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First published online 29 April 2008
doi: 10.1242/jcs.020958

Journal of Cell Science 121, 1704-1717 (2008)
Published by The Company of Biologists 2008
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Research Article

Integrin clustering enables anandamide-induced Ca2+ signaling in endothelial cells via GPR55 by protection against CB1-receptor-triggered repression

Markus Waldeck-Weiermair1,*, Cristina Zoratti1,*, Karin Osibow1, Nariman Balenga2, Edith Goessnitzer3, Maria Waldhoer2, Roland Malli1 and Wolfgang F. Graier1,*,{ddagger}

1 Institute of Molecular Biology and Biochemistry, Medical University Graz, Graz, A8010, Austria
2 Institute of Experimental and Clinical Pharmacology, Medical University Graz, Graz, A8010, Austria
3 Institute of Pharmaceutical Chemistry, University Graz, Graz Austria

{ddagger} Author for correspondence (e-mail: wolfgang.graier{at}meduni-graz.at)

Accepted 17 February 2008

Although the endocannabinoid anandamide is frequently described to act predominantly in the cardiovascular system, the molecular mechanisms of its signaling remained unclear. In human endothelial cells, two receptors for anandamide were found, which were characterized as cannabinoid 1 receptor (CB1R; CNR1) and G-protein-coupled receptor 55 (GPR55). Both receptors trigger distinct signaling pathways. It crucially depends on the activation status of integrins which signaling cascade becomes promoted upon anandamide stimulation. Under conditions of inactive integrins, anandamide initiates CB1R-derived signaling, including Gi-protein-mediated activation of spleen tyrosine kinase (Syk), resulting in NF{kappa}B translocation. Furthermore, Syk inhibits phosphoinositide 3-kinase (PI3K) that represents a key protein in the transduction of GPR55-originated signaling. However, once integrins are clustered, CB1R splits from integrins and, thus, Syk cannot further inhibit GPR55-triggered signaling resulting in intracellular Ca2+ mobilization from the endoplasmic reticulum (ER) via a PI3K-Bmx-phospholipase C (PLC) pathway and activation of nuclear factor of activated T-cells. Altogether, these data demonstrate that the physiological effects of anandamide on endothelial cells depend on the status of integrin clustering.

Key words: Anandamide, Bmx/Etk, Cannabinoid signaling, CB1 receptor, GPR55, Ca2+ signaling, Integrins, Syk






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