Transcriptional silencing by CpG island methylation is a prevalent mechanism of tumor-suppressor gene suppression in cancers. Genetic experiments have defined the importance of the DNA methyltransferase Dnmt1 for the maintenance of methylation in mouse cells and its role in neoplasia. In human bladder cancer cells, selective depletion of DNMT1 with antisense inhibitors has been shown to induce demethylation and reactivation of the silenced tumor-suppressor gene CDKN2A. In contrast, targeted disruption of DNMT1 alleles in HCT116 human colon cancer cells produced clones that retained CpG island methylation and associated tumor-suppressor gene silencing, whereas HCT116 clones with inactivation of both DNMT1 and DNMT3B showed much lower levels of DNA methylation, suggesting that the two enzymes are highly cooperative. We used a combination of genetic (antisense and siRNA) and pharmacologic (5-aza-2'-deoxycytidine) inhibitors of DNA methyl transferases to study the contribution of the DNMT isotypes to cancer-cell methylation. Selective depletion of DNMT1 using either antisense or siRNA resulted in lower cellular maintenance methyltransferase activity, global and gene-specific demethylation and re-expression of tumor-suppressor genes in human cancer cells. Specific depletion of DNMT1 but not DNMT3A or DNMT3B markedly potentiated the ability of 5-aza-2'-deoxycytidine to reactivate silenced tumor-suppressor genes, indicating that inhibition of DNMT1 function is the principal means by which 5-aza-2'-deoxycytidine reactivates genes. These results indicate that DNMT1 is necessary and sufficient to maintain global methylation and aberrant CpG island methylation in human cancer cells.

The efficacy of convalescent plasma for coronavirus disease 2019 (COVID-19) is unclear. Although most randomized controlled trials have shown negative results, uncontrolled studies have suggested that the antibody content could influence patient outcomes. We conducted an open-label, randomized controlled trial of convalescent plasma for adults with COVID-19 receiving oxygen within 12 d of respiratory symptom onset (NCT04348656). Patients were allocated 2:1 to 500 ml of convalescent plasma or standard of care. The composite primary outcome was intubation or death by 30 d. Exploratory analyses of the effect of convalescent plasma antibodies on the primary outcome was assessed by logistic regression. The trial was terminated at 78% of planned enrollment after meeting stopping criteria for futility. In total, 940 patients were randomized, and 921 patients were included in the intention-to-treat analysis. Intubation or death occurred in 199/614 (32.4%) patients in the convalescent plasma arm and 86/307 (28.0%) patients in the standard of care arm—relative risk (RR) = 1.16 (95% confidence interval (CI) 0.94–1.43, P = 0.18). Patients in the convalescent plasma arm had more serious adverse events (33.4% versus 26.4%; RR = 1.27, 95% CI 1.02–1.57, P = 0.034). The antibody content significantly modulated the therapeutic effect of convalescent plasma. In multivariate analysis, each standardized log increase in neutralization or antibody-dependent cellular cytotoxicity independently reduced the potential harmful effect of plasma (odds ratio (OR) = 0.74, 95% CI 0.57–0.95 and OR = 0.66, 95% CI 0.50–0.87, respectively), whereas IgG against the full transmembrane spike protein increased it (OR = 1.53, 95% CI 1.14–2.05). Convalescent plasma did not reduce the risk of intubation or death at 30 d in hospitalized patients with COVID-19. Transfusion of convalescent plasma with unfavorable antibody profiles could be associated with worse clinical outcomes compared to standard care.

Estrogen regulates target gene expression by binding to specific nuclear receptors that function as ligand-dependent transcription factors. Estrogen receptors (ERs) 1 contain two transcription activation domains, AF1 at the N terminus and AF2 in the C-terminal ligand-binding domain (1-3). Several proteins interact with AF2 in the presence of estrogen, some of which have the properties of transcriptional coactivators (4 -6).For instance, the p160 family of coactivators, which in humans includes the three proteins SRC1/N-CoA1 (7, 8), TIF2/GRIP1 (9, 10), and AIB1/ACTR/RAC3 (11-13), can interact with most nuclear receptors in a ligand-dependent manner and potentiate transcription of their target genes.The crystal structures of several nuclear receptor ligandbinding domains (LBDs) have now been determined (14 -19) and have revealed a striking conservation despite modest sequence homology (20). The LBD folds into a structure described as a sandwich of ␣-helices with a central hydrophobic ligandbinding pocket. In the presence of ligand, helices 3, 5, and 12 form a hydrophobic groove (21-24) important for interaction with the LXXLL motifs (9, 25-27) found in the p160 family members and also in other coactivators. However, the crystal structure of estrogen receptor ␣ (ER␣) revealed that helix 12 is repositioned in the presence of the antagonists tamoxifen (Tam) or raloxifene (Ral), thereby disrupting the surface of interaction with coactivators (16, 23). The side chain of these antiestrogens plays an important role in displacing helix 12. This suggests that amino acids of the ligand-binding domain that interact with the antiestrogen side chain play an important role in the transcriptionally inactive conformation of this domain. It has been suggested that integrity of aspartate 351, which forms a hydrogen bond with the tertiary amine present at the end of the side chains of Tam and Ral, is the key to the antiestrogenic character of these analogs (28). Indeed, a mutation of Asp-351 to tyrosine was isolated from an MCF7 tumor variant that was not inhibited but rather stimulated by Tam (29,30). Both Tam and Ral also behaved as agonists for expression of the estrogen target gene transforming growth factor-␣ in MDA-MB-231 cells stably transfected with this mutant of ER␣, while the full antiestrogen ICI182,780 remained inactive (28).Here we have introduced several mutations at position 351 and tested the functional consequences of these changes on ER␣ transactivation properties in the presence of estrogen and of antiestrogens. Our results demonstrate that Asp-351 can be mutagenized to Gly, Ala, or Val without diminishing the antagonist activity of antiestrogens in HeLa cells. However, we provide evidence for a stabilizing effect of Asp-351 on the active conformation of the wild-type ER LBD in the absence of hormones. EXPERIMENTAL PROCEDURESMaterials-Cell culture media and fetal bovine serum were purchased from Life Technologies, Inc. Estradiol, 4-hydroxytamoxifen (OHT), and ICI182,780 were purchased from Sigma. RU39,411 and RU...

We have analyzed interaction of coactivators with the wild-type estrogen receptor ␣ (ER), HEG0, and a mutant, L536P-HEG0, which is constitutively active in several transiently transfected cells and a HeLa line that stably propagates an estrogen-sensitive reporter gene. Different classes of coactivators do not recognize the ER ligand binding domain (LBD) in the same manner. Steroid receptor coactivator-1 (SRC-1), amplified in breast cancer-1 (AIB-1), transcriptional intermediary factor-1 (TIF-1), transcriptional intermediary factor-2 (TIF-2), and receptor interacting protein 140 (RIP140) interacted with HEG0 and L536P-HEG0 in the presence of estradiol, but generally not in the presence of anti-estrogens. However, ICI164,384 stimulated some interaction of RIP140 with LBDs. SRC-1, AIB-1, and RIP140 interacted constitutively with the L536P ER, whereas TIF-1 and TIF-2 interacted only weakly in the absence of hormone. Reciprocal competition for binding to the ER LBD was observed between different classes of coactivators. Moreover, coexpression of RIP140 blocked enhanced transactivation by HEG0 observed in the presence of TIF-2, suggesting that RIP140 may play a negative role in ER signaling. We conclude that constitutive activity of L536P-HEG0 is manifested to similar degrees in different cell types and likely arises from constitutive coactivator binding; different classes of coactivators recognize distinct but overlapping binding sites on the ER LBD. Finally, the observation that L536P-HEG0 interacted constitutively with AIB-1, a coactivator that has been implicated in ER signaling in breast and ovarian cancer, suggests that similar mutations in the ER may contribute to hormone-independent proliferation of breast and ovarian cells. The estrogen receptor (ER)1 is a member of the family of nuclear receptors (1-6). Similar to other nuclear receptors, the ER is a ligand-activated regulator of transcription that functions through stimulating formation of transcriptional preinitiation complexes. Preinitiation complexes include general transcription factors, RNA polymerase II, and multiple components of polymerase II holoenzyme (7-10). The ER stimulates the assembly of these components through interaction with factors collectively known as coactivators that interact with the receptor ligand binding domain (LBD) in the presence of hormone (11). This interaction requires the AF-2 activating function, located at the extreme C terminus of the LBD.

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