The Arabidopsis CUL4-DDB1 complex interacts with MSI1 and is required to maintainMEDEAparental imprinting

Abstract

Protein ubiquitylation regulates a broad variety of biological processes in all eukaryotes. Recent work identified a novel class of cullin-containing ubiquitin ligases (E3s) composed of CUL4, DDB1, and one WD40 protein, believed to act as a substrate receptor. Strikingly, CUL4-based E3 ligases (CRL4s) have important functions at the chromatin level, including responses to DNA damage in metazoans and plants and, in fission yeast, in heterochromatin silencing. Among putative CRL4 receptors we identified MULTICOPY SUPPRESSOR OF IRA1 (MSI1), which belongs to an evolutionary conserved protein family. MSI1-like proteins contribute to different protein complexes, including the epigenetic regulatory Polycomb repressive complex 2 (PRC2). Here, we provide evidence that Arabidopsis MSI1 physically interacts with DDB1A and is part of a multimeric protein complex including CUL4. CUL4 and DDB1 loss-of-function lead to embryo lethality. Interestingly, as in fis class mutants, cul4 mutants exhibit autonomous endosperm initiation and loss of parental imprinting of MEDEA, a target gene of the Arabidopsis PRC2 complex. In addition, after pollination both MEDEA transcript and protein accumulate in a cul4 mutant background. Overall, our work provides the first evidence of a physical and functional link between a CRL4 E3 ligase and a PRC2 complex, thus indicating a novel role of ubiquitylation in the repression of gene expression.

Epigenetic regulation of Kcna3 -encoding Kv1.3 potassium channel by cereblon contributes to regulation of CD4 + T-cell activation

“…Recent studies have shown that Cul4A, which binds to CRBN, plays a role in histone modification (12)(13)(14)(15). Moreover, analysis of the relative levels of Cul4A transcripts in multiple tissue types using the Novartis BioGPS expression array database (9) revealed that, like CRBN, Cul4A is expressed to the greatest extent in lymphoid cells (including CD4 + T cells) compared with other cell types (Fig.…”

RNAi and Heterochromatin Assembly

“…We know that, in some cases, DNA methylation and H3K9me2 in heterochromatic regions act to reinforce each other, bypassing the role of RNAi in heterochromatin maintenance. Interestingly, mutants in DNA polymerase epsilon and cullin 4, components of the Clr4-containing CLRC complex in S. pombe, relieve silencing of some RNAi-sensitive transgenes in Arabidopsis, implicating that it is a cell-cycle-restricted process in plants as well (Yin et al 2009;del Olmo et al 2010;Dumbliauskas et al 2011;Pazhouhandeh et al 2011). Furthermore, some of these mutants have elevated levels of HR repair, and Ago2 itself has been implicated in HR repair of double-strand breaks (Wei et al 2012), reminiscent of the role of DNA replication and repair in heterochromatic silencing and spreading in S. pombe Zaratiegui et al 2011).…”

Arabidopsis WD REPEAT DOMAIN55 Interacts with DNA DAMAGED BINDING PROTEIN1 and Is Required for Apical Patterning in the Embryo

“…Mutation of Arabidopsis CUL4 affects embryo and endosperm development and leads to recessive seed abortion as well as a small decrease in male and female gametophyte transmission, indicating that CUL4 is essential for seed development (Dumbliauskas et al, 2011). Arabidopsis has two DDB1 paralogs sharing more than 90% protein identity: DDB1A and DDB1B, both interacting with CUL4 (Schroeder et al, 2002).…”

“…Arabidopsis has two DDB1 paralogs sharing more than 90% protein identity: DDB1A and DDB1B, both interacting with CUL4 (Schroeder et al, 2002). ddb1a ddb1b double mutants have shown a critical requirement for DDB1 function both in embryo development as well as gametophyte development or function (Bernhardt et al, 2010;Dumbliauskas et al, 2011). DDB1 proteins are adaptors that bridge CUL4 to the substrate receptors referred to as DDB1-CUL4 associated factor (DCAF) proteins (Angers et al, 2006;He et al, 2006;Higa et al, 2006;Lee et al, 2008).…”