UBC12‐mediated SREBP‐1 neddylation worsens metastatic tumor prognosis

Abstract

Activation of sterol regulatory element‐binding protein 1 (SREBP‐1), a master lipogenic transcription factor, is associated with cancer metabolism and metabolic disorders. Neddylation, the process of adding NEDD8 to its substrate, contributes to diverse biological processes. Here, we identified SREBP‐1 as a substrate for neddylation by UBC12 and explored its impact on tumor aggressiveness. In cell‐based assays, SREBP‐1 neddylation prolonged SREBP‐1 stability with a decrease in ubiquitination. Consequently, NEDD8 overexpression facilitated proliferation, migration, and invasion of SK‐Hep1 liver tumor cells. MLN4924 (an inhibitor of the NEDD8‐activating enzyme‐E1) treatment or UBC12 knockdown prevented SREBP‐1 neddylation and tumor cell phenotype change. This effect was corroborated in an in vivo xenograft model. In human specimens, SREBP‐1, UBC12, and NEDD8 were all upregulated in hepatocellular carcinoma (HCC) compared to nontumorous regions. Moreover, SREBP‐1 levels positively correlated with UBC12. In GEO database analyses, SREBP‐1 levels were greater in metastatic HCC samples accompanying UBC12 upregulation. In HCC analysis, tumoral SREBP‐1 and UBC12 levels discriminated overall patient survival rates. Additionally, MLN4924 treatment destabilized SREBP‐1 in MDA‐MB‐231 breast cancer cells and in the tumor cell xenograft. SREBP‐1 and UBC12 were also highly expressed in human breast cancer tissues. Moreover, most breast cancers with lymph node metastasis displayed predominant SREBP‐1 and UBC12 expressions, which compromised overall patient survival rates. In summary, SREBP‐1 is neddylated by UBC12, which may contribute to HCC and breast cancer aggressiveness through SREBP‐1 stabilization, and these events can be intervented by MLN4924 therapy. Our findings may also provide potential reliable prognostic markers for tumor metastasis.

The Many Potential Fates of Non-Canonical Protein Substrates Subject to NEDDylation

“…A likely explanation for enhanced protein stability following the addition of NEDD8 to a substrate is that NEDDylation protects substrates from ubiquitination. Recently, Heo et al demonstrated that sterol regulatory elementbinding protein 1 (SREBP-1) stability is regulated by NEDDylation in multiple tumor cell lines [86]. Treatment with either MLN4924 or siRNA depletion of NEDD8, decreased levels of SREBP-1, presumably by allowing ubiquitination of SREBP-1.…”

Roles of Aminoacyl-tRNA Synthetases in Cancer

“… Mo et al (2016) discovered that glycyl-tRNA synthetase (GRS) had the strongest correlation with mortality by analyzing the expression of 20 ARSs in 3557 breast cancer patients. Neddylation is a post-translational modification that attaches ubiquitin-like protein NEDD8 to its substrates and is implicated in cancer progression ( Heo et al, 2020 ; Zhou X. et al, 2020 ). In particular, GRS captured and protected NEDD8-conjugated Ubc12 (activated E2) by binding to the APPBP1 subunit of E1, thereby increasing the global level of neddylation ( Mo et al, 2016 ).…”

Neddylation: A Versatile Pathway Takes on Chronic Liver Diseases

“…Deregulation of the neddylation pathway has been described in various pathological conditions. Focusing on the CLD context like liver fibrosis and HCC, both NAE1 and global protein neddylation expressions are upregulated (66,68). However, the initial triggering mechanism that overactivates neddylation pathways during CLD is not understood exactly.…”

“…Recently, it was reported that SREBP-1 can be neddylated by NEDD8 E3 ligase UBC12. Consequently, neddylation of SREBP-1 competing with its ubiquitination promotes the stability of SREBP-1 (68). Otherwise, liver kinase B1 (LKB1) and Akt kinases, critical regulators in proliferative metabolism of the liver, could be neddylated to enhance their stability.…”