Chalones and the Control of Normal, Regenerative, and Neoplastic Growth of the Skin

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Abstract
SYNOPSIS Chalones,inhibitors of cell dmsion have been isolated and studied from a number of mammalian tissues, most notably, the epidermis The epidermal rhalone is a glycoprotein It exhibits considerable, but not complete specificity The epidermal chalone decreases mitotic activity by inhibiting cells in the G 2 phase of the cell cycle from entering mitosis, and probably also by inhibiting ceils in the G 1 phase of the cell cycle from entering mitosis To inhibit cells in G 2 from entering mitosis the chilone requnes adrenalin, and for maximal activity hydrocortisone It is not known if idrenalin and hydrocortisone are required for chalone inhibition of cells in G 1 In addition to inhibiting cell division in normal epidermal cells the epidermal chalone can inhibit cell division in regenerating epidermal cells induced to proliferate by chemical damage The phase of the cell cycle in which the chalone inhibits legenerating epidermal cells from entering mitosis is not known Epidermal tumors contain a decreased amount of chalone Mitosis in epidermal tumors is inhibited by treatment with epidermal chalone Tumor cells are inhibitedfrom entering mitosis from either the G 1 or G 2 phases of the cell cycle Chalones are said to inhibit mitosis by a negative feedback mechanism However, experiments which presumably result in a decrease in chalone concentration do not result in an increase in mitotic activity It is suggested that if chalones are physiologi cal controllers of cell division they do not act by a simple negative feedback mechanism but require the action of a substance to decrease their concentration

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