Regulation of cell movement: the motogenic cytokines

Migrasomes and tetraspanins in hepatocellular carcinoma: current status and future prospects

In recent years, many studies have attempted to clarify the formation, structure and biological function of migrasomes, which are defined as specialized organelles formed by the tips and intersections of Retraction Fibrils during cell migration. It has confirmed that migrasomes were involved in various critical biological processes and diseases, and has became a new research hotspot. In this paper, we reviewed the formation and biological functions of migrasomes, explored the relationship between migrasomes, tetraspanins and hepatocellular carcinoma and discussed the potential applications of migrasomes in hepatocellular carcinoma.

Cell migration orchestrates migrasome formation by shaping retraction fibers

Migrasomes are recently discovered vesicle-like structures on retraction fibers of migrating cells that have been linked with transfer of cellular contents, shedding of unwanted materials, and information integration. However, whether and how the cell migration paradigm regulates migrasome formation is not clear. Here, we report that there are significantly fewer migrasomes in turning cells compared with straight persistently migrating cells. The major insight underlying this observation is that as the cells elongate, their rear ends become narrower, subsequently resulting in fewer retraction fibers during impersistent migration. In addition to migration persistence, we reveal that migration speed positively corelates with migrasome formation, owing to the derived length of retraction fibers. Substantiating our hypothesis, genetically removing vimentin compromises cell migration speed and persistence and leads to fewer migrasomes. Together, our data explicate the critical roles of two cell migration patterns, persistence and speed, in the control of migrasome formation by regulating retraction fibers.

FAK inhibitors as promising anticancer targets: present and future directions

FAK, a nonreceptor tyrosine kinase, has been recognized as a novel target class for the development of targeted anticancer agents. Overexpression of FAK is a common occurrence in several solid tumors, in which the kinase has been implicated in promoting metastases. Consequently, designing and developing potent FAK inhibitors is becoming an attractive goal, and FAK inhibitors are being recognized as a promising tool in our armamentarium for treating diverse cancers. This review comprehensively summarizes the different classes of synthetically derived compounds that have been reported as potent FAK inhibitors in the last three decades. Finally, the future of FAK-targeting smart drugs that are designed to slow down the emergence of drug resistance is discussed.

Cell migration: implications for repair and regeneration in joint disease

Connective tissues within the synovial joints are characterized by their dense extracellular matrix and sparse cellularity. With injury or disease, however, tissues commonly experience an influx of cells owing to proliferation and migration of endogenous mesenchymal cell populations, as well as invasion of the tissue by other cell types, including immune cells. Although this process is critical for successful wound healing, aberrant immune-mediated cell infiltration can lead to pathological inflammation of the joint. Importantly, cells of mesenchymal or haematopoietic origin use distinct modes of migration and thus might respond differently to similar biological cues and microenvironments. Furthermore, cell migration in the physiological microenvironment of musculoskeletal tissues differs considerably from migration in vitro. This Review addresses the complexities of cell migration in fibrous connective tissues from three separate but interdependent perspectives: physiology (including the cellular and extracellular factors affecting 3D cell migration), pathophysiology (cell migration in the context of synovial joint autoimmune disease and injury) and tissue engineering (cell migration in engineered biomaterials). Improved understanding of the fundamental mechanisms governing interstitial cell migration might lead to interventions that stop invasion processes that culminate in deleterious outcomes and/or that expedite migration to direct endogenous cell-mediated repair and regeneration of joint tissues.

Advanced 2D/3D cell migration assay for faster evaluation of chemotaxis of slow-moving cells

Considering the essential role of chemotaxis of adherent, slow-moving cells in processes such as tumor metastasis or wound healing, a detailed understanding of the mechanisms and cues that direct migration of cells through tissues is highly desirable. The state-of-the-art chemotaxis instruments (e.g. microfluidic-based devices, bridge assays) can generate well-defined, long-term stable chemical gradients, crucial for quantitative investigation of chemotaxis in slow-moving cells. However, the majority of chemotaxis tools are designed for the purpose of an in-depth, but labor-intensive analysis of migratory behavior of single cells. This is rather inefficient for applications requiring higher experimental throughput, as it is the case of e.g. clinical examinations, chemoattractant screening or studies of the chemotaxis-related signaling pathways based on subcellular perturbations. Here, we present an advanced migration assay for accelerated and facilitated evaluation of the chemotactic response of slow-moving cells. The revised chemotaxis chamber contains a hydrogel microstructure–the migration arena, designed to enable identification of chemotactic behavior of a cell population in respect to the end-point of the experiment. At the same time, the assay in form of a microscopy slide enables direct visualization of the cells in either 2D or 3D environment, and provides a stable and linear gradient of chemoattractant. We demonstrate the correctness of the assay on the model study of HT-1080 chemotaxis in 3D and on 2D surface. Finally, we apply the migration arena chemotaxis assay to screen for a chemoattractant of primary keratinocytes, cells that play a major role in wound healing, being responsible for skin re-epithelialization and a successful wound closure. In direction of new therapeutic strategies to promote wound repair, we identified the chemotactic activity of the epithelial growth factor receptor (EGFR) ligands EGF and TGFα (transforming growth factor α).

Growth factor induced proliferation, migration, and lumen formation of rat endometrial epithelial cells in vitro

Endometrial modulation is essential for the preservation of normal uterine physiology, and this modulation is driven by a number of growth factors. The present study investigated the mitogenic, motogenic, and morphogenic effects of epidermal growth factor (EGF) and hepatocyte growth factor (HGF) on rat endometrial epithelial (REE) cells. The REE cells were isolated and cultured and then characterized based on their morphology and their expression of epithelial cell markers. The MTT assay revealed that EGF and HGF induce proliferation of REE cells. Consistent with increased proliferation, we found that the cell cycle regulatory factor Cyclin D1 was also upregulated upon EGF and HGF addition. REE cell migration was prompted by EGF, as observed with the Oris Cell Migration Assay. The morphogenic impact of growth factors on REE cells was studied in a three-dimensional BD Matrigel cell culture system, wherein these growth factors also increased the frequency of lumen formation. In summary, we show that EGF and HGF have a stimulatory effect on REE cells, promoting proliferation, cell migration, and lumen formation. Our findings provide important insights that further the understanding of endometrial regeneration and its regulation.

Clinical significance of hepatocyte growth factor/c-Met expression in the assessment of gastric cancer progression

Among the mechanisms that control cancer progression, cell mobility is a significant factor required for cellular liberation from the primary focus and infiltration. Hepatocyte growth factor (HGF) has been shown to facilitate cell mobility. In the present study, the clinical significance of the HGF/c-Met pathway in the assessment of gastric cancer progression was evaluated. From a cohort of patients with gastric cancer who underwent surgical resection between April 1999 and March 2003, 110 subjects were randomly selected. Preoperative serum HGF levels were measured and various pathological factors were analyzed. Furthermore, 50 subjects were randomly selected from within this group and immunohistochemical staining of tissue preparations for HGF and its receptor c-Met were performed. In the infiltrative growth pattern [(INF)α,β vs. INFγ], advanced progression was associated with elevated preoperative serum HGF levels (P<0.001). No correlation was identified between serum HGF levels and immunostaining for HGF or c-Met in the tissue preparations. Immunostaining revealed a significant correlation between c-Met expression and lymphatic vessel invasion (ly0.1 vs. 2.3; P=0.0416), lymph node metastasis (n0.1 vs. 2; P=0.0184) and maximum tumor diameter (≤50 mm vs. >50 mm; P=0.0469). Furthermore, c-Met-positivity was associated with a significant difference in overall survival (P=0.0342), despite stage I and II cases accounting for 82% of the total cohort (41 of 50 cases). These results suggested that the expression of the HGF/c-Met pathway in gastric cancer may be a potential predictive factor for disease progression.

Mechanisms of endothelial cell migration

Cell migration plays a central role in a variety of physiological and pathological processes during our whole life. Cellular movement is a complex, tightly regulated multistep process. Although the principle mechanisms of migration follow a defined general motility cycle, the cell type and the context of moving influences the detailed mode of migration. Endothelial cells migrate during vasculogenesis and angiogenesis but also in a damaged vessel to restore vessel integrity. Depending on the situation they migrate individually, in chains or sheets and complex signaling, intercellular signals as well as environmental cues modulate the process. Here, the different modes of cell migration, the peculiarities of endothelial cell migration and specific guidance molecules controlling this process will be reviewed.

Biological influence of Hakai in cancer: a 10-year review

In order to metastasize, cancer cells must first detach from the primary tumor, migrate, invade through tissues, and attach to a second site. Hakai was discovered as an E3 ubiquitin-ligase that mediates the posttranslational downregulation of E-cadherin, a major component of adherens junctions in epithelial cells that is characterized as a potent tumor suppressor and is modulated during various processes including epithelial–mesenchymal transition. Recent data have provided evidences for novel biological functional role of Hakai during tumor progression and other diseases. Here, we will review the knowledge that has been accumulated since Hakai discovery 10 years ago and its implication in human cancer disease. We will highlight the different signaling pathways leading to the influence on Hakai and suggest its potential usefulness as therapeutic target for cancer.

Tumor cell migration in complex microenvironments

Tumor cell migration is essential for invasion and dissemination from primary solid tumors and for the establishment of lethal secondary metastases at distant organs. In vivo and in vitro models enabled identification of different factors in the tumor microenvironment that regulate tumor progression and metastasis. However, the mechanisms by which tumor cells integrate these chemical and mechanical signals from multiple sources to navigate the complex microenvironment remain poorly understood. In this review, we discuss the factors that influence tumor cell migration with a focus on the migration of transformed carcinoma cells. We provide an overview of the experimental and computational methods that allow the investigation of tumor cell migration, and we highlight the benefits and shortcomings of the various assays. We emphasize that the chemical and mechanical stimulus paradigms are not independent and that crosstalk between them motivates the development of new assays capable of applying multiple, simultaneous stimuli and imaging the cellular migratory response in real-time. These next-generation assays will more closely mimic the in vivo microenvironment to provide new insights into tumor progression, inform techniques to control tumor cell migration, and render cancer more treatable.

Serum hepatocyte growth factor and cancer mortality in an apparently healthy Japanese population

Background

In patients with cancer, hepatocyte growth factor (HGF) is elevated and is a predictor of prognosis. We investigated whether serum HGF was a predictive marker for cancer death in a population of community-dwelling Japanese.

Methods

We studied 1492 apparently healthy Japanese adults who underwent health examinations in 1999. Those who reported a history of liver disease or malignancy on a baseline questionnaire were excluded, and plasma HGF was measured in the remaining 1470 participants, who were followed periodically for 10 years. Multivariate proportional hazards regression was used to estimate cancer mortality.

Results

A total of 169 participants died during follow-up (61 from cancer, 32 from cerebrocardiovascular disease, and 76 from other diseases). Mean HGF at baseline was significantly higher among decedents than among survivors (0.26 ± 0.11 vs 0.23 ± 0.09 ng/ml, respectively; P < 0.01). The Cox proportional hazards model showed that age, systolic blood pressure, HGF (hazard ratio, 1.27; 95% CI, 1.06–1.52; P = 0.009), albumin level, smoking status, and creatinine were independent predictors of all-cause death. Age, HGF (hazard ratio, 1.31; 95% CI, 1.04–1.65; P = 0.02), and total cholesterol were independent predictive markers for cancer death.

Conclusions

Serum HGF was a predictor of cancer death in an apparently healthy population of community-dwelling Japanese.

Focal adhesion kinase and its signaling pathways in cell migration and angiogenesis

Focal adhesion kinase (FAK) is a cytoplasmic tyrosine kinase that plays critical roles in integrin-mediated signal transductions and also participates in signaling by other cell surface receptors. In integrin-mediated cell adhesion, FAK is activated via disruption of an auto-inhibitory intra-molecular interaction between its amino terminal FERM domain and the central kinase domain. The activated FAK forms a complex with Src family kinases, which initiates multiple downstream signaling pathways through phosphorylation of other proteins to regulate different cellular functions. Multiple downstream signaling pathways are identified to mediate FAK regulation of migration of various normal and cancer cells. Extensive studies in cultured cells as well as conditional FAK knockout mouse models indicated a critical role of FAK in angiogenesis during embryonic development and cancer progression. More recent studies also revealed kinase-independent functions for FAK in endothelial cells and fibroblasts. Consistent with its roles in cell migration and angiogenesis, increased expression and/or activation of FAK are found in a variety of human cancers. Therefore, small molecular inhibitors for FAK kinase activity as well as future development of novel therapies targeting the potentially kinase-independent functions of FAK are promising treatments for metastatic cancer as well as other diseases.

Random versus directionally persistent cell migration

Directional migration is an important component of cell motility. Although the basic mechanisms of random cell movement are well characterized, no single model explains the complex regulation of directional migration. Multiple factors operate at each step of cell migration to stabilize lamellipodia and maintain directional migration. Factors such as the topography of the extracellular matrix, the cellular polarity machinery, receptor signalling, integrin trafficking, integrin co-receptors and actomyosin contraction converge on regulation of the Rho family of GTPases and the control of lamellipodial protrusions to promote directional migration.

Inhibition of Rac activation as a mechanism for negative regulation of actin cytoskeletal reorganization and cell motility by cAMP

cAMP has been found to play a role in mediating the negative regulation of cell motility, although its underlying molecular mechanism remains poorly understood. By using CHO (Chinese-hamster ovary) cells that express the EP2 subtype of PGE2 (prostaglandin E2) receptors, we provide evidence that an increase in cellular cAMP content leads to inhibition of cellular Rac activity, which serves as a mechanism for this negative regulation. In CHO cells expressing EP2, but not in vector control cells, PGE2 dose-dependently inhibited chemotaxis towards IGF-I (insulin-like growth factor-I), which is a Rac-dependent process, with the maximal 75% inhibition observed at 10(-8) M PGE2. EP2 stimulation failed to inhibit tyrosine phosphorylation either of IGF-I receptor or IRS-1 (insulin receptor substrate-1), or activation of phosphoinositide 3-kinase or Akt in response to IGF-I, but potently and dose-dependently inhibited IGF-I-induced activation of cellular Rac activity and membrane ruffling. However, PGE2 failed to inhibit Val12-Rac-induced membrane ruffling. Similar to the case of CHO cells, PGE2 inhibited PDGF (platelet-derived growth factor)-induced Rac activation and chemotaxis in vascular smooth muscle cells endogenously expressing EP2. The inhibitory effects of PGE2 on IGF-I-induced chemotaxis, membrane ruffling and Rac activation were faithfully reproduced by a low concentration of forskolin, which induced a comparable extent of cAMP elevation as with 10(-8) M PGE2, and were potentiated by isobutylmethylxanthine. The protein kinase A inhibitor Rp isomer of adenosine 3',5'-cyclic monophosphorothioate reduced PGE2 inhibition of Rac activation and chemotaxis. These results indicate that EP2 mediates Rac inhibition through a mechanism involving cAMP and protein kinase A, thereby inhibiting membrane ruffling and chemotaxis.

Villin enhances hepatocyte growth factor-induced actin cytoskeleton remodeling in epithelial cells

Villin is an actin-binding protein localized to intestinal and kidney brush borders. In vitro, villin has been demonstrated to bundle and sever F-actin in a calcium-dependent manner. Although villin is not necessary for the bundling of F-actin in vivo, it is important for the reorganization of the actin cytoskeleton elicited by stress during both physiological and pathological conditions (Ferrary et al., 1999). These data suggest that villin may be involved in actin cytoskeleton remodeling necessary for many processes requiring cellular plasticity. Here, we study the role of villin in hepatocyte growth factor (HGF)-induced epithelial cell motility and morphogenesis. For this purpose, we used primary cultures of enterocytes derived from wild-type and villin knock-out mice and Madin-Darby canine kidney cells, expressing villin in an inducible manner. In vitro, we show that epithelial cell lysates from villin-expressing cells induced dramatic, calcium-dependent severing of actin filaments. In cell culture, we found that villin-expressing cells exhibit enhanced cell motility and morphogenesis upon HGF stimulation. In addition, we show that the ability of villin to potentiate HGF-induced actin reorganization occurs through the HGF-activated phospholipase Cgamma signaling pathway. Collectively, these data demonstrate that villin acts as a regulator of HGF-induced actin dynamics.

c-Met tyrosine kinase receptor expression and function in human and canine osteosarcoma cells

To further characterize the role of hepatocyte growth factor-scatter factor (HGF-SF) and its receptor (c-Met) in osteosarcoma (OS), human OS cell lines with low (SAOS-2) and high (SAOS-LM2) metastatic potential, and cell lines derived from spontaneous canine OS were studied. All cell lines were evaluated for c-Met and HGF-SF expression and receptor activation using Northern, RT-PCR, and Western blot analyses, respectively. Functional activity of receptor-ligand interaction was measured using c-Met phosphorylation status, proliferation assays (anchorage-dependent and -independent), Matrigel invasion, modulation of urokinase plasminogen activator (uPA) expression, and cell dispersion (scattering). All cell lines exhibited steady-state mRNA expression of c-Met. The canine OS cell lines also expressed HGF-SF mRNA as determined by RT-PCR analysis. Western analysis showed c-Met protein expression and HGF-stimulated (human) or constitutive (canine) receptor autophosphorylation. Treatment with recombinant human HGF resulted in enhanced proliferation in 3 of 5 OS cell lines and enhanced colony formation in 2 of 5 OS cell lines. Matrigel invasion was significantly enhanced in 3 of the cell lines and uPA levels were significantly increased in the SAOS-2 cells following HGF treatment. Scattering was enhanced in both the SAOS-2 and SAOS-LM2 cells. These data support the involvement of c-Met and HGF-SF in the growth and progression of human and canine OS, and may offer new targets for the development of therapeutic strategies for OS.

Gangliosides regulate tumor cell adhesion to collagen

The ability of tumor cells to adhere to extracellular matrix proteins is critical for migration and invasion. The factors that regulate tumor cell adhesion are poorly characterized. Gangliosides promote platelet adhesion and may also play a role in the adhesion of other cell types. We hypothesized that pharmacological depletion of membrane gangliosides from adherent cells would abrogate adhesion to collagen and promote migration and invasion. To test these hypotheses, LA-N1 neuroblastoma cells, which avidly adhere to collagen and are rich with membrane gangliosides (43.69 nmol/10(8) cells), were cultured in the presence of D-threo-1-phenyl-2-decanoylamino-3-morpholino-1-propanol-HCl. Endogenous gangliosides were reduced by 98% (0.76 nmol/10(8) cells) and adhesion to collagen decreased by 67%. There were no changes in cell morphology, viability, proliferation rate or apoptosis. Pre-incubation of ganglioside-depleted cells in conditioned medium from control cells restored adhesion to collagen (0.45 +/- 0.002), comparable to that of control cells (0.49 +/- 0.035). Similarly, pre-incubation of ganglioside-depleted cells with purified GD2 completely restored adhesion in a concentration-dependent manner. When LA-N1 cells were cultured with retinoic acid, a biological response modifier known to increase endogenous gangliosides, adhesion to collagen increased. Next, we questioned whether changes in adhesion would be reflected as changes in migration and invasion. Cells depleted of endogenous cellular gangliosides migrated more than control cells. Finally, control cells replete with their endogenous gangliosides demonstrated less invasive potential than control cells. The data demonstrate that endogenous tumor gangliosides increase neuroblastoma cell adhesion to collagen and reduce migration and invasion in vitro.

Role of the CD47-SHPS-1 system in regulation of cell migration

SHPS-1 is a transmembrane protein whose extracellular region interacts with CD47 and whose cytoplasmic region undergoes tyrosine phosphorylation and there by binds the protein tyrosine phosphatase SHP-2. Formation of this complex is implicated in regulation of cell migration by an unknown mechanism. A CD47-Fc fusion protein or antibodies to SHPS-1 inhibited migration of human melanoma cells or of CHO cells overexpressing SHPS-1. Overexpression of wild-type SHPS-1 promoted CHO cell migration, whereas expression of the SHPS-1-4F mutant, which lacks the phosphorylation sites required for SHP-2 binding, had no effect. Antibodies to SHPS-1 failed to inhibit migration of CHO cells expressing SHPS-1-4F. SHPS-1 ligands induced the dephosphorylation of SHPS-1 and dissociation of SHP-2. Antibodies to SHPS-1 also enhanced Rho activity and induced both formation of stress fibers and adoption of a less polarized morphology in melanoma cells. Our results suggest that engagement of SHPS-1 by CD47 prevents the positive regulation of cell migration by this protein. The CD47- SHPS-1 system and SHP-2 might thus contribute to the inhibition of cell migration by cell-cell contact.

Effect of deposited lipids in atheromatous lesions on the migration of vascular smooth muscle cells

In advanced atherosclerotic lesions, a decrease in smooth muscle cells is observed in the cap tissue. This causes the thinning of the cap, and may lead to plaque rupture. We studied the effect of deposited lipids on the migration of vascular smooth muscle cells, and identified the main cause of the effect. The lipids were extracted from atherosclerotic lesions in the human aorta at autopsy, and separated into three fractions with a Sep-Pak ODS cartridge. Then, each fraction was added to the lower part of a chemotaxis chamber, and cultured vascular smooth muscle cells to the upper part. After 4 hours incubation, the cells that had migrated to the opposite side were counted. The oxysterol-rich fraction (10 microg/ml) inhibited the migration, whereas the cholesterol ester and free cholesterol fractions did not. Finally, we tested the pure oxysterols, 7-ketocholesterol and 27-hydroxycholesterol. Both inhibited migration, whereas the free cholesterol and cholesterol ester did not. Oxysterols generated in the lipid pool might inhibit the migration of smooth muscle cells.

Inhibitory and stimulatory regulation of Rac and cell motility by the G12/13-Rho and Gi pathways integrated downstream of a single G protein-coupled sphingosine-1-phosphate receptor isoform

The G protein-coupled receptors S1P2/Edg5 and S1P3/Edg3 both mediate sphingosine-1-phosphate (S1P) stimulation of Rho, yet S1P2 but not S1P3 mediates downregulation of Rac activation, membrane ruffling, and cell migration in response to chemoattractants. Specific inhibition of endogenous Galpha12 and Galpha13, but not of Galphaq, by expression of respective C-terminal peptides abolished S1P2-mediated inhibition of Rac, membrane ruffling, and migration, as well as stimulation of Rho and stress fiber formation. Fusion receptors comprising S1P2 and either Galpha12 or Galpha13, but not Galphaq, mediated S1P stimulation of Rho and also inhibition of Rac and migration. Overexpression of Galphai, by contrast, specifically antagonized S1P2-mediated inhibition of Rac and migration. The S1P2 actions were mimicked by expression of V14Rho and were abolished by C3 toxin and N19Rho, but not Rho kinase inhibitors. In contrast to S1P2, S1P3 mediated S1P-directed, pertussis toxin-sensitive chemotaxis and Rac activation despite concurrent stimulation of Rho via G12/13. Upon inactivation of Gi by pertussis toxin, S1P3 mediated inhibition of Rac and migration just like S1P2. These results indicate that integration of counteracting signals from the Gi- and the G12/13-Rho pathways directs either positive or negative regulation of Rac, and thus cell migration, upon activation of a single S1P receptor isoform.

Matrix metalloproteinases in tumor invasion: role for cell migration

Matrix metalloproteinases (MMP) play a role in a wide range of tumorigenesis, including early carcinogenesis events, tumor growth and tumor invasion and metastasis. Given that the ability of tumor cells to infiltrate and disseminate widely is what makes the tumors malignant, a role of MMP in cell migration during this invasive and metastatic process is important. There are two types of cancer cell migration: single cell locomotion and cohort migration (cell movement en mass keeping cell-cell contact, which is frequently seen in better differentiated carcinomas). Cell surface localization and activation of MMP is essential for cells to migrate, through rearrangement of extracellular matrix (ECM) to suit cell migration. Certain MMP, such as gelatinases and membrane -type 1 MMP, have special mechanisms to localize at leading edges in both types of cell migration. Moreover, in cohort migration, expression of these MMP is regulated via cell-cell contact within migrating cell sheets and confined to the foremost pathfinder cells of the migrating cell sheets. New roles of cell surface MMP, such as cleavage of cell surface receptors or cofactors involved in cell-ECM interactions during cell migration, are also discussed.

Autocrine motility factor (neuroleukin, phosphohexose isomerase) induces cell movement through 12-lipoxygenase-dependent tyrosine phosphorylation and serine dephosphorylation events

Autocrine motility factor (AMF) is one of the motility cytokines regulating tumor cell migration, therefore identification of the signaling pathway coupled with it has critical importance. Previous studies revealed several elements of this pathway predominated by lipoxygenase-PKC activations but the role for tyrosine kinases remained questionable. Motility cytokines frequently have mitogenic effect as well, producing activation of overlapping signaling pathways therefore we have used B16a melanoma cells as models where AMF has exclusive motility effect. Our studies revealed that in B16a cells AMF initiated rapid (1-5 min) activation of the protein tyrosine kinase (PTK) cascade inducing phosphorylation of 179, 125, 95 and 40/37 kD proteins which was mediated by upstream cyclo- and lipoxygenases. The phosphorylated proteins were localized to the cortical actin-stress fiber attachment zones in situ by confocal microscopy. On the other hand, AMF receptor activation induced significant decrease in overall serine-phosphorylation level of cellular proteins accompanied by serine phosphorylation of 200, 90, 78 and 65 kd proteins. The decrease in serine phosphorylation was independent of PTKs, PKC as well as cyclo- and lipoxygenases. However, AMF induced robust translocation of PKCalpha to the stress fibers and cortical actin suggesting a critical role for this kinase in the generation of the motility signal. Based on the significant decrease in serine phosphorylation after AMF stimulus in B16a cells we postulated the involvement of putative serine/threonine phosphatase(s) upstream lipoxygenase and activation of the protein tyrosine kinase cascade downstream cyclo- and lipoxygenase(s) in the previously identified autocrine motility signal.

The tyrosine phosphatase SHP-2 is required for sustained activation of extracellular signal-regulated kinase and epithelial morphogenesis downstream from the met receptor tyrosine kinase

Epithelial morphogenesis is critical during development and wound healing, and alterations in this program contribute to neoplasia. Met, the hepatocyte growth factor (HGF) receptor, promotes a morphogenic program in epithelial cell lines in matrix cultures. Previous studies have identified Gab1, the major phosphorylated protein following Met activation, as important for the morphogenic response. Gab1 is a docking protein that couples the Met receptor with multiple signaling proteins, including phosphatidylinositol-3 kinase, phospholipase Cgamma, the adapter protein Crk, and the tyrosine specific phosphatase SHP-2. HGF induces sustained phosphorylation of Gab1 and sustained activation of extracellular signal-regulated kinase (Erk) in epithelial Madin-Darby canine kidney cells. In contrast, epidermal growth factor fails to promote a morphogenic program and induces transient Gab1 phosphorylation and Erk activation. To elucidate the Gab1-dependent signals required for epithelial morphogenesis, we undertook a structure-function approach and demonstrate that association of Gab1 with the tyrosine phosphatase SHP-2 is required for sustained Erk activation and for epithelial morphogenesis downstream from the Met receptor. Epithelial cells expressing a Gab1 mutant protein unable to recruit SHP-2 elicit a transient activation of Erk in response to HGF. Moreover, SHP-2 catalytic activity is required, since the expression of a catalytically inactive SHP-2 mutant, C/S, abrogates sustained activation of Erk and epithelial morphogenesis by the Met receptor. These data identify SHP-2 as a positive modulator of Erk activity and epithelial morphogenesis downstream from the Met receptor.

Involvement of an SHP-2-Rho small G protein pathway in hepatocyte growth factor/scatter factor-induced cell scattering

Hepatocyte growth factor/scatter factor (HGF/SF) induces cell scattering through the tyrosine kinase-type HGF/SF receptor c-Met. We have previously shown that Rho small G protein (Rho) is involved in the HGF/SF-induced scattering of Madin-Darby canine kidney (MDCK) cells by regulating at least the assembly and disassembly of stress fibers and focal adhesions, but it remains unknown how c-Met regulates Rho activity. We have found here a novel signaling pathway of c-Met consisting of SHP-2-Rho that regulates the assembly and disassembly of stress fibers and focal adhesions in MDCK cells. SHP-2 is a protein-tyrosine phosphatase that contains src homology-2 domains. Expression of a dominant negative mutant of SHP-2 (SHP-2-C/S) markedly increased the formation of stress fibers and focal adhesions in MDCK cells and inhibited their scattering. C3, a Clostridium botulinum ADP-ribosyltransferase, and Y-27632, a specific inhibitor for ROCK, reversed the stimulatory effect of SHP-2-C/S on stress fiber formation and the inhibitory effect on cell scattering. Vav2 is a GDP/GTP exchange protein for Rho. Expression of a dominant negative mutant of Vav2 blocked the stimulatory effect of SHP-2-C/S on stress fiber formation. Conversely, expression of mutants of Vav2 that increased stress fiber formation inhibited HGF/SF-induced cell scattering. These results indicate that SHP-2 physiologically modulates the activity of Rho to form stress fibers and focal adhesions and thereby regulates HGF/SF-induced cell scattering. In addition, Vav2 may be involved in the SHP-2-Rho pathway.

The mechanism of mononuclear cell infiltration in oral lichen planus: the role of cytokines released from keratinocytes

To clarify the pathogenesis of oral lichen planus (OLP), we investigated the roles of keratinocytes (KC) in mononuclear cell infiltration. When peripheral blood mononuclear cells (PBMC) obtained from healthy donors were cultured in the presence of culture supernatants of KC separated from the noninflamed gingivae (Nor-KC) and cheek mucosae of patients with OLP (OLP-KC), the number of migrated PBMC across monolayered human umbilical vein endothelial cells (HUVEC) were increased to about 1.3-fold and 1.5-fold of the control level, respectively, with increases of the expression of CD11a, CD11b, CD18, and CD49d on PBMC and intracellular adhesion molecule-1, vascular cell adhesion molecule-1, and endothelial-leukocyte adhesion molecule-1 on HUVEC. The number of migrated PBMC was reduced to about 60% of the control level by pretreatment of PBMC with anti-CD11a or anti-CD18 MAb and reduced to about 70% by pretreatment of HUVEC with anti-CD54 MAb. The pretreatment of PBMC with genistein, H-7, wortmannin, or exoenzyme C3 decreased the migrated PBMC by about 70 to 90%. In agreement with these results, the culture supernatants of OLP-KC up-regulated tyrosine phosphorylation of 62-kDa, 70-kDa, and 102-kDa proteins, phosphatidylinositol-3 kinase, and protein kinase C activities and activated Rho protein level more so than did those of Nor-KC. Additionally, actin reorganization with the formation of membrane ruffles and lamellipodia was distinctly induced by the culture supernatants of OLP-KC. These results indicate that cytokines generated by KC transduce their signals in PBMC, up-regulating the expression of cell surface adhesion molecules and migration activity with reorganization of actin filaments.

Regulation of E-cadherin: does hypoxia initiate the metastatic cascade?

The ability of tumours to metastasis is regarded as one of the hallmarks of malignancy. The process through which tumours evolve to achieve this has been termed the metastatic cascade. This cascade has been the subject of much investigation over many years. One of the vital events identified by these investigations is the reduction of adhesion between tumour cells facilitating invasion of the surrounding tissues and vascular channels, ultimately leading to the development of a distant metastasis. E-cadherin and its associated catenin complex have been identified as key molecules in cell adhesion. This review looks at the structure and interaction of the E-cadherin-catenin complex and the factors that appear to regulate E-cadherin expression and thus cell adhesion. From the data gathered, it has become possible to propose the hypothesis that the development of tumour hypoxia is the initiating factor that sets the tumour on the road to metastasis.

Autocrine and paracrine motility factors and their involvement in invasiveness in a human oral carcinoma cell line

Invasive potentials of malignant cancer cells are regulated by cell motility factors. To examine the regulation of motility and invasiveness in oral squamous carcinoma, we investigated autocrine- and/or paracrine-acting cell motility factors, using a newly established human cell line (IF cells) from oral squamous cell carcinoma, which has highly invasive and metastatic characteristics. Conditioned medium derived from IF cells stimulated cell scattering and migration of GB-d1 gallbladder carcinoma cells, indicating that IF cells secreted cell motility factors. Using antibodies, IF-derived cell motility factors proved to be transforming growth factor (TGF)-alpha and TGF-beta1. Antibodies against TGF-alpha and TGF-beta1 inhibited autonomous migration of the IF cells. On the other hand, in vitro invasion of IF cells was strongly enhanced by hepatocyte growth factor (HGF) but only slightly by TGF-alpha and TGF-beta1. The conditioned medium from fibroblasts enhanced in vitro invasion of IF cells, an event abrogated by anti-HGF antibody, but not by antibodies against TGF-alpha and TGF-beta1. Importantly, IF cells secreted a factor inducing HGF production in fibroblasts and the factor was identified as interleukin-1, which means that a mutual interaction exists between tumour cells and fibroblasts, as mediated by the HGF/HGF-inducer loop. These results indicate that IF cells utilize TGF-alpha and TGF-beta1 as autocrine-acting motility factors and HGF as a paracrine-acting motility factor, and that invasiveness of IF cells is particularly stimulated by HGF derived from stromal fibroblasts. Utilization of multiple cell motility/invasion factors that act in distinct pathways may confer highly invasive and metastatic potentials in IF oral squamous carcinoma cells.

Involvement of Cdc42 small G protein in cell-cell adhesion, migration and morphology of MDCK cells

The Rho small G protein family consists of the Rho, Rac, and Cdc42 subfamilies and regulates various cell functions through reorganization of the actin cytoskeleton. We previously showed that the Rho subfamily regulates the formation of stress fibers and focal adhesions whereas the Rac subfamily regulates the E-cadherin-based cell-cell adhesion in MDCK cells. We studied here the function of the Cdc42 subfamily, consisting of two members, Cdc42Hs and G25k, in cell adhesion, migration, and morphology of MDCK cells. For this purpose, we made and used MDCK cell lines stably expressing each of dominant active mutants of Cdc42Hs (sMDCK-Cdc42HsDA) and G25K (sMDCK-G25KDA). Actin filaments at the cell-cell adhesion sites increased in both sMDCK-Cdc42HsDA and -G25KDA cells. Both E-cadherin and beta-catenin, adherens junctional proteins, at the cell-cell adhesion sites also increased in both sMDCK-Cdc42HsDA and -G25KDA cells. Electron microscopic analysis revealed that sMDCK-Cdc42HsDA cells tightly contacted with each other throughout the lateral membranes. Moreover, both the HGF- and TPA-induced disruption of the cadherin-based cell-cell adhesion and the subsequent cell migration were inhibited in both sMDCK-Cdc42HsDA and -G25KDA cells. Co-expression of the dominant negative mutant of Rac1, a member of the Rac subfamily, with the dominant active mutant of Cdc42Hs did not inhibit the increased accumulation of actin filaments at the cell-cell adhesion sites. These results suggest that the Cdc42 subfamily is involved in the cadherin-based cell-cell adhesion in a manner independent of the Rac subfamily. Furthermore, the cells were frequently enveloped by the large multinuclear cells in both sMDCK-Cdc42HsDA and -G25KDA cells. Video microscopic analysis revealed that the cells were engulfed by the large cells during cytokinesis.

Rho and Rab small G proteins coordinately reorganize stress fibers and focal adhesions in MDCK cells

The Rho subfamily of the Rho small G protein family (Rho) regulates formation of stress fibers and focal adhesions in many types of cultured cells. In moving cells, dynamic and coordinate disassembly and reassembly of stress fibers and focal adhesions are observed, but the precise mechanisms in the regulation of these processes are poorly understood. We previously showed that 12-O-tetradecanoylphorbol-13-acetate (TPA) first induced disassembly of stress fibers and focal adhesions followed by their reassembly in MDCK cells. The reassembled stress fibers showed radial-like morphology that was apparently different from the original. We analyzed here the mechanisms of these TPA-induced processes. Rho inactivation and activation were necessary for the TPA-induced disassembly and reassembly, respectively, of stress fibers and focal adhesions. Both inactivation and activation of the Rac subfamily of the Rho family (Rac) inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly. Moreover, microinjection or transient expression of Rab GDI, a regulator of all the Rab small G protein family members, inhibited the TPA-induced reassembly of stress fibers and focal adhesions but not their TPA-induced disassembly, indicating that, furthermore, activation of some Rab family members is necessary for their TPA-induced reassembly. Of the Rab family members, at least Rab5 activation was necessary for the TPA-induced reassembly of stress fibers and focal adhesions. The TPA-induced, small G protein-mediated reorganization of stress fibers and focal adhesions was closely related to the TPA-induced cell motility. These results indicate that the Rho and Rab family members coordinately regulate the TPA-induced reorganization of stress fibers and focal adhesions that may cause cell motility.

Platelet-derived growth factor (PDGF) BB acts as a chemoattractant for human malignant mesothelioma cells via PDGF receptor beta-integrin alpha3beta1 interaction

Platelet-derived growth factor BB (PDGF BB) and the PDGF receptor beta are expressed on mesothelioma cells, but their biological function has not yet been defined. In the present study we used Boyden chambers fitted with filters coated with the adhesive matrix proteins fibronectin, laminin, collagen type IV or the nonmatrix adhesive molecule poly-L-lysine (PLL). Mesothelioma cells migrated towards PDGF BB at concentrations ranging from 0.78 to 12.5 ng/ml if matrix proteins were present as adhesive substrates. This migration was integrin dependent since the same cells failed to migrate if the adhesive interactions necessary for migration were provided by molecules other than integrins. Migration of mesothelioma cells on fibronectin, laminin or collagen-type IV in response to PDGF BB was inhibited if the cells were pretreated with blocking antibodies to alpha3beta1 integrin. These findings describe for the first time PDGF BB as a chemoattractant for malignant mesothelioma cells and that collaboration between PDGF receptor beta and integrin alpha3beta1 is necessary for the motile response of these cells to PDGF BB.

Localization of autocrine motility factor receptor to caveolae and clathrin-independent internalization of its ligand to smooth endoplasmic reticulum

Autocrine motility factor receptor (AMF-R) is a cell surface receptor that is also localized to a smooth subdomain of the endoplasmic reticulum, the AMF-R tubule. By postembedding immunoelectron microscopy, AMF-R concentrates within smooth plasmalemmal vesicles or caveolae in both NIH-3T3 fibroblasts and HeLa cells. By confocal microscopy, cell surface AMF-R labeled by the addition of anti-AMF-R antibody to viable cells at 4 degreesC exhibits partial colocalization with caveolin, confirming the localization of cell surface AMF-R to caveolae. Labeling of cell surface AMF-R by either anti-AMF-R antibody or biotinylated AMF (bAMF) exhibits extensive colocalization and after a pulse of 1-2 h at 37 degreesC, bAMF accumulates in densely labeled perinuclear structures as well as fainter tubular structures that colocalize with AMF-R tubules. After a subsequent 2- to 4-h chase, bAMF is localized predominantly to AMF-R tubules. Cytoplasmic acidification, blocking clathrin-mediated endocytosis, results in the essentially exclusive distribution of internalized bAMF to AMF-R tubules. By confocal microscopy, the tubular structures labeled by internalized bAMF show complete colocalization with AMF-R tubules. bAMF internalized in the presence of a 10-fold excess of unlabeled AMF labels perinuclear punctate structures, which are therefore the product of fluid phase endocytosis, but does not label AMF-R tubules, demonstrating that bAMF targeting to AMF-R tubules occurs via a receptor-mediated pathway. By electron microscopy, bAMF internalized for 10 min is located to cell surface caveolae and after 30 min is present within smooth and rough endoplasmic reticulum tubules. AMF-R is therefore internalized via a receptor-mediated clathrin-independent pathway to smooth ER. The steady state localization of AMF-R to caveolae implicates these cell surface invaginations in AMF-R endocytosis.

Identification and characterization of motility stimulating factor secreted from pancreatic cancer cells: role in tumor invasion and metastasis

Cell motility is an important factor in the process of invasion and metastasis of tumor. In this study, the relationship between cell motility and experimental metastatic potential was examined using two human pancreatic cancer cell lines, SW1990 and PANC-1. Serum-free conditioned medium from the highly metastatic cell line SW1990 was found to contain a factor that stimulated the migration of and induced a fibroblast-like morphological change in the weakly metastatic cell line PANC-1. Preincubation of PANC-1 cells with SW1990 conditioned medium (SW-C.M.) induced liver metastasis following splenic injection of PANC-1 cells in nude mice, although no liver metastasis was observed without pretreatment of SW-C.M. This factor, temporarily termed PDMF (pancreatic cancer-derived motility factor) is a heparin non-binding protein having a molecular weight of 40 kDa calculated by gel-filtration HPLC which acts not only chemotactically but also chemokinetically, and also acts mainly in a paracrine fashion. However, this factor had no effect on the proliferation of PANC-1 cells; it therefore appears to be a so-called motility factor. Only TGF-beta1 and IL-6 were recognized in the SW-C.M. among cytokines thought to stimulate cell motility. These cytokines stimulated the motility of PANC-1 cells, but differed from PDMF in the neutralizing test with antibody against these cytokines. Results of characterization and preliminary purification suggest that this factor may be a novel motility factor. The above findings suggest that this motility factor may play an important role in the invasion and metastasis of pancreatic cancer, and complete purification of it will be useful in elucidating the mechanism of progression of cancer and designing a strategy for inhibition of invasion and metastasis of pancreatic cancer.

Regulation of cell motility by mitogen-activated protein kinase

Cell interaction with adhesive proteins or growth factors in the extracellular matrix initiates Ras/mitogen-activated protein (MAP) kinase signaling. Evidence is provided that MAP kinase (ERK1 and ERK2) influences the cells' motility machinery by phosphorylating and, thereby, enhancing myosin light chain kinase (MLCK) activity leading to phosphorylation of myosin light chains (MLC). Inhibition of MAP kinase activity causes decreased MLCK function, MLC phosphorylation, and cell migration on extracellular matrix proteins. In contrast, expression of mutationally active MAP kinase kinase causes activation of MAP kinase leading to phosphorylation of MLCK and MLC and enhanced cell migration. In vitro results support these findings since ERK-phosphorylated MLCK has an increased capacity to phosphorylate MLC and shows increased sensitivity to calmodulin. Thus, we define a signaling pathway directly downstream of MAP kinase, influencing cell migration on the extracellular matrix.

Detection and characterization of an activity which aligns mesodermal cells into parallel arrays

A cell line of mesodermal origin, FS9, was found to release a Cell Orienting Factor into its culture medium. In contrast with the random migration of controls, the orienting activity causes migrating mesenchymal cells to form an orderly "halo' surrounding tissue explants; individual cells and their cytoskeletons are elongated and parallel to each other but at right angle to the explant. No effect on the rate of cell movement was apparent. The orienting activity could be quantified by counting the number of cells found within strings radiating at right angles to a single tissue explant in the presence of FS9 conditioned medium or by using NIH image analysis. A dose dependent relationship with half maximal activity occurring at a 25% dilution of conditioned medium was observed. Cells that migrated randomly in the absence of conditioned medium became oriented within 4 h of exposure to 50% conditioned medium. Conversely, when the conditioned medium was removed, parallel alignment was rapidly lost. The orienting activity was found in conditioned media from a variety of mesodermal derivatives. Transformation of Balb/c 3T3 cells using EJ-ras oncogene led to augmented production of the activity. Furthermore, insulin was required in serum-free medium to support its production, Laminin, fibronectin and collagen and a range of pure cytokines, neither promoted nor inhibited orientation. Cell alignment was also unaffected by treatments which interfered with cell-substrate interactions and motility including the addition of the RGD peptide or anti-integrin beta 1 and beta 3 antibodies. A protein is likely to be involved since the activity was heat and trypsin sensitive and non-dialysable. The possibility is discussed that the orienting activity is a novel protein(s) which alters intercellular interactions to promote the formation of an aligned pattern by migrating mesenchymal cells.

Cytokines in tumour growth, migration and metastasis

A wide variety of cytokines are involved at every stage of tumour growth and dissemination. Primary tumour growth is helped by growth factors and angiogenic factors. These may either be produced by tumour cells themselves or be provided by one of the infiltrating cell populations, such as vascular endothelium or leukocytes. The influx of these cells is, in turn, under the control of the chemokines, a chemoattractant subfamily of cytokines. Autocrine motility factors, in conjunction with cytokines that regulate the production and activity of proteases capable of breaking down components of the extracellular matrix, are involved in the dispersal of cells from primary tumours, leading to the formation of metastases. The development of metastases may also be under the control of circulating cytokines released from the primary tumour. The ways in which cytokines and allied growth factors regulate tumour growth and development are both complex and controversial. However, the study of this system will provide a more profound understanding of tumour biology and may lead the way for the development of novel therapeutic approaches.

Hepatocyte growth factor/scatter factor is present in most pleural effusion fluids from cancer patients

Pleural effusion samples were obtained from 55 patients with malignant disease, including patients with primary lung cancers and those with a variety of other tumours metastatic to the pleura. The effusions were assayed for the presence of hepatocyte growth factor/scatter factor (HGF/SF), by both ELISA and bioassay. The presence of malignant cells in the effusions was also assessed. Detectable amounts of the factor, as judged by both criteria, were found in over 90% of all the effusions, including those from patients with a wide variety of carcinomas and also lymphomas. A wide range of HGF/SF levels were found for all tumour classes, some effusions containing high levels above 4 ng ml-1. It is concluded that tumours within the pleura and adjacent lung tissue are usually exposed to biologically significant levels of HGF/SF.

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.

Receptor tyrosine kinase signaling required for integrin alpha v beta 5-directed cell motility but not adhesion on vitronectin

FG human pancreatic carcinoma cells adhere to vitronectin using integrin alpha v beta 5 yet are unable to migrate on this ligand whereas they readily migrate on collagen in an alpha 2 beta 1-dependent manner. We report here that epidermal growth factor receptor (EGFR) activation leads to de novo alpha v beta 5-dependent FG cell migration on vitronectin. The EGFR specific tyrosine kinase inhibitor tyrphostin 25 selectively prevents EGFR autophosphorylation thereby preventing the EGF-induced FG cell migration response on vitronectin without affecting constitutive migration on collagen. Protein kinase C (PKC) activation also leads to alpha v beta 5-directed motility on vitronectin; however, this is not blocked by tyrosine kinase inhibitors. In this case, PKC activation appears to be associated with and downstream of EGFR signaling since calphostin C, an inhibitor of PKC, blocks FG cell migration on vitronectin induced by either PKC or EGF. These findings represent the first report implicating a receptor tyrosine kinase in a specific integrin mediated cell motility event independent of adhesion.

A unique autophosphorylation site in the platelet-derived growth factor alpha receptor from a heterodimeric receptor complex

The platelet-derived growth factor (PDGF) alpha and beta receptors undergo dimerization as a consequence of ligand binding. Depending on the PDGF isoform (PDGF-AA, -AB or -BB), homodimers or heterodimers of receptors are formed. In this study, we have used transfected porcine aortic endothelial cells, coexpressing cDNAs for the alpha receptor and the beta receptor at comparable levels, to investigate the properties of the alpha beta-heterodimeric receptor complex. PDGF-AB, which mainly induced alpha beta-heterodimeric complexes, was the most efficient isoform for stimulating mitogenicity. Actin reorganization, in the form of circular membrane ruffling and chemotaxis, was induced by PDGF-AB and PDGF-BB, but not by PDGF-AA, thus indicating that the beta receptor in the homodimeric or heterodimeric configuration was required for induction of motility responses. The molecular basis for the apparent receptor dimer-specific properties was examined by analyzing receptor autophosphorylation and phosphorylation of substrates. The alpha receptor was found to be phosphorylated at an additional tyrosine residue, Tyr754, in the heterodimeric complex as compared to the alpha alpha receptor homodimer. Phosphorylation of this tyrosine residue could permit the binding of a specific signal-tranducing protein. A candidate is a 134,000-M(r) protein, which was shown to associate preferentially with the alpha receptor in the heterodimeric receptor complex. It is possible that phosphorylated Tyr754 in the alpha receptor mediates activation of specific signal-tranducing molecules like the 134,000-M(r) substrate, and thereby initiates signal-tranduction pathways from the alpha beta receptor heterodimer, which are distinct from those initiated via homodimeric receptor complexes.

Role of the microtubular system in morphological organization of normal and oncogene-transfected epithelial cells

To understand better the role of the microtubular system in the development and maintenance of morphological organization of nonpolarized and polarized cells of the same origin we examined the effects of two microtubule-specific drugs, colcemid and taxol, on discoid cultured epithelial rat cells of the IAR-2 line and on polarized cells obtained from this line by transfection of mutated N-ras oncogene; morphometric, immunomorphologic, and videomicroscopic methods were used. Depolymerization of microtubules by colcemid did not cause major changes in the discoid shape of IAR cells but altered organization of actin cortex; in particular, it led to disappearance of circumferential bundle of actin microfilaments. Taxol reorganized the normal network of microtubules radiating from the perinuclear centers into numerous arrays of short microtubules not associated with any centers. Taxol-treated cells had wider circumferential bundles of microfilaments than control cells and morphometric analysis showed that their contours were closer to geometric circle than those of control or of colcemid-treated cells. These data show that function of the microtubular system is essential for maintenance of the characteristic morphological organization of discoid cells; we propose to name this function "contra-polarization." Contra-polarization is not prevented and is even promoted by taxol; this result suggests that a decentralized system of microtubules is sufficient for this function. In contrast, maintenance of polarized morphology of IAR-2 cells transfected by the N-ras oncogene is inhibited not only by colcemid but also by taxol and thus requires the presence of a normal centralized microtubular system.

Involvement of S100-related calcium-binding protein pEL98 (or mts1) in cell motility and tumor cell invasion

We examined the relationship between cell motility and the expressions of pEL98 (mts1) mRNA and protein in various murine normal and transformed cells. The expression of pEL98 (mts1) in v-Ha-ras-transformed NIH3T3 cells and in normal rat kidney cells transformed by either v-Ha-ras or v-src was increased over that in the corresponding parental cells at both mRNA and protein levels. The expression in normal rat fibroblasts (3Y1) transformed by v-Ha-ras was also increased compared with that in 3Y1 cells. However, the expression of pEL98 (mts1) in 3Y1 cells transformed by v-src was increased in one clone (src 3Y1-K), but decreased in another clone (src 3Y1-H). The expression level of pEL98 (mts1) correlated well with cell motility, which was examined by measuring cell tracks by phagokinesis. In order to test direct involvement of the pEL98 (mts1) protein in cell motility, src 3Y1-H cells that showed low cell motility were transfected with pEL98 cDNA. The transfectants expressing large amounts of the pEL98 protein showed significantly higher cell motility than src 3Y1-H cells. The expression of pEL98 (mts1) was also found to be correlated with motile and invasive abilities in various clones derived from Lewis lung carcinoma. These results suggest that the pEL98 (mts1) protein plays a role in regulating cell motility and tumor cell invasiveness.

Hepatocyte growth factor stimulates invasion across reconstituted basement membranes by a new human small intestinal cell line

Hepatocyte growth factor/scatter factor (HGF/SF) is a protein growth factor whose pleiotropic effects on epithelial cells include the stimulation of motility, mitosis and tubulogenesis. These responses are mediated by the cell surface tyrosine kinase receptor c-met. Because both the cytokine and receptor are found in the gastrointestinal tract, we have studied the effects of HGF/SF on transformed gut epithelial cells which express c-met. Here we describe the response of a new transformed human jejunal epithelioid cell line (HIE-7) to HGF/SF. Morphologically HIE-7 cells are immature. Their epithelial lineage was confirmed by reactivity with the epithelial specific antibodies AE1/AE3, Cam 5.2, Ber-EP4 and anti-EMA and is consistent with their expression of c-met mRNA and protein. In addition, electron microscopic analysis revealed the presence of primitive junctions and rudimentary microvilli, but features of polarization were absent. When grown on reconstituted basement membranes, HIE-7 cells formed closely associated multicellular cord-like structures adjacent to acellular spaces. However, the cells did not mature structurally, form lumen-like structures or express disaccharidase mRNA, even in the presence of recombinant HGF (rHGF). On the other hand, rHGF induced HIE-7 cells to scatter and stimulated their rapid migration in a modified wound assay. To determine whether the mitogenic effect caused by rHGF is associated with HIE-7 cell invasiveness across reconstituted basement membranes, a Boyden chamber chemoinvasion assay was performed. rHGF stimulated a 10-fold increase in the number of HIE-7 cells that crossed the basement membrane barrier, while only stimulating a small increase in chemotaxis across a collagen IV matrix, suggesting that the cytokine activates matrix penetration by these cells. rHGF also stimulated the invasion of basement membranes by an undifferentiated rat intestinal cell line (IEC-6) and by two human colon cancer cell lines which are poorly differentiated (DLD-1 and SW 948). In contrast, two moderately well differentiated colon cancer cell lines (Caco-2 and HT-29) did not manifest an invasive response when exposed to rHGF. These results suggest that HGF/SF may play a significant role in the invasive behavior of anaplastic and poorly differentiated gut epithelial tumors.

Effect of hepatocyte growth factor/scatter factor and other growth factors on motility and morphology of non-tumorigenic and tumor cells

Using an automated cell analyzer system, the effect of hepatocyte growth factor/scatter factor (HGF/SF), epidermal growth factor (EGF), basic fibroblast growth factor (bFGF), endothelial acidic fibroblast growth factor (a-FGF), platelet derived growth factor (PDGF), and recombinant human insulinlike growth factor (IGF) on the motility and morphology of Madin-Darby canine kidney (MDCK), rat hepatomas, C2, and H5-6 and murine mammary carcinoma (EMT-6) cells was investigated. Treatment of MDCK cells with HGF/SF, bFGF, EGF, and a-FGF resulted in an increase in average cell velocity and in the fraction of moving cells. Cells treated with the PDGF and IGF did not show significant alterations in velocity. MDCK cells treated with each growth factor were classified into groups of "fast" and "slow" moving cells based on their average velocities, and the average morphologic features of the two groups were quantitated. Fast-moving cells had larger average area, circularity, and flatness as compared to slow-moving cells. Factors that stimulated cell movement also induced alterations in cell morphologic parameters including spreading, flatness, area, and circularity. HGF/SF also scattered and stimulated motility of C2 and H5-6 hepatoma cells. In contrast to MDCK cells, there was no significant difference between the morphology of the fast moving and slow moving C2 and H5-6 cells. These studies suggest that growth factor cytokines have specific effects on motility of normal and tumor cells.

Autonomous migration of human fetal skin fibroblasts into a denuded area in a cell monolayer is mediated by basic fibroblast growth factor and collagen

Human fetal skin fibroblasts (TIG-3S) were found to migrate into a denuded area in a cell monolayer when cultured in both serum-depleted and serum-supplemented media, unlike adult-donor skin fibroblasts which migrated well only when cultured in serum-supplemented medium. Therefore, a series of experiments was carried out to determine whether autocrine factors are involved in their migration. The migration of TIG-3S cells in serum-depleted medium was suppressed by the addition of suramin, a factor with growth factor antagonist properties, which suggests that growth factors are important for cell migration. The suramin-induced inhibition was reversed completely by adding excess basic fibroblast growth factor (bFGF) to the culture medium and partially by platelet-derived growth factor (PDGF). Treatment with neutralizing anti-PDGF antibody did not suppress TIG-3S cell migration, whereas neutralizing anti-bFGF antibody did, which indicates that bFGF is an autocrine and PDGF a paracrine factor involved in cell migration. Next, an experiment was performed to ascertain whether the extracellular matrix is involved in TIG-3S cell migration. Monensin, an inhibitor of extracellular matrix secretion, inhibited cell migration, which was reversed by adding excess type I collagen, but not excess plasma fibronectin. In addition, further evidence for the involvement of collagen was provided by the observation that ethyl-3,4-dihydroxybenzoate, a specific inhibitor of collagen synthesis, suppressed cell migration. These results suggest that the autonomous migration of TIG-3S human fetal skin fibroblasts is mediated by bFGF and type I collagen, which they produce and secrete.

TGF-beta 1 stimulation of cell locomotion utilizes the hyaluronan receptor RHAMM and hyaluronan

TGF-beta is a potent stimulator of motility in a variety of cell types. It has recently been shown that hyaluronan (HA) can directly promote locomotion of cells through interaction with the HA receptor RHAMM. We have investigated the role of RHAMM and HA in TGF-beta-stimulated locomotion and show that TGF-beta triggers the transcription, synthesis and membrane expression of the RHAMM receptor and the secretion of HA coincident with the induction of the locomotory response. This was demonstrated by both incubating cells with exogenous TGF-beta 1 and by stimulating the production of bioactive TGF-beta 1 in tumor cells transfected with TGF-beta 1 under the control of the metallothionein promoter. TGF-beta 1-induced locomotion was suppressed by antibodies that prevented HA/RHAMM interaction, using polyclonal antibodies to either RHAMM fusion protein or RHAMM peptides, or mAbs to purified RHAMM. Peptides corresponding to the HA-binding motif of RHAMM also suppressed TGF-beta 1-induced increases in motility rate. Spontaneous locomotion of fibrosarcoma cells was blocked by neutralizing secreted TGF-beta with panspecific TGF-beta antibodies and by inhibition of TGF-beta 1 secretion with antisense oligonucleotides. Polyclonal anti-RHAMM fusion protein antibodies and peptide from the RHAMM HA-binding motif also suppressed the spontaneous motility rate of fibrosarcoma cells. These data suggest that fibrosarcoma cell locomotion requires TGF-beta, and the pathway by which TGF-beta stimulates locomotion uses the HA receptor RHAMM and HA.

Enhancement of tumorigenicity of human breast adenocarcinoma cells in nude mice by matrigel and fibroblasts

The failure of MCF7 cells to induce the formation of tumours after sub-cutaneous inoculation into athymic nude mice can be obviated by the simultaneous injection of an extract of basement membrane proteins (matrigel). Tumour growth is promoted and the latency period is low (2 to 4 weeks). In the absence of matrigel, the simultaneous inoculation of fibroblasts and MCF7 cells also resulted in the development of tumours, but with a longer latency period (about 2 months). The tumorigenic synergy between matrigel and fibroblasts was evidenced by co-inoculating MCF7 cells MDA-MB 231 cells with fibroblasts and matrigel. This co-inoculation decreased the delay of appearance of the tumours and/or accelerated the tumour growth, depending upon the number of fibroblasts injected. Repeated injections of fibroblasts conditioned medium, at the site of inoculum of tumour cells also enhanced tumour growth, suggesting the involvement of soluble factors secreted by fibroblasts. Histologically, tumours induced by co-inoculation of tumour cells and fibroblasts contained more stromal structures including vimentin-positive cells, fibronectin and interstitial collagens. These data suggest that human tumours may be reconstituted and grown in athymic nude mice using basement membrane components and fibroblasts as inductors.

Effects of extracellular matrix components on cell locomotion

The extracellular matrix (ecm), which is composed of collagens, glycoproteins, and proteoglycans, has emerged as an important regulator of cell locomotion. This review describes some of the mechanisms by which the ecm may regulate locomotion, focusing primarily on cell extension and lamellae formation. Ecm-receptor interactions form an important part of cell recognition of ecm. Such interactions can result in altered cell adhesion, signal transduction, and cytoskeletal organization, all of which impact on cell locomotion. It is important to note that although the effects of single ecm components have been studied, generally, the cell is likely to perceive ecm in vivo as a macromolecular complex. It will fall to future work to define how complexes of ecm regulate cell behavior. Because of our own particular research bias, we focus on reviewing the role of fibronectin, integrins, chondroitin sulfate, hyaluronan, and hyaluronan receptors in the regulation of cell locomotion and examine their effect on adhesion, signal transduction, and cytoskeletal integrity. Cytoskeleton assembly mechanisms, particularly those that might be regulated by the ecm, are also described. These events are summarized in a working model of ecm-promoted locomotion.

Human neuroblastoma cells express alpha and beta platelet-derived growth factor receptors coupling with neurotrophic and chemotactic signaling

Both platelet-derived growth factor (PDGF) A- and B-chains are expressed in mammalian neurons, but their precise roles still remain to be clarified. In the present studies, we examined the expression of two PDGF receptor genes in human tumor cell lines derived from neural crest. The expression of alpha and/or beta PDGF receptors was detected in a wide variety of neural crest-derived human tumor cell lines such as neuroblastoma, primitive neuroectodermal tumor, and Ewing's sarcoma by RNA blot analysis, and confirmed by immunoblot analysis. We have also demonstrated that PDGF receptors on the human neuroblastoma cell lines were biologically functional. Accordingly, chemotactic and mitogenic activities were induced by either PDGF-AA or PDGF-BB in serum-free medium. PDGF isoforms as well as nerve growth factor induced morphological changes showing neuronal cell maturation. Moreover, PDGF coordinately increased the levels of the transcript of the midsize neurofilament gene. The neuroblastoma cell lines also expressed the transcripts of PDGF A- and B-chains. These findings suggest that PDGF isoforms are involved not only in the promotion of the neuroblastoma cell growth, but also in neuronal cell migration, growth, and differentiation in human brain development.