MAZ promotes prostate cancer bone metastasis through transcriptionally activating the KRas-dependent RalGEFs pathway

Qing Yang,Chuandong Lang,Yuhu Dai,Shuai Huang,Zhengquan Wu,Shaofu He,Wei Guo,Dong Ren,Xinsheng Peng,Hong Du

doi:10.1186/s13046-019-1374-x

Abstract

BackgroundClinically, prostate cancer (PCa) exhibits a high avidity to metastasize to bone. Myc-associated zinc-finger protein (MAZ) is a well-documented oncogene involved in the progression and metastasis of multiple cancer types, even in PCa. However, the clinical significance and biological roles of MAZ in bone metastasis of PCa remain unclear.MethodsMAZ expression was examined in PCa tissues with bone metastasis, PCa tissues without bone metastasis and metastatic bone tissues by real-time PCR and immunohistochemistry (IHC), respectively. Statistical analysis was performed to evaluate the clinical correlation between MAZ expression and clinicopathological features and bone metastasis-free survival in PCa patients. Biological roles of MAZ in bone metastasis of PCa were investigated both in vitro by transwell assay, and in vivo by a mouse model of left cardiac ventricle inoculation. The bioinformatics analysis, western blot, pull-down assays, chromatin immunoprecipitation (ChIP) and luciferase reporter assays were applied to demonstrate and examine the relationship between MAZ and its potential downstream signalling pathway. TaqMan copy number assay was performed to identify the underlying mechanism responsible for MAZ overexpression in PCa tissues.ResultsMAZ expression is elevated in PCa tissues with bone metastasis compared with that in PCa tissues without bone metastasis, and is further increased in metastatic bone tissues. High expression of MAZ positively correlates with poor overall and bone metastasis-free survival in PCa patients. Upregulating MAZ elevates, while silencing MAZ represses the invasion and migration abilities of PCa cells in vitro and bone metastasis ability in vivo. Our results further reveal that MAZ promotes bone metastasis of PCa dependent on KRas signalling, although MAZ transcriptionally upregulates KRas and HRas expression, where the Ral guanine nucleotide exchange factor (RalGEF) signaling is responsible for the different roles of KRas and HRas in mediating the pro-bone metastasis of MAZ in PCa. Finally, our results indicate that recurrent gains contribute to MAZ overexpression in a small portion of PCa tissues.ConclusionThese results indicate that the MAZ/Kras/ RalGEF signalling axis plays a crucial role in promoting PCa cell bone metastasis, suggesting a potential therapeutic utility of MAZ in bone metastasis of PCa.

Highlights

Prostate cancer (PCa) exhibits a high avidity to metastasize to bone
By in vitro and in vivo experiments, our research firstly proves that Myc-associated zincfinger protein (MAZ)/Kras/ Ral guanine nucleotide exchange factor (RalGEF) signaling axis plays an important role in the bone metastasis of PCa, suggesting a potential therapeutic utility of MAZ in bone metastasis of PCa
We further inspected the expression of MAZ in these tissues and found that it was upregulated in PCa tissues with bone metastasis (PCa/BM) compared with PCa/nBM and was further increased in metastatic bone tissues (Fig. 1b)

Summary

Introduction

Prostate cancer (PCa) exhibits a high avidity to metastasize to bone. Myc-associated zincfinger protein (MAZ) is a well-documented oncogene involved in the progression and metastasis of multiple cancer types, even in PCa. The Ras gene family consists of 3 functional genes, H-Ras, KRas and N-Ras, which primarily regulate multiple downstream signalling pathways, including the Ras–Raf–mitogen-activated and extracellular-signal regulated kinase kinase (MEK)–extracellular signal-regulated kinase (ERK) cascade, phosphatidylinositol 3-kinase (PI3K), and members of the Ral guanine nucleotide exchange factor (RalGEF) family [15]. All three of these signalling pathways have been proven to be critical for bone metastasis in various types of cancer, including PCa. For example, Ni et al have informed that PI3K/Akt signaling -mediated stabilization of histone methyltransferase WHSC1 greatly raised bone metastasis in PCa [16].

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