited invasion, we propose that this protein probably prevents ERalpha interaction with another unidentified invasion-regulating factor. The inhibitor role of the unliganded ER was also suggested in three ERalpha-positive cell lines, where ERalpha content was inversely correlated with cell migration. We conclude that ERalpha protects against cancer invasion in its unliganded form, probably by protein-protein interactions with the N-terminal zinc finger region, and after hormone binding by activation of specific gene transcription.

Caveolin-1 potentiates estrogen receptor alpha (ERalpha) signaling. caveolin-1 drives ligand-independent nuclear translocation and activation of ERalpha

Estrogen receptor alpha (ERalpha) is a soluble protein that mediates the effects of the gonadal estrogens such as 17beta-estradiol. Upon ligand binding, a cytoplasmic pool of ERalpha translocates to the nucleus, where it acts as a transcription factor, driving the expression of genes that contain estrogen-response elements. The activity of ERalpha is regulated by a number of proteins, including cytosolic chaperones and nuclear cofactors. Here, we show that caveolin-1 potentiates ERalpha-mediated signal transduction. Coexpression of caveolin-1 and ERalpha resulted in ligand-independent translocation of ERalpha to the nucleus as shown by both cell fractionation and immunofluorescence microscopic studies. Similarly, caveolin-1 augmented both ligand-independent and ligand-dependent ERalpha signaling as measured using a estrogen-response element-based luciferase reporter assay. Caveolin-1-mediated activation of ERalpha was sensitive to a well known ER antagonist, 4-hydroxytamoxifen. However, much higher concentrations of tamoxifen were required to mediate inhibition in the presence of caveolin-1. Interestingly, caveolin-1 expression also synergized with a constitutively active, ligand-independent ERalpha mutant, dramatically illustrating the potent stimulatory effect of caveolin-1 in this receptor system. Taken together, our results identify caveolin-1 as a new positive regulator of ERalpha signal transduction.

Tumor invasion: role of growth factor-induced cell motility

Cancer progression to the invasive and metastatic stage represents the most formidable barrier to successful treatment. To develop rational therapies, we must determine the molecular bases of these transitions. Cell motility is one of the defining characteristics of invasive tumors, enabling tumors to migrate into adjacent tissues or transmigrate limiting basement membranes and extracellular matrices. Invasive tumor cells have been demonstrated to present dysregulated cell motility in response to extracellular signals from growth factors and cytokines. Recent findings suggest that this growth factor receptor-mediated motility is one of the most common aberrations in tumor cells leading to invasiveness and represents a cellular behavior distinct from-adhesion-related haptokinetic and haptotactic migration. This review focuses on the emerging understanding of the biochemical and biophysical foundations of growth factor-induced cell motility and tumor cell invasiveness, and the implications for development of targeted agents, with particular emphasis on signaling from the epidermal growth factor (EGF) and hepatocyte growth factor (HGF) receptors, as these have most often been associated with tumor invasion. The nascent models highlight the roles of various intracellular signaling pathways including phospholipase C-gamma (PLC gamma), phosphatidylinositol (PI)3'-kinase, mitogen-activated protein (MAP) kinase, and actin cytoskeleton-related events. Development of novel agents against tumor invasion will require not only a detailed appreciation of the biochemical regulatory elements of motility but also a paradigm shift in our approach to and assessment of cancer therapy.