However, interpretation of airway hyperresponsiveness (AHR) and bronchodilation data in these mice must take into consideration the absence of β-arrestins, not only because β-arrestins modulate airway bronchoconstriction and bronchorelaxation, but also because genetic deletion of β-arrestins may affect the expression of βARs, especially in the airways. Here, CTBP1 is linked to airway hyperresponsiveness.