Casein Kinase 2 at the Intersection of Beta2-adrenoceptor Signaling and cAMP Egress

PROJECT SUMMARY/ABSTRACT Among patients with asthma, a disease that afflicts over 300 million people globally, for over 50% their asthma is not well-controlled by current therapies. β-agonists are a cornerstone medication used to prevent and relieve acute bronchospasm in asthma patients. Unfortunately, excessive use of β-agonists can cause desensitization, internalization, and downregulation of the β2-adrenoceptor (β2AR), leading to tachyphylaxis (loss of clinical efficacy). β-agonists act by binding to the cognate G protein-coupled receptor on human airway smooth muscle (HASM), the β2AR. Activation of the β2AR prompts Gαs to stimulate adenylyl cyclase production of cAMP. Increased intracellular cAMP levels activate protein kinase A (PKA), which phosphorylates mediators of excitation-contraction coupling, leading to HASM cell relaxation and bronchodilation. The regulation of cAMP is canonically considered “switch-like”: the “on-switch” (adenylyl cyclase) is counteracted by phosphodiesterases (PDEs) that degrade cAMP to its inactive form, AMP. Our laboratory recently reported that β-agonist-evoked intracellular cAMP is also negatively regulated by transport of cAMP into the extracellular space via ATP- binding cassette subfamily member C1 (ABCC1). This effect was observed in receptor-dependent (i.e. β- agonist) and receptor-independent (i.e. adenylyl cyclase agonist) manners, suggesting this is a universal response to elevated intracellular cAMP levels. However, the mechanism by which ABCC1 is regulated and the contribution of ABCC1 to β2AR desensitization remain unknown. Our preliminary data indicate that Casein Kinase 2 (CK2), a highly conserved serine/threonine protein kinase, directly phosphorylates and regulates ABCC1 in response to β2AR activation. In addition, the timing of ABCC1 phosphorylation coincides with recruitment of MAPK, an important step in β2AR desensitization and a demonstrated regulator of CK2. Therefore, the overarching hypothesis is that MAPK and CK2 are critical in β2AR-evoked ABCC1 activation, leading to physiological outcomes of increased cAMP efflux and β2AR desensitization. Aim 1 will determine the contribution of CK2 and MAPK in homeostatic and β-agonist-induced ABCC1 activity in cultured HASM cells. In Aim 2, we will assess whether the MAPK-CK2-ABCC1 axis regulates β2AR desensitization and internalization. This research investigates a novel regulatory mechanism of cAMP signaling with the goal of identifying druggable targets that can split β2AR signaling mechanisms and inhibit the loss of clinical efficacy of β-agonists. Further, the proposed training will strengthen the Principal Investigator as an independent researcher in obstructive lung disease and cell signaling.