Extracellular mitotic signals

Tea polyphenols exhibit a variety of biological properties, including antioxidative effects [6], inhibition of extracellular mitotic signals [7], inhibition of cell cycle at the G1 phase [8], suppression of inducible nitric oxide synthase (iNOS) [7, 9], and induction of apoptosis in cancer cells [10]. The natural history of carcinogenesis and cancer provides a strong rationale for a preventive approach to the control of this disease and leads to considerations of the possibility of active pharmacological intervention, or chemoprevention, to arrest or reverse the carcinogenesis prior to invasion and metastasis [11. 12]. 

Chalones are extracellular signal molecules that are produced and secreted by differentiated tissue and that act on adjacent cells (target cells) of adjacent tissue (target tissue) which are mitotically active. The chalones act to inhibit mitosis (see Chapter 7). Chalones are a special category of paracrine hormones and are thus not found in a circulating form. There is controversy concerning the nature and existence of chalones. 

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