Glucocorticoids are universally used in the treatment of acute lymphoblastic leukemia (ALL), and leukemia cell resistant to glucocorticoids confers a poor prognosis. To elucidate mechanisms of glucocorticoid resistance, we determined the sensitivity to prednisolone of primary leukemia cells from 444 newly diagnosed ALL patients, revealing significantly higher expression of caspase 1 (CASP1) and its activator NLRP3 in glucocorticoid resistant leukemia cells, due to significantly lower somatic methylation of CASP1 and NLRP3 promoters. Over-expression of CASP1 resulted in cleavage of the glucocorticoid receptor, diminished glucocorticoid-induced transcriptional response and increased glucocorticoid resistance. Knockdown or inhibition of CASP1 significantly increased glucocorticoid receptor levels and mitigated glucocorticoid resistance in CASP1 overexpressing ALL. Our findings establish a new mechanism by which the NLRP3/CASP1 inflammasome modulates cellular levels of the glucocorticoid receptor and diminishes cell sensitivity to glucocorticoids. The broad impact on glucocorticoid transcriptional response suggests this mechanism could also modify glucocorticoid effects in other diseases.
MicroRNAs are important regulators of gene expression, acting primarily by binding to sequence-specific locations on already transcribed messenger RNAs (mRNA) and typically down-regulating their stability or translation. Recent studies indicate that microRNAs may also play a role in up-regulating mRNA transcription levels, although a definitive mechanism has not been established. Double-helical DNA is capable of forming triple-helical structures through Hoogsteen and reverse Hoogsteen interactions in the major groove of the duplex, and we show physical evidence (i.e., NMR, FRET, SPR) that purine or pyrimidine-rich microRNAs of appropriate length and sequence form triple-helical structures with purine-rich sequences of duplex DNA, and identify microRNA sequences that favor triplex formation. We developed an algorithm (Trident) to search genome-wide for potential triplex-forming sites and show that several mammalian and non-mammalian genomes are enriched for strong microRNA triplex binding sites. We show that those genes containing sequences favoring microRNA triplex formation are markedly enriched (3.3 fold, p<2.2 × 10−16) for genes whose expression is positively correlated with expression of microRNAs targeting triplex binding sequences. This work has thus revealed a new mechanism by which microRNAs could interact with gene promoter regions to modify gene transcription.
Increasing
evidence implicates the orphan G protein-coupled receptor
88 (GPR88) in a number of striatal-associated disorders. In this study,
we report the design and synthesis of a series of novel (4-alkoxyphenyl)glycinamides
(e.g., 31) and the corresponding 1,3,4-oxadiazole bioisosteres
derived from the 2-AMPP scaffold (1) as GPR88 agonists.
The 5-amino-1,3,4-oxadiazole derivatives (84, 88–90) had significantly improved potency and lower lipophilicity compared
to 2-AMPP. Compound 84 had an EC50 of 59 nM
in the GPR88 overexpressing cell-based cAMP assay. In addition, 84 had an EC50 of 942 nM in the [35S]GTPγS
binding assay using mouse striatal membranes but was inactive in membranes
from GPR88 knockout mice, even at a concentration of 100 μM.
In vivo pharmacokinetic testing of 90 in rats revealed
that the 5-amino-1,3,4-oxadiazole analogues may have limited brain
permeability. Taken together, these results provide the basis for
further optimization to develop a suitable agonist to probe GPR88
functions in the brain.
The orphan receptor GPR88 has been implicated in a number of striatal-associated disorders, yet its endogenous ligand has not been discovered. We have previously reported that the amine functionality in the 2-AMPP-derived GPR88 agonists can be replaced with an amide (e.g., 4) without losing activity. Later, we have found that the amide can be replaced with a bioisosteric 1,3,4-oxadiazole with improved potency. Here, we report a further study of amide bioisosteric replacement with a variety of azoles containing three heteroatoms, followed by a focused structure-activity relationship study, leading to the discovery of a series of novel 1,4-disubstituted 1H-1,2,3-triazoles as GPR88 agonists. Collectively, our medicinal chemistry efforts have resulted in a potent, efficacious, and brain-penetrant GPR88 agonist 53 (cAMP EC 50 = 14 nM), which is a suitable probe to study GPR88 functions in the brain.
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