SUMmOning Daxx-mediated repression

Abstract

An intimate relationship exists between the transcriptional coregulator Daxx, SUMO, and PML nuclear bodies. In this issue, Chang et al. (2011) provide structural insights into how phosphorylation of Daxx increases its affinity toward SUMOs and functional insights into how enhanced SUMO binding affects Daxx-PML interactions, PML nuclear body localization, and Daxx-mediated repression of genes encoding for antiapoptotic factors.

Figure 1

CK2-dependent Daxx-SIM phosphorylation controls anti-apoptotic gene repression. CK2 phosphorylates two serine residues in the Daxx C-terminal SIM, increasing its affinity towards SUMOs, and particularly toward SUMO-1. This phosphorylation-induced enhancement of SUMO-1 binding results in preferential SUMO-1 modification and SUMO-1 dependent recruitment of Daxx to the promoters of genes coding for anti-apoptotic factors. Enhanced SUMO-1 binding also stabilizes interactions between Daxx and SUMO-1 modified PML, thereby affecting Daxx localization to PML-NBs. The effects of covalent SUMO-1 modification of Daxx, as well as the functional relationship between recruitment to PML-NBs and gene repression remain uncertain, as indicated by question marks.