Bifunctional modulator of guanine nucleotide-binding proteins (G proteins) (By similarity). Acts as a non-receptor guanine nucleotide exchange factor which binds to and activates guanine nucleotide-binding protein G(i) alpha subunits (By similarity). Also acts as a guanine nucleotide dissociation inhibitor for guanine nucleotide-binding protein G(s) subunit alpha GNAS (By similarity). Essential for cell migration (By similarity). Interacts in complex with G(i) alpha subunits with the EGFR receptor, retaining EGFR at the cell membrane following ligand stimulation and promoting EGFR signaling which triggers cell migration (By similarity). Binding to Gi-alpha subunits displaces the beta and gamma subunits from the heterotrimeric G-protein complex which enhances phosphoinositide 3-kinase (PI3K)-dependent phosphorylation and kinase activity of AKT1/PKB (By similarity). Phosphorylation of AKT1/PKB induces the phosphorylation of downstream effectors GSK3 and FOXO1/FKHR, and regulates DNA replication and cell proliferation (PubMed:15753085). Binds in its tyrosine-phosphorylated form to the phosphatidylinositol 3-kinase (PI3K) regulatory subunit PIK3R1 which enables recruitment of PIK3R1 to the EGFR receptor, enhancing PI3K activity and cell migration (By similarity). Plays a role as a key modulator of the AKT-mTOR signaling pathway, controlling the tempo of the process of newborn neuron integration during adult neurogenesis, including correct neuron positioning, dendritic development and synapse formation (PubMed:19778506). Inhibition of G(s) subunit alpha GNAS leads to reduced cellular levels of cAMP and suppression of cell proliferation (By similarity). Essential for the integrity of the actin cytoskeleton (By similarity). Required for formation of actin stress fibers and lamellipodia (By similarity). May be involved in membrane sorting in the early endosome (By similarity). Plays a role in ciliogenesis and cilium morphology and positioning and this may partly be through regulation of the localization of scaffolding protein CROCC/Rootletin (By similarity). Homodimer (By similarity). Interacts (via GBA motif) with guanine nucleotide-binding protein G(i) alpha subunits GNAI1, GNAI2 and GNAI3 (By similarity). Also interacts (via GNA motif) with guanine nucleotide-binding protein G(s) alpha subunit GNAS (By similarity). Interaction with G(i) alpha subunits occurs before interaction with GNAS and is regulated by phosphorylation; phosphorylation at Ser-1677 enhances binding to G(i) alpha subunits while phosphorylation at Ser-1692 abolishes G(i) alpha subunit binding, promoting binding to GNAS (By similarity). Interacts (via C-terminal SH2-like region) with growth factor receptors EGFR, INSR and KDR/VEGFR2 (via their autophosphorylated cytoplasmic tails) (By similarity). Forms a complex with EGFR and GNAI3 which leads to enhanced EGFR signaling and triggering of cell migration; ligand stimulation is required for recruitment of GNAI3 to the complex (By similarity). Interacts (tyrosine-phosphorylated form) with phosphatidylinositol 3-kinase (PI3K) regulatory subunit PIK3R1/p85a (via SH2 domains); the interaction enables recruitment of PIK3R1 to the EGFR receptor, enhancing PI3K activity and cell migration (By similarity). Interacts with serine/threonine-protein kinase PRKCQ; the interaction leads to phosphorylation of CCDC88A and inhibition of its guanine nucleotide exchange factor activity (By similarity). Interacts (via C-terminus) with DISC1; the interaction is direct (PubMed:19778506). Interacts with AKT proteins; the interaction is inhibited in the presence of DISC1 (PubMed:19778506). Interacts with AKT1/PKB (via C-terminus) (PubMed:15753085). The non-phosphorylated form interacts with phosphatidylinositol 4-phosphate [Pi(4)P] and weakly with phosphatidylinositol 3-phosphate [Pi(3)P] (By similarity). Interacts with microtubules (PubMed:15882442). Interacts with actin (By similarity). Localizes to the cytosol in unstimulated cells while EGF stimulation promotes membrane localization and guanine nucleotide exchange factor activity (By similarity). Localizes to the cell membrane through interaction with phosphoinositides (By similarity). Expressed in the dentate gyrus, pyramidal cell layer of hippocampal regions CA1 and CA3 at postnatal 15. Expressed highly in neurons. Weakly in neuron progenitors (at protein level). Expressed in the dentate granule cell layer of the hippocampus. Expressed highly in the adult testis, moderately in the brain and at a low level in the spleen, lungs and fat. Temporally and spatially restricted during embryogenesis. At 10.5 dpc, expressed in the branchial arches, nasal processes, limbs, somites and dorsal root ganglia. At 11.5 dpc, expression persists at these sites in addition to the eye and fore-, mid- and hindbrain. By 12.5 dpc, expressed in the interdigital mesenchyme of the limbs. At 13.5 dpc, expression in the limbs flanks the digits and also appears in a subset of tendons in the hind- and forelimbs. The GBA (G-alpha binding and activating) motif mediates binding to the alpha subunits of guanine nucleotide-binding proteins (G proteins). In the presence of tyrosine-autophosphorylated growth factor receptors, the C-terminus folds into an SH2-like region which promotes the stable recruitment of CCDC88A to the growth factor receptors. The SH2-like region is phosphorylated by the growth factor receptors prior to completion of folding. Phosphorylation is induced by epidermal growth factor (EGF) in a phosphoinositide 3-kinase (PI3K)-dependent manner (By similarity). Phosphorylation by AKT1/PKB is necessary for the delocalization from the cell membrane and for cell migration (By similarity). Phosphorylated on tyrosine residues which promotes binding to phosphatidylinositol 3-kinase (PI3K) regulatory subunit PIK3R1/p85a and enhances PI3K activity (By similarity). Tyrosine-phosphorylated by both receptor and non-receptor tyrosine kinases in vitro (By similarity). Tyrosine phosphorylation is required for AKT1-dependent phosphorylation of Ser-1417 (By similarity). Phosphorylation at Ser-1692 by PRKCQ disrupts interaction with GNAI3 and inhibits guanine nucleotide exchange factor activity (By similarity). CCDC88A knockout mice display mesial-temporal lobe epilepsy and early demise, and structural brain developmental defects affecting the corpus callosum and cerebrum. Belongs to the CCDC88 family.