STAT proteins act as signal transducers and activators of transcription in cells treated with cytokines or growth factors. Here we analyzed the possible cooperation between STAT3 and phosphatidylinositol-3 kinase (PI-3 kinase) and its involvement in antiproliferative signals induced by glucocorticoid hormones. Treatment of melanoma cells with dexamethasone (DEX) resulted in coexpression of STAT3 activation and increase in the PI-3 kinase protein level. Using plasmids-containing JAK2 and STAT3 constructs, we demonstrated that activation of JAK/STAT signaling led to up regulation of PI-3 kinase and enhancement of DEX's ability to increase PI-3 kinase levels in target cells. Prolonged DEX treatment of melanoma cells resulted in constitutive increases in both STAT3 and PI-3 kinase protein levels that were correlated with increased melanoma resistance to antiproliferative hormone action. Similarly, forced expression of both STAT3 and PI-3 kinase in melanoma cells led to enhanced resistance to hormone treatment. Forced expression of PI-3 kinase led to increase in STAT3 activity in a JAK-dependent manner, indicating the existence of a feedback regulatory cascade between the JAK/STAT3 and PI-3 kinase pathways. We suggest that protection of melanoma cells from antiproliferative effects of glucocorticoid hormones may be mediated, at least in part, by the constitutive activation of the STAT3/PI-3 kinase signaling pathway.