Angiopoietin2 enhances doxorubin resistance in HepG2 cells by upregulating survivin and Ref-1 via MSK1 activation

• Angiopoietin2 (Ang2) promotes HepG2 cell from doxorubicin induced apoptosis via upregulation of Survivin and Ref-1.
• Ang2 activates ERK-MSK cascade to induce histone H3 phosphorylation and anti-apoptotic gene expression.
• Activation of MSK1 by Ang2 phosphorylates the CREB and the phosho-CREB is recruited to Ref-1 promoter.

Angiopoietin2 (Ang2) and its Tie2 receptor have extensive effects on tumor malignancy including angiogenesis and metastasis. In this study, we evaluated the protective effect of Ang2 on doxorubicin-induced apoptosis in HepG2 cells. Ang2 (400 ng/ml) attenuated doxorubicin-mediated cytotoxicity by upregulating the expression of Survivin and Ref-1, which was reversed by a soluble extracellular domain of Tie2. Mechanistic study showed Ang2 activated ERK–MSK cascade to induce histone H3 phosphorylation and inducible gene expression. The stimulatory effect of Ang2 on anti-apoptotic genes was attenuated by either MSK inhibitor (H89) or by overexpression of a kinase-deficient MSK1. Activated MSK1 phosphorylated the CREB at Ser133 and phosho-CREB was recruited to Ref-1 promoter rapidly to initiate the gene expression. Moreover, knockdown of MSK1 by specific siRNA also attenuated the pro-survival activity of Ang2 and CREB phosphorylation. Hence, our study suggests the existence of an Ang2−ERK−MSK signaling axis mediating survival responses and drug resistance of tumor cells.