Effects of retinoic acid on cell proliferation and cell differentiation in a rat tracheal epithelial cell line

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Abstract
The effects of 3.3 times 10‐7 M to 3.3 times 10‐5 M all‐trans‐retinoic acid (vitamin‐A acid) on the total cell population dynamics of 165 S, a keratinizing epithelial cell line from carcinogen‐exposed rat trachea, were studied. During the first 6 days of culture, cells accumulated on the dish in the presence of the vitamin to twice the density of controls. [3H]thymidine incorporation into DNA and percentage of [3H]thymidine‐labelled cells in autoradiographs were stimulated in a dose‐dependent fashion to a maximum of 25‐ and 34‐fold, respectively. Exfoliation of cells from the cultures was also enhanced 2–3‐fold, resulting in nearly twice the total number of cells (attached plus exfoliated) in the presence of the vitamin.During 19 days of culture, retinoic acid maintained a higher level of [3H]thymidine incorporation and cell exfoliation in 165 S cells so that by day 19, total cell production was more than three times that seen in controls. At this time, vitamin‐treated cultures showed a reduced cell saturation density compared to controls. The higher final cell density in the control cultures was a result of multilayering and papillary formation which did not occur in the presence of retinoic acid. The papillae in control cultures stained specifically with Rhodamine B or with the eosin and orange G components of the Papanicolaou method. A count of the number of eosin and orange G positive cells in the attached and exfoliated cell compartments showed an 8‐fold reduction of keratinization in retinoic acid‐exposed cultures. Our results show that retinoic acid is a growth stimulant in these cell cultures, causing increased cell proliferation and exfoliation accompanied by inhibition of keratinization.

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