Guanine nucleotide-binding proteins (G proteins) are involved as modulators or transducers in various transmembrane signaling systems (PubMed:21212405, PubMed:19151758, PubMed:16388592). Activates effector molecule RhoA by binding and activating RhoGEFs (ARHGEF1/p115RhoGEF, ARHGEF11/PDZ-RhoGEF and ARHGEF12/LARG) (PubMed:16388592). GNA13-dependent Rho signaling subsequently regulates transcription factor AP-1 (activating protein-1) (PubMed:19151758, PubMed:21212405). Promotes tumor cell invasion and metastasis by activating Rho/ROCK signaling pathway (By similarity). Inhibits CDH1-mediated cell adhesion in process independent from Rho activation (By similarity). G proteins are composed of 3 units; alpha, beta and gamma (PubMed:16388592). The alpha chain contains the guanine nucleotide binding site (PubMed:16388592). Interacts with UBXD5 (By similarity). Interacts with HAX1 (By similarity). Interacts (in GTP-bound form) with PPP5C (via TPR repeats); activates PPP5C phosphatase activity and translocates PPP5C to the cell membrane (By similarity). Interacts with RGS22 (By similarity). Interacts (in GTP-bound form) with ARHGEF1 (PubMed:16388592). Interacts (in GTP-bound form) with ARHGEF11 (via RGS domain) (PubMed:18940608). Interacts (in GTP-bound form) with ARHGEF12 (via RGS domain) (PubMed:16388592). Interacts with CTNND1 (PubMed:15240885). Interacts with GAS2L2 (PubMed:23994616). Cytoplasmic in adult somatic cells, but mainly nuclear in spermatids in the testes. Translocates from the cytoplasm to the nucleus during spermatogenesis, hence predominantly observed in the cytoplasm of round spermatids but localized in the nuclei of elongating or elongated spermatids and testicular spermatozoa. Expressed in brain and testis, as well as in kidney and sperm (at protein level). Phosphorylation on Thr-203 destabilizes the heterotrimer of alpha, beta and gamma, and inhibits Rho activation. Belongs to the G-alpha family. G(12) subfamily.