Changes in cell surface proteins of culturedDrosophila cells exposed to 20-hydroxyecdysone

Drosophila cell lines have provided popular material for study of the mechanisms by which steroid hormones regulate cellular events. Previous investigations at the organismic or organ level have suggested that ecdysteroids are bound by a cytoplasmic receptor, and that the resulting complex translocates to the nucleus where it results in active transcription of a few genes. The protein products of these primary responding genes then modulate a larger series of secondary transcriptional changes. In cultured cells, other investigators have detected the hormonally-induced synthesis of only 4-5 new polypeptides through 72 h of treatment. Although these proteins may represent the gene products associated with the primary response, this small number of changes is surprising in view of the rapid morphological alteration of the cells and changes in such surface-mediated behavior as substrate adhesion and agglutinability observed within the same time interval. In this report, we show that lactoperoxidase-catalyzed radioiodination followed by 2-dimensional polyacrylamide gel electrophoresis and autoradiography provide an effective protocol for visualizing cell surface proteins of a Drosophila cell line. Among the more than 175 labeled species detected, comparisons of control cells with those treated by 20-hydroxyecdysone for 72 h shows at least 27 differences. We interpret these differences as the result of the secondary transcriptional response to the hormone.