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KRAB domain-associated protein 1 (KAP-1) has been reported to be an oncogene in diverse tumors. KAP-1 was found to have abundant existence in malignant thyroid tissues, but its role in thyroid cancer hasn’t been elucidated clearly. This study was carried out to explore the role of KAP-1 in thyroid cancer, and to clarify its molecular mechanism. The expressions of KAP-1 and P68/DEAD box protein 5 (DDX5) were assessed under the help of qRT-PCR and western blot. Then, we downregulated KAP-1 or upregulated DDX5 by cell transfection in TPC-1 cells. A series of cellular experiments on proliferation, apoptosis, migration and invasion were conducted with CCK-8, EdU, TUNEL, wound-healing and Transwell assays. Besides, the relationship between KAP-1 and DDX5 was verified by co-immunoprecipitation (Co-IP). The results showed that both of KAP-1 and DDX5 were upregulated in thyroid cancer cells. Loss-of-function experiments revealed that KAP-1 knockdown imparted suppressive effects on cell proliferation, migration and invasion, but promoted cell apoptosis. Additionally, KAP-1 was demonstrated to interact with DDX5 and positively regulate DDX5 expression. The following rescued experiments exhibited that the inhibitory effects of KAP-1 knockdown on cellular activities of thyroid cancer and Wnt/β-catenin signaling were also partly reversed by DDX5 overexpression. Moreover, activation of Wnt/β-catenin signaling retarded the anti-tumor activity of KAP-1 knockdown. In conclusion, the data in this study disclosed that KAP-1 silence helped to repress the cell proliferation, migration and invasion by degrading DDK5, so as to hinder the development of thyroid cancer.

X-ray repair cross-complementing group 1 (XRCC1) plays an important role in the base excision repair. Many studies have reported the association of XRCC1 Arg399Gln, Arg194Trp and Arg280His polymorphisms with lung cancer risk, but the results remained controversial. In this meta-analysis, we performed a meta-analysis of ten published case-control studies in Caucasian populations to investigate the associations between lung cancer risk and XRCC1 Arg399Gln (2187 cases and 3453 controls from ten studies), Arg194Trp (857 cases and 2108 controls from six studies) and Arg280His (894 cases and 1133 controls from five studies). The results in total population showed that XRCC1 codon 399 polymorphism (OR=0.93, 95% CI=0.82-1.04) and codon 194 (OR=0.94, 95% CI=0.73-1.21) was significantly associated with lung cancer risk. However, no association was found between lung cancer risk and codon 280 (OR=1.17, 95% CI=0.89-1.54). In conclusion, this meta-analysis has demonstrated that codon 399 and codon 194 might have contributed to individual susceptibility to lung cancer in Caucasian populations. To further evaluate effect of XRCC1 polymorphisms, large studies with thousands of subjects are required to get conclusive results.