The mitochondrial chaperone Prohibitin 1 negatively regulates interleukin-8 in human liver cancers

Jin Won Yang,Ben Murray,Lucia Barbier-Torres,Ting Liu,Zhenqiu Liu,Heping Yang,Wei Fan,Jiaohong Wang,Yuan Li,Ekihiro Seki,José M Mato,Shelly C Lu

doi:10.1074/jbc.ra118.004863

Abstract

Prohibitin 1 (PHB1) is a mitochondrial chaperone whose expression is dysregulated in cancer. In liver cancer, PHB1 acts as a tumor suppressor, but the mechanisms of tumor suppression are incompletely understood. Here we aimed to determine PHB1 target genes to better understand how PHB1 influences liver tumorigenesis. Using RNA-Seq analysis, we found interleukin-8 (IL-8) to be one of the most highly up-regulated genes following PHB1 silencing in HepG2 cells. Induction of IL-8 expression also occurred in multiple liver and nonliver cancer cell lines. We examined samples from 178 patients with hepatocellular carcinoma (HCC) and found that IL-8 mRNA levels were increased, whereas PHB1 mRNA levels were decreased, in the tumors compared with adjacent nontumorous tissues. Notably, HCC patients with high IL-8 expression have significantly reduced survival. An inverse correlation between PHB1 and IL-8 mRNA levels is found in HCCs with reduced PHB1 expression. To understand the molecular basis for these observations, we altered PHB1 levels in liver cancer cells. Overexpression of PHB1 resulted in lowered IL-8 expression and secretion. Silencing PHB1 increased c-Jun N-terminal kinase (JNK) and NF-κB activity, induced nuclear accumulation of c-JUN and p65, and enhanced their binding to the IL-8 promoter containing AP-1 and NF-κB elements. Conditioned medium from PHB1-silenced HepG2 cells increased migration and invasion of parental HepG2 and SK-hep-1 cells, and this was blocked by co-treatment with neutralizing IL-8 antibody. In summary, our findings show that reduced PHB1 expression induces IL-8 transcription by activating NF-κB and AP-1, resulting in enhanced IL-8 expression and release to promote tumorigenesis.

Highlights

Prohibitin 1 (PHB1) is a mitochondrial chaperone whose expression is dysregulated in cancer
PHB1 is best known as a mitochondrial chaperone protein, increasing evidence shows that it has many other important functions, some of which pertain to cancer
We found that PHB1 is mainly localized in the nucleus in three different hepatocellular carcinoma (HCC) cell types, including the HepG2, Huh7, and Hep3B cancer cell lines (Fig. S3)

Summary

Introduction

Prohibitin 1 (PHB1) is a mitochondrial chaperone whose expression is dysregulated in cancer. Reduced PHB1 expression occurs in patients with inflammatory bowel disease, a chronic inflammatory condition that predisposes to colon cancer, and overexpression of PHB1 inhibits colitis-associated colon cancer tumorigenesis in mice [9]. We found that hepatic PHB1 expression is down-regulated at the mRNA level in the majority of human patients with HCC and CCA, and reduced PHB1 expression increases the growth of HCC and CCA cells and inversely correlates with tumor growth in the murine CCA model [13]. Our findings are confirmed in human HCC samples and suggest that PHB1 plays an important role in suppressing the development of liver cancers by multiple mechanisms

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