FUNCTIONAL INTERFERENCE BETWEEN THE SPI-1 PU.1 ONCOPROTEIN AND STEROID-HORMONE OR VITAMIN RECEPTORS

The Spi-1/PU.1 protein is an Ets-related transcription factor, whose o verexpression is a consequence of SFFV integration in Friend erythrole ukemic cells. We present evidence that Spi-1/PU.1 can specifically rep ress the glucocorticoid-induced activation of promoters carrying a glu cocorticoid response element (GRE). Conversely, the glucocorticoid rec eptor (GR) represses Spi-1/PU.1-mediated transcriptional activation in the presence of hormone. Spi-1/PU.1 also antagonized activation by ot her nuclear receptors, such as the thyroid hormone or the retinoic aci d receptors, in several cell lines, including K562 erythroteukemic cel ls. These observations suggest that accumulation of the Spi-1/PU.1 pro tein may interfere with the action of hormones in the erythrocyte diff erentiation pathway.