A two-dimensional model of cell movement. Well differentiated human rectal adenocarcinoma cells move as coherent sheets upon TPA stimulation

Immunohistochemical analysis of IQGAP1 expression in human colorectal carcinomas: its overexpression in carcinomas and association with invasion fronts

In histopathological sections, it is frequently observed that carcinoma cells move in and invade the stroma as coherent cell nests, rather than single cells. We have called this type of movement 'cohort migration (CM)' and developed an in vitro model, in which human colon adenocarcinoma cells move as coherent cell sheets when stimulated with naturally occurring motogenic factor, hepatocyte growth factor/scatter factor (HGF/SF). In this CM model, localized release from cell-cell adhesion is essential for cell movement. Recently, we have shown that IQGAP1, a target molecule of Cdc42 and Rac1 small GTPases, is involved in this localized release from the E-cadherin-based cell-cell adhesion during CM. In this study, we examined expression of IQGAP1 immunohistochemically in human colorectal tissues and found that IQGAP1 was overexpressed in carcinoma tissues compared with normal counterparts. Within the carcinoma tissue, IQGAP1 tended to be expressed more at the invasion front than at the upper portions, and higher levels of expression were observed in deeper two-thirds of carcinoma tissues than in the superficial one-third. This expression pattern showing stronger signals in deeper portions was most apparent in advanced carcinomas that invaded into the subserosa. These findings supported a role of IQGAP1 in colon carcinoma invasion.

Hepatocyte growth factor/scatter factor induces not only scattering but also cohort migration of human colorectal-adenocarcinoma cells

We presented earlier a 2-dimensional cell-motility assay using a highly metastatic variant (L-10) of human rectal-adenocarcinoma cell line RCM-1 as a motility model of tumor cells of epithelial origin. In this model, L-10 cells moved as coherent cell sheets when stimulated with 12-O-tetradecanoylphorbol-13-acetate (TPA), and we called this type of movement "cohort migration". Electron- and immunoelectron-microscope study of the migrating cell sheets demonstrated localized release from cell-cell adhesion only at the lower portion of the cells with loss of E-cadherin immunoreactivity, and this change was associated with increased tyrosine phosphorylation of the E-cadherin-catenin complex, including beta-catenin. In the present study, to obtain evidence to support the relevance of our model to carcinoma-cell movement in vivo, we sought a naturally occurring motogenic factor(s) able to induce this cohort migration. Among the factors examined, hepatocyte growth factor/scatter factor (HGF/SF) clearly induced cohort migration of L-10 cells. Additionally, not only L-10 but several other human colorectal-carcinoma cell lines showed this type of migration in response to HGF/SF, while yet others showed scattering-type motility. In this HGF/SF-induced migration, localized release from cell-cell adhesion was induced only at the lower portion of the cells, allowing them to extend leading lamellae, whereas close cell-cell contacts remained at the upper portion of the cells, as seen in TPA-induced cohort migration. Scattering-type cell lines tended to express more c-Met (receptor for HGF/SF) mRNA than the cell lines that showed cohort-type migration. LoVo, one of the scattering-type cell lines, expressed more c-Met protein and less E-cadherin than L-10, which showed cohort-type migration. HGF/SF treatment of LoVo reduced the amount of alpha-catenin complexed with E-cadherin more markedly than in L-10, but in both cell lines this reduction was not accompanied by increased tyrosine phosphorylation of beta-catenin, suggesting the presence of a mechanism other than phosphorylation for release from cell-cell adhesion during cell motility.

Protein phosphatase-2A association with microtubules and its role in restricting the invasiveness of human head and neck squamous cell carcinoma cells

The role of protein phosphatase-2A (PP-2A) in regulating the motility and adhesion of human head and neck squamous cell carcinomas (HNSCC) was investigated. Immunofluorescent staining of these HNSCC cells showed PP-2A can co-localize with microtubules. That the PP-2A influences motility was shown by the increase in HNSCC cell migration through laminin and vitronectin when PP-2A was selectively inhibited with low dose okadaic acid, and by the reduction in invasion through these same matrix components by elevators of PP-2A activity. Motility of HNSCC cells through collagen I or fibronectin was not modulated by PP-2A. The reduction in HNSCC migration through vitronectin or laminin that resulted from treatment with PP-2A elevators was associated with an increase in cellular adhesiveness to these same ECM components. These studies show the association of PP-2A with the cellular cytoskeleton and its role in restricting the invasiveness of tumor cells through select extracellular matrix components.

Ultrastructural study of TPA-induced cell motility: human well-differentiated rectal adenocarcinoma cells move as coherent sheets via localized modulation of cell-cell adhesion

We previously found that 12-O-tetradecanoylphorbol-13-acetate (TPA)-enhanced invasion of Matrigel was associated with augmentation of cell motility but not with metalloproteinase activity in a highly metastatic variant (L-10) of human rectal adenocarcinoma cell line RCM-1. In a two-dimensional cell motility assay, TPA induced active L-10 cell locomotion with characteristic morphology; the cells moved outwards from the cell islands mainly as a localized coherent sheet of cells. The leading cells showed locomotor morphologies with fan-shaped leading lamellae while the following cells had cell contacts on all sides and appeared to lack leading lamellae. In the present ultrastructural study, the following cells frequently showed tapering cytoplasmic protrusions and leading lamella-like processes underlapping a preceding cell, indicating that the locomotion mechanism is almost the same for both the leading and following cells. For this type of locomotion as a coherent sheet we propose that localized modulation of cell-cell adhesion was induced such that wide intercellular gaps occurred at the lower portion of the cells to allow the cells to extend the tapering cytoplasmic processes and leading lamellae while close cell-cell contacts remained at the upper portion of the cells. These TPA-induced changes took place predominantly in the cells at the periphery of the cell islands, while the cells in the middle of the cell islands maintained close cell-cell contacts including complex interdigitation all around the cells, suggesting the modulation of TPA action by cell-cell interaction. Additionally, consistent with the evidence for junctional complexes between the cells moving outwards, the Lucifer-yellow dye transfer studies showed some, limited cell-cell coupling, suggesting the presence of at least some gap junctional intercellular communication in the moving cell sheets.