Targeting COX-2/PGE2 Pathway in HIPK2 Knockdown Cancer Cells: Impact on Dendritic Cell Maturation

Alessia Garufi,Claudia Ceci,Alberto Faggioni,Livia Di Renzo,Roberta Santarelli,Mara Cirone,Gabriella D’Orazi,Giuseppa Pistritto

doi:10.1371/journal.pone.0048342

Abstract

BackgroundHomeodomain-interacting protein kinase 2 (HIPK2) is a multifunctional protein that exploits its kinase activity to modulate key molecular pathways in cancer to restrain tumor growth and induce response to therapies. For instance, HIPK2 knockdown induces upregulation of oncogenic hypoxia-inducible factor-1 (HIF-1) activity leading to a constitutive hypoxic and angiogenic phenotype with increased tumor growth in vivo. HIPK2 inhibition, therefore, releases pathways leading to production of pro-inflammatory molecules such as vascular endothelial growth factor (VEGF) or prostaglandin E2 (PGE2). Tumor-produced inflammatory mediators other than promote tumour growth and vascular development may permit evasion of anti-tumour immune responses. Thus, dendritic cells (DCs) dysfunction induced by tumor-produced molecules, may allow tumor cells to escape immunosurveillance. Here we evaluated the molecular mechanism of PGE2 production after HIPK2 depletion and how to modulate it.Methodology/Principal findingsWe show that HIPK2 knockdown in colon cancer cells resulted in cyclooxygenase-2 (COX-2) upregulation and COX-2-derived PGE2 generation. At molecular level, COX-2 upregulation depended on HIF-1 activity. We previously reported that zinc treatment inhibits HIF-1 activity. Here, zinc supplementation to HIPK2 depleted cells inhibited HIF-1-induced COX-2 expression and PGE2/VEGF production. At translational level, while conditioned media of both siRNA control and HIPK2 depleted cells inhibited DCs maturation, conditioned media of only zinc-treated HIPK2 depleted cells efficiently restored DCs maturation, seen as the expression of co-stimulatory molecules CD80 and CD86, cytokine IL-10 release, and STAT3 phosphorylation.Conclusion/SignificanceThese findings show that: 1) HIPK2 knockdown induced COX-2 upregulation, mostly depending on HIF-1 activity; 2) zinc treatment downregulated HIF-1-induced COX-2 and inhibited PGE2/VEGF production; and 3) zinc treatment of HIPK2 depleted cells restored DCs maturation.

Highlights

Homeodomain interacting protein kinase 2 (HIPK2) is a multifunctional kinase whose activity restrains tumor progression
Analyses of datasets obtained from specimens of normal tissues and primary colon adenocarcinomas revealed an inverse correlation between Homeodomain-interacting protein kinase 2 (HIPK2) and COX-2 expression
HIPK2 expression was high in normal tissues and significantly reduced in colon adenocarcinomas, while COX-2 expression was low in normal tissues and significantly increased in colon adenocarcinomas (Fig. 1A)

Summary

Introduction

Homeodomain interacting protein kinase 2 (HIPK2) is a multifunctional kinase whose activity restrains tumor progression. Increased HIF-1a levels are frequently found in many human cancers and are stimulated by low oxygen and by genetic alterations In this regard, HIPK2 knockdown induces HIF-1a upregulation with increased HIF-1 activity leading to vascular endothelial growth (VEGF) production, tumor angiogenesis and chemoresistance [6,7]. Homeodomain-interacting protein kinase 2 (HIPK2) is a multifunctional protein that exploits its kinase activity to modulate key molecular pathways in cancer to restrain tumor growth and induce response to therapies. HIPK2 knockdown induces upregulation of oncogenic hypoxia-inducible factor-1 (HIF-1) activity leading to a constitutive hypoxic and angiogenic phenotype with increased tumor growth in vivo. HIPK2 inhibition, releases pathways leading to production of pro-inflammatory molecules such as vascular endothelial growth factor (VEGF) or prostaglandin E2 (PGE2). We evaluated the molecular mechanism of PGE2 production after HIPK2 depletion and how to modulate it

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