Glucocorticoid-Dependent Phosphorylation of the Transcriptional Coregulator GRIP1

Abstract

Much of the regulatory diversity in eukaryotic transcription is provided by coregulators, which are recruited by DNA-binding factors to propagate signaling to basal machinery or chromatin. p160 family members, including the glucocorticoid receptor (GR)-interacting protein 1 (GRIP1), function as coactivators for GR, a ligand-dependent transcription factor of the nuclear receptor superfamily. Unlike other p160s, GRIP1 also potentiates GR-mediated repression of AP1 and NF-B targets and, surprisingly, transcriptional activation by interferon regulatory factors. What enables GRIP1 activating or repressing properties or discrimination between physiologically antagonistic pathways is unknown. We found that endogenous GRIP1 in mammalian cells undergoes glucocorticoid-induced, GR interaction-dependent phosphorylation and identified one constitutive and six inducible phosphorylation sites and two putative GRIP1 kinases, casein kinase 2 and cyclin-dependent kinase 9. We raised phosphospecific antibodies to the four closely spaced sites in a previously uncharacterized part of GRIP1 which, combined with mutagenesis, revealed the conservation of GRIP1 phosphorylation across several cell types and species and its functional relevance to GRactivated transcription and to response element-specific recruitment of phospho-GRIP1 to native GR targets. We propose that cofactor engagement by GR is neither passive nor stochastic; rather, GR actively imparts modifications that dictate GRIP1 function in a subset of complexes, adding a layer of specificity to GR transcriptional control.

Role of transcriptional coregulator GRIP1 in the anti-inflammatory actions of glucocorticoids

“…Indeed, GRIP1 has a wide-ranging specificity of protein:protein interactions, including those with MEF2C, MyoD, and IRFs (33,35,38,39), regulating processes as diverse as muscle-cell differentiation and innate immune response to double-stranded RNA. What promotes the preferential targeting of GRIP1 to a specific regulatory complex or its ability to inhibit or activate transcription is unknown, but recently discovered GRIP1 posttranslational modifications such as SUMOylation and phosphorylation (40,41) may serve as such a mechanism. In addition, GRIP1 expression itself is potentially amenable to regulation: it was found to be overexpressed or fused to other regulators, including MOZ, HEY1, and ETV6 in a number of cancers (refs.…”

Minireview: Nuclear Receptor Coregulators of the p160 Family: Insights into Inflammation and Metabolism

“…NCOAs integrate diverse upstream signals and can undergo phosphorylation, ubiquitination, SUMOylation, acetylation and methylation that modulate regulatory properties of these factors. For example, NCOA3 is phosphorylated at S543 and S505, and its dephosphorylation by PP2A and PDXP attenuates the interaction with and coactivation of ER (43), whereas GC-dependent phosphorylation of NCOA2 at S469, S487, S493 and S499 potentiates activation of a subset of GR targets (44). Further, methylation of the NCOA3 C-terminal region by CARM1 was shown to promote dissociation of CBP and CARM1 from NCOA3 and lead to its destabilization (45,46).…”

“…Although the nature of phosphorylation-dependent NCOA3-interacting TFs remains to be determined, the idea that the PTM code of NCOAs control distinct transcription programs in the context of metabolic genes is certainly compelling. Considering the recent discovery that NCOA2 is phosphorylated on a panel of serine residues in a GC-and GR interaction-dependent manner which potentiated GR-mediated activation of specific genes (44), it is tempting to speculate that a distinct NCOA2 phosphorylation pattern is triggered by other TFs preferentially affecting its ability to modulate transcription of metabolic genes.…”

Global Gene Repression by the Steroid Receptor Coactivator SRC-1 Promotes Oncogenesis

“…However, SRC-2 has a somewhat amphipathic role in transcriptional regulation, working as both a trans-activator and repressor of the glucocorticoid receptor (GR) depending on the transcriptional context (13,14). This dual regulatory role for SRC-2 opens up the possibility that SRC-1 could also suppress transcriptional activity to fulfill its oncogenic potential.…”