Several lines of evidence have revealed that newly emerging transformed cells are often eliminated from the epithelium, though the underlying molecular mechanisms of this cancer preventive phenomenon still remain elusive. In this study, using mammalian cell culture systems we have identified plectin, a versatile cytoskeletal linker protein, as a novel regulator for apical extrusion of RasV12-transformed cells. Plectin is accumulated in RasV12 cells when they are surrounded by normal epithelial cells. Similarly, cytoskeletal proteins tubulin, keratin, and Epithelial Protein Lost In Neoplasm (EPLIN) are also accumulated in the transformed cells surrounded by normal cells. Knockdown or functional disruption of one of these molecules diminishes the accumulation of the others, indicating that the accumulation process of the individual protein mutually depends on each other. Furthermore, plectin-knockdown attenuates caveolin-1 (Cav-1) enrichment and PKA activity in RasV12 cells and profoundly suppresses the apical extrusion. These results indicate that the plectin-microtubules-EPLIN complex positively regulates apical elimination of RasV12-transformed cells from the epithelium in a coordinated fashion. Further development of this study would open a new avenue for cancer preventive medicine.
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