RRM2 and Fanconi anemia: Additionally, mass spectrometry analysis of NCI-H1299 and A549 cells treated with SHCBP1 siRNA and low-dose ETOP further indicated that the combination treatment not only compromised the cell cycle checkpoint but also attenuated DNA damage repair, as revealed by decreased levels of DNA damage repair proteins, including pCHK2, DDB2, XLF, RRM2 and etc. Therefore, the homologous recombination (HR) function and Fanconi anemia pathway were relatively dampened (Fig. 8E).