A new hypothesis on mitotic control mechanism in eukaryotic cells: cell-specific mitosis-inhibiting protein excretion hypothesis.

Recent experimental studies on the regulatory mechanism of cell division in the regenerating rat liver have suggested that α₁acid glycoprotein is a primary mitotic inhibitor, whose intracellular concentration over a critical level inhibits cell division, while α₁-antitrypsin is one of secondary mitotic inhibitors, whose extracellular concentration below a critical level facilitates the excretion of the primary mitotic inhibitor from the hepatocyte, allowing cell division. Based on these findings, the essential part of the mitotic control mechanism in the regenerating rat liver is concretely discussed.To expand the basic concept to more general biological phenomena, the cell-specific mitosis-inhibiting protein excretion hypothesis is proposed. The hypothesis depends on two basic presuppositions: (1) Every cell has a cell-specific mitosis-inhibiting protein synthesized by the cell itself. (2) Every cell will be released from the suppression of cell division when the cell-specific mitosis-inhibiting protein has been excreted and the intracellular concentration of the protein has fallen below a critical level.On the basis of this hypothesis, the mitotic control mechanism in normal eukaryotic cells is briefly discussed on the level of the interrelation between cell division and cell differentiation, and the core of the puzzle of carcinogenesis, the problem of the so-called indefinite or autonomous proliferation of the cancer cell in the host, is also discussed.