Regulation of Janus-activated kinase-2 (JAK2) by diindolylmethane in ovarian cancer in vitro and in vivo

Abstract

Janus-activated kinase-2 (JAK2) plays an important role in the activation of signal transducer and activation of transcription 3 (STAT3), which is over expressed in majority of ovarian tumors. We have reported previously that diindolylmethane (DIM) induces apoptosis in ovarian cancer cells by inhibiting STAT3. However, the role of JAK2 in our model was not yet understood and hence evaluated in this report. SKOV-3 human ovarian cancer cells were used to evaluate concentration and time dependent effects of DIM. Interleukin 3 (IL-3) and epidermal growth factor (EGF) were used to activate JAK2. Tumor xenograft studies were used to determine modulation of JAK2 in vivo. DIM treatment blocked the phosphorylation of JAK2 at Tyr-1007 in a concentration-dependent manner. In a time-dependent study, inhibition of JAK2 by DIM was as early as 1 h, which was followed by the inhibition of STAT3 and survivin. IL-3-induced phosphorylation of JAK2 and STAT3 was significantly blocked by DIM. IL-3 treatment blocked DIM-induced apoptosis. EGF treatment resulted in the activation of JAK2 and STAT3 but suppressed by DIM. These results indicate the involvement of cytokines and growth factors in the activation of JAK2/STAT3 and that DIM suppress their activation. Furthermore, DIM in combination with cisplatin drastically reduced the phosphorylation of JAK2 when compared to cisplatin alone. Western blot analysis of tumors from DIM treated mice showed significant inhibition of JAK2 activation as compared with controls. These findings provide a rationale for further clinical investigation of DIM for its potential use alone or in combination with chemotherapy of ovarian cancer.