SPIN1 promotes tumorigenesis by blocking the uL18 (universal large ribosomal subunit protein 18)-MDM2-p53 pathway in human cancer.

Ziling Fang,Kevin D Plummer,Jun Deng,Jun-Ming Liao,David Margolin,Kun Zhang,Bo Cao,Peng Liao,Tao Liu,Jianping Xiong,Hua Lu,Li Li,Shelya X Zeng,Wensheng Zhang

doi:10.7554/elife.31275

Abstract

Ribosomal proteins (RPs) play important roles in modulating the MDM2-p53 pathway. However, less is known about the upstream regulators of the RPs. Here, we identify SPIN1 (Spindlin 1) as a novel binding partner of human RPL5/uL18 that is important for this pathway. SPIN1 ablation activates p53, suppresses cell growth, reduces clonogenic ability, and induces apoptosis of human cancer cells. Mechanistically, SPIN1 sequesters uL18 in the nucleolus, preventing it from interacting with MDM2, and thereby alleviating uL18-mediated inhibition of MDM2 ubiquitin ligase activity toward p53. SPIN1 deficiency increases ribosome-free uL18 and uL5 (human RPL11), which are required for SPIN1 depletion-induced p53 activation. Analysis of cancer genomic databases suggests that SPIN1 is highly expressed in several human cancers, and its overexpression is positively correlated with poor prognosis in cancer patients. Altogether, our findings reveal that the oncogenic property of SPIN1 may be attributed to its negative regulation of uL18, leading to p53 inactivation.

Highlights

The well-documented tumor suppressor p53, referred as ‘the guardian of the genome’, is activated upon exposure to a myriad of cellular stresses
The mass spectrometric (MS) results revealed several previously described p53 regulatory proteins, such as Myb-binding protein 1A (MYBBP1A), Protein arginine N-methyltransferase 5 (PRMT5) and Serine/arginine-rich splicing factor 1 (SRSF1), as uL18 binding proteins (Table 1), and identified Spindlin 1 (SPIN1) as a novel uL18-binding protein candidate that was previously shown to play a role in tumorigenesis and rDNA transcription (Wang et al, 2012, 2011)
Only uL18, but not uL5, was co-immunoprecipitated with SPIN1. In line with this result, when comparing ectopic FlaguL18 with Flag-uL5 and Flag-uL14, we found that only uL18, but not the other Ribosomal proteins (RPs), could pull down Myc-SPIN1 (Figure 1E), further bolstering the specific interaction between uL18 and SPIN1. These results demonstrate that SPIN1 binds to uL18, but not uL5 or uL14, in cancer cells

Summary

Introduction

The well-documented tumor suppressor p53, referred as ‘the guardian of the genome’, is activated upon exposure to a myriad of cellular stresses. SPIN1 knockdown inhibited cell proliferation and induced apoptosis in a predominantly p53-dependent manner in vitro and in vivo, suppressing tumor growth in a xenograft model. These results for the first time demonstrate that SPIN1 can regulate the RP-MDM2-p53 pathway by directly interacting with uL18, and suggest SPIN1 as a potential molecule target in this pathway for developing anticancer therapy in the future

Results

Discussion

Materials and methods