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Nidharshan, S.

Publications and source records attributed to Nidharshan, S..

2 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↗

Acute Activation of Genes Through Transcriptional Condensates Impact Non-target Genes in a Chromatin Domain

Transcription activation of genes by estrogen is driven by enhancers, which are often located within the same Topologically Associating Domain (TAD) as non-targeted promoters. We investigated how acute enhancer-driven activation affects neighbouring non-target genes within the same TAD. Using single-molecule RNA FISH (smFISH), we tracked the transcription of TFF1 (enhancer-target gene) and TFF3 (non-target gene) during estrogen stimulation. We observed mutually exclusive expression patterns: TFF1 expression peaked at 1 hour, while TFF3 reached its peak at 3 hours, after TFF1 activation had diminished. Chromatin looping data indicated that the enhancer loops with TFF1 but not TFF3, suggesting that TFF3 upregulation is not due to direct enhancer-promoter interactions. CRISPR deletion of the enhancer, affected TFF1 transcription more acutely than TFF3. 1,6-hexanediol (HD) exposure suggested that the TFF1 enhancer:promoter undergo a potential ER-mediated condensate formation, which sequesters the transcriptional machinery and inhibits TFF3 expression. As estrogen signalling fades at 3h, TFF1 expression declines while TFF3 expression increases. Our findings reveal that enhancer-driven activation can indirectly repress neighbouring genes within the same TAD, highlighting a dynamic shift in gene expression as signalling progresses.

molecular biology↗