Magnolol promotes the autophagy of esophageal carcinoma cells by upregulating HACE1 gene expression

Abstract

Esophagus cancer (EC) is one of the most aggressive malignant digestive system tumors and has a high clinical incidence worldwide. Magnolol, a natural compound, has anticancer effects on many cancers, including esophageal carcinoma, but the underlying mechanism has not been fully elucidated. Here, we first find that magnolol inhibits the proliferation of esophageal carcinoma cells and enhances their autophagy activity in a dose- and time-dependent manner. This study demonstrates that magnolol increases the protein levels of LC3 II, accompanied by increased HACE1 protein levels in both esophageal carcinoma cells and xenograft tumors. HACE1-knockout (KO) cell lines are generated, and the ablation of HACE1 eliminates the anti-proliferative and autophagy-inducing effects of magnolol on esophageal carcinoma cells. Additionally, our results show that magnolol primarily promotes HACE1 expression at the transcriptional level. Therefore, this study shows that magnolol primarily exerts its antitumor effect by activating HACE1-OPTN axis-mediated autophagy. It can be considered a promising therapeutic drug for esophageal carcinoma.

1. Introduction

Esophagus cancer (EC) is one of the most aggressive malignant tumors and is a highly prevalent malignancy worldwide. It ranks first for mortality of digestive system tumors in the United States [1]. The five-year survival rate for EC patients is only 20%, which is slightly higher than the 10% survival rate for patients with pancreatic cancer [1]. EC is divided into two categories: esophagus adenocarcinoma (EADC) and esophagus squamous cell carcinoma (ESCC). EADC accounts for the majority of oesophageal cancer patients in high-income countries. However, more than 90% of oesophageal cancer cases in China are ESCC [2]. The main risk factors for ESCC include smoking, alcohol consumption, nutritional deficiencies, and gene mutations [3‒5].

Currently, surgery remains the most effective therapeutic method for patients with EC without metastasis. Unfortunately, most patients are diagnosed at an advanced stage of the disease [3,6]. Metastatic EC is commonly treated with chemotherapy and radiation therapy, which can cause severe side effects [7,8]. However, natural compounds can be a viable alternative for treatment due to their high specificity, low cost, and few side effects. The antioxidant and antitumor properties of natural compounds found in vegetables, fruits, and herbs are currently being extensively studied [9‒11]. Previous studies have shown that natural compounds can inhibit the growth of cancer cells and reduce cancer relapse and metastasis in patients with EC [12,13].

Magnolol, also known as 5,5′-diallyl-2,2′-dihydroxybiphenyl, is extracted from Magnolia officinalis, a famous traditional Chinese medicine. At low concentrations, it has been found to possess antitumor properties in various cancers, including human hepatocellular carcinoma cells, esophageal cancer cells, and lung squamous carcinoma cells [3,14,15]. Autophagy is a conserved metabolic pathway in eukaryotes that plays a crucial role in carcinogenesis and cancer therapy [16,17]. It is widely accepted that autophagy exerts an inhibitory effect during the early stages of tumorigenesis [18]. Autophagy can limit cytoplasmic damage, genomic instability, and inflammation, thereby inhibiting the initiation of tumorigenesis [16]. Loss of certain autophagy-related genes can lead to cancer. For example, Beclin1 is monoallelically deleted in half of breast, ovarian, and prostate cancers [19,20]. Mutations in the ATG2B, ATG5, ATG9B, and ATG12 genes are frequently reported in colorectal and gastric cancers [21].