Increased expression of p21Sdi1 in adrenocortical cells when they are placed in culture.

Expression of the cell cycle inhibitor p21Sdi1/WAF1/Cip1 was investigated in a differentiated cell type, the adrenocortical cell, at different stages of culture, from the preparation of cells from the adrenal gland to senescence after long-term growth. In bovine adrenocortical cells, expression of SDI1 was much higher in culture than in vivo. Elevation of SDI1 mRNA, accompanied by elevation of the level of a protein reacting with anti-p21Sdi1 antibodies, was observed as early as 3 h after the start of the tissue dissociation procedure used to prepare cells for culture. This level of expression was then maintained during plating and subsequent long-term growth in culture. Growth and quiescence in bovine adrenocortical cells can be modulated by inclusion or removal of FGF from the culture medium. In these cells SDI1 mRNA was not increased by long-term mitotic quiescence resulting from FGF deprivation. In cultured fetal human adrenocortical cells, SDI1 mRNA was also detected at all stages of the culture life span, including 2 days after isolation of cells from the adrenal gland and plating in culture. Mid-life-span cells had higher SDI1 mRNA than senescent human fibroblasts. Clones of human adrenocortical cells nearing senescence in culture had somewhat higher SDI1 mRNA than early passage cells. Thus, SDI1 expression in adrenocortical cells is not associated with mitotic quiescence either in vivo or in vitro, yet isolation of the cells and culturing them exerts a powerful inductive influence on its expression.