Abstract 8142: By Virtue of Its Interaction with the β 2 -adrenergic Receptor, CXCR4 Plays a Role in the Regulation of β 2 -adrenergic Receptor Signaling Pathway Affecting Calcium and Contractility in Cardiac Myocytes

Abstract

Chemokines are small secreted proteins with chemoattractant properties that play a key role in inflammation, metastasis, and embryonic development. We previously demonstrated a nonchemotactic role for one such chemokine pair, stromal cell-derived factor-1α (SDF-1α) and its G-protein coupled receptor, CXCR4. SDF-1 α /CXCR4 are expressed on cardiac myocytes and have direct consequences on cardiac myocyte physiology by inhibiting contractility in response to the nonselective β-adrenergic receptor (βAR) agonist, isoproterenol. As a result of the importance of β-adrenergic signaling in heart failure pathophysiology, we investigated the underlying mechanism involved in CXCR4 modulation of βAR signaling. We hypothesis that β 2 adrenergic receptor in the heart is negatively modulated by interactions with CXCR4 chemokine receptor. For this we have used biophysical techniques such as bioluminescence resonance energy transfer assay and biochemical techniques such as immunoprecipitation and signaling assays to identify the CXCR4-β2AR interaction and determine the physiological significance of this interaction. Our studies demonstrate activation of CXCR4 by SDF-1 leads to a decrease in βAR-induced PKA activity as assessed by cAMP accumulation and PKA-dependent phosphorylation of phospholamban, an inhibitor of SERCA2a. We determined CXCR4 regulation of βAR downstream targets is β2AR-dependent. In conclusion, we demonstrated a physical interaction between CXCR4 and β2AR as determined by coimmunoprecipitation, confocal microscopy, and BRET techniques. The CXCR4-β2AR interaction leads to G-protein signal switching from Gαs to Gαi-mediated pathway and suggests the interaction is a novel mechanism for regulating cardiac myocyte calcium handling and subsequent contractility. Chemokines are physiologically and developmentally relevant to myocardial biology and represent a novel receptor class of cardiac modulators. The CXCR4- β2AR complex could represent a hitherto unknown target for therapeutic intervention.