The effect of growth-promoting agents on replication and cell cycle withdrawal in cultures of epidermal keratinocytes.
Epidermal keratinocytes grow in culture to form a stratified squamous epithelium. These cultures contain a replicating as well as a terminally differentiating population and undergo surface desquamation. Epidermal growth factor (EGF) and cholera toxin are usually employed as growth-promoting agents because they reduce the population doubling time; that is, the period required to increase the total cell number twofold. There are three ways in which this reduction in population doubling time could be achieved: (a) the time for one cell cycle or the cell cycle length may be shortened; (b) the number of cells that withdraw from the cell cycle and terminally differentiate may be reduced; or (c) the number of cells that desquamate into the medium over a set period of time may be reduced. We have explored these possibilities in growing cultures of epidermal keratinocytes using a newly developed double-label assay. This assay gives a measure of both cell length and cell cycle withdrawal. Results show that the growth enhancement induced by EGF and cholera toxin can be attributed primarily to a reduction in cell cycle withdrawal and, to a lesser degree, to a reduction in cell cycle length. EGF and cholera toxin have no significant effect on the rate of desquamation. A linear correlation was noted between cell cycle lengths and withdrawal, suggesting an interconnection between the rate of cell renewal and the likelihood of undergoing terminal differentiation.
Greif
F
F
Department of Surgery, School of Medicine, State University of New York, Stony Brook.
Soroff
H S
HS
Setzer
R W
RW
Taichman
L B
LB
D002453:Cell Cycle / Q000187:drug effects; D002454:Cell Differentiation / Q000187:drug effects; D002455:Cell Division / Q000187:drug effects; D002478:Cells, Cultured; D002772:Cholera Toxin / Q000494:pharmacology; D000078404:Epidermal Cells; D004815:Epidermal Growth Factor / Q000494:pharmacology; D006801:Humans; D007231:Infant, Newborn; D007633:Keratins; D008297:Male
D004815:Epidermal Growth Factor; D007633:Keratins; D002772:Cholera Toxin