PCK1 negatively regulates cell cycle progression and hepatoma cell proliferation via the AMPK/p27Kip1 axis

Lin Tuo,Yuan Hu,Jin Xiang,Xuanming Pan,Li Liang,Ni Tang,Jieli Hu,Hua Tang,Ailong Huang,Wenlu Zhang,Jie Xia,Kai Wang

doi:10.1186/s13046-019-1029-y

Abstract

BackgroundAltered glucose metabolism endows tumor cells with metabolic flexibility for biosynthesis requirements. Phosphoenolpyruvate carboxykinase 1 (PCK1), a key enzyme in the gluconeogenesis pathway, is downregulated in hepatocellular carcinoma (HCC) and predicts poor prognosis. Overexpression of PCK1 has been shown to suppress liver tumor growth, but the underlying mechanism remains unclear.MethodsmRNA and protein expression patterns of PCK1, AMPK, pAMPK, and the CDK/Rb/E2F pathway were determined using qRT-PCR and western blotting. Cell proliferation ability and cell cycle were assessed by MTS assay and flow cytometric analysis. The effect of PCK1 on tumor growth was examined in xenograft implantation models.ResultsBoth gain and loss-of-function experiments demonstrated that PCK1 deficiency promotes hepatoma cell proliferation through inactivation of AMPK, suppression of p27Kip1 expression, and stimulation of the CDK/Rb/E2F pathway, thereby accelerating cell cycle transition from the G1 to S phase under glucose-starved conditions. Overexpression of PCK1 reduced cellular ATP levels and enhanced AMPK phosphorylation and p27Kip1 expression but decreased Rb phosphorylation, leading to cell cycle arrest at G1. AMPK knockdown significantly reversed G1-phase arrest and growth inhibition of PCK1-expressing SK-Hep1 cells. In addition, the AMPK activator metformin remarkably suppressed the growth of PCK1-knockout PLC/PRF/5 cells and inhibited tumor growth in an orthotropic HCC mouse model.ConclusionThis study revealed that PCK1 negatively regulates cell cycle progression and hepatoma cell proliferation via the AMPK/p27Kip1 axis and supports a potential therapeutic and protective effect of metformin on HCC.

Highlights

Altered glucose metabolism endows tumor cells with metabolic flexibility for biosynthesis requirements
Phosphoenolpyruvate carboxykinase 1 (PCK1) suppresses hepatoma cell proliferation via G1 to S phase (G1/S) phase cell cycle arrest Previous studies have indicated that PCK1 expression is significantly lower in tumor tissues than in normal liver tissues and that downregulated PCK1 expression correlates with poor prognosis [18, 19]
The present study revealed that the gluconeogenic enzyme PCK1 negatively regulates cell cycle progression and cellular proliferation via the 5’-AMP-activated protein kinase (AMPK)/p27Kip1 axis, indicating a tumor suppressor role for PCK1 in hepatocellular carcinoma (HCC)

Summary

Introduction

Altered glucose metabolism endows tumor cells with metabolic flexibility for biosynthesis requirements. Tumor cells undergo aerobic glycolysis even in the presence of oxygen, known as the Warburg effect, which is critical for meeting the metabolic requirements of rapid cancer cell growth and proliferation [2]. Cancer cells require sufficient glucose to facilitate rapid tumor growth through the generation of building blocks, which are necessary for the synthesis of essential cellular components [9, 11]. Cancer cells require delicate energy sensing and metabolic adaptation pathways. Mammalian AMP-activated protein kinase (AMPK) is a central cellular sensor of adenine nucleotides that plays a key role in sensing cellular energy availability and regulating metabolic adaptation pathways [11, 12]. AMPK activation has been reported to suppress cell proliferation by regulating cell cycle progression or inhibiting the synthesis of certain proteins, such as p27Kip1 [14,15,16]

Methods

Results

Discussion

Conclusion