Research Papers:

Hyperglycemia triggers HIPK2 protein degradation

Silvia Baldari, Alessia Garufi, Marisa Granato, Laura Cuomo, Giuseppa Pistritto, Mara Cirone and Gabriella D’Orazi _

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Oncotarget. 2017; 8:1190-1203. https://doi.org/10.18632/oncotarget.13595

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Silvia Baldari1,*, Alessia Garufi1,2,*, Marisa Granato3, Laura Cuomo4, Giuseppa Pistritto5, Mara Cirone3, Gabriella D’Orazi1,2

1Department of Research, Advanced Diagnostics, and Technological Innovation, Regina Elena National Cancer Institute, 00144 Rome, Italy

2Department of Medical Sciences, Tumor Biology Unit, University ‘G. d’Annunzio’, 66013 Chieti, Italy

3Department of Experimental Medicine, Pasteur-Fondazione Cenci Bolognetti Institute, Sapienza University, 00100 Rome, Italy

4U.O.C. Clinical Pathology, A.C.O., San Filippo Neri Hospital, 00100 Rome, Italy

5Department of Systems Medicine, University Tor Vergata, 00133 Rome, Italy

*These authors have contributed equally to this work

Correspondence to:

Gabriella D’Orazi, email: [email protected]

Keywords: HIPK2, cancer, hyperglycemia, p53, PP2A

Received: August 04, 2016    Accepted: November 08, 2016    Published: November 25, 2016


Homeodomain interacting protein kinase-2 (HIPK2) is an evolutionary conserved kinase that modulates several key molecular pathways to restrain tumor growth and induce p53-depending apoptotic cell-death in response to anticancer therapies. HIPK2 silencing in cancer cells leads to chemoresistance and cancer progression, in part due to p53 inhibition. Recently, hyperglycemia has been shown to reduce p53 phosphorylation at serine 46 (Ser46), the target residue of HIPK2, thus impairing p53 apoptotic function. Here we asked whether hyperglycemia could, upstream of p53, target HIPK2. We focused on the effect of high glucose (HG) on HIPK2 protein stability and the underlying mechanisms. We found that HG reduced HIPK2 protein levels, therefore impairing HIPK2-induced p53 apoptotic activity. HG-triggered HIPK2 protein downregulation was rescued by both proteasome inhibitor MG132 and by protein phosphatase inhibitors Calyculin A (CL-A) and Okadaic Acid (OA). Looking for the phosphatase involved, we found that protein phosphatase 2A (PP2A) induced HIPK2 degradation, as evidenced by directly activating PP2A with FTY720 or by silencing PP2A with siRNA in HG condition. The effect of PP2A on HIPK2 protein degradation could be in part due to hypoxia-inducible factor-1 (HIF-1) activity which has been previously shown to induce HIPK2 proteasomal degradation through several ubiquitin ligases. Validation analysed performed with HIF-1α dominant negative or with silencing of Siah2 ubiquitin ligase clearly showed rescue of HG-induced HIPK2 degradation. These findings demonstrate how hyperglycemia, through a complex protein cascade, induced HIPK2 downregulation and consequently impaired p53 apoptotic activity, revealing a novel link between diabetes/obesity and tumor resistance to therapies.

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