PARP1 and head and neck squamous cell carcinoma: Given its critical role in DNA damage repair and tumorigenesis, we examined the interaction between the two proteins via exogenous co-IP in MRPL21-overexpressing cells (Fig. 3B) and an endogenous Co-IP experiment using MRPL21 IP antibody in native HNSCC cells, and this analysis confirmed specific binding between MRPL21 and PARP1 (Fig. 3C).