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 (PubMed:23624934). Interacts with JUN, independently of JUN phosphorylation (PubMed:20852630). Interacts (via C-terminus) with TRIM7 (PubMed:25851810). Predominantly located in the cytoplasm. Shuttles between the cytoplasm and the nucleus. The RING-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 (PubMed:20852630). 'Lys-48'-autoubiquitination leads to degradation by the proteasome, while MAP3K1-induced 'Lys-63'-linked polyubiquitination results in the stabilization of the protein (PubMed:20852630). 'Lys-48'- and 'Lys-63'-linked polyubiquitinations occur most probably on the same 3 C-terminal lysine residues (Lys-195, Lys-223 and Lys-224) and are thus mutually exclusive (PubMed:20852630). Other sites of ubiquitination are not excluded (PubMed:20852630). 'Lys-63'-linked polyubiquitination by TRIM7 in response to growth factor signaling via the MEK/ERK pathway enhances protein stability (PubMed:25851810). 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. Extended N-terminus. Unusual initiator. The initiator methionine is coded by a non-canonical CTG leucine codon.