New studies of migration of specialized follicle cells known as border cells in Drosophila point to an unexpected role for steroid hormones in control of cell motility. In a screen for mutations that disrupted border cell migration, Bai et al. identified mutations in a gene they call taiman (tai). The TAI protein has sequence similarity to the human protein AIB1, which is a steroid hormone receptor cofactor that shows increased expression in some breast and ovarian cancers. In vitro, TAI bound in a ligand-dependent manner to the ecdysone receptor (ecdysone is the only steroid hormone so far identified in flies). Furthermore, mutant border cells lacking a component of the ecdysone receptor failed to migrate, and the timing of cell migration in vivo was dependent on the amount of ecdysone present. The steroid receptor signaling appeared to affect the border cells only in motility and not proliferation. The results may have implications for understanding the mechanisms by which mammalian steroid hormones promote metastasis of highly invasive breast and ovarian cancers.
Bai1 J., Uehara, Y., and Montell, D. J. (2000) Regulation of invasive cell behavior by Taiman, a Drosophila protein related to AIB1, a steroid receptor coactivator amplified in breast cancer. Cell 103: 1047-1058. [Online Journal]