Selective regulation of β2AR-mediated effects on cellular signaling mechanisms is governed by the estrogen receptor status of the breast cancer cell lines.

Sympathetic noradrenergic stimuli are transduced at the systemic and cellular level through multiple adrenergic receptor subtypes, the predominant of which is the β2-adrenoceptor (β2-AR). In female-specific hormone-sensitive cancers like breast cancer, the effects of adrenergic stimulation and altered hormone sensitivity on cancer cell survival signaling in the context of estrogen receptor (ER) status-dependent cellular responsiveness remain incompletely understood. ER-positive (MCF-7) and ER-negative (MDA-MB-231) breast cancer cell lines were cultured in vitro and treated with the β2-AR specific agonist terbutaline (10- 6 M and 10- 9 M) and non-selective β-AR antagonist propranolol (10- 5M) to examine their effects on proliferation by cell cycle analysis, expression of pro-angiogenic (VEGF-A, VEGF-C) and signaling (p-ERK, p-CREB) molecules by ELISA, nitric oxide (NO) production by Griess assay, and miRNA expression (miR-21, miR-191) by RT-qPCR. Terbutaline elicited distinct and opposing cellular responses depending on ER status, enhancing proliferation, VEGF-C expression, miR-191 levels, and p-ERK signaling in ER-positive MCF-7 cells, while attenuating proliferation, VEGF-C expression, miR-191 levels, and p-ERK signaling in ER-negative MDA-MB-231 cells. In contrast, p-CREB signaling was enhanced in both cell lines. VEGF-A expression was downregulated in both cell lines, whereas NO production and miR-21 expression were increased in an ER-independent manner, suggesting involvement of β-adrenergic signaling mechanisms beyond direct ER mediation. Propranolol significantly attenuated terbutaline-induced effects in both cell lines, with greater magnitude of inhibition observed in ER-positive cells. These findings demonstrate that β2-AR-mediated regulation of proliferation, angiogenic signaling, and epigenetic modulators in breast cancer cells is differentially modulated by ER status, likely through selective engagement of ERK- and CREB-dependent signaling pathways. While ER-dependent crosstalk contributes to divergent outcomes, ER-independent β-adrenergic mechanisms may also play a role, underscoring the complexity of adrenergic signaling in breast cancer progression.