BMC Cancer 2001, 1:19 http://www.biomedcentral.com/1471-2407/1/19 (AA) NRP-152 (BB) NRP-154 C D Figure 5 Dexamethasone treatment inhibited IL-6 expression in NRP-152 but not NRP-154 cells. Cells were grown in charcoal-adsorbed serum-containing medium prior to beginning dexamethasone treatment (10-6 M) for 2 days. Cells were har- vested, fixed, and permeabilized, stained for IL-6, then analyzed for fluorescence in FL2, as described above. Panel A, NRP-152 cells. Panel B, NRP-154 cells. Panel C, NRP-154 clone A3 (high IL-6 – expressing. Panel D, NRP-154 clone G7 (low IL-6- expressing). All panels, purple line = no dexamethasone; red line in panels A & B = + dexamethasone; blue line in panels C & D = + dexamethasone. survival of NRP-152 cells, but that NRP-154 cells did not require activated JAK2 for survival, regardless of amount of IL-6 produced by the cell. Further experi- ments are underway to determine if STAT3 requires phosphorylation by a different kinase, such as JAK1, in NRP-154 cells. Discussion We observed that STAT3 was constitutively phosphor- ylated in NRP-154, but not NRP-152 cells (Figure 1). Treatment of NRP-154 cells with testosterone did not in- crease the level of phosphorylation in NRP-154 cells (da- ta not shown). Even after testosterone treatment, STAT3 was not phosphorylated in NRP-152 cells (data not shown). There is evidence that androgen treatment may increase the survival of PCA cells through activation of STAT3 [29]. Further experiments are underway to test this possibility. STAT1, another signaling intermediate in the IL-6 pathway, has been observed to be activated in non-tumorigenic cells, and may function as a "check" for STAT3 phosphorylation, a possible oncogenic event [30,31]. We are investigating whether or not STAT1 is phosphorylated by JAK2 in NRP-152 cells, and whether STAT1 phosphorylation is required for the survival of