Crosstalk between BER and NHEJ in XRCC4-Deficient Cells Depending on hTERT Overexpression

Area of Science:

• Molecular Biology
• Genetics
• Cancer Research

Background:

• DNA repair pathways, including Base Excision Repair (BER) and Non-Homologous End Joining (NHEJ), are crucial for maintaining genome integrity.
• Interactions between DNA repair systems can influence anticancer therapy efficacy.
• Previous research indicated that BER deficiency downregulates NHEJ gene expression.

Purpose of the Study:

• To investigate the impact of NHEJ deficiency, specifically XRCC4 knockdown, on BER pathway gene expression.
• To compare the cellular response to XRCC4 knockdown in normal (TIG-1) and hTERT-modified (NBE1) cells.
• To analyze the effects on key DNA repair and cell cycle regulatory genes at both mRNA and protein levels.

Main Methods:

• Xenograft models were not used in this study.
• Cell lines (TIG-1 and NBE1) underwent XRCC4 knockdown.
• Quantitative PCR and Western blotting were employed to assess gene and protein expression levels of BER (XRCC1, LIG3, APE1), NHEJ (LIG4, Ku70/Ku80), and regulatory factors (p53, Sp1, PARP1).
• Cell cycle progression was monitored.

Main Results:

• XRCC4 knockdown decreased mRNA levels of both BER and NHEJ genes in both cell lines.
• Protein level changes were not uniform across all investigated genes.
• XRCC4 knockdown increased p53 and Sp1 protein levels.
• G1/S phase delay was observed in normal cells but not in hTERT-modified cells, despite increased p53.
• p21 levels did not significantly increase in NBE1 cells, correlating with the absence of G1/S delay.

Conclusions:

• The XRCC4 scaffold protein plays a significant regulatory role in DNA repair pathways.
• XRCC4's function may be linked to transcriptional regulation or mRNA metabolism.
• Differential cellular responses to NHEJ deficiency highlight the complexity of DNA repair interactions in cancer therapy.