Function of Histone Deacetylase 6 as a Cofactor of Nuclear Receptor Coregulator LCoR

Abstract

Ligand-dependent corepressor LCoR was identified as a protein that interacts with the estrogen receptor ␣ (ER␣) ligand binding domain in a hormone-dependent manner. LCoR also interacts directly with histone deacetylase 3 (HDAC3) and HDAC6. Notably, HDAC6 has emerged as a marker of breast cancer prognosis. However, although HDAC3 is nuclear, HDAC6 is cytoplasmic in many cells. We found that HDAC6 is partially nuclear in estrogen-responsive MCF7 cells, colocalizes with LCoR, represses transactivation of estrogen-inducible reporter genes, and augments corepression by LCoR. In contrast, no repression was observed upon HDAC6 expression in COS7 cells, where it is exclusively cytoplasmic. LCoR binds to HDAC6 in vitro via a central domain, and repression by LCoR mutants lacking this domain was attenuated. Kinetic chromatin immunoprecipitation assays revealed hormone-dependent recruitment of LCoR to promoters of ER␣-induced target genes in synchrony with ER␣. HDAC6 was also recruited to these promoters, and repeat chromatin immunoprecipitation experiments confirmed the corecruitment of LCoR with ER␣ and with HDAC6. Remarkably, however, although we find evidence for corecruitment of LCoR and ER␣ on genes repressed by the receptor, LCoR and HDAC6 failed to coimmunoprecipitate, suggesting that they are part of distinct complexes on these genes. Although small interfering RNA-mediated knockdown of LCoR or HDAC6 augmented expression of an estrogen-sensitive reporter gene in MCF7 cells, unexpectedly their ablation led to reduced expression of some endogenous estrogen target genes. Taken together, these data establish that HDAC6 can function as a cofactor of LCoR but suggest that they may act in enhance expressing some target genes.Nuclear receptors are ligand-regulated transcription factors whose activities are controlled by a variety of lipophilic extracellular signals, including steroid and thyroid hormones, metabolites of vitamins A (retinoids) and D (1, 2). DNA-bound nuclear receptors regulate transcription by recruiting complexes of coregulatory proteins, classified as coactivators or corepressors depending on whether they act to stimulate or repress transcription (2-4). Many coactivators interact with receptors through signature LXXLL motifs, known as NR boxes, which are oriented within a hydrophobic pocket of agonist-bound receptor ligand binding domains (5). Several coactivators or their associated cofactors possess histone acetyltransferase activity, which essentially caps positively charged lysine residues and loosens their association with DNA, facilitating chromatin remodeling and subsequent access of the transcriptional machinery to promoters.Nuclear receptor corepressors NCoR 7 and SMRT were isolated as factors that interacted with hormone-free but not hormone-bound thyroid and retinoid receptors (6, 7). They bind to receptor ligand binding domains through extended LXXX-IXXX(L/I) motifs known as CoRNR boxes (8, 9) and recruit multiprotein complexes implicated in transcriptional repression and histone deacetylatio...

Ligand-dependent Corepressor LCoR Is an Attenuator of Progesterone-regulated Gene Expression

“…Other experiments showed that deletion of the C-terminal HTH domain severely abrogated corepression, although this domain had no apparent role in CtBP1 recruitment. The HTH domain is distinct from the central region of LCoR identified in the accompanying manuscript (29) as being required for interaction with HDAC6. Together, these findings emphasize that LCoR is a multidomain protein that exerts its coregulator function through diverse mechanisms.…”

“…The accompanying paper showed that LCoR recruits HDAC6 through a central domain (29). In this study we have analyzed the roles of domains controlling recruitment of CtBPs and the C-terminal HTH motif in corepression by LCoR.…”

“…In addition to its N-terminal CtBP interaction motifs and a central HDAC binding domain (29), LCoR contains a C-terminal helix-turn-helix (HTH) domain that is homologous to motifs encoded by the Eip93F (CG18389 gene product from transcript CG18389-Rb) and MBLK-1 genes of Drosophila and Honeybee (Apis mellifera) (30), respectively. The LCoR HTH domain also bears 35% homology to pipsqueak motifs (PSQ).…”

Histone Deacetylase 6 Represents a Novel Drug Target in the Oncogenic Hedgehog Signaling Pathway

“…In addition, HDAC6 is involved in the regulation of autophagy and several signal transduction cascades (39,41,(56)(57)(58)(59). Moreover, HDAC6 plays a role in the nucleus as a modifier of gene transcription (42,(60)(61)(62). Given the plethora of actions in which HDAC6 is involved, it is more than surprising to note that Hdac6-null animals are viable and healthy and have only a very gentle phenotype (19).…”

Ligand-dependent Corepressor (LCoR) Recruitment by Krüppel-like Factor 6 (KLF6) Regulates Expression of the Cyclin-dependent Kinase Inhibitor CDKN1A Gene

“…LCoR is also present in a CtBP corepressor complex (25), and interacts with lysine-specific demethylase 1 (LSD1), a pivotal member of the ZEB1-CtBP-CoREST-LSD1 repressive complex (26). Surprisingly, in MCF-7 breast adenocarcinoma cells, knockdown of LCoR had either no effect or decreased expression of estrogen receptor ␣-regulated genes (22,23,27). Hence, LCoR may have promoter-specific effects on transcriptional regulation, similar to another member of the ligand-dependent repressor family, RIP140/NRIP1 (28,29).…”