Accumulation of the myosin-II-spectrin complex plays a positive role in apical extrusion of Src-transformed epithelial cells.

At the initial stage of carcinogenesis, transformation occurs in single cells within the epithelium. Recent studies have revealed that the newly emerging transformed cells are often apically eliminated from epithelial tissues. However, the underlying molecular mechanisms of this cancer preventive phenomenon still remain elusive. In this study, we first demonstrate that myosin-II accumulates in Src-transformed cells when they are surrounded by normal epithelial cells. Knock-down of the heavy chains of myosin-II substantially diminishes apical extrusion of Src cells, suggesting that accumulated myosin-II positively regulates the apical elimination of transformed cells. Furthermore, we have identified β-spectrin as a myosin-II-binding protein under the coculture of normal and Src-transformed epithelial cells. β-spectrin is also accumulated in Src cells that are surrounded by normal cells, and the β-spectrin accumulation is regulated by myosin-II. Moreover, knock-down of β-spectrin significantly suppresses apical extrusion of Src cells. Collectively, these results indicate that accumulation of the myosin-II-spectrin complex plays a positive role in apical extrusion of Src-transformed epithelial cells. Further elucidation of the molecular mechanisms of apical extrusion would lead to the establishment of a novel type of cancer preventive medicine.