Data from Activation of Phosphatidylinositol-3′-kinase/AKT Signaling Is Essential in Hepatoblastoma Survival

Abstract

<div>Abstract<p><b>Purpose:</b> Hepatoblastoma represents the most frequent malignant liver tumor in childhood. The phosphatidylinositol-3′-kinase (PI3K)/AKT pathway is crucial in downstream signaling of multiple receptor tyrosine kinases of pathogenic importance in hepatoblastoma. Increased PI3K/AKT signaling pathway activity and activating mutations of <i>PIK3CA</i>, encoding a PI3K catalytic subunit, have been reported in different childhood tumors. The current study was done to analyze the role of PI3K/AKT signaling in hepatoblastoma.</p><p><b>Experimental Design:</b> Immunohistochemical stainings of (Ser473)-phosphorylated (p)-AKT protein, its targets p-(Ser9)-GSK-3β and p-(Ser2448)-mTOR, as well as the cell cycle regulators Cyclin D1, p27<sup>KIP1</sup>, and p21<sup>CIP1</sup> were done and the <i>PIK3CA</i> gene was screened for mutations. <i>In vitro</i>, two hepatoblastoma cell lines treated with the PI3K inhibitor LY294002 were analyzed for AKT and GSK-3β phosphorylation, cell proliferation, and apoptosis. Additionally, simultaneous treatments of hepatoblastoma with LY294002 and cytotoxic drugs were carried out.</p><p><b>Results:</b> Most tumors strongly expressed p-AKT, p-GSK-3β, and p-mTOR; subgroups showed significant Cyclin D1, p27<sup>KIP1</sup>, and p21<sup>CIP1</sup> expression. One hepatoblastoma carried an E545A mutation in the <i>PIK3CA</i> gene. <i>In vitro</i>, PI3K inhibition diminished hepatoblastoma cell growth being accompanied by reduced AKT and GSK-3β phosphorylation. Flow cytometry and 4', 6-diamidino-2-phenylindole stainings showed that PI3K pathway inhibition leads to a substantial increase in apoptosis and a decrease in cellular proliferation linked to reduced Cyclin D1 and increased p27<sup>KIP1</sup> levels. Simultaneous treatment of hepatoblastoma cell lines with LY294002 and cytotoxic drugs resulted in positive interactions.</p><p><b>Conclusions:</b> Our findings imply that PI3K signaling plays an essential role in growth control of hepatoblastoma and might be successfully targeted in multimodal therapeutic strategies.</p></div>