Abstract

The G12/13 subfamily of heterotrimeric guanine nucleotide binding proteins (G proteins) has been shown to regulate the RhoA-mediated serum response element (SRE) signaling pathway. The α-subunit Gα12/13 does this by binding Rho-specific guanine nucleotide exchange factors (RhoGEFs) at their regulator of G protein signaling (RGS) homology (RH) domain and activating them, and these activated RhoGEFs subsequently bind and activate RhoA. The SRE growth signaling pathway has been implicated in gene transcription, cell migration, and proliferation, processes critical to carcinogenesis and metastasis. Chimeric Gα12/13 proteins containing the N-terminal region of the homologous Drosophila protein Concertina were found to exhibit selective binding to different RhoGEFs, interacting with leukemia-associated RhoGEF and PDZ-RhoGEF but not p115RhoGEF. Because these chimeric G proteins show normal growth signaling to SRE, an evolutionary and structural comparison was performed to identify N-terminal amino acids in Gα12/13 that are different or absent in Concertina. Based on these findings, we constructed a mutant Gα13 lacking Thr127 and Arg128, two residues previously shown to provide rgRGS contact points that were found to be absent in Concertina. Future work will analyze binding between this mutant Gα13 and known downstream effectors. p115 has also been found to promote the proliferation of gastric cancer cells through interacting with and stimulating the secretion of macrophage migration inhibitory factor (MIF), a cytokine that has been demonstrated to promote tumor progression. Identification of specific G12/13 residues critical for binding p115 could provide a novel target for cancer therapeutic strategies.

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