Hypertonic stress regulates amino acid transport and cell cycle proteins in chick embryo hepatocytes

Hyperosmotic stress affects cell growth and causes a decrease in cell volume and an increase in the uptake of organic osmolytes; however, the sensitivity of embryonic cells to osmotic treatment remain to be established. In this study we analyzed some aspects of cell cycle control and amino acid transport in hypertonic conditions during prenatal life. The effects of hyperosmotic stress on aminoacid uptake mediated by system A and on 3H-thymidine incorporation, and on the regulation of cell cycle proteins were analyzed in chick embryo hepatocytes. Hypertonic stress was able to increase system A activity and to cause cell cycle delay. Effects on amino acid transport involved p38 kinase activation and new carrier synthesis. Cyclin D1, cdk4 and PCNA levels decreased, while cyclin E, p21 and p53 levels were unchanged. Incorporation of 3H-leucine revealed a decreased synthesis of cyclin D1 protein. In contrast, the analysis of mRNA by qRT-PCR showed a net increase of cyclin D1 transcript, suggesting post-transcriptional regulation. Our data show that chick embryo hepatocytes respond to hyperosmotic conditions by arresting cell growth to prevent DNA damage and by increasing osmolyte uptake to regulate cell volume, indicating that the adaptive response to environmental stress is already present during prenatal life