[Role of cell-cell interaction in tumor promotion].

Before a potentially tumorigenic cell meets a carcinogenic stimulus, its proliferation and differentiation are under tight control along with other neighbouring cells and their functions are well coordinated. In other words, cells in a given tissue form an orderly society and a cancer cell is a rebel against such a society. Therefore, it is important to study how the cellular society is maintained and how carcinogenic stimuli produce chaos in that society. The hypothesis that cell-cell interaction plays an important role in carcinogenesis has recently been reinforced by the finding that the prototype tumor promoter, phorbol esters, inhibits junctional intercellular communication. We present here several lines of evidence which suggest that block of intercellular communication is an important determinant in carcinogenesis, especially during tumor promotion process.