Autophagy regulates myeloid cell differentiation by p62/SQSTM1-mediated degradation of PML-RARα oncoprotein.
PML-RARα oncoprotein is a fusion protein of promyelocytic leukemia (PML) and the retinoic acid receptor-α (RARα) and causes acute promyelocytic leukemias (APL). A hallmark of all-trans retinoic acid (ATRA) responses in APL is PML-RARα degradation which promotes cell differentiation. Here, we demonstrated that autophagy is a crucial regulator of PML-RARα degradation. Inhibition of autophagy by short hairpin (sh) RNA that target essential autophagy genes such as Atg1, Atg5 and PI3KC3 and by autophagy inhibitors (e.g. 3-methyladenine), blocked PML-RARα degradation and subsequently granulocytic differentiation of human myeloid leukemic cells. In contrast, rapamycin, the mTOR kinase inhibitor, enhanced autophagy and promoted ATRA-induced PML-RARα degradation and myeloid cell differentiation. Moreover, PML-RARα co-immunoprecipitated with ubiquitin-binding adaptor protein p62/SQSTM1, which is degraded through autophagy. Furthermore, knockdown of p62/SQSTM1 inhibited ATRA-induced PML-RARα degradation and myeloid cell differentiation. The identification of PML-RARα as a target of autophagy provides new insight into the mechanism of action of ATRA and its specificity for APL.
Pubmed ID: 21187718 RIS Download
Adaptor Proteins, Signal Transducing | Apoptosis | Autophagy | Cell Differentiation | Gene Expression Regulation, Leukemic | HL-60 Cells | Humans | Leukocytes, Mononuclear | Microscopy, Electron, Transmission | Microscopy, Fluorescence | Models, Biological | Myeloid Cells | Oncogene Proteins, Fusion | RNA, Small Interfering | Sirolimus | Time Factors