Targeting TROY-mediated p85[alpha]/AKT/TBX3 signaling attenuates tumor stemness and elevates treatment response in hepatocellular carcinoma

Abstract

Hepatocellular carcinoma (HCC) is the sixth commonest malignant tumor and the fourth universal cause of cancer death in 2018. Limited diagnostic indicators for early screening and restricted therapeutic strategies for cancer recurrence, metastasis, and chemoresistance are the main reasons for the high death rate in liver carcinoma. Cancer stem cells (CSCs) are a minor subset of tumor cells sharing analogical features with tissue progenitor cells such as capabilities of stemness maintenance and multi-lineage differentiation, which are necessary for cancer recurrence and metastasis. Research focusing on the phenotype and mechanism of cancer stem cells can offer new ideas for the explanation of the occurrence, development, and treatment of liver cancer. Using an in vitro hepatocyte differentiation model, we found that TROY was uniquely expressed in liver stem/progenitor cells and a small proportion of hepatocellular carcinoma cells, implying that TROY may play a crucial part in HCC stemness maintenance. The immunohistochemistry study using an HCC tissue microarray showed that a high probability of TROY-positive cells was detected in 53/130 (40.8%) of HCC cases, which was related to poor prognosis and tumor metastasis. Functional studies revealed that TROY could enhance tumorigenicity, cell motility, drug-resistance, and stemness ability of HCC cells. Mechanism study found that TROY could interact with PI3K subunit p85α, inducing its polyubiquitylation and degradation, and subsequently activate PI3K/AKT/TBX3 signaling in HCC. As an essential protein maintaining pluripotency, TBX3 transcriptionally upregulates pluripotent genes expression including SOX2, NANOG, and OCT4 in HCC cells. Interestingly, a tumor microenvironment study found that upregulation of TROY in HCC tissues was induced by TGF-β1 secreted from Cancer associated fibroblasts (CAFs). The therapeutic potential by targeting TROY-positive CSCs was also tested with PI3K inhibitor wortmannin. The result showed that wortmannin could effectively impair tumor stemness and sensitize tumor cells to sorafenib, elevating treatment response in HCCs. Taken together, we demonstrated that TROY is an HCC CSC marker and regulates the HCC stemness function. Targeting TROY-positive CSCs with PI3K inhibitor wortmannin in combination with chemo- or targeted drugs could be a new therapeutic approach for HCC patients.