Has E3 ubiquitin-protein ligase activity. In the absence of an external substrate, it can catalyze self-ubiquitination. Stimulates ubiquitination of potassium channel KCNJ1, enhancing it's dynamin-dependent and clathrin-independent endocytosis. Acts as a scaffold protein that coordinates with MAPK8IP1/JIP1 in organizing different components of the JNK pathway, including RAC1 or RAC2, MAP3K11/MLK3 or MAP3K7/TAK1, MAP2K7/MKK7, MAPK8/JNK1 and/or MAPK9/JNK2 into a functional multiprotein complex to ensure the effective activation of the JNK signaling pathway. Regulates the differentiation of CD4(+) and CD8(+) T-cells and promotes T-helper 1 (Th1) cell differentiation. Regulates the activation of MAPK8/JNK1 and MAPK9/JNK2 in CD4(+) T-cells and the activation of MAPK8/JNK1 in CD8(+) T-cells. Controls proper cortical neuronal migration and the formation of proximal cytoplasmic dilation in the leading process (PCDLP) in migratory neocortical neurons by regulating the proper localization of activated RAC1 and F-actin assembly. S-ubiquitinyl-[E2 ubiquitin-conjugating enzyme]-L-cysteine + [acceptor protein]-L-lysine = [E2 ubiquitin-conjugating enzyme]-L-cysteine + N(6)-ubiquitinyl-[acceptor protein]-L-lysine. Protein modification; protein ubiquitination. Interacts with HERP1. Interacts with RAC1; in a GTP-dependent manner. Interacts with MAP3K10/MLK2 and MAP3K11/MLK3. Interacts with MAPK8IP; this interaction leads to the PJAC complex (POSH-JIP or SH3RF1/MAPK8IP apoptotic complex) with a 1:1 ratio. Interacts with SIAH1. Probably part of a signaling complex that may contain SH3RF1, MAPK8IP, DLK1, MAP2K4/MKK4, MAP2K7/MKK7, MAPK8/JNK1, MAPK9/JNK2, AKT1 and AKT2. Found in a complex with RAC2, MAP3K7/TAK1, MAP2K7/MKK7, MAPK8IP1/JIP1, MAPK8/JNK1 and MAPK9/JNK2. Found in a complex with RAC1, MAP3K11/MLK3, MAP2K7/MKK7, MAPK8IP1/JIP1 and MAPK8/JNK1. Interacts with SH3RF2. Colocalizes, with AKT2, in lamellipodia. Colocalizes, with HERP1, in trans-Golgi network. The RING finger domain is required for ubiquitin ligase activity and autoubiquitination. Phosphorylated at Ser-304 by AKT1 and AKT2. When phosphorylated, it has reduced ability to bind Rac. Autoubiquitinated. Ubiquitinated by SH3RF2, leading to proteasome-mediated degradation. Belongs to the SH3RF family.