Opposing Effects of PML and PML/RARα on STAT3 activity Short title: Effects of PML and PML/RARα on STAT3 activity

Promyelocytic leukemia protein PML acts as a tumor suppressor, while its chimeric mutant PML/RARα causes acute promyelocytic leukemia (APL). Because PML has been shown to form transcription-regulatory complexes with various molecules, we speculated that PML and/or PML/RARα might affect STAT3 activity, which plays a crucial role in G-CSF-induced growth and survival of myeloid cells. In luciferase assays, PML inhibited STAT3 activity in NIH3T3, 293T, HepG2 and 32D cells. PML formed a complex with STAT3 through B-box and COOH-terminal regions in vitro and in vivo, thereby inhibiting its DNA-binding activity. Although PML/RARα did not interact with STAT3, it dissociated PML from STAT3 and restored its activity suppressed by PML. To assess the biological significance of these findings, we introduced PML and PML/RARα into IL-3-dependent Ba/F3 cells expressing the chimeric receptor composed of extracellular domain of G-CSF-R and cytoplasmic domain of gp130, in which gp130-mediated growth is essentially dependent on STAT3 activity. Neither PML nor PML/RARα affected IL-3-dependent growth of these clones. By contrast, gp130-mediated growth was abrogated by PML, while it was enhanced by PML/RARα. These results revealed new functions of PML and PML/RARα, and proposed a possibility that dysregulated STAT3 activity by PML/RARα may participate in the pathogenesis of APL. For personal use only. on October 3, 2017. by guest www.bloodjournal.org From