HERC4 Is Overexpressed in Hepatocellular Carcinoma and Contributes to the Proliferation and Migration of Hepatocellular Carcinoma Cells

Small molecule induced STING degradation facilitated by the HECT ligase HERC4

Stimulator of interferon genes (STING) is a central component of the cytosolic nucleic acids sensing pathway and as such master regulator of the type I interferon response. Due to its critical role in physiology and its' involvement in a variety of diseases, STING has been a focus for drug discovery. Targeted protein degradation (TPD) has emerged as a promising pharmacology for targeting previously considered undruggable proteins by hijacking the cellular ubiquitin proteasome system (UPS) with small molecules. Here, we identify AK59 as a STING degrader leveraging HERC4, a HECT-domain E3 ligase. Additionally, our data reveals that AK59 is effective on the common pathological STING mutations, suggesting a potential clinical application of this mechanism. Thus, these findings introduce HERC4 to the fields of TPD and of compound-induced degradation of STING, suggesting potential therapeutic applications.

HERC4 modulates ovarian cancer cell proliferation by regulating SMO-elicited hedgehog signaling

BACKGROUND

HERC4 has been reported to have functions in several types of tumors, but its roles in ovarian cancer have not been studied yet.

METHODS

Primary tissues from ovarian cancer patients and cell lines were collected for real-time PCR. Kaplan-Meier Plotter was used to predict the prognosis of ovarian cancer patients. HERC4 was overexpressed in cells by lentivirus, and CCK-8 assay was performed to evaluate cell viability. Real-time PCR and Western blot were carried out to analyze the mRNA and protein expression, respectively. Xenograft tumor models were established to analyze HERC4 function in vivo.

RESULTS

Firstly, we found that HERC4 was significantly downregulated in ovarian cancer. We then found that ovarian cancer patients with high HERC4 expression had significantly higher overall survival and progression-free survival rates compared with patients with low expression. Then, HERC4 was overexpressed in ovarian cancer cells, and we found that overexpression of HERC4 significantly inhibited ovarian cancer cell growth, as well as the expression of the target protein SMO, and the key proteins in the downstream hedgehog signaling pathway. Finally, the xenograft tumor models revealed that overexpression of HERC4 significantly inhibited tumor growth in vivo.

CONCLUSIONS

Overall, these results indicate that overexpression of HERC4 inhibits cell proliferation of ovarian cancer in vitro and in vivo, suggesting that HERC4 may serve as an effective target for the treatment of ovarian cancer.

HERC Ubiquitin Ligases in Cancer

HERC proteins are ubiquitin E3 ligases of the HECT family. The HERC subfamily is composed of six members classified by size into large (HERC1 and HERC2) and small (HERC3-HERC6). HERC family ubiquitin ligases regulate important cellular processes, such as neurodevelopment, DNA damage response, cell proliferation, cell migration, and immune responses. Accumulating evidence also shows that this family plays critical roles in cancer. In this review, we provide an integrated view of the role of these ligases in cancer, highlighting their bivalent functions as either oncogenes or tumor suppressors, depending on the tumor type. We include a discussion of both the molecular mechanisms involved and the potential therapeutic strategies.

HECT E3 ubiquitin ligases - emerging insights into their biological roles and disease relevance

Homologous to E6AP C-terminus (HECT) E3 ubiquitin ligases play a critical role in various cellular pathways, including but not limited to protein trafficking, subcellular localization, innate immune response, viral infections, DNA damage responses and apoptosis. To date, 28 HECT E3 ubiquitin ligases have been identified in humans, and recent studies have begun to reveal how these enzymes control various cellular pathways by catalyzing the post-translational attachment of ubiquitin to their respective substrates. New studies have identified substrates and/or interactors with different members of the HECT E3 ubiquitin ligase family, particularly for E6AP and members of the neuronal precursor cell-expressed developmentally downregulated 4 (NEDD4) family. However, there still remains many unanswered questions about the specific roles that each of the HECT E3 ubiquitin ligases have in maintaining cellular homeostasis. The present Review discusses our current understanding on the biological roles of the HECT E3 ubiquitin ligases in the cell and how they contribute to disease development. Expanded investigations on the molecular basis for how and why the HECT E3 ubiquitin ligases recognize and regulate their intracellular substrates will help to clarify the biochemical mechanisms employed by these important enzymes in ubiquitin biology.

A miRNA-HERC4 pathway promotes breast tumorigenesis by inactivating tumor suppressor LATS1

The E3 ligase HERC4 is overexpressed in human breast cancer and its expression levels correlated with the prognosis of breast cancer patients. However, the roles of HERC4 in mammary tumorigenesis remain unclear. Here we demonstrate that the knockdown of HERC4 in human breast cancer cells dramatically suppressed their proliferation, survival, migration, and tumor growth in vivo, while the overexpression of HERC4 promoted their aggressive tumorigenic activities. HERC4 is a new E3 ligase for the tumor suppressor LATS1 and destabilizes LATS1 by promoting the ubiquitination of LATS1. miRNA-136-5p and miRNA-1285-5p, expression of which is decreased in human breast cancers and is inversely correlated with the prognosis of breast cancer patients, are directly involved in suppressing the expression of HERC4. In summary, we discover a miRNA-HERC4-LATS1 pathway that plays important roles in the pathogenesis of breast cancer and represents new therapeutic targets for human breast cancer.