EBF1-Mediated Upregulation of Ribosome Assembly Factor PNO1 Contributes to Cancer Progression by Negatively Regulating the p53 Signaling Pathway.

Aling Shen,Qiongyu Li,Liya Liu,Yue Huang,Na Yu,Thomas J Sferra,Zhiqing Shen,Meizhu Wu,Liman Qiu,Jiumao Lin,Fei Qi,Xiangyan Wu,Hongwei Chen,Jun Peng,Youqin Chen

doi:10.1158/0008-5472.can-18-3238

Abstract

The RNA-binding protein PNO1 is critical for ribosome biogenesis, but its potential role in cancer remains unknown. In this study, online data mining, cDNA, and tissue microarrays indicated that PNO1 expression was higher in colorectal cancer tissue than in noncancerous tissue, and its overexpression was associated with worse patient survival. Gain-of-function and loss-of-function studies demonstrated that PNO1 knockdown suppressed growth of colorectal cancer cells in vitro and in vivo, while PNO1 overexpression promoted colorectal cancer cell proliferation in vitro. In colorectal cancer cells expressing wild-type p53, PNO1 knockdown enhanced expression of p53 and its downstream gene p21, and reduced cell viability; these effects were prevented by p53 knockout and attenuated by the p53 inhibitor PFT-α. Moreover, PNO1 knockdown in HCT116 cells decreased levels of 18S rRNA, of 40S and 60S ribosomal subunits, and of the 80S ribosome. It also reduced global protein synthesis, increasing nuclear stress and inhibiting MDM2-mediated ubiquitination and p53 degradation. Overexpressing EBF1 suppressed PNO1 promoter activity and decreased PNO1 mRNA and protein, inhibiting cell proliferation and inducing cell apoptosis through the p53/p21 pathway. In colorectal cancer tissues, the expression of EBF1 correlated inversely with PNO1. Data mining of online breast and lung cancer databases showed increased PNO1 expression and association with poor patient survival; PNO1 knockdown reduced cell viability of cultured breast and lung cancer cells. Taken together, these findings indicate that PNO1 is overexpressed in colorectal cancer and correlates with poor patient survival, and that PNO1 exerts oncogenic effects, at least, in part, by altering ribosome biogenesis. SIGNIFICANCE: This study identifies the ribosome assembly factor PNO1 as a potential oncogene involved in tumor growth and progression of colorectal cancer.

Highlights

Colorectal cancer is the third most common cancer and fourth leading cause of cancer-related death worldwide, with 1.2 million new cases and over 600,000 deaths each year [1, 2]
Quantitative PCR of an independent sample of 50 colorectal cancer cases previously collected from our laboratory showed that levels of partner of NOB1" (PNO1) mRNA were elevated in colorectal cancer (Fig. 2A), and these results were confirmed by Western blot analysis (Fig. 2B; n 1⁄4 12) and IHC (Fig. 2C; n 1⁄4 10)
Quantitative PCR analysis of a cDNA array based on a commercially available set of 80 colorectal cancer primary lesions and 15 noncancerous surrounding tissues (Shanghai Outdo Biotech) showed increased PNO1 expression in colorectal cancer (Fig. 2D), but no significant relationship was observed between PNO1 mRNA and patient survival

Summary

Introduction

Colorectal cancer is the third most common cancer and fourth leading cause of cancer-related death worldwide, with 1.2 million new cases and over 600,000 deaths each year [1, 2]. Despite recent progress in treatment, outcomes in colorectal cancer remain poor. A better understanding of the molecular mechanisms of colorectal cancer is urgently required, as is the discovery of new. Note: Supplementary data for this article are available at Cancer Research Online (http://cancerres.aacrjournals.org/).

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