CHOP negatively regulates Polo-like kinase 2 expression via recruiting C/EBPα to the upstream-promoter in human osteosarcoma cell line during ER stress

Polo-like kinase 2 (Plk2) is a member of the serine/threonine protein kinase family involved in cell-cycle regulation and cellular response to stresses. However, the alteration of Plk2 in response to endoplasmic reticulum (ER) stress has not been well described. In the present study, we focused on the regulation of Plk2 regulation in response to ER stress. Plk2 expression was dramatically decreased under ER stress induced by brefeldin A (BFA), thapsigargin (TG), or tunicamycin (TM), and this down regulation of Plk2 expression was dependent on activating transcription factor 4 (ATF4) and C/EBP homology protein (CHOP). Luciferase activity analysis of the truncated Plk2 promoter indicated that regions from -2506 to -1806 and from -1002 to -830 of the Plk2 promoter were sensitive to BFA. Additionally, ChIP and ChIP Re-IP assays showed that CHOP and C/EBP alpha were assembled on the same region of Plk2 promoter. Notably, we identified two C/EBP alpha responsive elements at positions -2002 and -948, to which C/EBP alpha or CHOP binding was enhanced by BFA under in vitro and in vivo conditions. Finally, overexpression of Plk2 inhibits cell apoptosis and promotes cell proliferation in response to ER stress. In summary, these results demonstrated that ER stress plays a crucial role in Plk2 expression. CHOP may up-regulate DNA-binding affinities after BFA treatment, via recruiting C/EBP alpha to the upstream-promoter of Plk2. These findings may contribute to the understanding of the molecular mechanism of Plk2 regulation.