The β-subunit of G proteins is a substrate of protein histidine phosphatase

Increasing evidence suggests that reversible phosphorylation of histidine residues in proteins is important for signaling cascades in eukaryotic cells. Recently, the first eukaryotic protein histidine phosphatase (PHP) was identified. The β1-subunit of heterotrimeric G proteins (Gβ) undergoes phosphorylation on His266 which is apparently involved in receptor-independent G protein activation. We studied whether phosphorylated Gβ-subunits are substrates of PHP. Phosphorylated Gβγ dimers of the retinal G protein transducin and Gβ in membrane preparations of H10 cells (neonatal rat cardiomyocytes) were dephosphorylated by PHP. Overexpression of PHP in H10 cells showed that PHP and Gβ also interfere within cells. In membranes of cells overexpressing PHP, the amount of phosphorylated Gβ was largely reduced. Both our in vitro and cell studies indicate that phosphorylated Gβ-subunits of heterotrimeric G proteins are substrates of PHP. Therefore, PHP might play a role in the regulation of signal transduction via heterotrimeric G proteins.