Associate Scientist, Hospital for Special Surgery
Associate Professor, Department of Microbiology and Immunology, Weill Medical College of Cornell University
Member, Graduate Program in Immunology and Microbial Pathogenesis, Weill-Cornell
Member, Allied Graduate Program in Biochemistry, Cell and Molecular Biology (BCMB), Weill-Cornell
Rogatsky I., Zarember K.A. and Yamamoto K.R. (2001) Factor recruitment and TIF2/GRIP1 corepressor activity at a collagenase-3 response element that mediates regulation by phorbol esters and hormones. EMBO J. 20:6071-83.
Rogatsky I., Wang J.-C., Derynck M.K., Nonaka D.F., Khodabakhsh D.B., Haqq C.M., Darimont B.D., Garabedian M.J. and Yamamoto K.R. (2003) Target-specific utilization of transcriptional regulatory surfaces by the glucocorticoid receptor. Proc. Natl. Acad. Sci. USA, 100:13845-50.
Reily M.M., Pantoja C., Hu X., Chinenov Y. and Rogatsky I. (2006) The GRIP1:IRF3 interaction as a target for glucocorticoid receptor-mediated immunosuppression. EMBO J. 25:108-17.
Chinenov Y. and Rogatsky I. (2007) Glucocorticoids and the innate immune system: Crosstalk with the Toll-like receptor signaling network. Mol. Cell. Endocrinol. 275:30-42.
Chinenov Y., Sacta M.A., Cruz A.R., Rogatsky I. (2008) GRIP1-associated SET-domain methyltransferase in glucocorticoid receptor target gene expression. Proc. Natl. Acad. Sci. USA 105: 20185-90.
Adelman K., Kennedy M.A., Nechaev S., Gilchrist D.A., Muse G.W.,Chinenov Y., Rogatsky I. (2009) Immediate mediators of the inflammatory response are poised for gene activation through RNA polymerase II stalling. Proc. Natl. Acad. Sci. USA 106:18207-12.
Flammer J.R., Dobrovolna J., Kennedy M.A., Chinenov Y., Glass C.K., Ivashkiv L.B., Rogatsky I. (2010) Type I interferon signaling pathway is a target for glucocorticoid inhibition. Mol. Cell. Biol. 30: 4564-4574 Supplementary Material
Flammer J.R. and Rogatsky I. (2011) Glucocorticoids in autoimmunity: unexpected targets and mechanisms. Mol. Endocrinol. 7: 1075-86
Dobrovolna J., Chinenov Y., Kennedy M.A., Liu B. and Rogatsky I. (2012) Glucocorticoid-dependent phosphorylation of the transcriptional coregulator GRIP1. Mol. Cell. Biol. 32:730-9
Chinenov Y., Gupte R., Dobrovolna J., Flammer J.R., Liu B., Michelassi F.E. and Rogatsky I. (2012) The role of transcriptional coregulator GRIP1 in the anti-inflammatory actions of glucocorticoids. Proc. Natl. Acad. Sci. USA 109:11776-81
Transcriptional Cross-talk Between Glucocorticoids and the Immune System
Glucocorticoid hormones (GC) are potent immunosuppressors, which interfere with the immune system function by promoting killing of lymphocytes, and by suppressing the production of numerous cytokines, chemokines and other mediators of inflammation. Not surprisingly, GCs have been used for decades to combat inflammatory and autoimmune diseases. GC signal through the intracellular glucocortcoid receptor (GR), a ligand-dependent transcription factor which upon exposure to hormone, translocates to the nucleus, binds GC response elements (GREs) on DNA and triggers the assembly of multiprotein transcriptional regulatory complexes which activate or repress a wide variety of genes. Our goals are to understand the molecular composition and mechanisms of action of these complexes, as well as the genomic targets of GR in immune cells vs. other cell types
1. Interferon (IFN) Regulatory Factors (IRFs) and glucocorticoids.
We previously found that an established transcriptional coactivator for GR - GRIP1/TIF2/NCoA2 – potentiates transcription by IRF3 and the heterotrimeric Stat1/Stat2/IRF9 complex, which drive type I IFN gene expression (in response to toll-like receptor activation) and signaling, respectively (Reily et al, EMBO J 2006, Flammer et al, Mol Cell Biol 2010). Furthermore, in macrophages, where GRIP1 protein levels are low, glucocorticoid-activated GR sequesters GRIP1 away from IRFs, thereby attenuating type I IFN-dependent gene expression. This mutually exclusive utilization of a shared coregulator between the GR and IFN networks represents a novel mechanism of GC-mediated immunosuppression. We want to understand what drives selective use of GRIP1 at certain IFN-inducible genes making them more susceptible to GC inhibition than others, what is the mechanistic basis of GRIP1 coactivator functions in the context of IRFs, and finally, what are the implications of this unexpected function of GRIP1 in the context of IFN response to viral infections in vivo.
2. GRIP1, GR-mediated transcriptional repression and the anti-inflammatory actions of GCs.
In addition to activating transcription by binding to palindromic GREs, GR is well known to ‘tether’ to other DNA-bound transcription factors, including AP1 and NFkB, and repress their activity. Because AP1 and NFkB are responsible for activating a great variety of pro-inflammatory cytokine and chemokine genes, repression by GR via tethering is considered a key component of the anti-inflammatory and immunosuppressive actions of GCs, however its molecular mechanisms remain obscure. Earlier studies revealed that GRIP1, in addition to its ‘traditional’ function as a GR coactivator at palindromic GREs, is recruited to GR ‘tethering’ sites potentially facilitating repression (Rogatsky et al, EMBO J 2001, Rogatsky et al, Mol Cell Biol 2002). To dissect the role of GRIP1 in GR-mediated repression and in inflammation in vivo, we generated a mouse strain enabling GRIP1 deletion in macrophages in adult animals. Using this genetic system, we pursued genome-wide transcriptome analyses in WT vs GRIP1 knockout macrophages under inflammatory or immunosuppressive conditions, as well as mechanistic and in vivo studies to delineate the glucocorticoid control of inflammation.
3. Transcription initiation and elongation can be regulated by anti-inflammatory signals.
Recruitment of RNA Polymerase II (Pol II) to target promoters is often the rate-limiting step for gene activation, yet in recent years, a different view has emerged. Many genes are occupied by transcriptionally engaged Pol II even prior to stimulation, however no full-length transcript is produced. Instead, Pol II stalls at the promoter-proximal region until signal-dependent phosphorylation, which dismisses the Negative Elongation Factor (NELF) complex from the promoter enabling productive elongation. We recently discovered that many mediators of inflammation are activated by such Pol II release from promoter-proximal stalling, and typically undergo a strikingly rapid induction relative to genes which are induced via Pol II recruitment (Adelman et al, Proc Natl Acad Sci USA 2009). Interestingly, inflammatory genes of both classes are repressed by GR raising the question regarding the molecular mechanisms underlying repression in each case.
4. Regulation of GRIP1 by phosphorylation.
GRIP1 is a multi-functional coregulator that can elicit opposite transcriptional responses (activation vs repression) or engage in complexes with biologically antagonistic functions, such as immunosuppression in conjunction with GR or innate immune response when bound by IRFs. What enables this regulatory diversity is unknown. Unexpectedly, we discovered that in response to GCs, GRIP1 is phosphorylated on multiple sites and by multiple kinases in a GR-interaction dependent manner, which affects its transcriptional activity (Dobrovolna et al, Mol Cell Biol 2011). Out goal is to understand the interplay between individual GRIP1 phospho-sites and kinases with respect to GRIP1 target gene-specific recruitment. In addition, we aim to identify posttranslational modifications that may occur in response to signals that activate non-GR GRIP1 partners (e.g., IRFs) as a potential mechanism for selectivity in GRIP1 functions in different pathways.
5. Inhibitory histone methyltransferases (HMTase) and GR-dependent gene expression.
In a yeast-2-hybrid screen for novel factors potentially recruited by GRIP1 to GR transcription complexes we identified an HMTase Suv4-20 (Chinenov et al, Proc Natl Acad Sci USA 2008), which specifically di- and tri-methylates histone H4 lysine 20. Although the only known function of Suv4-20 was the establishment and maintenance of constitutive transcriptionally silent heterochromatin, we found that Suv4-20 actively regulates a subset of GR target genes, including known suppressors of inflammation. Current projects are focusing on the mechanisms of Suv4-20 action on GR targets and its genome-wide impact on GC-regulated gene expression program.
We use biochemical, molecular, cell-based and in vivo approaches to identify points of cross-talk between the GC and the pathways mediating inflammation, autoimmunity and uncontrolled cell proliferation. Understanding the major players and mechanisms of such interactions is essential for developing more specific therapies.
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