The JNK-interacting protein (JIP) group of scaffold proteins selectively mediates JNK signaling by aggregating specific components of the MAPK cascade to form a functional JNK signaling module. Required for JNK activation in response to excitotoxic stress. Cytoplasmic MAPK8IP1 causes inhibition of JNK-regulated activity by retaining JNK in the cytoplasm and thus inhibiting the JNK phosphorylation of c-Jun. May also participate in ApoER2-specific reelin signaling. Directly, or indirectly, regulates GLUT2 gene expression and beta-cell function. Appears to have a role in cell signaling in mature and developing nerve terminals. May function as a regulator of vesicle transport, through interactions with the JNK-signaling components and motor proteins. Functions as an anti-apoptotic protein and whose level seems to influence the beta-cell death or survival response. Acts as a scaffold protein that coordinates with SH3RF1 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 activation of MAPK8/JNK1 and differentiation of CD8(+) T-cells. Forms homo- or heterooligomeric complexes (PubMed:16456539). Binds specific components of the JNK signaling pathway namely MAPK8/JNK1, MAPK9/JNK2, MAPK10/JNK3, MAP2K7/MKK7, MAP3K11/MLK3 and DLK1. Also binds the proline-rich domain-containing splice variant of apolipoprotein E receptor 2 (ApoER2). Interacts, via the PID domain, with ARHGEF28 (By similarity). Binds the cytoplasmic tails of LRP1 and LRP2 (Megalin). Binds the TPR motif-containing C-terminal of kinesin light chain, KLC1. Pre-assembled MAPK8IP1 scaffolding complexes are then transported as a cargo of kinesin, to the required subcellular location. Interacts with the cytoplasmic domain of APP (By similarity). Interacts with DCLK2, VRK2 and MAP3K7/TAK1. Found in a complex with SH3RF1, RAC1, MAP3K11/MLK3, MAP2K7/MKK7 and MAPK8/JNK1. Found in a complex with SH3RF1, RAC2, MAP3K7/TAK1, MAP2K7/MKK7, MAPK8/JNK1 and MAPK9/JNK2 (By similarity). Interacts with SH3RF2 (PubMed:22128169). Accumulates in cell surface projections. Under certain stress conditions, translocates to the perinuclear region of neurons. In insulin-secreting cells, detected in both the cytoplasm and nucleus. Highly expressed in brain and pancreatic beta-cells. Weaker expression found in kidney. The SH3 domain mediates homodimerization. Phosphorylated by MAPK8, MAPK9 and MAPK10. Phosphorylation on Thr-103 is also necessary for the dissociation and activation of MAP3K12. Phosphorylated by VRK2. Hyperphosphorylated during mitosis following activation of stress-activated and MAP kinases (By similarity). Ubiquitinated. Two preliminary events are required to prime for ubiquitination; phosphorylation and an increased in intracellular calcium concentration. Then, the calcium influx initiates ubiquitination and degradation by the ubiquitin-proteasome pathway (By similarity). Belongs to the JIP scaffold family.