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Activation of Human PLC‐eta2 by Gbetagamma

The phospholipase C‐η subfamily of PLC isozymes was recently identified, and PLC‐η2 was shown to be activated by Gβ1γ2 after transient expression in COS‐7 cells. We show here that activation of expressed PLC‐η2 also occur in the presence of other Gβγ dimers in addition to Gβ1γ2, and illustrate that their activation occur with a truncation mutant that lacks the long carboxyl terminus. To define the enzymatic properties of PLC‐η2 and its potential direct activation by Gβγ, a construct of PLC‐η2 encompassing PH through C2 domain was purified to homogeneity after expression from a baculovirus in insect cells and assayed after reconstitution with phospholipid vesicles. Purified PLC‐η2 hydrolyzed PI(4,5)P2 with an apparent Km of 9.4 μM and Vmax of 5 μmol/min/mg, similar to activities previously observed with purified PLC‐β or ‐ε. Moreover, Gβ1γ2 stimulated the lipase activity of PLC‐η2 in a concentration dependent manner similar to that observed with purified PLC‐β2. Activation was dependent on the presence of free Gβ1γ2 since its sequestration in the presence of Gαi1 or GRK2‐ct reversed Gβ1γ2‐promoted activation. The PH domain of PLC‐η2 is not required for Gβ1γ2‐mediated regulation since a purified fragment lacking the PH domain nonetheless was activated by Gβ1γ2. Taken together these studies illustrate that PLC‐η2 is a direct downstream effector of Gβγ and therefore, of receptor‐activated heterotrimeric G proteins.