Stimulation of Cellular Signaling and G Protein Subunit Dissociation by G Protein βγ Subunit-binding Peptides

• Published in: The Journal of biological chemistry Vol. 278; no. 22; p. 19634
• Main Authors: Farida Goubaeva, Mousumi Ghosh, Sundeep Malik, Jay Yang, Patricia M. Hinkle, Kathy K. Griendling, Richard R. Neubig, Alan V. Smrcka
• Format: Journal Article
• Language: English
• Published: American Society for Biochemistry and Molecular Biology 30-05-2003
• ISSN: 0021-9258; 1083-351X
• DOI: 10.1074/jbc.M300052200

We previously developed peptides that bind to G protein βγ subunits and selectively block interactions between βγ subunits
and a subset of effectors in vitro (Scott, J. K., Huang, S. F., Gangadhar, B. P., Samoriski, G. M., Clapp, P., Gross, R. A., Taussig, R., and Smrcka, A. V.
(2001) EMBO J. 20, 767–776). Here, we created cell-permeating versions of some of these peptides by N-terminal modification with either
myristate or the cell permeation sequence from human immunodeficiency virus TAT protein. The myristoylated βγ-binding peptide
(mSIRK) applied to primary rat arterial smooth muscle cells caused rapid activation of extracellular signal-regulated kinase
1/2 in the absence of an agonist. This activation did not occur if the peptide lacked a myristate at the N terminus, if
the peptide had a single point mutation to eliminate βγ subunit binding, or if the cells stably expressed the C terminus
of βARK1. A human immunodeficiency virus TAT-modified peptide (TAT-SIRK) and a myristoylated version of a second peptide
(mSCAR) that binds to the same site on βγ subunits as mSIRK, also caused extracellular signal-regulated kinase activation.
mSIRK also stimulated Jun N-terminal kinase phosphorylation, p38 mitogen-activated protein kinase phosphorylation, and phospholipase
C activity and caused Ca 2+ release from internal stores. When tested with purified G protein subunits in vitro , SIRK promoted α subunit dissociation from βγ subunits without stimulating nucleotide exchange. These data suggest a novel
mechanism by which selective βγ-binding peptides can release G protein βγ subunits from heterotrimers to stimulate G protein
pathways in cells.