An essential regulator of gene transcription, nuclear receptor liver receptor homologue 1 (LRH-1) controls cell differentiation in the developing pancreas and maintains cholesterol homeostasis in adults. Recent genome-wide association studies linked mutations in the LRH-1 gene and its up-stream regulatory regions to development of pancreatic cancer. In this work, we show that LRH-1 transcription is activated up to 30-fold in human pancreatic cancer cells compared to normal pancreatic ductal epithelium. This activation correlates with markedly increased LRH-1 protein expression in human pancreatic ductal adenocarcinomas in vivo. Selective blocking of LRH-1 by receptor specific siRNA significantly inhibits pancreatic cancer cell proliferation in vitro. The inhibition is tracked in part to the attenuation of the receptor's transcriptional targets controlling cell growth, proliferation, and differentiation. Previously, LRH-1 was shown to contribute to formation of intestinal tumors. This study demonstrates the critical involvement of LRH-1 in development and progression of pancreatic cancer, suggesting the LRH-1 receptor as a plausible therapeutic target for treatment of pancreatic ductal adenocarcinomas.protein target | gene regulation W ith mortality rate nearing its incidence, pancreatic ductal adenocarcinoma (PDAC) presents a challenge for modern oncology. Current chemotherapy drugs approved for pancreatic cancer are not organ specific and are modestly effective. Thus, there is a need for improved therapeutic options and effective pancreatic cancer drugs. Recent studies reveal that signaling pathways are similar in pancreatic development and malignant growth in the adult pancreas (1, 2). One of the common driving factors in pancreatic embryo-and oncogenesis is the nuclear receptor liver receptor homologue 1 (LRH-1,

Thyroid hormone (3,5,3-triiodo-L-thyronine, T3) is an endocrine hormone that exerts homeostatic regulation of basal metabolic rate, heart rate and contractility, fat deposition, and other phenomena (1, 2). T3 binds to the thyroid hormone receptors (TRs) and controls their regulation of transcription of target genes. The binding of TRs to thyroid hormone induces a conformational change in TRs that regulates the composition of the transcriptional regulatory complex. Recruitment of the correct coregulators (CoR) is important for successful gene regulation. In principle, inhibition of the TR-CoR interaction can have a direct influence on gene transcription in the presence of thyroid hormones. Herein we report a high throughput screen for small molecules capable of inhibiting TR coactivator interactions. One class of inhibitors identified in this screen was aromatic ␤-aminoketones, which exhibited IC 50 values of ϳ2 M. These compounds can undergo a deamination, generating unsaturated ketones capable of reacting with nucleophilic amino acids. Several experiments confirm the hypothesis that these inhibitors are covalently bound to TR. Optimization of these compounds produced leads that inhibited the TR-CoR interaction in vitro with potency of ϳ0.6 M and thyroid signaling in cellular systems. These are the first small molecules irreversibly inhibiting the coactivator binding of a nuclear receptor and suppressing its transcriptional activity. Thyroid hormone receptors (TRs)3 regulate development, growth, and metabolism (1, 2). The TRs are nuclear receptors (NR), part of a superfamily whose members function as hormone-activated transcription factors (3). The majority of thyroid hormone responses are induced by regulation of transcription by the thyroid hormone T3 (4). Two genes, THRA and THRB encode the two protein isoforms TR␣ and TR␤, which yield four distinct subtypes by alternative splicing (5). Several functional domains of TRs have been identified: a ligand-independent transactivation domain (AF-1) on the amino terminus, a central DNA binding domain, a ligand binding domain (LBD), and a carboxylterminal ligand dependent activation function (AF-2) (6). TR binds specific sequences of DNA in the 5Ј-flanking regions of T3-responsive genes, known as thyroid response elements, most often as a heterodimer with the retinoid X receptor (7). Both unliganded and liganded TRs can bind thyroid response elements and regulate genes under their control. The unliganded TR complex can recruit a nuclear receptor corepressor (NCoR) or a silencing mediator of retinoic acid to silence basal transcription (8). In the presence of T3, TRs undergo a conformational change with the result that the composition of the coregulator complex can change with strong effects on transcriptional regulation. Several coactivator proteins have been identified (9). The best studied group of coactivators is the p160 or steroid receptor coactivator (SRC) proteins (7) including SRC1 (10), SRC2 (11,12), and SRC3 (13). Another group of ligand-dependent-interactin...

The development of nuclear hormone receptor antagonists that directly inhibit the association of the receptor with its essential coactivators would allow useful manipulation of nuclear hormone receptor signaling. We previously identified 3-(dibutylamino)-1-(4-hexylphenyl)-propan-1-one (DHPPA), an aromatic beta-amino ketone that inhibits coactivator recruitment to thyroid hormone receptor beta (TRbeta), in a high-throughput screen. Initial evidence suggested that the aromatic beta-enone 1-(4-hexylphenyl)-prop-2-en-1-one (HPPE), which alkylates a specific cysteine residue on the TRbeta surface, is liberated from DHPPA. Nevertheless, aspects of the mechanism and specificity of action of DHPPA remained unclear. Here, we report an x-ray structure of TRbeta with the inhibitor HPPE at 2.3-A resolution. Unreacted HPPE is located at the interface that normally mediates binding between TRbeta and its coactivator. Several lines of evidence, including experiments with TRbeta mutants and mass spectroscopic analysis, showed that HPPE specifically alkylates cysteine residue 298 of TRbeta, which is located near the activation function-2 pocket. We propose that this covalent adduct formation proceeds through a two-step mechanism: 1) beta-elimination to form HPPE; and 2) a covalent bond slowly forms between HPPE and TRbeta. DHPPA represents a novel class of potent TRbeta antagonist, and its crystal structure suggests new ways to design antagonists that target the assembly of nuclear hormone receptor gene-regulatory complexes and block transcription.

The mechanisms of functional repression of the androgen receptor (AR) are crucial for the regulation of genes involved in physiological development as well as for the progression of prostate cancer. To date, only two in vivo inhibitors of AR-mediated transcription have been identified: DAX-1 and SHP (small heterodimer partner). SHP is a regulatory nuclear receptor (NR) that lacks DNA-binding and activation domains. Using X-ray crystallography, the interaction between peptide segments of the SHP repressor containing LxxLL-like motifs and the ligand-binding domain of AR have been investigated. Under the crystallization conditions used, it was found that of the three NR Boxes present in the SHP protein sequence, only NR Box 2 (LKKIL motif) formed a complex with AR. Determination of the crystal structure revealed that ten amino acids of the SHP peptide (14-mer) are ordered through interactions with AR. Two side chains make unique interactions that were not reported for other AR-peptide complexes. The NR Box 2 of SHP binds to an adaptable hydrophobic groove on the surface of AR in a fashion observed for other NR-LxxLL-like complexes. Comparisons of AR structures bound to coactivator peptides and the SHP peptide revealed structural similarity of their binding sites, suggesting that transcriptional AR activity may be inhibited by SHP by competing with AR coactivators.

The androgen receptor (AR) regulates gene transcription in many tissues and is profoundly important in prostate cancer. Antiandrogens compete with the natural hormone and are front line therapeutics to treat prostate cancer. However, antiandrogens frequently become ineffective after prolonged treatment because of development of tumor resistance. This paper reviews design principles for new generations of antiandrogens: super antagonists and surface allosteric modulators. Super antiandrogens are compounds with higher binding affinity than natural agonists and that contain precisely engineered hydrophobic groups that disrupt AR function. AR surface is also an attractive alternative target. Surface inhibitors are small molecules that directly block the receptor-co-activator interface, preventing co-activator recruitment. The challenges to designing these compounds are significant but so is the potential for treatment of the disease.