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

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.