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Fig. 6. The impact of Tiam1 expression on MV3 melanoma migration. (A) Wound closure in a 2D cell motility assay. Closure of a scratch wound in a confluent monolayer of cells was monitored over a period of at least 7 hours. Tiam1 expression strongly inhibited migration of the metastatic MV3-Tiam1 cells (filled circles) compared with the parental cell line MV3 (open circles). The migration potential of non-metastatic cells 1F6 (open triangles) and 1F6-Tiam1 (filled triangles) was not significantly altered in the 2D system. A slight inhibition of migration was detectable. (B) Characterization of MV3 and MV3-Tiam1 cells in human skin reconstructs. Upper panel: MV3 melanoma cells form band-like tumor cell aggregates at the epidermal-dermal junction and exhibit invasive tumor growth of tumor cell strands into the deeper dermis (arrows). Lower panel: MV3-Tiam1 melanoma cells display a high proliferation rate (red) and form giant tumor masses at the epidermal-dermal junction and in the upper dermis; stained with Ki 67 (red), x50. (C) Magnified zones (tetragons) highlight the different cell morphology and position in greater detail. (D) Reinforced cell-cell adhesions and impaired migration after expression of Tiam1. Multicellular spheroids of MV3 control cells (left panel) or Tiam1-expressing MV3 cells (right panel) were incorporated into 3D collagen lattices and monitored by time-lapse videomicroscopy. Paths of individual cells and resulting migration speed were obtained from single cell tracking (after 11 hours). Upon long-term observation, stringent cell-cell junctions preventing cell detachment in Tiam1-positive cells were retained for up to 72 hours (not shown). Bar, 0.6 mm..
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