The WD40 repeat protein, WDR36, orchestrates sphingosine kinase-1 recruitment and phospholipase C-β activation by G-coupled receptors.

Sphingosine kinases (SphK) catalyse the formation of sphingosine-1-phosphate (S1P) and play important roles in the cardiovascular, nervous and immune systems. We have shown before that G-coupled receptors induce a rapid and long-lasting translocation of SphK1 to the plasma membrane and cross-activation of S1P receptors. Here, we further addressed G regulation of SphK1 by analysing the influence of the WD40 repeat protein, WDR36. WDR36 has been described as a scaffold tethering Gα to phospholipase C (PLC)-β and the thromboxane A receptor-β (TPβ receptor). Overexpression of WDR36 in HEK-293 cells enhanced TPβ receptor-induced inositol phosphate production, as reported (Cartier et al. 2011), but significantly attenuated inositol phosphate production induced by muscarinic M and bradykinin B receptors. In agreement with its effect on PLCβ, WDR36 augmented TPβ receptor-induced [Ca] increases. Surprisingly, WDR36 also augmented M receptor-induced [Ca] increases, which was due to increased Ca mobilization while the Ca content of thapsigargin-sensitive stores remained unaltered. Interestingly, overexpression of WDR36 significantly delayed SphK1 translocation by G-coupled M, B and H receptors in HEK-293 cells, while TPβ receptor-induced SphK1 translocation was generally slow and not altered by WDR36 in these cells. Finally, in C2C12 myoblasts, overexpression of WDR36 delayed SphK1 translocation induced by B receptors. It is concluded that WDR36 reduces signalling of G-coupled receptors other than TPβ towards PLC and SphK1, most likely by scavenging Gα and PLCβ. Our results support a role of WDR36 in orchestration of G signalling complexes, and might help to functionally unravel its genetic association with asthma and allergy.