MAMMARY PROTEIN-SYNTHESIS IS ACUTELY REGULATED BY THE CELLULAR HYDRATION STATE

The effect of cell volume pertubations on mammary tissue protein synth esis has been examined. Cell-swelling, induced by a hyposmotic shock, increased the rate of incorporation of radiolabelled leucine and methi onine into trichloroacetic acid precipitable material. The incorporati on of radiolabel under both isosmotic and hyposmotic conditions was in hibited by cycloheximide. The increases in mammary protein synthesis a s a result of cell-swelling may be attributable to an increase in case in synthesis. Conversely, cell-shrinking, as a consequence of a hypero smotic challenge, almost abolished mammary protein (casein) synthesis. The finding that cell-volume pertubations had no significant effect o n steady-state casein mRNA levels suggests that the regulation, within the time course of the experiments, is at the level of translation. T he results strongly suggest that mammary cell volume may be an importa nt cellular signal in the control of mammary protein synthesis in gene ral and casein synthesis in particular. (C) 1997 Academic Press