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Biology subjects

Najar, A. H.

Publications and source records attributed to Najar, A. H..

3 recordsLinked to original sources

Enhancers require an active resetting phase after transcriptional activation

Signal-responsive enhancers must activate transcription and then return to a competent but inactive state, yet whether this transition is passive or actively driven has remained unresolved. We define this process as enhancer resetting and identify the androgen receptor (AR) as the factor that executes it as an endogenous response to estrogen signaling, independent of exogenous androgen. As estrogen receptor- (ER) undergoes ligand-induced proteasomal degradation during late-phase signaling, AR progressively accumulates in the nucleus and preferentially occupies highly active, persistent ER enhancers in a transcriptionally silent manner. This late-phase AR binding evicts the pioneer factor FOXA1 from chromatin while preserving baseline accessibility, a handoff mechanism that decouples chromatin openness from active transcription. Conversely, augmenting AR activity by DHT treatment or AR overexpression accelerates FOXA1 eviction, while disrupting AR chromatin binding, either by AR knockdown or a DNA-binding-deficient mutant, prevents it, leaving enhancers in an aberrantly permissive state that drives amplified ER rebinding and transcriptional hyperactivation upon subsequent estrogen stimulation. These findings establish active enhancer resetting as a mechanism safeguarding the fidelity of repeated transcriptional responses. Failure of this mechanism may underlie the transcriptional dysregulation that drives tumor progression and endocrine therapy resistance in ER-positive breast cancer, where estrogen signaling is chronic and cyclic.

molecular biology↗

Nuclear myosin I mediates genomic clustering of estrogen receptor-α without affecting ligand-induced transcriptional robustness

Ligand-induced transcriptional responses are rapid and robust. Estrogen, one such ligand, exerts its rapid effects through the steroid hormone receptor estrogen receptor-alpha (ER). Upon stimulation, ER binds to clustered enhancers to drive target gene expression. Here, we identify nuclear myosin 1 (NM1/Myo1c) as a positive regulator of ER clustering on enhancers, promoting condensate formation on chromatin. NM1 is enriched on chromatin at the peak of the signaling response, and its depletion leads to a genome-wide reduction in ER occupancy and condensates. Surprisingly, these alterations in chromatin occupancy of ER have minimal impact on estrogen-regulated gene expression, suggesting that transcriptional output remains robust despite disruptions in transcription factor clustering. This study reveals a regulatory axis between Myo1c and ER clustering, offering fresh insights into the intricacies of transcriptional regulation.

molecular biology↗

Niclosamide inhibits SARS-CoV2 entry by blocking internalization through pH-dependent CLIC/GEEC endocytic pathway

Many viruses utilize the host endo-lysosomal network to infect cells. Tracing the endocytic itinerary of SARS-CoV2 can provide insights into viral trafficking and aid in designing new therapeutic targets. Here, we demonstrate that the receptor binding domain (RBD) of SARS-CoV2 is internalized via the clathrin and dynamin-independent, pH-dependent CLIC/GEEC (CG) endocytic pathway. Endosomal acidification inhibitors like BafilomycinA1 and NH4Cl, which inhibit the CG pathway, strongly block the uptake of RBD. Using transduction assays with SARS-CoV2 Spike-pseudovirus, we confirmed that these acidification inhibitors also impede viral infection. By contrast, Chloroquine neither affects RBD uptake nor extensively alters the endosomal pH, yet attenuates Spike-pseudovirus entry, indicating a pH-independent mechanism of intervention. We screened a subset of FDA-approved acidification inhibitors and found Niclosamide to be a potential SARS-CoV2 entry inhibitor. Niclosamide, thus, could provide broader applicability in subverting infection of similar category viruses entering host cells via this pH-dependent endocytic pathway.

cell biology↗