Deubiquitinase Usp9x Controls Tumorigenicity Through Regulation Of The Ets-1 Transcription Factor In Melanoma

Transcription factors are frequently deregulated in cancer cells and may be good therapeutic targets, but few successful targeting strategies have been reported. Deubiquitinases (DUBs) are specialized enzymes that regulate the ubiquitin (Ub) content on many proteins and DUB expression and activity are elevated in a number of cancers where they can act to alter tumor suppressor and/or oncoprotein levels. We previously described Usp9x activity and expression in melanoma; here we sought to investigate its role in primary melanoma and metastatic disease. Usp9x was upregulated in tumor cells compared to normal melanocytes and Usp9x expression and activity were found to be essential for 3D growth and melanoma tumor expansion in vivo. We defined the Usp9x ubiquitinated protein landscape and demonstrate that Usp9x regulates Ets-1, a cancer-promoting transcription factor. Usp9x binds, deubiquitinates and thereby stabilizes Ets-1 protein, and primary tissue and tumor analysis demonstrated elevated and coincident Usp9x/Ets-1 protein expression in melanoma compared to normal skin or benign nevi. Usp9x knockdown or Usp9x inhibition with small molecule G9 reduced Ets-1 protein levels and blocked tumor growth in vitro and in vivo. Conversely, Usp9x overexpression in melanoma cells increased Ets-1 protein levels and enhanced 3D tumor growth in vitro and in vivo, which were all reversible by treatment with G9. We conclude that Usp9x is essential for Ets-1 protein stability and may be therapeutically exploited with small molecule Usp9x inhibitors to reduce Ets-1-dependent gene expression and tumorigenicity. Citation Format: Harish Potu, Luke F. Peterson Peterson, Malathi Kandarpa Kandarpa, Anupama Pal Pal, Hanshi Sun Sun, Paul W. Harms Harms, Peter C. Hollenhorst Hollenhorst, Ugur Eskiocak Eskiocak, Moshe Talpaz Talpaz, Nicholas J. Donato Donato. Deubiquitinase Usp9x controls tumorigenicity through regulation of the Ets-1 transcription factor in melanoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 2881.