Regulation and functions of TRE17/ubiquitin-specific protease 6 (USP6) oncogene in aneurysmal bone cyst

Aneurysmal bone cyst (ABC) is a locally aggressive bone tumor characterized by extensive bone degradation and inflammatory recruitment, however its etiology remains poorly understood. Recent studies reveal that the TRE17 (a.k.a. ubiquitin specific protease 6, USP6) locus is a recurrent target of chromosomal translocation in ABC. The mechanism by which TRE17 contributes to formation of these complex lesions and the role of its USP activity in ABC pathogenesis has not been investigated.;The goal of my thesis has been to elucidate the molecular functions and regulation of TRE17. Given the central role that matrix proteases play in establishment of a degradative and inflammatory microenvironment, we explored whether TRE17 regulates the production of matrix proteases. We found that TRE17 induces the transcription of the matrix metalloproteinases MMP-9 and MMP-10, in a manner that requires its USP activity. Induction of these MMPs arises in part through activation of NF-kappaB, mediated by the RhoA GTPases and its effector ROCK. Xenografts of cell lines expressing wild type TRE17 yielded tumors that recapitulate various aspects of ABC pathology, including a richly vascularized loose bland spindle cell proliferation. TRE17 mutants defective in Arf6 activation or USP activity failed to induce tumor formation, revealing essential roles for both the TBC and USP domains in vivo .;In addition to the induction of MMPs, we also investigate other mechanisms of how TRE17 regulate degradation of microenvironment and cell invasion. Here, we identify a downstream effector of Cdc42 and Rac1, IQGAP1, binds directly to TRE17. Their interaction is negatively regulated by Ca2+/calmodulin. Furthermore, TRE17 and IQGAP1 co-localize in invadopodia-like structures along with F-actin and beta1-integrin, suggesting their potential in cell invasion.;In parallel with the studies above, we sought to identify mechanisms of TRE17 regulation. We identified the calcium-binding protein calmodulin (CaM) as a Ca2+-dependent binding partner of TRE17. We further found that TRE17 is mono-ubiquitinated, and promotes its own deubiquitination in vivo. These modifications are regulated by the association of TRE17 with CaM. Our work thus reveals a role for Ca2+/calmodulin in regulation of ubiquitination through its direct interaction with TRE17.;In summary, our studies define possible mechanisms by which TRE17 induces a degradative and inflammatory environment in ABC, as well as lend insights into its regulation.