Dosage‐dependent regulation of cell proliferation and adhesion through dual β₂‐adrenergic receptor/cAMP signals

Abstract

The role of β-adrenergic receptors (β-ARs) remains controversial in normal and tumor breast. Herein we explore the cAMP signaling involved in β-AR-dependent control of proliferation and adhesion of nontumor human breast cell line MCF-10A. Low concentrations of a β-agonist, isoproterenol (ISO), promote cell adhesion (87.5% cells remaining adherent to the plastic dishes following specific detachment vs. 35.0% in control, P<0.001), while increasing concentrations further engages an additional 36% inhibition of Erk1/2 phosphorylation (p-Erk1/2)-dependent cell proliferation (P<0.01). Isoproterenol dose response on cell adhesion was fitted to a 2-site curve (EC50(1): 16.5±11.5 fM, EC50(2): 4.08±3.09 nM), while ISO significantly inhibited p-Erk1/2 according to a 1-site model (EC50: 0.25±0.13 nM). Using β-AR-selective agonist/antagonists and cAMP analogs/inhibitors, we identified a dosage-dependent signaling in which low ISO concentrations target a β2-AR population localized in raft microdomains and stimulate a Gs/cAMP/Epac/adhesion-signaling module, while higher concentrations engage a concomitant activation of another β2-AR population outside rafts and inhibit the proliferation by a Gs/cAMP/PKA-dependent signaling module. Our data provide a new molecular basis for the dose-dependent switch of β-AR signaling. This study also sheds light on a new cAMP pathway core mechanism with a single receptor triggering dual cAMP signaling controlled by PKA or Epac but with different cellular outputs.

The β 2 ‐adrenoceptor activates a positive cAMP‐calcium feedforward loop to drive breast cancer cell invasion

“…It is plausible that in addition to β 2 AR signaling within the tumor microenvironment (2), the positive feedforward cAMP/Ca 2+ loop identified here may occur in a tumor cell‐type dependent manner that could impact β‐blocker efficacy in vivo. Indeed, previous studies have reported that β 2 AR‐dependent inhibition of pERK leads to reduced cell proliferation and/or tumor growth in the breast cancer cell lines MDA‐MB‐231, IBH‐4, and IBH‐6 and in the normal mammary epithelial cell line MCF10A (13, 14, 60). The authors suggested that β 2 AR agonists may be useful adjuvant treatments for breast cancer.…”

Intracellular cAMP Sensor EPAC: Physiology, Pathophysiology, and Therapeutics Development

“…Indeed, adhesion to poly-L-lysine-coated plates in serumstarved conditions and the use of a minimal integrin-binding region peptide (arginine, glycine, aspartic acid, serine; RGDS) competition assay both demonstrated reduction in cAMP-induced adhesion supporting that integrin-ECM association is required (631). Although with growing evidence in various cell types for a role of EPAC/Rap1 in cAMP-induced integrin adhesion (97,117,145,855), the role of adhesion in osteoblasts appears to be dominated by PKA regulation. Exploring the roles for the two cAMP sensors revealed that PKA activation, but not an EPAC agonist, induced adhesion similar to that seen with elevated cAMP, while inhibition of PKA reversed these effects (631).…”

β2-Adrenergic receptors in immunity and inflammation: Stressing NF-κB

“…In addition, it is well known that different b 2 -AR ligands stabilise different receptor conformations, which impacts on downstream signalling (Bosmann et al, 2012). Also, even the same ligand can have a different effect on b 2 -AR activation, depending on the concentration at which it is used (Bruzzone et al, 2014). Importantly, pro-inflammatory stimuli can also modulate the activity of the b 2 -AR, which could explain altered responses to b-agonists during inflammation.…”