E3 ubiquitin ligase that plays important roles in the regulation of neuronal apoptosis, selective autophagy or cell proliferation (PubMed:22023800, PubMed:19358823, PubMed:27562068). Stimulates the degradation of kinetochore ZW10 interacting protein ZWINT in a proteasome-dependent manner, leading to negative regulation of cell proliferation (PubMed:22023800). Inhibits autophagic degradation of diverse known targets while contributing to autophagy of midbodies. Autophagy-inhibitory activity involves MCL1, which TRIM17 assembles into complexes with the key autophagy regulator BECN1 (PubMed:27562068). Controls neuronal apoptosis by mediating ubiquitination and degradation of MCL1 to initiate neuronal death. In addition, regulates NFAT transcription factors NFATC3 and NFATC4 activities by preventing their nuclear localization, thus inhibiting their transcriptional activities. Decreases TRIM41-mediated degradation of ZSCAN2 thereby stimulating alpha-synuclein/SNCA transcription in neuronal cells (By similarity). Prevents the E3 ubiquitin-ligase activity of TRIM28 and its interaction with anti-apoptotic BCL2A1, blocking TRIM28 from ubiquitinating BCL2A1 (PubMed:19358823). 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 (via coiled coil) with TRIM44 (via coiled coil) (PubMed:19358823). Interacts with TRIM28; this interaction prevents TRIM28 activity on BCL2A1 (PubMed:30042493). Interacts with TRIM41; this interaction prevents TRIM41 activity on ZSCAN2 (By similarity). Interacts with BECN1 (PubMed:27562068). Interacts with NFATC3 and NFATC4; these interactions prevent NFATC3 and NFATC4 nuclear localization (By similarity). Almost exclusively in the testis. Auto-ubiquitinated. Belongs to the TRIM/RBCC family.