C-terminal mutation of G protein β subunit affects differentially extracellular signal-regulated kinase and c-Jun N-terminal kinase pathways in human embryonal kidney 293 cells

Abstract

G protein β and γ subunits (Gβ and Gγ) form a complex that is involved in various signaling pathways. We reported that the C-terminal 10 amino acids of Gβ are required for association with Gγ (Yamauchi, J., Kaziro, Y., and Itoh, H. (1995) Biochem. Biophys. Res. Commun., 214, 694- 700). To evaluate further the significance of the C-terminal region of Gβ in the formation of a Gβγ complex and its signal transduction, we constructed several C-terminal mutants and expressed them in human embryonal kidney 293 cells. The mutant lacking the C-terminal 2 amino acids (ΔC2) failed to associate with Gγ, whereas deletion of the C-terminal amino acid (ΔC1), replacement of Trp at -2 position by Ala (W339A), and addition of six histidines ((His)6) at the C terminus did not affect the association with Gγ. We also studied the effect of these mutations on the activation of mitogen-activated protein kinase/extracellular signal-regulated kinase (MAPK/ERK) and c-Jun N-terminal kinase/stress-activated protein kinase (JNK/SAPK). Co-expression of the ΔC2 or (His)6 mutant with Gγ did not activate MAPK/ERK at all, whereas the ΔC1 or W339A mutant showed the MAPK/ERK activation. The JNK/SAPK activity was stimulated by the W339A, ΔC2, or (His)6 mutant, but not by the ΔC1 mutant. These results suggest that the C-terminal region of Gβ participates differentially in the signaling for MAPK/ERK and JNK/SAPK activations in mammalian cells.