Dankert John F, Pagan Julia K, Starostina Natalia G, Kipreos Edward T, Pagano Michele
a Department of Biochemistry and Molecular Pharmacology , New York University, School of Medicine , New York , NY , USA.
b Perlmutter NYU Cancer Center , New York University, School of Medicine , New York , NY , USA.
Cell Cycle. 2017 Mar 19;16(6):556-564. doi: 10.1080/15384101.2017.1284715. Epub 2017 Jan 24.
FEM1A, FEM1B, and FEM1C are evolutionarily-conserved VHL-box proteins, the substrate recognition subunits of CUL2-RING E3 ubiquitin ligase complexes. Here, we report that FEM1 proteins are ancient regulators of Stem-Loop Binding Protein (SLBP), a conserved protein that interacts with the stem loop structure located in the 3' end of canonical histone mRNAs and functions in mRNA cleavage, translation and degradation. SLBP levels are highest during S-phase coinciding with histone synthesis. The ubiquitin ligase complex SCF targets SLBP for degradation in G2 phase; however, the regulation of SLBP during other stages of the cell cycle is poorly understood. We provide evidence that FEM1A, FEM1B, and FEM1C interact with and mediate the degradation of SLBP. Cyclin F, FEM1A, FEM1B and FEM1C all interact with a region in SLBP's N-terminus using distinct degrons. An SLBP mutant that is unable to interact with all 4 ligases is expressed at higher levels than wild type SLBP and does not oscillate during the cell cycle. We demonstrate that orthologues of SLBP and FEM1 proteins interact in C. elegans and D. melanogaster, suggesting that the pathway is evolutionarily conserved. Furthermore, we show that FEM1 depletion in C. elegans results in the upregulation of SLBP ortholog CDL-1 in oocytes. Notably, cyclin F is absent in flies and worms, suggesting that FEM1 proteins play an important role in SLBP targeting in lower eukaryotes.
FEM1A、FEM1B和FEM1C是进化上保守的VHL-box蛋白，是CUL2-RING E3泛素连接酶复合物的底物识别亚基。在此，我们报告FEM1蛋白是茎环结合蛋白（SLBP）的古老调节因子，SLBP是一种保守蛋白，与位于经典组蛋白mRNA 3'端的茎环结构相互作用，并在mRNA切割、翻译和降解中发挥作用。SLBP水平在与组蛋白合成一致的S期最高。泛素连接酶复合物SCF在G2期靶向降解SLBP；然而，细胞周期其他阶段SLBP的调节机制尚不清楚。我们提供证据表明FEM1A、FEM1B和FEM1C与SLBP相互作用并介导其降解。细胞周期蛋白F、FEM1A、FEM1B和FEM1C都使用不同的降解结构域与SLBP N端的一个区域相互作用。一个无法与所有4种连接酶相互作用的SLBP突变体的表达水平高于野生型SLBP，并且在细胞周期中不发生振荡。我们证明SLBP和FEM1蛋白的直系同源物在秀丽隐杆线虫和黑腹果蝇中相互作用，表明该途径在进化上是保守的。此外，我们表明秀丽隐杆线虫中FEM1的缺失导致卵母细胞中SLBP直系同源物CDL-1的上调。值得注意的是，果蝇和蠕虫中不存在细胞周期蛋白F，这表明FEM1蛋白在低等真核生物中靶向SLBP方面发挥重要作用。
