Background

Hepatocellular Carcinoma (HCC) is a lethal malignant tumor with a very low 5-year survival rate after diagnosis. For patients with advanced disease where surgery is not feasible, chemotherapy using drugs such as Doxorubicin (DX) remains a primary treatment option. However, cancer cells frequently develop resistance to these drugs rapidly during exposure. This resistance is often a result of abnormally activated DNA damage repair pathways within the cancer cells. Over the years, research has continuously aimed to clarify the molecular mechanisms controlling chemosensitivity. Nevertheless, the interaction between RNA modifications and DNA repair mechanisms occurring within the cell nucleus has not been fully elucidated. To overcome the limitations of existing cancer therapies, it is essential to re-examine the root causes of drug resistance in cancer cells at the molecular level.

Key Findings

A research team led by Viktor Kalbermatter Boell at the Institute of Chemistry, University of Sao Paulo (USP), discovered that Dual-Specificity Phosphatase 12 (DUSP12) directly regulates the activity of N-Acetyltransferase 10 (NAT10), an RNA acetyltransferase. Using CRISPR-Cas9 gene editing technology, the team inactivated DUSP12 in the hepatocellular carcinoma cell line HuH-7. In cancer cells with DUSP12 inhibition, phosphorylation levels on specific tyrosine residues of NAT10 protein were observed to increase due to incomplete dephosphorylation. This condition significantly reduced the N4-acetylcytidine (ac4C) RNA acetylation mediated by NAT10. The study established that DUSP12 functions as an upstream regulator by dephosphorylating and controlling NAT10 activity.

The researchers also analyzed spatial changes under drug stress conditions. Upon DX treatment, NAT10, which was previously confined to the nucleus, was observed to translocate to the nucleoplasm and bind with DUSP12, as confirmed by fluorescence microscopy. Cells lacking DUSP12 function exhibited significantly impaired DNA double-strand break repair capacity, evidenced by a sharp accumulation of gamma-H2AX, a marker of DNA damage. The team evaluated treatment responsiveness under conditions involving the small-molecule NAT10 inhibitor Remodelin. When Remodelin was combined with a DUSP12-deficient environment, a synthetic lethality effect was induced, accelerating cancer cell death and increasing DX sensitivity. Analysis of patient genomic data revealed that patients with DUSP12 gene amplification had significantly shorter survival times.

Significance and Prospects

This study provides molecular-level evidence of the interaction between RNA acetylation and DNA repair mechanisms, offering a new target for overcoming chemoresistance. The approach of inhibiting the DUSP12-NAT10-ac4C axis to control cancer cell survival is expected to provide valuable insights for the development of targeted therapies for hepatocellular carcinoma. In particular, it holds significant potential for application as a combination therapy strategy to enhance the efficacy of existing doxorubicin-based chemotherapy. By addressing the root mechanisms that induce drug resistance, this approach could significantly reduce treatment failure rates.

However, there are still challenges to overcome before clinical implementation. Since NAT10 and ac4C modifications are also involved in normal cellular processes such as ribosome synthesis and protein translation in healthy cells, unexpected toxicity may arise with systemic administration. Therefore, the development of a precise targeted delivery system to ensure drug action is restricted to liver cancer tissue is essential. In vivo efficacy and safety validation using animal models has not yet been conducted, and substantial follow-up research is required before clinical application.