Glucocorticoid induction of the adipocyte clone 5 gene requires high cell density.

We have previously reported the identification of a glucocorticoid and cell-density inducible gene (clone 5) that appears to play a regulatory role in adipocyte differentiation. In the current studies we have more carefully investigated the interplay between cell growth or differentiation and the glucocorticoid responsiveness of clone 5 RNA. We find that inducibility by steroid hormone is independent of the differentiated state but surprisingly, occurs only when cells are at high cell density. In subconfluent TA1 cells clone 5 RNA is refractory to induction whereas well characterized glucocorticoid-inducible promoters such as the those from mouse mammary tumor virus and alpha-1-acid glycoprotein are induced under all conditions. These results point to the necessity of ancillary factors, absent in low density cell culture, that are required for glucocorticoid responsiveness of the clone 5 gene.