CRL4ADTL degrades DNA-PKcs to modulate NHEJ repair and induce genomic instability and subsequent malignant transformation

Maoxiao Feng,Jian-Hua Mao,Zhongxi Zhao,Pengju Zhang,Lei Bi,Guangwei Wei,Huaizhi Wang,Yunshan Wang

doi:10.1038/s41388-021-01690-z

Abstract

Genomic instability induced by DNA damage and improper DNA damage repair is one of the main causes of malignant transformation and tumorigenesis. DNA double strand breaks (DSBs) are the most detrimental form of DNA damage, and nonhomologous end-joining (NHEJ) mechanisms play dominant and priority roles in initiating DSB repair. A well-studied oncogene, the ubiquitin ligase Cullin 4A (CUL4A), is reported to be recruited to DSB sites in genomic DNA, but whether it regulates NHEJ mechanisms of DSB repair is unclear. Here, we discovered that the CUL4A-DTL ligase complex targeted the DNA-PKcs protein in the NHEJ repair pathway for nuclear degradation. Overexpression of either CUL4A or DTL reduced NHEJ repair efficiency and subsequently increased the accumulation of DSBs. Moreover, we demonstrated that overexpression of either CUL4A or DTL in normal cells led to genomic instability and malignant proliferation. Consistent with the in vitro findings, in human precancerous lesions, CUL4A expression gradually increased with increasing malignant tendency and was negatively correlated with DNA-PKcs and positively correlated with γ-H2AX expression. Collectively, this study provided strong evidence that the CUL4A-DTL axis increases genomic instability and enhances the subsequent malignant transformation of normal cells by inhibiting NHEJ repair. These results also suggested that CUL4A may be a prognostic marker of precancerous lesions and a potential therapeutic target in cancer.

Highlights

Genomic stability plays a crucial role in maintaining the normal function of cells
Cullin 4A (CUL4A), an E3 ubiquitin ligase, recognizes, ubiquitinates, and degrades proteins to regulate multiple physiological processes, including DNA replication and some DNA repair processes, such as nucleotide excision repair (NER) and HR [38]. All these processes mainly occur in the S or G2 phases of the cell cycle, and there are few reports on the function of CUL4A in nonhomologous end-joining (NHEJ), a major DNA damage repair process executed throughout the cell cycle [6]
We reported a novel function of CUL4A in regulating the NHEJ mechanism and promoting genomic instability and malignant transformation of normal cells by degrading DNA-PKcs through its substrate receptor DTL (Fig. 8)

Summary

1234567890();,: 1234567890();,: Introduction

Genomic stability plays a crucial role in maintaining the normal function of cells. As a core member of the NHEJ repair machinery, DNA-PKcs plays an important role in maintaining genomic stability [11, 12], and cooperates with p53 to induce the apoptosis of mutant cells [13]. Other studies have shown that CUL4A inhibits the nucleotide excision repair (NER) mechanism of UV-induced DNA damage through histone ubiquitination modification and degradation of XPC, DDB2, and p21 [22, 26, 27]. We provided strong evidence that the CUL4A-DTL ligase complex attenuates the efficiency of NHEJ repair via the degradation of DNA-PKcs, which subsequently increases genomic instability and in turn affects the malignant transformation of normal cells

Results

Discussion

Materials and methods

Compliance with ethical standards