The APC/C E3 Ligase Complex Activator FZR1 Restricts BRAF Oncogenic Function.


BRAF drives tumorigenesis by coordinating the activation of the RAS/RAF/MEK/ERK oncogenic signaling cascade. However, upstream pathways governing BRAF kinase activity and protein stability remain undefined. Here, we report that in primary cells with active APCFZR1, APCFZR1 earmarks BRAF for ubiquitination-mediated proteolysis, whereas in cancer cells with APC-free FZR1, FZR1 suppresses BRAF through disrupting BRAF dimerization. Moreover, we identified FZR1 as a direct target of ERK and CYCLIN D1/CDK4 kinases. Phosphorylation of FZR1 inhibits APCFZR1, leading to elevation of a cohort of oncogenic APCFZR1 substrates to facilitate melanomagenesis. Importantly, CDK4 and/or BRAF/MEK inhibitors restore APCFZR1 E3 ligase activity, which might be critical for their clinical effects. Furthermore, FZR1 depletion cooperates with AKT hyperactivation to transform primary melanocytes, whereas genetic ablation of Fzr1 synergizes with Pten loss, leading to aberrant coactivation of BRAF/ERK and AKT signaling in mice. Our findings therefore reveal a reciprocal suppression mechanism between FZR1 and BRAF in controlling tumorigenesis.Significance: FZR1 inhibits BRAF oncogenic functions via both APC-dependent proteolysis and APC-independent disruption of BRAF dimers, whereas hyperactivated ERK and CDK4 reciprocally suppress APCFZR1 E3 ligase activity. Aberrancies in this newly defined signaling network might account for BRAF hyperactivation in human cancers, suggesting that targeting CYCLIN D1/CDK4, alone or in combination with BRAF/MEK inhibition, can be an effective anti-melanoma therapy. Cancer Discov; 7(4); 424-41. ©2017 AACR.See related commentary by Zhang and Bollag, p. 356This article is highlighted in the In This Issue feature, p. 339.





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Publication Info

Wan, Lixin, Ming Chen, Juxiang Cao, Xiangpeng Dai, Qing Yin, Jinfang Zhang, Su-Jung Song, Ying Lu, et al. (2017). The APC/C E3 Ligase Complex Activator FZR1 Restricts BRAF Oncogenic Function. Cancer discovery, 7(4). pp. 424–441. 10.1158/2159-8290.CD-16-0647 Retrieved from

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Ming Chen

Associate Professor in Pathology

Our laboratory is interested in understanding the molecular and genetic events underlying cancer progression and metastasis. The focus of our work is a series of genetically engineered mouse models that faithfully recapitulate human disease. Using a combination of mouse genetics, omics technologies, cross-species analyses and in vitro approaches, we aim to identify cancer cell–intrinsic and –extrinsic mechanisms driving metastatic cancer progression, with a long–term goal of developing new therapeutic strategies for preventing and treating metastatic disease. 

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