Oncogenic Y641 mutations in EZH2 prevent Jak2/β-TrCP-mediated degradation

Abstract

EZH2 (enhancer of zeste homolog 2) is a critical enzymatic subunit of the polycomb repressive complex 2 (PRC2), which trimethylates histone H3 (H3K27) to mediate gene repression. Somatic mutations, overexpression and hyperactivation of EZH2 have been implicated in the pathogenesis of several forms of cancer. In particular, recurrent gain-of-function mutations targeting EZH2 Y641 occur most frequently in follicular lymphoma and aggressive diffuse large B-cell lymphoma and are associated with H3K27me3 hyperactivation, which contributes to lymphoma pathogenesis. However, the post-translational mechanisms of EZH2 regulation are not completely understood. Here we show that EZH2 is a novel interactor and substrate of the SCF E3 ubiquitin ligase β-TrCP (FBXW1). β-TrCP ubiquitinates EZH2 and Jak2-mediated phosphorylation on Y641 directs β-TrCP-mediated EZH2 degradation. RNA interference-mediated silencing of β-TrCP or inhibition of Jak2 results in EZH2 stabilization with attendant increase in H3K27 trimethylation activity. Importantly, the EZH2(Y641) mutants recurrently implicated in lymphoma pathogenesis are unable to bind β-TrCP. Further, endogenous EZH2(Y641) mutants in lymphoma cells exhibit increased EZH2 stability and H3K27me3 hyperactivity. Our studies demonstrate that β-TrCP has an important role in controlling H3K27 trimethylation activity and lymphoma pathogenesis by targeting EZH2 for degradation.

EZH2 phosphorylation by JAK3 mediates a switch to noncanonical function in natural killer/T-cell lymphoma

“…20,[23][24][25] Intriguingly, JAK2 has been found in a recent study to phosphorylate EZH2 at tyrosine 641 (Y641), which promotes the interaction of EZH2 with E3 ubiquitin ligase b-TrCP and degradation of EZH2. 26 On the other hand, our study in NKTL shows a distinct mechanism by which JAK3-mediated EZH2 phosphorylation at Y244 converts EZH2 silencing activity into an activating effector. We point out that the possibility of Y641 as a potential phosphorylation site in EZH2 mediating the effects of JAK3 in NKTL can be ruled out for 3 reasons.…”

A novel recurrent NPM1-TYK2 gene fusion in cutaneous CD30-positive lymphoproliferative disorders

“…The NPM1-TYK2 fusion gene was amplified from MyLa cells and cloned into a mammalian expression vector for functional studies. Stable MyLa cell lines depleted of TYK2 were generated using lentiviral-mediated gene transduction 6 of short hairpin RNAs (shRNAs) and used in cell proliferation assays.…”

Fbxo45 Inhibits Calcium-sensitive Proteolysis of N-cadherin and Promotes Neuronal Differentiation

“…FLAG-tagged F-box protein constructs, including Fbxl1(Skp2), Fbxw1(␤-TrCP), Fbxw2, Fbxw4, Fbxw5, Fbxw7, and Fbxo22 were kindly pro-vided by Dr. Michele Pagano. Both Skp2 and ␤-TrCP were also subcloned into the tandem affinity purification tag vector (20). Skp1 and N-cadherin cDNAs were obtained from Open Biosystems.…”