PRR34-AS1 promotes mitochondrial division and glycolytic reprogramming in hepatocellular carcinoma cells through upregulation of MIEF2

Abstract

LncRNA PRR34-AS1 overexpression promotes the proliferation and invasion of hepatocellular carcinoma (HCC) cells, but whether it affects HCC energy metabolism remains unclear. Mitochondrial division and glycolytic reprogramming play important roles in tumor development. In this study, the differential expression of PRR34-AS1 is explored via TCGA analysis, and higher levels of PRR34-AS1 are detected in patients with liver cancer than in healthy individuals. A series of experiments, such as CCK-8, PCR, and immunofluorescence staining, reveal that the proliferation, invasion, glycolysis, and mitochondrial division of PRR34-AS1-overexpressing hepatoma cells are significantly promoted. TCGA analysis and immunohistochemistry reveal high expression of the mitochondrial dynamin MIEF2 in liver cancer tissues. Dual-luciferase reporter assays confirm that miR-498 targets and binds to mitochondrial elongation factor 2 (MIEF2). In addition, we show that PRR34-AS1 can sponge miR-498. Therefore, we further investigate the effects of the lncRNA PRR34-AS1/miR-498/MIEF2 axis on the growth, glucose metabolism, and mitochondrial division in hepatocellular carcinoma cells. A series of experiments are performed on hepatocellular carcinoma cells after different treatments. The results show that the proliferative activity, invasive ability, and glycolytic level of hepatocellular carcinoma cells are decreased in HCC cells with low PRR34-AS1 expression, and the miR-498 expression level is increased in these cells. Inhibition of miR-498 or overexpression of MIEF2 restored the proliferative activity, invasive ability, glycolysis, and mitochondrial division in hepatocellular carcinoma cells. Thus, PRR34-AS1 regulates MIEF2 by sponging miR-498, thereby promoting mitochondrial division, mediating glycolytic reprogramming and ultimately driving the growth and invasion of HCC cells. Furthermore, in vivo mouse experiments yield results similar to those of the in vitro experiments, verifying the above results.

1. Introduction

Hepatocellular carcinoma (HCC) is one of the most common clinical malignant tumors, and its mortality rate ranks the third [1]. Liver cancer can be classified as a primary or secondary tumor, and 90% of primary liver cancers are liver hepatocellular carcinoma (LIHC) [2]. Surgical resection can be performed for early-stage liver cancer [3]. However, the proportion of patients with early-stage liver cancer is relatively small, and fewer than 15% of patients are good candidates for surgical treatment [4]. Treatment options for advanced HCC are severely limited. Systemic chemotherapy is the preferred treatment for advanced HCC. However, due to drug resistance mechanisms, treatment efficacy is low. Therefore, new targets are urgently needed to increase therapeutic efficacy and improve patient prognosis.

PRR34-AS1 is a newly discovered lncRNA. Previous studies have shown that it participates in various biological behaviors of liver cancer cells by regulating mRNA expression. PRR34-AS1 has been described as a proto-oncogene and is thus a new biological target for liver cancer research [5,6]. Our previous study revealed that PRR34-AS1 can bind to miR-498 and that overexpression of PRR34-AS1 can upregulate the expressions of mitochondrial outer membrane 20 (TOMM20) and integrin subunit alpha 6 (ITGA6) and inhibit miR-498 expression. Thus, these factors may regulate the proliferation, migration, and invasion of hepatoma cells [6].

Mitochondrial division and fusion homeostasis are required for mitochondrial functions [7]. Previous studies in various malignant tumors have shown that mitochondrial division in tumor cells is abnormally activated. Activated mitochondrial division can further promote tumor progression [8‒10]. During the process of mitochondrial division, the dynamin protein Drp1 located in the cytoplasm is activated, translocates to the mitochondria and is located at the potential division site together with Fis1. Subsequently, the two cooperate to form a ring structure and promote the division of mitochondria [11]. Mitochondrial elongation factor 2 (MIEF2) is a key regulator of mitochondrial dynamics, and overexpression of MIEF2 induces the accumulation of Drp1 in the mitochondrial outer membrane [12], thus promoting mitochondrial division. Some studies have shown that mitochondrial division may play a role in tumors by generating energy products through the preferential use of glycolysis, increasing the biosynthesis of macromolecules, changing tumor metabolism, and promoting tumor cell proliferation [13].

The reprogramming of energy metabolism in tumor cells, especially glucose metabolism reprogramming, has received increasing attention from researchers [14]. In liver cancer, the reprogramming of glucose metabolism is a hallmark, and understanding the underlying mechanisms is crucial for developing targeted therapies.