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Cancer Discov. 2017 Apr;7(4):424-441. doi: 10.1158/2159-8290.CD-16-0647. Epub 2017 Feb 7.

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

Author information

1
Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts. wwei2@bidmc.harvard.edu lixin.wan@moffitt.org caojuxi@gmail.com rutaocui@bu.edu ppandolf@bidmc.harvard.edu.
2
Department of Molecular Oncology, H. Lee Moffitt Cancer Center and Research Institute, Tampa, Florida.
3
Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
4
Department of Pharmacology and Experimental Therapeutics, Boston University School of Medicine, Boston, Massachusetts. wwei2@bidmc.harvard.edu lixin.wan@moffitt.org caojuxi@gmail.com rutaocui@bu.edu ppandolf@bidmc.harvard.edu.
5
Department of Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts.
6
Department of Systems Biology, Harvard Medical School, Boston, Massachusetts.
7
Center for Mitochondrial Biology and Medicine, The Key Laboratory of Biomedical Information Engineering of Ministry of Education, School of Life Science and Technology and Frontier Institute of Life Science, FIST, Xi'an Jiaotong University, Xi'an 710049, P.R. China.
8
Department of Molecular and Cellular Oncology, The University of Texas MD Anderson Cancer Center, Houston, Texas.
9
Department of Microbiology and Immunobiology, Harvard Medical School, Boston, Massachusetts.
10
Cancer Research Institute, Beth Israel Deaconess Cancer Center, Department of Medicine and Pathology, Beth Israel Deaconess Medical Center, Harvard Medical School, Boston, Massachusetts. wwei2@bidmc.harvard.edu lixin.wan@moffitt.org caojuxi@gmail.com rutaocui@bu.edu ppandolf@bidmc.harvard.edu.

Abstract

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.

PMID:
28174173
PMCID:
PMC5380472
DOI:
10.1158/2159-8290.CD-16-0647
[Indexed for MEDLINE]
Free PMC Article

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