IMPORTANCEApproximately 25% of patients with early-stage breast cancer who receive (neo)adjuvant chemotherapy experience a recurrence within 5 years. Improvements in therapy are greatly needed.OBJECTIVE To determine if pembrolizumab plus neoadjuvant chemotherapy (NACT) in early-stage breast cancer is likely to be successful in a 300-patient, confirmatory randomized phase 3 neoadjuvant clinical trial. DESIGN, SETTING, AND PARTICIPANTSThe I-SPY2 study is an ongoing open-label, multicenter, adaptively randomized phase 2 platform trial for high-risk, stage II/III breast cancer, evaluating multiple investigational arms in parallel. Standard NACT serves as the common control arm; investigational agent(s) are added to this backbone. Patients with ERBB2 (formerly HER2)-negative breast cancer were eligible for randomization to pembrolizumab between November 2015 and November 2016.INTERVENTIONS Participants were randomized to receive taxane-and anthracycline-based NACT with or without pembrolizumab, followed by definitive surgery. MAIN OUTCOMES AND MEASURESThe primary end point was pathologic complete response (pCR). Secondary end points were residual cancer burden (RCB) and 3-year event-free and distant recurrence-free survival. Investigational arms graduated when demonstrating an 85% predictive probability of success in a hypothetical confirmatory phase 3 trial. RESULTSOf the 250 women included in the final analysis, 181 were randomized to the standard NACT control group (median [range] age, 47 [24.77] years). Sixty-nine women (median [range] age, 50 [27-71] years) were randomized to 4 cycles of pembrolizumab in combination with weekly paclitaxel followed by AC; 40 hormone receptor (HR)-positive and 29 triple-negative. Pembrolizumab graduated in all 3 biomarker signatures studied. Final estimated pCR rates, evaluated in March 2017, were 44% vs 17%, 30% vs 13%, and 60% vs 22% for pembrolizumab vs control in the ERBB2-negative, HR-positive/ERBB2-negative, and triple-negative cohorts, respectively. Pembrolizumab shifted the RCB distribution to a lower disease burden for each cohort evaluated. Adverse events included immune-related endocrinopathies, notably thyroid abnormalities (13.0%) and adrenal insufficiency (8.7%). Achieving a pCR appeared predictive of long-term outcome, where patients with pCR following pembrolizumab plus chemotherapy had high event-free survival rates (93% at 3 years with 2.8 years' median follow-up).CONCLUSIONS AND RELEVANCE When added to standard neoadjuvant chemotherapy, pembrolizumab more than doubled the estimated pCR rates for both HR-positive/ERBB2negative and triple-negative breast cancer, indicating that checkpoint blockade in women with early-stage, high-risk, ERBB2-negative breast cancer is highly likely to succeed in a phase 3 trial. Pembrolizumab was the first of 10 agents to graduate in the HR-positive/ERBB2-negative signature.

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The peroxisome proliferator-activated receptor ␥ (PPAR␥) is a central regulator of adipogenesis and recruits coactivator proteins in response to ligand. However, the role of another class of nuclear cofactors, the nuclear receptor corepressors, in modulating PPAR␥ transcriptional activity is less clear. Such corepressors include the nuclear receptor corepressor (NCoR) and the silencing mediator of retinoid and thyroid hormone receptors (SMRT). Our data suggest that PPAR␥ recruits SMRT and NCoR in the absence of ligand and that these corepressors are capable of down-regulating PPAR␥-mediated transcriptional activity. The addition of the PPAR␥ ligand pioglitazone results in dissociation of the PPAR␥-corepressor complex. To define the role of SMRT and NCoR in PPAR␥ action, 3T3-L1 cells deficient in SMRT or NCoR were generated by RNA interference. When these cells are exposed to differentiation media, they exhibit increased expression of adipocyte-specific genes and increased production of lipid droplets, as compared with control cells. These data suggest that the nuclear receptor corepressors decrease PPAR␥ transcriptional activity and repress the adipogenic program in 3T3-L1 cells. The thyroid hormone receptors (TRs)1 and retinoic acid receptors (RARs) are nuclear receptors that repress gene transcription in the absence of their respective ligands. This ligandindependent repression is mediated by nuclear receptor corepressors, such as the nuclear receptor corepressor protein (NCoR) and the silencing mediator of retinoid and thyroid hormone receptors (SMRT) (1, 2). NCoR and SMRT are recruited by TR and RAR isoforms in the absence of ligand and are released upon ligand binding. NCoR and SMRT, in turn, recruit a complex with histone deacetylase activity to repress transcription of target genes. More recently, NCoR and SMRT have been shown to be recruited by other nuclear receptors, some of which bind nuclear receptor corepressors in the presence of antagonists. However, it has been controversial whether NCoR and SMRT play a significant role in gene regulation by the peroxisome proliferator-activated receptor ␥ (PPAR␥) isoforms (3).Two types of PPAR␥ isoforms exist, PPAR␥1 and PPAR␥2. These receptors differ only in their amino-terminal A/B domain, such that PPAR␥2 contains an extra 30 amino acids (4). The function of PPAR␥2 has attracted considerable interest because it is specifically expressed in adipocytes and is an essential regulator of adipogenesis. In addition, many important adipocyte-specific genes contain response elements for PPAR␥ in their promoter regions. Although PPAR␥ clearly recruits coactivators in response to exogenous ligands, its ability to recruit corepressors is less certain. In contrast to the TR, PPAR␥ does not appear to be a strong repressor in the absence of its ligand. Such experiments, however, have been limited by the lack of information concerning physiologic endogenous ligands. Early work into PPAR␥ and corepressor recruitment suggested that PPAR␥ might not recruit NCoR or SMRT in the p...

Congenital hypothyroidism and the thyroid hormone (T3) resistance syndrome are associated with severe central nervous system (CNS) dysfunction. Because thyroid hormones are thought to act principally by binding to their nuclear receptors (TRs), it is unexplained why TR knock-out animals are reported to have normal CNS structure and function. To investigate this discrepancy further, a T3 binding mutation was introduced into the mouse TR-␤ locus by homologous recombination. Because of this T3 binding defect, the mutant TR constitutively interacts with corepressor proteins and mimics the hypothyroid state, regardless of the circulating thyroid hormone concentrations. Severe abnormalities in cerebellar development and function and abnormal hippocampal gene expression and learning were found. These findings demonstrate the specific and deleterious action of unliganded TR in the brain and suggest the importance of corepressors bound to TR in the pathogenesis of hypothyroidism.

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c NCoR1 (nuclear receptor corepressor) and SMRT (silencing mediator of retinoid and thyroid hormone receptors; NCoR2) are well-recognized coregulators of nuclear receptor (NR) action. However, their unique roles in the regulation of thyroid hormone (TH) signaling in specific cell types have not been determined. To accomplish this we generated mice that lacked function of either NCoR1, SMRT, or both in the liver only and additionally a global SMRT knockout model. Despite both corepressors being present in the liver, deletion of SMRT in either euthyroid or hypothyroid animals had little effect on TH signaling. In contrast, disruption of NCoR1 action confirmed that NCoR1 is the principal mediator of TH sensitivity in vivo. Similarly, global disruption of SMRT, unlike the global disruption of NCoR1, did not affect TH levels. While SMRT played little role in TH-regulated pathways, when disrupted in combination with NCoR1, it greatly accentuated the synthesis and storage of hepatic lipid. Taken together, these data demonstrate that corepressor specificity exists in vivo and that NCoR1 is the principal regulator of TH action. However, both corepressors collaborate to control hepatic lipid content, which likely reflects their cooperative activity in regulating the action of multiple NRs including the TH receptor (TR).T hyroid hormone (TH) is one of the most important metabolic regulators in humans, and its actions in the liver include the regulation of cholesterol and lipid metabolism. Thyroxine (T4) is the major circulating form of thyroid hormone, and it is converted to its active form, triiodothyronine (T3), by a family of deiodinases (1). T3 regulates metabolic processes via thyroid hormone receptor (TR) isoforms that are expressed in all peripheral tissues, including liver. The TRs mediate target gene regulation by recruiting a constellation of coregulators that include corepressors (CoRs) and coactivators depending upon the presence of T3 (2). While classical models suggest that the corepressors are mainly recruited by the unliganded TR, the mechanisms by which T3 coordinates specific signaling in the liver both positively and negatively are still unknown (3). Indeed, recent work by our laboratory and others has demonstrated that the corepressors appear to play a critical role in mediating ligand sensitivity regardless of the concentration of ligand (4-7).The two principal corepressors that are suggested to be involved in mediating TH action are nuclear receptor corepressor 1 (NCoR1) and silencing mediator of retinoid and thyroid hormone receptors (SMRT) (4). They are highly homologous modular proteins and have three similar nuclear receptor (NR) interaction domains (NRIDs) at their C termini (8). Importantly, whole-body gene knockouts (KOs) of NCoR1 or SMRT result in embryonic lethality, but mutation or deletion of only the NRIDs allows for full development (6, 9, 10). In NCoR⌬ID mice, which express an altered NCoR1 allele that lacks the N3 and N2 NRIDs, there is evidence for increased thyroid hormone sensitivity...

The thyroid hormone receptor (TR) recruits the nuclear corepressors, nuclear receptor corepressor (NCoR) and silencing mediator of retinoid and thyroid hormone receptors (SMRT), to target DNA elements in the absence of ligand. While the TR preferentially recruits NCoR, the mechanism remains unclear. The corepressors interact with the TR via interacting domains (IDs) present in their C terminus which contain a conserved motif termed a CoRNR box. Despite their similarity, the corepressor IDs allow for nuclear receptor specificity. Here we demonstrate that NCoR stabilizes the TR homodimer when bound to DNA by preventing its dissociation from thyroid hormone response elements. This suggests that NCoR acts to hold the repression complex in place on target elements. The TR homodimer recruits NCoR through two of its three IDs, one of which is not present in SMRT. This unique ID, N3, contains a CoRNR box but lacks the extended helical motif present in each of the other IDs. Instead, N3 contains an isoleucine just proximal to this motif. This isoleucine is also conserved in N2 but not in the corresponding S2 domain in SMRT. On thyroid hormone response elements and in mammalian cells this residue is critical in both N3 and N2 for high-affinity TR binding. In addition, this residue also controls specificity for the interactions of TR with NCoR. Together these data suggest that the specific recruitment of NCoR by the TR through a unique motif allows for stabilization of the repression complex on target elements.

HESX1 is a paired-like homeodomain transcription factor that functions as a repressor of PROP1-mediated gene stimulation. Mutations in HESX1 have been implicated in cases of septooptic dysplasia and congenital hypopituitarism. All mutations in HESX1 identified to date have resulted in impaired DNA binding and defective HESX1 action. We have identified a novel HESX1 mutation in genomic nucleotide position 1684 (g.1684delG), which results in a mutant protein with increased DNA binding. In turn, this mutation causes increased repression of PROP1-dependent gene activity. These data suggest that enhancement of transcriptional repression during pituitary organogenesis is a novel mechanism for the development of congenital pituitary disorders.