Identification of DNA-PKcs as a primary resistance factor of salinomycin in osteosarcoma cells
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Yun-fang Zhen1,*, Song-tao Li2,*, Yun-rong Zhu3,*, Xiao-dong Wang1, Xiao-zhong Zhou2, Lun-qing Zhu1
1The Center of Diagnosis and Treatment for Children’s Bone Diseases, The Children’s Hospital Affiliated to Soochow University, Suzhou, China
2The Department of Orthopedics, The Second Affiliated Hospital of Soochow University, Suzhou, China
3Department of Orthopedics, The Affiliated Jiangyin Hospital of Medical College of Southeast University, Jiangyin, China
*These authors have contributed equally to this work
Lun-qing Zhu, email: firstname.lastname@example.org
Xiao-dong Wang, email: email@example.com
Xiao-zhong Zhou, email: firstname.lastname@example.org
Keywords: osteosarcoma (OS), salinomycin, DNA-PKcs, microRNA-101, autophagy
Received: September 09, 2016 Accepted: September 26, 2016 Published: October 17, 2016
Malignant osteosarcoma (OS) is still a deadly disease for many affected patients. The search for the novel anti-OS agent is extremely urgent and important. Our previous study has proposed that salinomycin is a novel anti-OS agent. Here we characterized DNA-dependent protein kinase catalytic subunit (DNA-PKcs) as a primary salinomycin resistance factor in OS cells. DNA-PKcs inhibitors (NU7026, NU7441 and LY294002) or DNA-PKcs shRNA knockdown dramatically potentiated salinomycin-induced death and apoptosis of OS cells (U2OS and MG-63 lines). Further, forced-expression of microRNA-101 (“miR-101”) downregulated DNA-PKcs and augmented salinomycin’s cytotoxicity against OS cells. Reversely, over-expression of DNA-PKcs in OS cells inhibited salinomycin’s lethality. For the mechanism study, we show that DNA-PKcs is required for salinomycin-induced pro-survival autophagy activation. DNA-PKcs inhibition (by NU7441), shRNA knockdown or miR-101 expression inhibited salinomycin-induced Beclin-1 expression and autophagy induction. Meanwhile, knockdown of Beclin-1 by shRNA significantly sensitized salinomycin-induced OS cell lethality. In vivo, salinomycin administration suppressed U2OS xenograft tumor growth in severe combined immuno-deficient (SCID) mice, and its anti-tumor activity was dramatically potentiated with co-administration of the DNA-PKcs inhibitor NU7026. Together, these results suggest that DNA-PKcs could be a primary resistance factor of salinomycin in OS cells. DNA-PKcs inhibition or silence may thus significantly increase salinomycin’s sensitivity in OS cells.
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