The nuclear receptor interaction domain of GRIP1 is modulated by covalent attachment of SUMO-1.

The steroid receptor coactivator (SRC) proteins comprise a well-characterized family of nuclear receptor (NR) coactivators that increase transcriptional activation by NRs via covalent modification of chromatin proteins and recruitment of other coactivators. We have recently shown that the SRC family member GRIP1 interacts with a class of SUMO-1 (small ubiquitin-like modifier 1) E3 ligases, the PIAS proteins, and that the coactivator is subjected to SUMO-1 modifications (sumoylation). In this work, we demonstrate that lysine residues 239, 731, and 788 of GRIP1 serve as principal attachment sites for SUMO-1. Lys-731 and Lys-788 are located in the NR interaction domain (NID), and their substitution by arginines impairs the ability of GRIP1 to colocalize with androgen receptor (AR) in nuclei. Likewise, Lys-731 and Lys-788 mutants of GRIP1 have attenuated ability to enhance AR-dependent transcription and fail to synergize with PIASx beta-mediated activation of AR function, indicating that sumoylation modifies the ability of GRIP1 to function as a steroid receptor coactivator. The Lys-731 sumoylation site is conserved in SRC-3 and SRC-1, and the NIDs of the latter coactivators harbor one or two additional sites matching with the consensus sites for SUMO-1 attachment, respectively, suggesting a more general role for the modification in the regulation of SRC protein activity.