We previously established a human fibroblast cell line, HFL 6-2, that contains a temperature sensitive simian virus 40 (SV40) T antigen, permitting cell growth at 35 °C but restricting growth at 39 °C. p21 (Waf1/Cip1) was significantly induced by temperature shifts in HFL 6-2 cells. Here we show that all-trans-retinoic acid (RA) treatment prevented the growth restriction of HFL 6-2 cells at 39 °C. In the presence of RA, HFL 6-2 cells proliferated into sizeable colonies even at 39 °C. [3H]Thymidine incorporation and flow cytometry analysis revealed that cells exposed to RA maintained DNA synthesis at 39 °C. Prevention of growth restriction by RA was correlated with a lack of induction of p21 at the transcription level. These observations suggest that RA may prevent the senescence process by repressing p21 gene expression, and perturb the growth regulation of somatic cells.

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