Hypoxia upregulates Rab11-family interacting protein 4 through HIF-1α to promote the metastasis of hepatocellular carcinoma.

F Hu,W Chu,X Huo,Y Zhang,C Wang,W Qin,X Deng,D Gu,T Ge,X Yang,F Zhao,H Jin,Q Shen,J Fan,Q Luo,M Yao,H Shu,X Lv

doi:10.1038/onc.2015.49

Abstract

Hypoxic microenvironment is a powerful driving force for the invasion and metastasis of hepatocellular carcinoma (HCC). Hypoxia-inducible factor 1α (HIF-1α), as a crucial regulator of transcriptional responses to hypoxia, induces the expression of multiple target genes involved in different steps of HCC metastatic process. It is critical to find target genes associated with metastasis under hypoxia for shedding new light on molecular mechanism of HCC metastasis. In this study, we uncovered that hypoxia could induce the upregulation of Rab11-family interacting protein 4 (Rab11-FIP4) and activation of Rab11-FIP4 promoter by HIF-1α. The overexpression of Rab11-FIP4 significantly enhanced the mobility and invasiveness of HCC cells in vitro, also contributed to distant lung metastasis in vivo, whereas silencing of Rab11-FIP4 decreased the ability of migration and invasion in HCC cells in vitro and suppressed lung metastasis in vivo. Rab11-FIP4 facilitated HCC metastasis through the phosphorylation of PRAS40, which was regulated by mTOR. Furthermore, the expression level of Rab11-FIP4 was significantly increased in HCC tissues and high expression of Rab11-FIP4 was closely correlated with vascular invasion and poor prognosis in HCC patients. A markedly positive correlation between the expression of Rab11-FIP4 and HIF-1α was observed in HCC tissues and combination of Rab11-FIP4 and HIF-1α was a more valuable predictor of poor prognosis for HCC patients. In conclusion, Rab11-FIP4 is a target gene of HIF-1α and has a pro-metastatic role in HCC, suggesting that Rab11-FIP4 may be a promising candidate target for HCC treatment.

Highlights

Hepatocellular carcinoma (HCC) is one of the most frequently diagnosed malignancies[1] and the third most common cause of cancer-related death worldwide.[2]
Under hypoxia, Hypoxiainducible factor 1α (HIF-1α) is stable and translocates to the nucleus where it develops into a heterodimer with HIF-1β to activate transcription of target genes involved in tumor invasion, metastasis, angiogenesis and metabolism, by binding to hypoxia-responsive elements (HREs; 5’-RCGTG-3’) within the promoter of target genes.[12,13,14,15]
A known mammalian target of rapamycin (mTOR) pathway inhibitor, we found that phosphorylation levels of PRAS40 were downregulated in a concentration-dependent manner by rapamycin in HCC cells stably transfected with Rab11-FIP4, and the ability of migration and invasion of HCC cells stably transfected with Rab11-FIP4 was inhibited by rapamycin (Figures 7d and e)

Summary

Introduction

Hepatocellular carcinoma (HCC) is one of the most frequently diagnosed malignancies[1] and the third most common cause of cancer-related death worldwide.[2]. The tumor microenvironment has a key role in the initiation and progression of HCC, and hypoxia is a represented physicochemical feature of tumor microenvironment.[6] The existence of hypoxic microenvironment in HCC is due to an imbalance between inadequate oxygen supply from structurally and functionally abnormal tumor vasculature and increased oxygen consumption of dysregulated tumor cell proliferation.[7] It has been described that hypoxia contributes to the invasion and metastasis of HCC,[8,9,10] and the expression levels of hypoxia-inducible factor 1 (HIF-1) correlate with a worse prognosis of HCC patients.[11] HIF-1, acted as a critical regulator of adaptive responses to hypoxia in HCC cells including increased metastatic ability, induction of angiogenesis, and switch to glycolytic pathway,[7] is a heterodimeric protein consisted of a constitutively expressed HIF-1β subunit and an oxygen-regulated HIF-1α subunit. Under hypoxia, HIF-1α is stable and translocates to the nucleus where it develops into a heterodimer with HIF-1β to activate transcription of target genes involved in tumor invasion, metastasis, angiogenesis and metabolism, by binding to hypoxia-responsive elements (HREs; 5’-RCGTG-3’) within the promoter of target genes.[12,13,14,15]

Methods

Results

Conclusion