Identification of Ser/Thr phosphorylation sites in the C2-domain of phospholipase C γ2 (PLCγ2) using TRPM7-kinase

PLC-isozymes are central elements of cellular signaling downstream of numerous receptors. PLCγ2 is a pivotal component of B cell receptor (BCR) signaling. The regulation of PLCγ2-dependent signaling functions by Tyr-phosphorylation is well characterized, however, the potential role of Ser/Thr phosphorylation events remains undefined. TRPM7 is the fusion of a Ser/Thr kinase with an ion channel, and an essential component of Mg2+-homeostasis regulation. Although the interaction between the C2 domain of several PLC-isozymes and TRPM7 is well established, previous studies have focused on the effect of PLC-activity on TRPM7. Here, we investigated whether Ser/Thr phosphorylation sites in the C2 domain of PLCγ2 could be identified using TRPM7-kinase. We show that TRPM7-kinase phosphorylates PLCγ2 in its C2-domain at position Ser1164 and in the linker region preceding the C2-domain at position Thr1045. Using a complementation approach in PLCγ2−/− DT40 cells, we found that the PLCγ2-S1164A mutant fully restores BCR mediated Ca2+-responses under standard growth conditions. However, under hypomagnesic conditions, PLCγ2-S1164A fails to reach Ca2+-levels seen in cells expressing PLCγ2 wildtype. These results suggest that Mg2+-sensitivity of the BCR signaling pathway may be regulated by Ser/Thr phosphorylation of PLCγ2. ► PLCγ2 interacts with the Mg2+-sensing channel-kinase TRPM7. ► The C2-domain of PLCγ2 is phosphorylated by TRPM7's Ser/Thr kinase. ► TRPM7-mediated PLCγ2 phosphorylation reveals two novel phospho-sites, T1045 and S1164. ► PLCγ2-S1164A mutation results in diminished BCR-mediated Ca2+-signal under low Mg2+.