Fig. 6. WWOX-negative cells rapidly induce redox activity and apoptosis of WWOX-positive cells.

a–c By time-lapse microscopy, rapid upregulation of redox activity and apoptosis of wild type MEF cells were shown in the coculture of Wwox knockout and wild type MEF cells. d Direct mixing of WWOX-negative L929R cells with L929 for culturing 48 h at 37 °C led to apoptosis of L929 cells, as measured by DNA fragmentation analysis. Non-specific death of L929R cells was deducted from the total death of L929. e–h MDA-MB-231 cells were treated with methylation inhibitor 5-aza-2′ deoxycytidine (5-aza, 5 μM) for 5 days. 5-aza induced WWOX protein expression in MDA-MB-231, as determined by Western blot. The untreated parental cells underwent retrograde movement upon facing 5-aza-treated cells. In controls, both sides of untreated MDA-MB-231 migrated in an anterograde manner and merged with each other smoothly. Migration distance and velocity of cell migration are shown (n = 10, all samples versus 5-aza-treated cells; Student’s t test). Also, see Video S15. i A schematic model is shown for how WWOX-negtaive cells undergo retrograde migration upon facing WWOX-positive cells. WWOX-negative cells activate multiple pathways that may converge ERK, and this leads to evasion of WWOX-negative cells by retrograde migration and apoptosis of a portion of WWOX-positive cells. TGF-β abolishes the retrograde migration and apoptosis, and induces anterograde migration and merge of WWOX-positive and -negative cells