Gα12 structural determinants of Hsp90 interaction are necessary for serum response element-mediated transcriptional activation

• Published in: Molecular pharmacology Vol. 85; no. 4; p. 586
• Main Authors: Montgomery, Ellyn R, Temple, Brenda R S, Peters, Kimberly A, Tolbert, Caitlin E, Booker, Brandon K, Martin, Joseph W, Hamilton, Tyler P, Tagliatela, Alicia C, Smolski, William C, Rogers, Stephen L, Jones, Alan M, Meigs, Thomas E
• Format: Journal Article
• Language: English
• Published: United States 01-04-2014
• Subjects: Animals; Cell Line; Drosophila melanogaster - cytology; Drosophila Proteins - genetics; Drosophila Proteins - metabolism; GTP-Binding Protein alpha Subunits, G12-G13 - genetics; GTP-Binding Protein alpha Subunits, G12-G13 - metabolism; HEK293 Cells; HSP90 Heat-Shock Proteins - metabolism; Humans; Mutation; Phylogeny; Protein Binding; rho GTP-Binding Proteins - metabolism; Serum Response Element; Signal Transduction; Transcriptional Activation
• ISSN: 1521-0111
• DOI: 10.1124/mol.113.088443

The G12/13 class of heterotrimeric G proteins, comprising the α-subunits Gα12 and Gα13, regulates multiple aspects of cellular behavior, including proliferation and cytoskeletal rearrangements. Although guanine nucleotide exchange factors for the monomeric G protein Rho (RhoGEFs) are well characterized as effectors of this G protein class, a variety of other downstream targets has been reported. To identify Gα12 determinants that mediate specific protein interactions, we used a structural and evolutionary comparison between the G12/13, Gs, Gi, and Gq classes to identify "class-distinctive" residues in Gα12 and Gα13. Mutation of these residues in Gα12 to their deduced ancestral forms revealed a subset necessary for activation of serum response element (SRE)-mediated transcription, a G12/13-stimulated pathway implicated in cell proliferative signaling. Unexpectedly, this subset of Gα12 mutants showed impaired binding to heat-shock protein 90 (Hsp90) while retaining binding to RhoGEFs. Corresponding mutants of Gα13 exhibited robust SRE activation, suggesting a Gα12-specific mechanism, and inhibition of Hsp90 by geldanamycin or small interfering RNA-mediated lowering of Hsp90 levels resulted in greater downregulation of Gα12 than Gα13 signaling in SRE activation experiments. Furthermore, the Drosophila G12/13 homolog Concertina was unable to signal to SRE in mammalian cells, and Gα12:Concertina chimeras revealed Gα12-specific determinants of SRE activation within the switch regions and a C-terminal region. These findings identify Gα12 determinants of SRE activation, implicate Gα12:Hsp90 interaction in this signaling mechanism, and illuminate structural features that arose during evolution of Gα12 and Gα13 to allow bifurcated mechanisms of signaling to a common cell proliferative pathway.