Usp9x regulates Ets-1 ubiquitination and stability to control NRAS expression and tumorigenicity in melanoma

Harish Potu,Paul W Harms,Luke F Peterson,Alison Durham,Malathi Kandarpa,Hanshi Sun,Moshe Talpaz,Nicholas J Donato,Ugur Eskiocak,Peter C Hollenhorst,Anupama Pal

doi:10.1038/ncomms14449

Abstract

ETS transcription factors are commonly deregulated in cancer by chromosomal translocation, overexpression or post-translational modification to induce gene expression programs essential in tumorigenicity. Targeted destruction of these proteins may have therapeutic impact. Here we report that Ets-1 destruction is regulated by the deubiquitinating enzyme, Usp9x, and has major impact on the tumorigenic program of metastatic melanoma. Ets-1 deubiquitination blocks its proteasomal destruction and enhances tumorigenicity, which could be reversed by Usp9x knockdown or inhibition. Usp9x and Ets-1 levels are coincidently elevated in melanoma with highest levels detected in metastatic tumours versus normal skin or benign skin lesions. Notably, Ets-1 is induced by BRAF or MEK kinase inhibition, resulting in increased NRAS expression, which could be blocked by inactivation of Usp9x and therapeutic combination of Usp9x and MEK inhibitor fully suppressed melanoma growth. Thus, Usp9x modulates the Ets-1/NRAS regulatory network and may have biologic and therapeutic implications.

Highlights

ETS transcription factors are commonly deregulated in cancer by chromosomal translocation, overexpression or post-translational modification to induce gene expression programs essential in tumorigenicity
Tumour cells grown in 3D had higher levels of Usp9x activity/expression than those measured in 2D cultures and G9 inhibited Usp9x activity in cells from either culture condition (Fig. 1f)
We noted that melanoma was unexpectedly dependent on Usp9x for 3D growth and in vivo expansion, with potential Usp9x addiction noted in NRAS mutant melanoma

Summary

Introduction

ETS transcription factors are commonly deregulated in cancer by chromosomal translocation, overexpression or post-translational modification to induce gene expression programs essential in tumorigenicity. Targeted destruction of these proteins may have therapeutic impact. The ETS (E26 transformation-specific or E-twenty-six; based on the gene transduced by the leukaemia virus, E26) transcription factor family is composed of 28 members, which recognize a DNA binding sequence minimally consisting of GGA(A/T)[18,19,20] Specific members of this highly conserved family are frequently activated by chromosomal translocation, overexpression and stabilization (by altered ubiquitination) and are essential in tumorigenesis[21]. We provide evidence that Usp9x plays an important role in Ets-1 regulation and melanoma tumorigenicity, in part through NRAS transcription which may be of particular importance in tumours driven by NRAS mutation

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Conclusion