Guanine nucleotide exchange factor (GEF) for RHOA and RAC1 GTPases. Involved in coordinating actin remodeling, which is necessary for cell migration and growth (By similarity). Plays a key role in the regulation of neurite outgrowth and lamellipodia formation (By similarity). In developing hippocampal neurons, limits dendrite formation, without affecting the establishment of axon polarity. Once dendrites are formed, involved in the control of synaptic function by regulating the endocytosis of AMPA-selective glutamate receptors (AMPARs) at CA1 excitatory synapses (By similarity). May act as a regulator of adipogenesis (PubMed:22666460). ATP + L-seryl-[protein] = ADP + H(+) + O-phospho-L-seryl-[protein] ATP + L-threonyl-[protein] = ADP + H(+) + O-phospho-L-threonyl-[protein] Interacts with CARMIL1. Interacts with PTPRF/LAR. Interacts with ANKRD26 (By similarity). Interacts with Bassoon/BSN and Piccolo/PCLO (By similarity). Interacts with the cytoplasmic region of the heterodimer formed by NGFR and SORCS2. ProNGF binding mediates dissociation of TRIO from the receptor complex (By similarity). Widespread in the brain, with more intense signals in the hippocampus, olfactory bulb, cortical layers and cerebellum. Isoform 2 is predominantly expressed in Purkinje neurons of brain. The N-terminal DBL/GEF domain specifically catalyzes nucleotide exchange for RAC1, leading to the activation of Jun kinase and the production of membrane ruffles. The second DBL/GEF domain is an exchange factor for rhoa and induces the formation of stress fibers (By similarity). Belongs to the protein kinase superfamily. CAMK Ser/Thr protein kinase family. Truncated N-terminus.