Adhesion of tumor cells to host cell layers and subsequent transcellular migration are pivotal steps in cancer invasion and metastasis. The small GTPase Rho controls cell adhesion and motility through reorganization of the actin cytoskeleton and regulation of actomyosin contractility. Cultured rat MM1 hepatoma cells migrate through a mesothelial cell monolayer in vitro in a serum-dependent, Rho-mediated manners. Among several proteins isolated as putative target molecules of Rho, the ROCK (ROK) family of Rho-associated serine-threonine protein kinases are thought to participate in the induction of focal adhesions and stress fibers in cultured cells, and to mediate calcium sensitization of smooth muscle contraction by enhancing phosphorylation of the regulatory light chain of myosin. Transfection of MM1 cells with cDNA encoding a dominant active mutant of ROCK conferred invasive activity independently of serum and Rho. In contrast, expression of a dominant negative, kinase-defective ROCK mutant substantially attenuated the invasive phenotype. A specific ROCK inhibitor (Y-27632) blocked both Rho-mediated activation of actomyosin and invasive activity of these cells. Furthermore, continuous delivery of this inhibitor using osmotic pumps considerably reduced the dissemination of MM1 cells implanted into the peritoneal cavity of syngeneic rats. These results indicate that ROCK plays an essential part in tumor cell invasion, and demonstrate its potential as a therapeutic target for the prevention of cancer invasion and metastasis.

We established a murine osteosarcoma cell line (LM8) with high metastatic potential to the lung from murine Dunn osteosarcoma using 8 repeated Fidler's procedures. We performed the biological characterization of the LM8 and the maternal Dunn cell lines in vitro and in vivo. Morphologically, LM8 possesses many fillopodial protrusions, lamellipodial structures surrounding the cell surface and membrane ruffles suggesting enhanced cell motility. The increased matrix metalloproteinase (MMP) 2 activity of this cell line might help cell invasion after penetration of the endothelial (mesothelial) cell layer. This cell line exhibited high in vitro invasive activity when seeded onto the mesothelial cell monolayer. Higher expression of VEGF mRNA in this cell line might facilitate neovascularization at the site of metastaisis, resulting in extremely high metastaic potency after i.v. injection. LM8 also showed a high metastic incidence (7/7) to the lung even after s.c. transplantation into the back space of mice. This cell line can provide an excellent tool for studying inhibitory agents against pulmonary metastasis as well as the various important factors involved in metastasis of osteosarcoma. Int. J. Cancer 76:418–422, 1998.© 1998 Wiley‐Liss, Inc.

Metastasis is responsible for most cancer deaths. Here, we show that Aes (or Grg5) gene functions as an endogenous metastasis suppressor. Expression of Aes was decreased in liver metastases compared with primary colon tumors in both mice and humans. Aes inhibited Notch signaling by converting active Rbpj transcription complexes into repression complexes on insoluble nuclear matrix. In tumor cells, Notch signaling was triggered by ligands on adjoining blood vessels, and stimulated transendothelial migration. Genetic depletion of Aes in Apc(Δ716) intestinal polyposis mice caused marked tumor invasion and intravasation that were suppressed by Notch signaling inhibition. These results suggest that inhibition of Notch signaling can be a promising strategy for prevention and treatment of colon cancer metastasis.

Synovial sarcoma (SS) is a malignant soft tissue tumor characterized by its unique t(X;18)(p11;q11) chromosomal translocation leading to the formation of the SS18-SSX fusion gene. The resulting fusion protein product is considered to play as an aberrant transcription factor and transform target cells by perturbing their gene expression program. However, the cellular origin of SS is highly debated. We herein established two novel human SS cell lines, named Yamato-SS and Aska-SS, and investigated their biological properties. We found the self-renewal ability of these cells to generate sarcospheres, to form tumors in serial xenotransplantation and reconstitute the tumor phenotypes without fractionation by any surface markers. Both SS cells as well as clinical tissue specimens from 15 patients expressed the marker genes-associated stem cell identity, Oct3/4, Nanog, and Sox2. We also found that both SS cells displayed limited differentiation potentials for mesenchymal lineages into osteocytes and chondrocytes albeit with the expression of early mesenchymal and hematopoietic lineage genes. Upon SS18-SSX silencing with sequence-specific siRNAs, these SS cells exhibited morphological transition from spherical growth in suspension to adherent growth in monolayer, additional expression of later mesenchymal and hematopoietic lineage genes, and broader differentiation potentials into osteocytes, chondrocytes, adipocytes, and macrophages in appropriate differentiation cocktails. Collectively, these data suggest that a human multipotent mesenchymal stem cell can serve as a cell of origin for SS and SS is a stem cell malignancy resulting from dysregulation of self-renewal and differentiation capacities driven by SS18-SSX fusion protein.

In this study, we show that LIM kinase 1 (LIMK1), a critical regulator of actin dynamics, plays a regulatory role in tumor cell invasion. We found that the level and activity of endogenous LIMK1 is increased in invasive breast and prostate cancer cell lines in comparison with less invasive cells. Overexpression of LIMK1 in MCF-7 and in MDA-MB-231 human breast cancer cell lines increased their motility, whereas the specific ROCK and Rho inhibitors Y-27632 and C3, respectively, attenuated this effect. In addition, inhibition of LIMK1 activity in the MDA-MB-231 cells by expression of dominantnegative LIMK1 resulted in decreased motility and formation of osteolytic bone lesions in an animal model of tumor invasion. This study shows an important role for LIMK1 signaling in invasion of cancer, demonstrating its potential as a therapeutic molecular target to decrease metastasis.T umor invasion and metastasis is a critical event for cancer patients as it often results in death. Current therapies are of limited value in most patients with disseminated disease, leaving us with the goal of identifying genes that regulate the metastatic process and designing drugs that target their function. During progression of tumor cells to a metastatic phenotype, they undergo a series of changes that begin with loss of contact inhibition and increased motility, allowing them to migrate from the primary tumor site, invade distant organs, and induce neo-vascularization resulting in metastasis (1). Many of these changes are associated with dynamic actin reorganization and activation of signaling pathways through transmembrane receptors, including receptor tyrosine kinases and phosphatidylinositol 3-kinases (2, 3), G-protein-coupled receptors (4), chemokine receptors (5), and transforming growth factor-␤ receptor (6). In association with cell adhesion molecules at the plasma membrane, the cytoskeleton affects the nature of cell-to-cell and cell-to-substrate interactions via clustered transmembrane integrins that are associated with extracellular matrix proteins (7). These complexes provide the driving force for cell movement and surface remodeling, including neurite extension and axon formation.Members of the small guanosine triphosphatase (GTPase) family control cell adhesion and motility through reorganization of the actin cytoskeleton and regulation of actomyosin contractility (8). We have previously demonstrated the role of the Rho-actomyosin system in tumor cell invasion (9). Both RhoA (10) and the related RhoC (11) are expressed at a relatively higher level in metastatic tumors, and their expression levels positively correlate with the stage of the tumors (12). However, mutations in the Rho gene have not yet been found in human tumors; rather, the overexpression of RhoA in the cell facilitates its translocation from the cytosol to the plasma membrane, where its activation results in stimulation of the actomyosin system, followed by cellular invasion both in vitro and in vivo (13).One of the target molecules of Rho is the family of Rh...