E3 ubiquitin-protein ligase that acts as a coactivator of JUN-mediated gene activation in response to growth factor signaling via the MAP3K1 pathway, independently from MAPK8. 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. Homodimer. Interacts with JUN, independently of JUN phosphorylation. Interacts (via C-terminus) with TRIM7. Shuttles between the cytoplasm and the nucleus. The RING-CH-type zinc finger domain is required for E3 ligase activity. Ubiquitinated; undergoes 'Lys-48'-linked autoubiquitination in the absence of growth factors and MAP3K1-induced 'Lys-63'-linked polyubiquitination. 'Lys-48'-autoubiquitination leads to degradation by the proteasome, while MAP3K1-induced 'Lys-63'-linked polyubiquitination results in the stabilization of the protein. 'Lys-48'- and 'Lys-63'-linked polyubiquitinations occur most probably on the same 3 C-terminal lysine residues (Lys-195, Lys-224 and Lys-225) and are thus mutually exclusive. Other sites of ubiquitination are not excluded. 'Lys-63'-linked polyubiquitination by TRIM7 in response to growth factor signaling via the MEK/ERK pathway enhances protein stability. Arginine methylation by PRMT1 stabilizes RNF187 by facilitating K63-linked ubiquitin chain formation, and enables dimerization, c-Jun interaction and subsequent AP1 target gene expression. This sequence initiates at a CTG codon.