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A steroid hormone crosses the lipid bilayer and binds an intracellular nuclear receptor. For a cytoplasmic glucocorticoid receptor, ligand binding alters association with molecular chaperones, exposes nuclear-targeting functions and promotes accumulation in the cell nucleus. Other steroid hormone receptors already have substantial nuclear localization. The activated receptor binds specific hormone response elements in DNA, often as a dimer, and changes recruitment of transcription coactivators or transcription corepressors. These factors alter local chromatin and recruitment or activity of the RNA polymerase II machinery. The result is selective activation or repression of target genes, followed by altered messenger RNA and protein abundance; the hormone itself does not act as an RNA polymerase or directly rewrite the DNA sequence.

Without added HNF1β, both TCF transcription factor isoforms increase reporter output over the empty-vector baseline, with TCF-short giving the larger increase. Adding HNF1β leaves TCF-short output near $3800$–$4000$ arbitrary units, but reduces TCF-long-associated output from roughly $3200$ to $300$–$400$, approximately a tenfold reduction. The empty-vector baseline falls only modestly. HNF1β therefore supports strong isoform-selective repression associated with TCF-long, while TCF-short remains activating in this assay.

This pattern is consistent with recruitment of a transcription corepressor through the long-specific interaction motif. To test that mechanism directly, mutate the motif while preserving expression and DNA binding, rescue with the intact version, mutate the promoter binding sites, and measure the abundance and localization of both factors. Reporter output alone does not establish the molecular contact or the same quantitative effect at the endogenous GLP-1 receptor locus. The question prose and figure caption name different host cell lines, so cell-line-specific mechanistic conclusions require clarification of that source inconsistency.