Hypoxia-induced macropinocytosis represents a metabolic route for liver cancer

Misty Shuo Zhang,Vincent Wai-Hin Yuen,Chi Ching Goh,Jane Di Cui,Carrie Yiling Chen,Derek Lee,Chun-Ming Wong,Irene Oi-Lin Ng,David Kung-Chun Chiu,Carmen Chak-Lui Wong,Macus Hao-Ran Bao,Aki Pui-Wah Tse,Jacinth Wing-Sum Cheu,Bowie Po Yee Wong

doi:10.1038/s41467-022-28618-9

Abstract

Hepatocellular carcinoma (HCC) invariably exhibits inadequate O2 (hypoxia) and nutrient supply. Hypoxia-inducible factor (HIF) mediates cascades of molecular events that enable cancer cells to adapt and propagate. Macropinocytosis is an endocytic process initiated by membrane ruffling, causing the engulfment of extracellular fluids (proteins), protein digestion and subsequent incorporation into the biomass. We show that macropinocytosis occurs universally in HCC under hypoxia. HIF-1 activates the transcription of a membrane ruffling protein, EH domain-containing protein 2 (EHD2), to initiate macropinocytosis. Knockout of HIF-1 or EHD2 represses hypoxia-induced macropinocytosis and prevents hypoxic HCC cells from scavenging protein that support cell growth. Germline or somatic deletion of Ehd2 suppresses macropinocytosis and HCC development in mice. Intriguingly, EHD2 is overexpressed in HCC. Consistently, HIF-1 or macropinocytosis inhibitor suppresses macropinocytosis and HCC development. Thus, we show that hypoxia induces macropinocytosis through the HIF/EHD2 pathway in HCC cells, harnessing extracellular protein as a nutrient to survive.

Highlights

Hepatocellular carcinoma (HCC) invariably exhibits inadequate O2 and nutrient supply
To study whether hypoxia affects the macropinocytic capacity of HCC cells, we evaluated the ability of HCC cells to form macropinosomes and degrade engulfed proteins under 21 and 1% O2 conditions
To study whether Eps15 homology-domain (EHD) contribute to hypoxia-induced macropinocytosis in HCC cells, we evaluated the expression levels of EHDs in various HCC cell lines exposed to 21% or 1% O2

Summary

Introduction

Hepatocellular carcinoma (HCC) invariably exhibits inadequate O2 (hypoxia) and nutrient supply. Hypoxia-inducible factor (HIF) mediates cascades of molecular events that enable cancer cells to adapt and propagate. Knockout of HIF-1 or EHD2 represses hypoxia-induced macropinocytosis and prevents hypoxic HCC cells from scavenging protein that support cell growth. We show that hypoxia induces macropinocytosis through the HIF/EHD2 pathway in HCC cells, harnessing extracellular protein as a nutrient to survive. For advanced HCC, two tyrosine-kinase inhibitors (TKIs), sorafenib and lenvatinib, are the major first-line targeted therapies, but they have a modest survival benefit of only 3 months[1,2]. Another TKI, regorafenib, and an immune-checkpoint inhibitor, nivolumab (anti-PD-1 antibody), are the second-line treatments for sorafenib-resistant HCC3,4. HIFs induce the less-active electron-transport-chain components, NUDFA4 mitochondrial complex-associated-like 2 (NDUFA4L2) and cytochrome c oxidase subunit IV isoform 2 (COX4–2), to decelerate electron transfer and reduce ROS accumulation[14,15]

Methods

Results

Conclusion