Arabidopsis CRL4 Complexes: Surveying Chromatin States and Gene Expression.

Sandra Fonseca,Vicente Rubio

doi:10.3389/fpls.2019.01095

Abstract

CULLIN4 (CUL4) RING ligase (CRL4) complexes contain a CUL4 scaffold protein, associated to RBX1 and to DDB1 proteins and have traditionally been associated to protein degradation events. Through DDB1, these complexes can associate with numerous DCAF proteins, which directly interact with specific targets promoting their ubiquitination and subsequent degradation by the proteasome. A characteristic feature of the majority of DCAF proteins that associate with DDB1 is the presence of the DWD motif. DWD-containing proteins sum up to 85 in the plant model species Arabidopsis. In the last decade, numerous Arabidopsis DWD proteins have been studied and their molecular functions uncovered. Independently of whether their association with CRL4 has been confirmed or not, DWD proteins are often found as components of additional multimeric protein complexes that play key roles in essential nuclear events. For most of them, the significance of their complex partnership is still unexplored. Here, we summarize recent findings involving both confirmed and putative CRL4-associated DCAF proteins in regulating nuclei architecture remodelling, DNA damage repair, histone post-translational modification, mRNA processing and export, and ribosome biogenesis, that definitely have an impact in gene expression and de novo protein synthesis. We hypothesized that, by maintaining accurate levels of regulatory proteins through targeted degradation and transcriptional control, CRL4 complexes help to surveil nuclear processes essential for plant development and survival.

Highlights

Proteins participate in every function of a living cell, from metabolic to signalling events, and as cellular structural components
Arabidopsis CDDD subunit COP10, which corresponds to an E2 Ub variant, has been shown to enhance the Ub binding activity of genuine E2 enzymes in vitro, including UBIQUITIN CONJUGATING ENZYME 1 (UBC1) and UBC2 (Yanagawa et al, 2004; Lau and Deng, 2009). The latter act in coordination with E3 Ub ligases HISTONE UBIQUITINASE 1 (HUB1) and HUB2 to ubiquitinate Histone 2B (H2B) (Xu et al, 2009). These findings suggest that COP10, and by extent the CRL4-CDDD, might modulate both H2B ubiquitination and deubiquitination
Characterization of the pleiotropic defects in csn mutants in Arabidopsis, Drosophila, and humans showed that the COP9 signalosome (CSN) has other functions besides the inhibition of the CULLIN RING ligases (CRLs) E3 Ub ligase activity, that were related to its ability to associate with chromatin (Dessau et al, 2008; Singer et al, 2014; Chamovitz, 2009)

Summary

Introduction

Proteins participate in every function of a living cell, from metabolic to signalling events, and as cellular structural components. These proteins, together with the DDB1-associated CDDD module, involved in surveying chromatin states and gene expression as part of CRL4 complexes are the focus of this review (Figure 1).

Results

Conclusion