title: The E3 ubiquitin protein ligase MDM2 dictates all-trans retinoic acid-induced osteoblastic differentiation of osteosarcoma cells by modulating the degradation of RARα.
abstract: Retinoic acid receptor alpha (RARα) has a critical role in the differentiation process of osteosarcoma cells induced by all-trans retinoic acid (ATRA). However, degradation of RARα through ubiquitin proteasome pathway weakens the differentiation efficiency of osteosarcoma cells. In this study, we discover that murine double minute-2 (MDM2) acts as an E3 ubiquitin ligase to target RARα for degradation. We observe that MDM2 is required for RARα polyubiquitination and proteasomal degradation because downregulation of MDM2 by short hairpin RNA results in the accumulation of RARα, and MDM2 overexpression promotes the degradation of RARα. We also demonstrate that the N-terminal domain of MDM2 (amino acids 1-109) is the major RARα-binding site. Importantly, endogenous MDM2 levels are not only upregulated in human primary osteosarcoma blasts but are also inversely correlated with the level of osteopontin, which is a marker of bone differentiation. Moreover, MDM2 impairs the ATRA-induced osteoblastic differentiation of osteosarcoma cells, whereas an inhibitor of the MDM2 ubiquitin ligase synergizes with ATRA to enhance the differentiation of osteosarcoma cells and primary osteosarcoma blasts. Therefore, our study indicates that MDM2 serves as an E3 ubiquitin ligase to regulate the degradation of RARα and suggests that MDM2 is a novel therapeutic target for ATRA-based differentiation therapeutic approaches in osteosarcoma.
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: M
authors.initials: M
authors.lastname: Ying
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: L
authors.initials: L
authors.lastname: Zhang
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Q
authors.initials: Q
authors.lastname: Zhou
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: X
authors.initials: X
authors.lastname: Shao
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: J
authors.initials: J
authors.lastname: Cao
authors.affiliation: Department of Orthopedics, The Second Affiliated Hospital of Zhejiang University, Zhejiang University, Hangzhou, China.
authors.forename: N
authors.initials: N
authors.lastname: Zhang
authors.affiliation: Department of Orthopedics, The Second Affiliated Hospital of Zhejiang University, Zhejiang University, Hangzhou, China.
authors.forename: W
authors.initials: W
authors.lastname: Li
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: H
authors.initials: H
authors.lastname: Zhu
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: B
authors.initials: B
authors.lastname: Yang
authors.affiliation: Zhejiang Province Key Laboratory of Anti-Cancer Drug Research, College of Pharmaceutical Sciences, Zhejiang University, Hangzhou, China.
authors.forename: Q
authors.initials: Q
authors.lastname: He
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D001859:Bone Neoplasms / Q000473:pathology*; D002454:Cell Differentiation / Q000187:drug effects; D045744:Cell Line, Tumor; D006801:Humans; D010006:Osteoblasts / Q000166:cytology / Q000187:drug effects*; D012516:Osteosarcoma / Q000473:pathology*; D051736:Proto-Oncogene Proteins c-mdm2 / Q000502:physiology*; D000072482:Retinoic Acid Receptor alpha / Q000378:metabolism*; D014212:Tretinoin / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D000072482:Retinoic Acid Receptor alpha; D014212:Tretinoin; D051736:Proto-Oncogene Proteins c-mdm2