The APC/C E3 ligase complex activator fzr1 restricts braf oncogenic function

Lixin Wan, Ming Chen, Juxiang Cao, Xiangpeng Dai, Qing Yin, Jinfang Zhang, Su Jung Song, Ying Lu, Jing Liu, Hiroyuki Inuzuka, Jesse M. Katon, Kelsey Berry, Jacqueline Fung, Christopher Ng, Pengda Liu, Min Sup Song, Lian Xue, Roderick T. Bronson, Marc W. Kirschner, Rutao CuiPier Paolo Pandolfi, Wenyi Wei

Research output: Contribution to journalArticlepeer-review

57 Scopus citations


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 mel-anocytes, 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.

Original languageEnglish
Pages (from-to)424-441
Number of pages18
JournalCancer Discovery
Issue number4
StatePublished - Apr 2017
Externally publishedYes


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